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The direct involvment of the Wilm's tumor suppressor gene (WTl) in Denys-Drash syndrome through mutations within exons 8 or 9 has recently been established. The absence of such alterations in three patients with Frasier syndrome provides a molecular basis for distinguishing these two syndromes that are associated with streak gonads, pseudohermaphroditism and renal failure.
Pericentric intrachromosomal insertion responsible for recurrence of del(11)(p13p14) in a family
(1993)
The combined use of qualitative and quantitative analysis of I I p I 3 polymorphic markers tagether with chromosomal in situ suppression hybridization (CISS) with biotin labeled probes mapping to I I p allowed us to characterize a complex rearrangement segregating in a family. We detected a pericentric intrachromosomal insertion responsible (or recurrence of del( I I )(p 13p 14) in the family: an insertion of band I I p 13-p 14 carrying the genes for predisposition to Wilms' tumor, WT I, and for aniridia, AN2, into the long arm of chromosome I I in II q 13-q 1<4. Asymptomatic balanced carriers were observed over three generations. Classical cytogenetics had failed to detect this anomaly in the balanced carriers, who were first considered to be somatic mosaics for del( II )(p 13). Two of these women gave birth to children carrying a deleted chromosome II. most likely resulting from the loss of the I I p 13 band inserted in I I q. Although in both cases the deletion encompassed exactly the same maternally inherited markers, there was a wide Variation in clinical expression. One child, with the karyotype 46,XY,del(ll)(pllpl4), presented the full-blown WAGR syndrome with anlridia, mental retardation, Wilms' tumor, and pseudohermaphroditism, but also had proteinuria and glomerular sclerosis reminiscent of Drash syndrome. In contrast, the other one, a girl with the karyotype 46,XX,del( I I )(p I 3), only had aniridia. Although a specific set of mutational sites has been observed in Drash patients, these findings suggest that the loss of one copy of the WTI gene can result in similar genital and kidney abnormalities.
Wilms' tumor is a childhood nephroblastoma that is postulated to arise through the inactivation of a tumor suppressor gene by a two-hit mechanism. A candidate II p 13 Wilms' tumor gene, WTI, has been cloned and shown to encode a zinc finger protein. Patients with the WAGR syndrome (Wilms' tumor, aniridia, genitourinary abnormalities, and mental retardation) have a high risk of developing Wilms' tumor and they carry constitutional deletions of one chromosome II allele encompassing the WTI gene. Analysis of the remaining WTI allele in a Wilms' tumor from a WAGR patient revealed the deletion of a single nucleotide in exon 7. This mutation likely played a key role in tumor formation, as it prevents translation of the DNA-binding zinc finger domain that is essential for the function of the WTI polypeptide as a transcriptional regulator.
The human recombination activating gene 1 (RAGl) has previously been mapped to chromosomes 14q and 11 p. Here we confirm the chromosome 11 assignment by two independent approaches: autoradiographic and fluorescence in situ hybridization to metaphase spreads and analysis of human-hamster somatic cell hybrid DNA by the polymerase chain reaction (PCR) and Southern blotting. Our results unequivocally localize RAG1 to llp13.
Developmental delay or mental retardation is a frequent component of multi-system anomaly syndromes associated with chromosomal deletions. Isolation of genes involved in the mental dysfunction in these disorders should define loci important in brain formation or function. We have identified a highly conserved locus in the distal part of 11 p 13 that is prominently expressed in fetal brain. Minimal expression is observed in a number of other fetal tissues. The gene maps distal to PAX-6 but proximal to the loci for brain-derived neurotrophic factor (BDNF) and the beta subunit of follicle stimulating hormone (FSHB), within a region previously implicated in the mental retardation component of some WAGR syndrome patients. Within fetal brain, the corresponding transcript is prominent in frontal, motor and primary visual cortex as weil as in the caudate-putamen. The characteristics of this gene, including the striking evolutionary conservation at the locus, suggest that the encoded protein may function in brain development.
No abstract available
T~e N,N'-dicrclohexylcarbodiimide-binding proteolipid subumt of the mitochondrial adenosinetriphosphatases (ATP phosphohydrolase, EC 3.6.1.3) of Neurosporacrassa and Saccharomyces cerevisiae were purified from mitochondria incubated with the radioactively labeled inhibitor. The specifically labeled subunit was cleaved with cyanogen bromide and N-bromosuccinimide, and the resultant fragments were separated by gel chromatography in the presence of 80% (vol/vol) formic acid. The N,N'-dicyclohexylcarbodiimide label was recovered in each organism exclusively in a 17-residue fragment. Further analysis by automated solid-phase Edman degrada.ti.on revealed tha~ the bound label was present at only one positIOn, correspondmg to a glutamyl residue. The NN'~ icyc~ohexyl~a~bodiiJ?1~de-'!l0dified glutamyl residue is the ~nly Id~ntIcal aCidic posItIon m both proteins and occurs in the middle of a hydrophobic sequence of about 25 residues.
b-Type cytochromes
(1980)
The amino acid sequence of the proteolipid subunit of the A TP synthase was analyzed in six mutant strains from Escherichia coli K 12, selected for their increased resistance towards the inhibitor N,N'-dicyclohexylcarbodiimide. All six inhibitor-resistant mutants were found to be altered at the same position of the proteolipid, namely at the isoleucine at residue 28. Two substitutions could be identified. In type I this residue was substituted by a valine resulting in a moderate decrease in sensitivity to dicyclohexylcarbodiimide. Type II contained a threonine residue at this position. Here a strong resistance was observed. These two amino acid substitutions did not influence functional properties of the ATPase complex. ATPase as well as A TP-dependent proton-translocating activities of mutant membranes were indistinguishable from the wild type. At elevated concentrations, dicyclohexylcarbodiimide still bound specifically to the aspartic acid at residue 61 of the mutant proteolipid as in the wild type, and thereby inhibited the activity of the ATPase complex. It is suggested that the residue 28 substituted in the resistant mutants interacts with dicyclohexylcarbodiimide during the reactions leading to the covalent attachment of the inhibitor to the aspartic acid at residue 61. This could indicate that these two residues are in close vicinity and would thus provide a first hint on the functional conformation of the proteolipid. Its polypeptide chain would have to fold back to bring together these two residues separated by a segment of 32 residues.
Heritabilities and repeatabilities are presented for various behavioural attributes affecting foraging performance and fitness in Aquarius (Gerris) remigis (Heteroptera: Gerridae) females. These behavioural attributes were patch choice, foraging success, capture accuracy, and measures of mobility, activity, skittishness and aggressiveness. Most heritabilities were not significantly different from zero, which may be related to the low sampIe size. Conclusions as to the potential of direct selection on behaviour in this species were consequently limited. In contrast, with a few exceptions (capture accuracy, foraging success), most repeatabilities were significant and at times high (range=O'22-O'79), indicating consistent, stereotypical individual behaviour. Tbe Iife history or reproductive state of the daughter generation individuals signifieantly affected the magnitude of the repeatabilities as weil as the mean values of many of the variables (notably mobility and aggressiveness), the latter in a manner consistent with field observations. This indicates that the state of the organism affects the general environmental variance, thus contributing to the discrepancies between the repeatabilities and the heritabilities obtained. It is suggested that common physiological proeesses (e.g. hormones) may underlie several of the behavioural attributes examined, resulting in possible pleiotropie effects and eonstraints on selection in a heterogeneous environment. It is further suggested that field studies of selection on behavioural attributes may be a more fruitful approach in this species, whose suitability for genetic analysis is limited.
Vegetation structure can profoundly influence patterns of abundance, distribution, and reproduction of herbivorous insects and their susceptibility to natural enemies. The three main structural traits of herbaceous vegetation are density, height, and connectivity. This study determined the herbivore response to each of these three parameters by analysing oviposition patterns in the field and studying the underlying mechanisms in laboratory bioassays. The generalist leaf beetle, Galeruca tanaceti L. (Coleoptera: Chrysomelidae), preferentially deposits its egg clutches on non-host plants such as grasses. Earlier studies revealed that oviposition within structurally complex vegetation reduces the risk of egg parasitism. Consequently, leaf beetle females should prefer patches with dense, tall, or connected vegetation for oviposition in order to increase their reproductive success. In the present study, we tested the following three hypotheses on the effect of stem density, height, and connectivity on oviposition: (1) Within habitats, the number of egg clutches in areas with high stem densities is disproportionately higher than in low-density areas. The number of egg clutches on (2) tall stems or (3) in vegetation with high connectivity is higher than expected for a random distribution. In the field, stem density and height were positively correlated with egg clutch presence. Moreover, a disproportionately high presence of egg clutches was determined in patches with high stem densities. Stem height had a positive influence on oviposition, also in a laboratory two-choice bioassay, whereas stem density and connectivity did not affect oviposition preferences in the laboratory. Therefore, stem height and, potentially, density, but not connectivity, seem to trigger oviposition site selection of the herbivore. This study made evident that certain, but not all traits of the vegetation structure can impose a strong influence on oviposition patterns of herbivorous insects. The results were finally compared with data on the movement patterns of the specialised egg parasitoid of the herbivore in comparable types of vegetation structure.
1. Species assemblages of naturally disturbed habitats are governed by the prevailing disturbance regime. Consequently, stochastic flood events affect river banks and the inhabiting biota. Predatory arthropods occupy predominantly river banks in relation to specific habitat conditions. Therefore, species sorting and stochastic processes as induced by flooding are supposed to play important roles in structuring riparian arthropod assemblages in relation to their habitat preference and dispersal ability. 2. To ascertain whether assemblages of spiders and carabid beetles from disturbed river banks are structured by stochastic or sorting mechanisms, diversity patterns and assemblage-wide trait-displacements were assessed based on pitfall sampling data. We tested if flooding disturbance within a lowland river reach affects diversity patterns and trait distribution in both groups. 3. Whereas the number of riparian spider species decreased considerably with increased flooding, carabid beetle diversity benefited from intermediate degrees of flooding. Moreover, regression analyses revealed trait-displacements, reflecting sorting mechanisms particularly for spiders. Increased flooding disturbance was associated with assemblage-wide increases of niche breadth, shading and hygrophilic preference and ballooning propensity for spider (sub)families. Trait patterns were comparable for Bembidiini carabids, but were less univocal for Pterostichini species. Body size decreased for lycosid spiders and Bembidiini carabids with increased flooding, but increased in linyphiid spiders and Pterostichini carabids. 4. Our results indicate that mainly riparian species are disfavoured by either too high or too low degrees of disturbance, whereas eurytopic species benefit from increased flooding. Anthropogenic alterations of flooding disturbance constrain the distribution of common hygrophilous species and/or species with high dispersal ability, inducing shifts towards less specialized arthropod assemblages. River banks with divergent degrees of flooding impact should be maintained throughout dynamic lowland river reaches in order to preserve typical riparian arthropod assemblages.
River banks are naturally disturbed habitats, in which local flood events and the landscape structure are expected to govern riparian species assemblages. Not solely effects of flooding per se, but also related changes in vegetation structure will affect species’ distribution. By elucidating the relationships between species’ occurrence and multivariate habitat conditions on a restricted spatial scale, insight into conservation strategies to preserve riparian species is gained. Ordination and grouping methods revealed important environmental and functional trait constraints on species composition of predatory riparian arthropod assemblages. Mainly flooding disturbance appeared to affect spider and carabid beetle species composition. Habitat affinity and dispersal ability were retained as important traits explaining similarity between arthropod assemblages. River banks similar in species composition differed in absolute and functional group species richness. Furthermore, Poisson regressions demonstrated the importance of variation in discharge regime, sediment composition and vegetation structure for the preservation of rare riparian arthropods. Whereas hygrophilic species benefited from increased vegetation cover, xerothermophilic specialists were favoured by increased flooding disturbance. In contrast to flight-active riparian carabids occurring throughout the river system, especially cursorial spiders are expected to go extinct under increased anthropogenic alterations of discharge regimes. We show the importance of a dynamic and evidence-based approach of river management on a local scale to preserve vulnerable riparian arthropods. In general, river restoration should generate the required heterogeneity in environmental conditions (e.g. dynamic processes) at the river bank level, thereby increasing the sustainability of riverine landscapes. More-over, we argue that the understanding of functional responses towards environmental factors results in general and widely applicable guiding concepts for species conservation.
1. Host plant finding in walking herbivorous beetles is still poorly understood. Analysis of small-scale movement patterns under semi-natural conditions can be a useful tool to detect behavioural responses towards host plant cues. 2. In this study, the small-scale movement behaviour of the monophagous leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) was studied in a semi-natural arena (r = 1 m). In three different settings, a host (Salvia pratensis L., Lamiales: Lamiaceae), a non-host (Rumex conglomeratus Murr., Caryophyllales: Polygonaceae), or no plant was presented in the centre of the arena. 3. The beetles showed no differences in the absolute movement variables, straightness and mean walking speed, between the three settings. However, the relative movement variables, mean distance to the centre and mean angular deviation from walking straight to the centre, were significantly smaller when a host plant was offered. Likewise, the angular deviation from walking straight to the centre tended to decline with decreasing distance from the centre. Finally, significantly more beetles were found on the host than on the non-host at the end of all the trials. 4. It is concluded that C. canaliculata is able to recognise its host plant from a distance. Whether olfactory or visual cues (or a combination of both) are used to find the host plant remains to be elucidated by further studies.
The importance of olfactory versus contact cues for host plant recognition was investigated in the tortoise beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae), which is strictly monophagous on meadow sage. The reaction of adult beetles to olfactory and contact host cues was tested using three bioassays (locomotion compensator, six-chamber-olfactometer, stem arena') to account for different behavioral contexts. Bioassay-guided fractionation of plant extracts was elaborated to characterize the nature of contact stimuli. The beetles were only slightly attracted to odors from small amounts of leaf material. However, when contact cues were provided additionally, the beetles showed strong preferences for samples of their host plant over controls. Bioassay-guided fractionation led to isolation of at least two non-polar contact stimuli acting in concert that are sufficient for host plant identification in C. canaliculata.
Based on a marginal value approach, we derive a nonlinear expression for evolutionarily stable (ES) dispersal rates in a metapopulation with global dispersal. For the general case of density-dependent population growth, our analysis shows that individual dispersal rates should decrease with patch capacity and-beyond a certain threshold-increase with population density. We performed a number of spatially explicit, individual-based simulation experiments to test these predictions and to explore further the relevance of variation in the rate of population increase, density dependence, environmental fluctuations and dispersal mortality on the evolution of dispersal rates. They confirm the predictions of our analytical approach. In addition, they show that dispersal rates in metapopulations mostly depend on dispersal mortality and inter-patch variation in population density. The latter is dominantly driven by environmental fluctuations and the rate of population increase. These conclusions are not altered by the introduction of neighbourhood dispersal. With patch capacities in the order of 100 individuals, kin competition seems to be of negligible importance for ES dispersal rates except when overall dispersal rates are low.
We established a library of chromosomal DNA of Listeria ivanovii in the pTZ19R plasmid system, using Escherichia coli DH5alpha as the host. One recombinant clone reacted strongly with a polyclonal antiserum raised against the listeriolysin 0 and a second exoprotein (24kDa) of L. ivanovii, which is most probably also involved in cytolytic processes. The recombinant E. coli clone may contain part of the listeriolysin 0 gene of L. ivanovii.
Several exoproteins from Listeria monocytogenes serovar 4b (NCTC 10527) and Listeria ivanovii (ATCC) 19119, SLCC 2379), respectively, have been purified to homogeneity by thiol-disulfide exchange chromatography and gel filtration. Both strains produce a haemolytic/cytolytic protein of Mr 58 kDa, which has all the properties of a SH-activated cytolysin, the prototype of which is streptolysin 0 (SLO), and this protein has therefore heen termed Iisteriolysin 0 (LLO). In addition a protein of Mr 24 kDa from culture supernatants of L. ivanovii co-purified withLLO. The N-terminal aminoacid sequences of both proteins from L. ivanovii have been determined. By mutagenesis with transposons of Gram-positive origin (Tn916 and TnI545), which have been introduced via conjugation into L. ivanovii, several phenotypic mutants (altered haemolysis on sheep blood agar or lecithinase-negative) were obtained. Results on the properties of these muntants will he presented.
The plasmid pBC16 (4.25 kbases), ongtnally isolated from Bacillus cereus, determines tetracycline resistance and can be transformed into competent cells of B. subtilis. A miniplasmid of pBCl6 (pBCI6-1), 2,7 kb) which has lost an EcoRI fragment of pBCI6 retains the replication functions and the tetracycline resistance. This plasmid which carries only one EcoRI site has been joined in vitro to pBS], a cryptic plasmid previously isolated from B. subtilis and shown to carry also a single EcoRI site (Bernhard et aI., 1978). The recombinant plasmid is unstable and dissociates into the plasmid pBSl61 (8.2 kb) and the smaller plasmid pBS162 (2. I kb). Plasmid pBS161 retains the tetracycline resistance. It possesses a single EcoRI site and 6 HindlII sites. The largest HindIII fragment of pBS161 carries the tetracycline resistance gene and the replication function. After circularization in vitro of this fragment a new plasmid, pBS161-l is generated, which can be used as a HindlII and EcoRI cloning vector in Bacillus suhtilis. Hybrid plasmids consisting of the E. coli plasmids pBR322, p WL 7 or pACl84 and different HindlII fragments of pBSI61 were constructed in vitro. Hybrids containing together with the E. coli plasmid the largest HindlII fragment of pBS161 can replicate in E. coli and B. sublilis. In E. coli only the replicon of the E. coli plasmid part is functioning whereas in B. suhtilis replication of the hybrid plasmid is under the control of the Bacillus replicon. The tetracycline resistance of the B. subtilis plasmid is expressed in E. coli, but several antibiotic resistances of the E. coli plasmids (ampicillin, kanamycin and chloramphenicol) are not expressed in B. suhtilis. The hybrid plasmids seem to be more unstable in B. subtilis than in E. coli.
When reovirus-infected Hela cells are incubated at 43°C virus-specific messenger RNA is released ~rom the polysomes. It accumulates free in the cytoplasm as messenger ribonucleoprotem partIcles (mRNPs). The:e part~cles have a sedimentati~n rate of about 50S and a buoyant densIty m CsCI of 1.42 g/cm . ReovIrus mRNPs contam, beSIdes all three size classes of reovirus messenger RNA, the same spectrum of proteins found in the polysomal mRNPs from uninfected cells, plus t~o addi~ional pr?teins with molecular masses of 7000~ d and 110000 d, respectively. Electron mIcroscoPIc exammatlOn of the reovIrus mRNP fractIOn reveals specific Y-shaped structures wIth a total mean length ofO.5Ilm.
Incubation of the colicinogenic Escherichia coli strain JC 411 (ColE1) at elevated temperatures (47-49°) leads to the accumulation of catenated molecules and replicative intermediates of this plasmid. Mature supercoiled OolE1 DNA molecules synthesized under these conditions have an increased number of tertiary turns as shown by electron microscopy. The monomeric tightly supercoiled molecules possess a slightly slower sedimentation rate and a higher binding capacity for ethidium bromide than supercoiJed monomers synthesized at lower temperatures. Recombination deficient mutants of E. coli recA, recB and recC, which carry the ColE1 plasmid, form about the same amount of catenated molecules at the elevated temperature as a rec+ strain. In addition, we have observed by electron microscopy a small percentage (.--.5% of the circular DNA molecules) of minicircular DNA molecules in all preparations of JC 411 (CoIE1). They are homogenous in size, with a molecular weight of 1.4 X 106 daltons. Addition of chloramphenicol to a culture of Proteus mirabilis (ColE1) leads to an increased amount of higher multiple circular oligomers and to a stimulated accumulation of catenated OolE1 DNA molecules of varying sizes. ColE1 DNA synthesis is more thermosensitive than chromosomal DNA replication in P. mirabili8. Plasmid replication stops completely at temperatures above 43°C.
Abstract: Understanding the causes and consequences of dispersal is a prerequisite for the effective management of natural populations. Rather than treating dispersal as a fixed trait, it should be considered a plastic process that responds to both genetic and environmental conditions. Here, we consider how the ambient temperature experienced by juvenile Erigone atra, a spider inhabiting crop habitat, influences adult dispersal. This species exhibits 2 distinct forms of dispersal, ballooning (long distance) and rappelling (short distance). Using a half-sib design we raised individuals under 4 different temperature regimes and quantified the spiders' propensity to balloon and to rappel. Additionally, as an indicator of investment in settlement, we determined the size of the webs build by the spiders following dispersal. The optimal temperature regimes for reproduction and overall dispersal investment were 20 °C and 25 °C. Propensity to perform short-distance movements was lowest at 15 °C, whereas for long-distance dispersal it was lowest at 30 °C. Plasticity in dispersal was in the direction predicted on the basis of the risks associated with seasonal changes in habitat availability; long-distance ballooning occurred more frequently under cooler, spring-like conditions and short-distance rappelling under warmer, summer-like conditions. Based on these findings, we conclude that thermal conditions during development provide juvenile spiders with information about the environmental conditions they are likely to encounter as adults and that this information influences the spider's dispersal strategy. Climate change may result in suboptimal adult dispersal behavior, with potentially deleterious population level consequences.
Abstract: Inbreeding avoidance and asymmetric competition over resources have both been identified as factors favoring the evolution of sex-biased dispersal. It has also been recognized that sex-specific costs of dispersal would select for sex-biased dispersal, but there is little quantitative information on this aspect. In this paper we explore (i) the quantitative relationship between cost-asymmetry and a bias in dispersal, (ii) the influence of demographic stochasticity on this effect, and (iii) how inbreeding and cost-asymmetry interact in their effect on sex-specific dispersal. We adjust an existing analytical model to account for sex-specific costs of dispersal. Based on numerical calculations we predict a severe bias in dispersal already for small differences in dispersal costs. We corroborate these predictions in individual-based simulations, but show that demographic stochasticity generally leads to more balanced dispersal. In combination with inbreeding, cost asymmetries will usually determine which of the two sexes becomes the more dispersive.
Abstract: Inbreeding depression, asymmetries in costs or benefits of dispersal, and the mating system have been identified as potential factors underlying the evolution of sex-biased dispersal. We use individual-based simulations to explore how the mating system and demographic stochasticity influence the evolution of sex-specific dispersal in a metapopulation with females competing over breeding sites, and males over mating opportunities. Comparison of simulation results for random mating with those for a harem system (locally, a single male sires all offspring) reveal that even extreme variance in local male reproductive success (extreme male competition) does not induce male-biased dispersal. The latter evolves if the between-parch variance in reproductive success is larger for males than females. This can emerge due to demographic stochasticity if the habitat patches are small. More generally, members of a group of individuals experiencing higher spatio-temporal variance in fitness expectations may evolve to disperse with greater probability than others.
Abstract: 1. The response of dispersal towards evolution largely depends on its heritability for which upper limits are determined by the trait's repeatability. 2. In the Linyphiid spider E. atra, we were able to separate long- and short-distance dispersal behaviours (respectively ballooning and rappelling) under laboratory conditions. By performing repeated behavioural trials for females, we show that average dispersal trait values decrease with increasing testing days. By comparing mated and unmated individuals during two periods (before and after mating for the mated group, and the same two periods for the unmated group), we show that mating has no effect on the mean displayed dispersal behaviour or its within-individual variation. Repeatabilities were high and consistent for ballooning motivation, but not for rappelling. 3. Ballooning motivation can be regarded as highly individual-specific behaviour, while general pre-dispersal and rappelling behaviours showed more individual variation. Such difference in repeatability between long-and short-distance dispersal suggests that short-and long-distance dispersal events are triggered by different ecological and evolutionary mechanisms.
Abstract: From a conservation point of view, species- tolerances towards disturbance are often generalised and lack reference to spatial scales and underlying processes. In order to investigate how average typical species react to habitat fragmentation and disturbance, we adopted a multi-species approach to address occupancy patterns of five specialised dune arthropods (butterflies Hipparchia semele, Issoria lathonia; grasshopper Oedipoda caerulescens; spiders Alopecosa fabrilis, Xysticus sabulosus) in recently fragmented coastal dune habitats which are subjected to varying levels and modes of local disturbance, i.e. trampling by cattle or people. Occupancy patterns were assessed during two successive years in 133 grey dune fragments of the Flemish coastal dunes (Belgium, France). By treating species as a random factor in our models, emphasis was placed on generalisations rather than documenting species-specific patterns. Our study demonstrates that deteriorating effects of local disturbance on arthropod incidence cannot be interpreted independent of its landscape context, and appear to be more severe when patch area and connectivity decrease. When controlled for patch area and trampling intensity, the probability of species occupancy in poorly connected patches is higher under cattle trampling than under recreation. Incidences additionally decrease with increasing intensity of cattle trampling, but increases with trampling by tourists. This study provides evidence of mode- and landscape-dependent effects of local disturbance on species occupancy patterns. Most importantly, it demonstrates that trampling of sensitive dune fragments will lead to local and metapopulation extinction in landscapes where trampling occurs in a spatially autocorrelated way, but that the outcome (spatial patterns) varies in relation to disturbance mode, indicating that effects of disturbance cannot be generalised.
Abstract: Intensification of land-use in agricultural landscapes is responsible for a decline of biodiversity which provide important ecosystem services like pest-control. Changes in landscape composition may also induce behavioural changes of predators in response to variation in the biotic or abiotic environment. By controlling for environmentally confounding factors, we here demonstrate that the orb web spider Araneus diadematus alters its web building behaviour in response to changes in the composition of agricultural landscapes. Thereby, the species increases its foraging efficiency (i.e. investments in silk and web asymmetry) with an increase of agricultural land-use at intermediate spatial scales. This intensification is also related to a decrease in the abundance of larger prey. A negative effect of landscape properties at similar spatial scales on spider fitness was recorded when controlling for relative investments in capture thread length. This study consequently documents the web building flexibility in response to changes in landscape composition, possibly due to changes in prey availability.
Background: Male killing endosymbionts manipulate their arthropod host reproduction by only allowing female embryos to develop into infected females and killing all male offspring. Because of the reproductive manipulation, we expect them to have an effect on the evolution of host dispersal rates. In addition, male killing endosymbionts are expected to approach fixation when fitness of infected individuals is larger than that of uninfected ones and when transmission from mother to offspring is nearly perfect. They then vanish as the host population crashes. High observed infection rates and among-population variation in natural systems can consequently not be explained if defense mechanisms are absent and when transmission efficiency is perfect. Results: By simulating the host-endosymbiont dynamics in an individual-based metapopulation model we show that male killing endosymbionts increase host dispersal rates. No fitness compensations were built into the model for male killing endosymbionts, but they spread as a group beneficial trait. Host and parasite populations face extinction under panmictic conditions, i.e. conditions that favor the evolution of high dispersal in hosts. On the other hand, deterministic 'curing' (only parasite goes extinct) can occur under conditions of low dispersal, e.g. under low environmental stochasticity and high dispersal mortality. However, high and stable infection rates can be maintained in metapopulations over a considerable spectrum of conditions favoring intermediate levels of dispersal in the host. Conclusion: Male killing endosymbionts without explicit fitness compensation spread as a group selected trait into a metapopulation. Emergent feedbacks through increased evolutionary stable dispersal rates provide an alternative explanation for both, the high male-killing endosymbiont infection rates and the high among-population variation in local infection rates reported for some natural systems.
Background: Male killing endosymbionts manipulate their arthropod host reproduction by only allowing female embryos to develop into infected females and killing all male offspring. Because the resulting change in sex ratio is expected to affect the evolution of sex-specific dispersal, we investigated under which environmental conditions strong sex-biased dispersal would emerge, and how this would affect host and endosymbiont metapopulation persistence. Results: We simulated host-endosymbiont metapopulation dynamics in an individual-based model, in which dispersal rates are allowed to evolve independently for the two sexes. Prominent male-biased dispersal emerges under conditions of low environmental stochasticity and high dispersal mortality. By applying a reshuffling algorithm, we show that kin-competition is a major driver of this evolutionary pattern because of the high within-population relatedness of males compared to those of females. Moreover, the evolution of sex-specific dispersal rescues metapopulations from extinction by (i) reducing endosymbiont fixation rates and (ii) by enhancing the extinction of endosymbionts within metapopulations that are characterized by low environmental stochasticity. Conclusion: Male killing endosymbionts induce the evolution of sex-specific dispersal, with prominent male-biased dispersal under conditions of low environmental stochasticity and high dispersal mortality. This male-biased dispersal emerges from stronger kin-competition in males compared to females and induces an evolutionary rescue mechanism.
The optimal probability and distance of dispersal largely depend on the risk to end up in unsuitable habitat. This risk is highest close to the habitat’s edge and consequently, optimal dispersal probability and distance should decline towards the habitat’s border. This selection should lead to the emergence of spatial gradients in dispersal strategies. However, gene flow caused by dispersal itself is counteracting local adaptation. Using an individual based model we investigate the evolution of local adaptations of dispersal probability and distance within a single, circular, habitat patch. We compare evolved dispersal probabilities and distances for six different dispersal kernels (two negative exponential kernels, two skewed kernels, nearest neighbour dispersal and global dispersal) in patches of different size. For all kernels a positive correlation between patch size and dispersal probability emerges. However, a minimum patch size is necessary to allow for local adaptation of dispersal strategies within patches. Beyond this minimum patch area the difference in mean dispersal distance between center and edge increases linearly with patch radius, but the intensity of local adaptation depends on the dispersal kernel. Except for global and nearest neighbour dispersal, the evolved spatial pattern are qualitatively similar for both, mean dispersal probability and distance. We conclude, that inspite of the gene-flow originating from dispersal local adaptation of dispersal strategies is possible if a habitat is of sufficient size. This presumably holds for any realistic type of dispersal kernel.
Oviposition site selection in insects is essential in terms of low egg mortality, high offspring survival and therefore a high reproductive output. Although oviposition height could be a crucial factor for the fitness of overwintering eggs, it has rarely been investigated. In this study the oviposition height of a polyphagous leaf beetle, Galeruca tanaceti Linnaeus in different habitats and at different times of the season was examined and its effect on egg clutch mortality was recorded. The leaf beetle occurs as an occasional pest on several agricultural plants. It deposits its eggs within herbaceous vegetation in autumn. Eggs are exposed to numerous biotic and abiotic mortality factors summarized as egg parasitism and winter mortality. Oviposition height of the leaf beetle was not uniform, but changed significantly with the structure of the habitat and during the season. Mean oviposition height per site (70.2±4.9 cm) was significantly higher than mean vegetation height (28.4±2.4 cm). Height of plants with egg clutches attached and oviposition height were significantly positively correlated. The results suggest that females try to oviposit as high as possible in the vegetation and on the plants selected. In accordance with this, the probability of egg parasitism and of winter egg clutch mortality significantly declined with increasing oviposition height. A preference of G. tanaceti for oviposition sites high up in the vegetation might therefore have evolved due to selection pressures by parasitoids and winter mortality.
Caterpillars of the butterfly Maculinea rebeli develop as parasites inside ant colonies. In intensively studied French populations, about 25% of caterpillars mature within 1 year (fast-developing larvae [FDL]) and the others after 2 years (slow-developing larvae [SDL]); all available evidence indicates that this ratio is under the control of egg-laying females. We present an analytical model to predict the evolutionarily stable fraction of FDL (pESS). The model accounts for added winter mortality of SDL, general and kin competition among caterpillars, a competitive advantage of SDL over newly entering FDL (priority effect), and the avoidance of renewed infection of ant nests by butterflies in the coming season (segregation). We come to the following conclusions: (1) all factors listed above can promote the evolution of delayed development; (2) kin competition and segregation stabilize pESS near 0.5; and (3) a priority effect is the only mechanism potentially selecting for. However, given the empirical data, pESS is predicted to fall closer to 0.5 than to the 0.25 that has been observed. In this particular system, bet hedging cannot explain why more than 50% of larvae postpone growth. Presumably, other fitness benefits for SDL, for example, higher fertility or longevity, also contribute to the evolution of delayed development. The model presented here may be of general applicability for systems where maturing individuals compete in small subgroups.
Questions: What are the relative contributions of kin selection and individual selection to the evolution of dispersal rates in fragmented landscapes? How do environmental parameters influence the relative contributions of both evolutionary forces? Features of the model: Individual-based simulation model of a metapopulation. Logistic local growth dynamics and density-dependent dispersal. An optional shuffling algorithm allows the continuous destruction of any genetic structure in the metapopulation. Ranges of key variables: Depending on dispersal mortality (0.05-0.4) and the strength of environmental fluctuations, mean dispersal probability varied between 0.05 and 0.5. Conclusions: For local population sizes of 100 individuals, kin selection alone could account for dispersal probabilities of up to 0.1. It may result in a ten-fold increase of optimal dispersal rates compared with those predicted on the basis of individual selection alone. Such a substantial contribution of kin selection to dispersal is restricted to cases where the overall dispersal probabilities are small (textless 0.1). In the latter case, as much as 30% of the total fitness of dispersing individuals could arise from the increased reproduction of kin left in the natal patch.
More recently, it became clear that conclusions drawn from traditional ecological theory may be altered substantially if the spatial dimension of species interactions is considered explicitly. Regardless of the details of these models, spatially explicit simulations of ecological processes have nearly universally shown that spatial or spatio-temporal patterns in species distributions can emerge even from homogeneous starting conditions; limited dispersal is one of the key factors responsible for the development of such aggregated and patchy distributions (cf., Pacala 1986, Holmes et al. 1994, Molofsky 1994, Tilman 1994, Bascompte and Sole 1995, 1997, 1998, Jeltsch et al. 1999). In line with these ideas, we wish to draw attention to the fact that in heterogeneous landscapes differences in characteristic dispersal distances between species are a sufficient precondition for the emergence of a successional pattern. We will use a simple, spatially explicit simulation program to demonstrate the validity of this statement. We will also show that the speed of the successional progress depends on scale and heterogeneity in the distribution of suitable habitat.
Scorpions commonly are assumed to hunt on living prey. But under laboratory conditions they also respond very sensitively to dead insects lying on the substrate. In many cases the motionless prey is seized and consumed. It was investigated how this behavior can be elicited. The buthid scorpions Androctonus australis (L.) and Buthus occitanus (Am.) not only find motionless prey again which was stung but managed to escape before dying: They also respond to extracts of the cuticle of prey insects. After touching prey marks' either with the tips of the chelae fingers or the tarsi of the walking legs or the pectine organs specific responses (searching, seizing, feeding) are released at a high rate. Behavioral experiments demonstrate for the first time the chemosensitivity of the pectine organs for which only mechanosensitivity had been proofed formerly. Mechanical as well as contact chemical stimulation of these organs cause scorpions to orient towards the stimulus source which is grasped, retained and consumed or rejected depending on its quality. The probably responsible chemosensitive receptors are already described in the literature. The possible adaptive value and the biological significance of contact chemoreception in prey catching and in other aspects of the life of scorpions is discussed.
Background: According to the classical model of Macevicz and Oster, annual eusocial insects should show a clear dichotomous "bang-bang" strategy of resource allocation; colony fitness is maximised when a period of pure colony growth (exclusive production of workers) is followed by a single reproductive period characterised by the exclusive production of sexuals. However, in several species graded investment strategies with a simultaneous production of workers and sexuals have been observed. Such deviations from the "bang-bang" strategy are usually interpreted as an adaptive (bet-hedging) response to environmental fluctuations such as variation in season length or food availability. To generate predictions about the optimal investment pattern of insect colonies in fluctuating environments, we slightly modified Macevicz and Oster's classical model of annual colony dynamics and used a dynamic programming approach nested into a recurrence procedure for the solution of the stochastic optimal control problem. Results: 1) The optimal switching time between pure colony growth and the exclusive production of sexuals decreases with increasing environmental variance. 2) Yet, for reasonable levels of environmental fluctuations no deviation from the typical bang-bang strategy is predicted. 3) Model calculations for the halictid bee Lasioglossum malachurum reveal that bet-hedging is not likely to be the reason for the graded allocation into sexuals versus workers observed in this species. 4) When environmental variance reaches a critical level our model predicts an abrupt change from dichotomous behaviour to graded allocation strategies, but the transition between colony growth and production of sexuals is not necessarily monotonic. Both, the critical level of environmental variance as well as the characteristic pattern of resource allocation strongly depend on the type of function used to describe environmental fluctuations. Conclusion: Up to now bet-hedging as an evolutionary response to variation in season length has been the main argument to explain field observations of graded resource allocation in annual eusocial insect species. However, our model shows that the effect of moderate fluctuations of environmental conditions does not select for deviation from the classical bang-bang strategy and that the evolution of graded allocation strategies can be triggered only by extreme fluctuations. Detailed quantitative observations on resource allocation in eusocial insects are needed to analyse the relevance of alternative explanations, e.g. logistic colony growth or reproductive conflict between queen and workers, for the evolution of graded allocation strategies.
Abstract: Background Social insects show considerable variability not only in social organisation but also in the temporal pattern of nest cycles. In annual eusocial sweat bees, nest cycles typically consist of a sequence of distinct phases of activity (queen or workers collect food, construct, and provision brood cells) and inactivity (nest is closed). Since the flight season is limited to the time of the year with sufficiently high temperatures and resource availability, every break reduces the potential for foraging and, thus, the productivity of a colony. This apparent waste of time has not gained much attention. Results We present a model that explains the evolution of activity breaks by assuming differential mortality during active and inactive phases and a limited rate of development of larvae, both reasonable assumptions. The model predicts a systematic temporal structure of breaks at certain times in the season which increase the fitness of a colony. The predicted pattern of these breaks is in excellent accordance with field data on the nest cycle of the halictid Lasioglossum malachurum. Conclusion Activity breaks are a counter-intuitive outcome of varying mortality rates that maximise the reproductive output of primitively eusocial nests.
Abstract: Background Group formation and food sharing in animals may reduce variance in resource supply to breeding individuals. For some species it has thus been interpreted as a mechanism of risk avoidance. However, in many groups reproduction is extremely skewed. In such groups resources are not shared equally among the members and inter-individual variance in resource supply may be extreme. The potential consequences of this aspect of group living have not attained much attention in the context of risk sensitive foraging. Results We develop a model of individually foraging animals that share resources for reproduction. The model allows analyzing how mean foraging success, inter-individual variance of foraging success, and the cost of reproduction and offspring raising influence the benefit of group formation and resource sharing. Our model shows that the effects are diametrically opposed in egalitarian groups versus groups with high reproductive skew. For individuals in egalitarian groups the relative benefit of group formation increases under conditions of increasing variance in foraging success and decreasing cost of reproduction. On the other hand individuals in groups with high skew will profit from group formation under conditions of decreasing variance in individual foraging success and increasing cost of reproduction. Conclusion The model clearly demonstrates that reproductive skew qualitatively changes the influence of food sharing on the reproductive output of groups. It shows that the individual benefits of variance reduction in egalitarian groups and variance enhancement in groups with reproductive skew depend critically on ecological and life-history parameters. Our model of risk-sensitive foraging thus allows comparing animal societies as different as spiders and birds in a single framework.
Many organisms show polymorphism in dispersal distance strategies. This variation is particularly ecological relevant if it encompasses a functional separation of short- (SDD) and long-distance dispersal (LDD). It remains, however, an open question whether both parts of the dispersal kernel are similarly affected by landscape related selection pressures. We implemented an individual-based model to analyze the evolution of dispersal traits in fractal landscapes that vary in the proportion of habitat and its spatial configuration. Individuals are parthenogenetic with dispersal distance determined by two alleles on each individual‘s genome: one allele coding for the probability of global dispersal and one allele coding for the variance of a Gaussian local dispersal with mean value zero. Simulations show that mean distances of local dispersal and the probability of global dispersal, increase with increasing habitat availability, but that changes in the habitat's spatial autocorrelation impose opposing selective pressure: local dispersal distances decrease and global dispersal probabilities increase with decreasing spatial autocorrelation of the available habitat. Local adaptation of local dispersal distance emerges in landscapes with less than 70% of clumped habitat. These results demonstrate that long and short distance dispersal evolve separately according to different properties of the landscape. The landscape structure may consequently largely affect the evolution of dispersal distance strategies and the level of dispersal polymorphism.
Clerodendrumjistulosum Becc. is a true myrmecophyte as it offers nesting space for ants in hollow intemodes. In contrast to previous reports our investigations proved that these domatia open by themselves, thus providing cavities for a variety of different ant species. In Sarawak, Malaysia, we did not find an obligate relationship between C. jistulosum and a specific ant-partner. For comparison, studies on herbarium material of other Clerodendrum species were carried out a further species, C. deflexum from the Malay Peninsula and Sumatra presumably also is myrmecophytic.
In the humid tropics of SE Asia there are some 14 myrmecophytic species of the pioneer tree genus Macaranga (Euphorbiaceae). In Peninsular Malaysia a close association exists between the trees and the small, non-stinging myrmicine Crema togas ter borneensis. These ants feed mainly on food bodies provided by the plants and have their colonies inside the hollow intemodes. In a ten months field study we were able to demonstrate for four Macaranga species (M. triloba, M. hypoleuca, M. hosei, M. hulletti) that host plants also benefit considerably from ant-occupation. Ants do not contribute to the nutrient demands of their host plant, they do, however, protect it against herbivores and plant competition. Cleaning behaviour of the ants results in the removal of potential herbivores already in their earliest developmental stages. Strong aggressiveness and a mass recruiting system enable the ants to defend the host plant against many herbivorous insects. This results in a significant decrease in leaf damage due to herbivores on ant-occupied compared to ant-free myrmecophytes as well as compared to non-myrmecophytic Macaranga species. Most important is the ants' defense of the host plant against plant competitors, especially vines, which are abundant in the well-lit pioneer habitats where Macaranga grows. Ants bite off any foreign plant part coming into contact with their host plant. Both ant-free myrmecophytes and non-myrmecophytic Macaranga species had a significantly higher incidence of vine growth than specimens with active ant colonies. This may be a factor of considerable importance allowing Macaranga plants to grow at sites of strongest competition.
The woody climber Millettia niuewenhuisii (Fabaceae) and the shrub Myrmeconauclea strigosa (Rubiaceae) in Sabah, Borneo are associated with ants. The hollow stems of Millettia nieuwenhuisii are regularly inhabited by an aggressive Cladomyrma sp., which keeps pseudococcids inside the stem. On Myrmeconauclea strigosa the ants live in hollow internodal swellings near the end of the branches. In this plant many different ant species use the nesting space in an opportunistic manner.
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Ficus obscura var. borneensis is a true myrmecophyte. It spontaneously forms cavities (domatia) in parts of its twigs which open by slits, These occur in the internodes and are usually not swollen. The domatia are inhabited by a variety of non-specific tree-living ants including Crematogaster spp., Cataulacus sp., Tetramorium sp., Cardio condyla sp. and Camponotus sp.. Additionally the plant providL a su~ar-containing secretion from extrafloral nectaries on the lower surfaces of the leaves. Examination of herbarium specimens of 37 other South-east Asian Ficus species did not reveal a single specimen with domatia.
1. Oviposition site selection is crucial for the reproductive success of herbivorous insects. According to the preference–performance hypothesis, females should oviposit on host plants that enhance the performance of their offspring. More specifically, the plant vigour hypothesis predicts that females should prefer large and vigorously growing host plants for oviposition and that larvae should perform best on these plants. 2. The present study examined whether females of the monophagous leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) prefer to oviposit on large host plant individuals of the meadow clary and whether large host plants are of higher nutritional quality than small host plants. Subsequently, it was tested whether the female preference correlates with offspring performance and survival. 3. In the field, females preferred large host plant individuals for oviposition and host plant quality, i.e. leaf nitrogen content, was significantly higher in leaves of large than of small host plants. 4. In the laboratory, larval development time was shorter on leaves of large host plant individuals than on small host plant individuals, but this could not be shown in the field. 5. However, a predator-exclusion experiment in the field resulted in a higher survival of larvae on large host plants than on small host plants when all predators had free access to the plants. On caged host plants there was no difference in survival of larvae between plant size categories. 6. It is concluded that females of C. canaliculata select oviposition sites that enhance both performance and survival of their offspring, which meets the predictions of the plant vigour hypothesis.
Egg distribution in herbivorous beetles can be affected by bottom-up (host plant), and by top-down factors (parasitoids and predators), as well as by other habitat parameters. The importance of bottom-up and top-down effects may change with spatial scale. In this study, we investigated the influence of host plant factors and habitat structure on egg distribution in the leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae), a monophagous herbivore on Salvia pratensis L. (Lamiales: Lamiaceae), on four spatial scales: individual host plant, microhabitat, macrohabitat, and landscape. At the individual host plant scale we studied the correlation between egg clutch incidence and plant size and quality. On all other scales we analyzed the relationship between the egg clutch incidence of C. canaliculata and host plant percentage cover, host plant density, and the surrounding vegetation structure. Vegetation structure was examined as herbivores might escape egg parasitism by depositing their eggs on sites with vegetation factors unfavorable for host searching parasitoids. The probability that egg clutches of C. canaliculata were present increased with an increasing size, percentage cover, and density of the host plant on three of the four spatial scales: individual host plant, microhabitat, and macrohabitat. There was no correlation between vegetation structure and egg clutch occurrence or parasitism on any spatial scale. A high percentage of egg clutches (38–56%) was parasitized by Foersterella reptans Nees (Hymenoptera: Tetracampidae), the only egg parasitoid, but there was no relationship between egg parasitism and the spatial distribution of egg clutches of C. canaliculata on any of the spatial scales investigated. However, we also discuss results from a further study, which revealed top-down effects on the larval stage.
Fragmentation, deterioration, and loss of habitat patches threaten the survival of many insect species. Depending on their trophic level, species may be differently affected by these factors. However, studies investigating more than one trophic level on a landscape scale are still rare. In the present study we analyzed the effects of habitat size, isolation, and quality for the occurrence and population density of the endangered leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) and its egg parasitoid, the hymenopteran wasp Foersterella reptans Nees (Hymenoptera: Tetracampidae). C. canaliculata is strictly monophagous on meadow sage (Salvia pratensis), while F. reptans can also parasitize other hosts. Both size and isolation of habitat patches strongly determined the occurrence of the beetle. However, population density increased to a much greater extent with increasing host plant density ( = habitat quality) than with habitat size. The occurrence probability of the egg parasitoid increased with increasing population density of C. canaliculata. In conclusion, although maintaining large, well-connected patches with high host plant density is surely the major conservation goal for the specialized herbivore C. canaliculata, also small patches with high host plant densities can support viable populations and should thus be conserved. The less specialized parasitoid F. reptans is more likely to be found on patches with high beetle density, while patch size and isolation seem to be less important.
We present the results of individual-based simulation experiments on the evolution of dispersal rates of organisms living in metapopulations. We find conflicting results regarding the relationship between local extinction rate and evolutionarily stable (ES) dispersal rate depending on which principal mechanism causes extinction: if extinction is caused by environmental catastrophes eradicating local populations, we observe a positive correlation between extinction and ES dispersal rate; if extinction is a consequence of stochastic local dynamics and environmental fluctuations, the correlation becomes ambiguous; and in cases where extinction is caused by dispersal mortality, a negative correlation between local extinction rate and ES dispersal rate emerges. We conclude that extinction rate, which both affects and is affected by dispersal rates, is not an ideal predictor for optimal dispersal rates.
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Vogelzwerge des Waldes
(1964)
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Vögel am Roten Meer
(1965)
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1. Scorpions can orient menotactically to horizontal air currents (Fig. 1). 2. Changing the wind velocity from 0,05-0,1 m/sec to 3--5 m/sec has no influence on the menotactic angle kept by an anemomenotactic oriented scorpion (Fig. 2). 3. The receptors percieving the direction of air currents are the trichobothria. 4. Orientation to horizon landmarks, anemomenotactic and astromenotactic orientation does not exclude each other but complete themthelves mutually: a) A scorpion orienting to horizon landmarks learns the corresponding anemomenotactic and astromenotactic angle (Fig. 4). b) While orienting anemomenotactically (which is normally the main means of orientation when landmarks are absent) they continously learn new astromenotactical angles (Fig. 5), thus compensating for the movement of the moon or sun which can not be compensated otherwise. c) Short calms and short changes of wind direction can be overcome by astrotaxis.
Werben und Drohen gehören zu den Verhaltensweisen mit Mitteilungswert, die besonders häufig - im Dienste ihrer SignalIunktion umgestaltet - zu Auslösern werden. Solche Auslöser, seien es nun besondere Bewegungsweisen und/oder spezielle morphologische Strukturen, sind an das Individuum gebunden. Eine optische Werbung oder ein Drohen mit körperfremden Mitteln, stellvertretend für ein Individuum, galt bislang als Privileg des Menschen. Die folgenden Ausführungen werden aber zeigen, daß auch andere Lebewesen derartige "Aushängeschilder" gebrauchen.
1. Die Feistkäfer Pimelia grossa, P. tenuicornis, der Mehlkäfer Tenebrio molitor, die Mistkäfer Geotrupes silvaticus und G. stercorarius konnen sich unter entsprechenden Bedingungen rein anemomenotaktisch orientieren (Abb. 1-8). Sie bevorzugen Laufwinkel, die in relativ enge Winkelbereiche rechts und links der beiden Grundrichtungen führen (Abb. 3, 4, 26). 2. Die Bevorzugung bestimmter Winkelgrößen andert sich bei Geotrupes nicht gesetzmig mit der Tageszeit, der Temperatur (im Bereich 18-28° C) oder dem Fütterungszustand (Abb. 8-11). 3. Die untere Grenze der Windstärke, die eine menotaktische Einstellung ermöglicht, liegt für die Mistkäfer bei etwa 0,15 m/sec, für die Feistkäfer bei etwa 0,4 m/sec. Die obere Grenze befindet sich bei Geschwindigkeiten, die den Käfern ein Vorwärtskommen unmöglich machen. 4. Bei der menotaktischen Einstellung wird nur die Reizrichtung nicht aber die Reizstarke bewertet (Abb. 13-15). 5. Die Kontinuitat des Luftstroms ist keine Voraussetzung für die anemomenotaktische Orientierung: Die Käfer orientieren sich auch nach kurzen Windstößen (Abb. 17, 19, 21). Während der Windstille kommt es zu regelhaften Abweichungen von dem bei Wind eingehaltenen Kurs (Abb. 18). Das Ausmaß dieser Abweichungen wird nach häufigen Windunterbrechungen stark verringert (Abb. 20). 6. Gegen Turbulenzen des Luftstroms, wie sie über unebenem Untergrund entstehen, ist die Anemomenotaxis der Käfer nicht sehr anfällig (Abb. 22). 7. Die Sinnesorgane, die dem intakten Käfer die Windrichtungsbestimmung ermöglichen, sprechen auf Bewegungen im Pedicellus-Flagellumgelenk an. Ein Verlust der Endkolben hat beim Mistkäfer keinen Einfluß auf die Richtungs- und Winkelgrößenwahl, auch die Streuung wird nicht signifikant größer. 2 Flagellenglieder pro Antenne ermöglichen bei Windgeschwindigkeiten um oder über 1 m/sec noch eine anemomenotaktische Orientierung (Tabelle 3). 8. Bei 3 Mistkäfern, deren Fühler 4 Wochen bzw. 4 Monate vor dem Versuch entfernt worden waren, konnte wieder eine Orientierung nach der Windrichtung nachgewiesen werden (Abb. 23, Tabelle 1). 9. Die Kafer konnen Laufwinkel intramodal vierdeutig transponieren (z.B. Abb. 28, 29). Am deutlichsten tritt diese Fähigkeit bei Versuchsneulingen zutage, deren Laufe rein fluchtmotiviert sind: Sie wählen normalerweise denjenigen der 4 möglichen Laufwinkel, der der Aufsetzrichtung am nächsten liegt (vgl. Abb. 25, 26). 10. Die Existenz und die Wirkungsrichtung eines Drehkommandos, sowie die Beteiligung beider Grundorientierungen an der Anemomenotaxis werden nachgewiesen (Abb. 31). Die Fähigkeit, eine gleichbleibende Drehkommandogröße (die nie zu einer stärkeren Abweichung als 90° von einer Grundrichtung führen kann) mit verschiedenem Vorzeichen der Drehrichtung versehen zu konnen und die Möglichkeit zur Taxisumkehr (Abb. 32) erklären die orientierungsphysiologische Seite des vierdeutigen intramodalen Transponierens. 11. Versuchsergebnisse, die Aussagen uber den physiologischen Mechanismus der Anemomenotaxis der Käfer zulassen, sprechen für einen Kompensationsmechanismus. Die gegen die Kompensationstheorie der Menotaxis (JANDER, 1957) vorgebrachten Argumente werden im Rahmen der bisherigen Resultate kurz diskutiert. 12. Die möglichen biologischen Bedeutungen der Anemomenotaxis werden besprochen. Es wird angenommen, daß sie beim Appetenzverhalten des nach geruchlichen Schlüsselreizen "suchenden" Käfers ihre biologisch wichtigste Aufgabe erfüllt. Sie kann auch die basalen Aufgaben einer Raumorientierung übernehmen und so z.B. kompaßtreue Fluchtkurse steuern.
1. Bei der Anemomenotaxis arbeiten die Windrichtungen perzipierenden, paarigen Sinnesorgane der Antennen - vermutlich die Johnstonschen Organe - als Synergisten zusammen. Der Ausfall der für die Windrichtung spezifischen afferenten Meldungen eines Fühlers führt zu einer Halbierung der Drehtendenzstärke (Abb.I-ll). Es konnten keine Anhaltspunkte gefunden werden, die auf eine direkte zentrale Kompensation dieses Effektes hinweisen. Verschiedene Arten der Ausschaltung, totalc (Abb.2) oder teilweise (Abb. 4) Amputation (bei der der Pedicellus unverletzt bleibt) oder Blockierung des Pedicellus-Flagellumgelenks durch Lackierung (Abb.3), bewirken dieselben Änderungen im Orientierungsverhalten. 2. Der einzelne Fühler fungiert bei der Anemomenotaxis als "zweisinniger Lenker". Ein Käfer mit nur einem Fühler ist - nach einer genügend langen Erholungszeit - noch fähig, die Windrichtung festzustellen und zu ihr eindeutige menotaktische Kurse zu steuern (vgl. z. B. Abb. 1, 9). Außerdem kann er sich wie ein intakter Käfer (Abb. 14) bei plötzlicher Anderung der Reizrichtung um den kleineren Winkelbetrag zu seiner Sollrichtung zurückdrehen (Abb. 15). 3. Zwischen Drehtendenzstärke und Reizrichtung besteht nach den Ergebnissen der Ausschaltversuche eine Sinusfunktion. Gleichgroße Rechts- oder Linksabweichungen des Käfers von der positiven oder negativen Grundrichtung werden von rechtem und linkem Fühler mit der gleichen Drehtendenzstärke bewertet (Abb. 13). Es ist deshalb naheliegend, anzunehmen, daß jeder Fühler bei der Reizrichtungsbewertung seinen Abweichungsbetrag von der nächsten der beiden Grundstellungen mißt. In einer Grundstellung befindet sich der Fühler jeweils dann, wenn sich der Käfer genau gegen oder mit dem Wind eingestellt hat. 4. Afferente Drehtendenz und efferentes Drehkommando sind Dreherregungsgrößen, die sich bei Einstellung des Sollwinkels durch ihre antagonistische Wirkung aufheben. Halbierung der Drehtendenzstärke durch Ausschaltung eines Fühlers führt demnach erwartungsgemäß zu einer Verdopplung der Drehkommandowirkung. Daraus und aus der Sinusförmigkeit der Drehtendenzstärkenkurve ergibt sich, daß Drehkommandogrößen, die beim intakten Käfer die Einhaltung von Menotaxiswinkeln von > 30° zur Folge haben, von der halbierten Drehtendenz nicht mehr kompensiert werden können. Die Käfer können dann Dauerrotationen vermeiden, indem sie das Drehkommando soweit abschwächen, daß es von der halbierten Drehtendenz wieder kompensiert wird (Abb. 8). 5. Standardabweichung und mittlere Laufwinkelgröße sind miteinander korreliert. Die Korrelation gilt in gleicher Weise für das intakte und das einseitig antennenamputierte Versuchstier. 6. Nach einer einseitigen Fühlerausschaltung bevorzugen Tenebrio molitor und Scaurus dubius anfänglich Laufrichtungen zur Seite der intakten Antenne hin. Bei allen VT-Arten nimmt die Neigung zum intramodalen Winkeltransponieren nach Fühlerausschaltung sehr stark zu (Abb. 12). 7. Den Grundorientierungen - positive und negative Anemotaxis - liegt, wie auch der Menotaxis, kein tropotaktischer Mechanismus der Fühlerverschaltung zugrunde. Anemotaxis und Anemomenotaxis unterscheiden sich lediglich dadurch, daß bei letzterer ein efferentes Drehkommando die Sollrichtung verstellt. 8. Die experimentellen Befunde werden im Hinblick auf den, der Anemomenotaxis zugrunde liegenden, physiologischen Mechanismus diskutiert: Sie lassen sich alle widerspruchslos mit einem Kompensationsmechanismus vereinen.
Unter den Krebsen ist als größerer Gruppe allein den Landasseln (Oniscoidea) eine Eroberung des Festlandes gelungen. Ihre Anpassung an das Landleben blieb aber bislang recht mangelhaft, z. B. fehlt ein wirksamer Verdunstungsschutz. Wie zu erwarten, bewohnen daher die meisten Landasselarten feuchte Lebensstätten. Zu den wenigen Ausnahmen zählt die Wüstenassel Hemilepistus reaumuri, die nordafrikanische und kleinasiatische Halbwüsten - stellenweise auch echte Wüstengebiete - besiedelt. Es sind vor allem Verhaltensanpassungen, die den Wüstenasseln in diesen während vieler Monate trockenheißen Extrembiotopen nicht nur ein Oberleben erlauben, sondern sie darüber hinaus noch vielerorts zum erfolgreichsten Faunenelement machen.
A novel chromatin configuration is described in lampbrush chromosomes of Pleurodeles waltlii oocytes which is different from transcriptionally inactive chromatin as weil as from the various forms of transcribed chromatin hitherto described. This novel type of chromatin is not arranged in Christmas tree-Iike configurations of densely packed lateral ribonucleoprotein (RNP) fibriIs but is characterized by a periodic alternating pattern of thick and thin regions which occur in clusters 01 some 10,000 repeats. Each thickened unit with an average length of 45 nm contains two c10sely spaced particles, the putative RNA polymerases, and each thickened unit is separated from the next one by a beaded chromatin spacer with a length of about 80 nm. This chromatin spacer contains on average two particles of approximately 14 nm in diameter, assumed to be nucleosomes. The thickened regions are interpreted to represent short transcriptional units containing approximately 130 base pairs of DNA which are separated from each other by nontranscribed spacers of 240-400 base pairs of DNA. The possibility is discussed that these transcriptional units represent 5S rRNA or tRNA genes.
No abstract available
An ordered NotI fragment map containing over 60 loci and encompassing approximately 17 Mb has been constructed for human chromosome band llpl5. Forty-two probes, including 11 NotI-linking cosmids, were subregionaUy mapped to llpl5 using a subset of the Jl-deletion hybrids. These and 23 other probes defining loci previously mapped to 11p15 were hybridized to genomic DNA digested with NotI and 5 other infrequently cleaving restriction enzymes and separated by pulsed-field gel electrophoresis. Thirty-nine distinct NotI fragments were detected encompassing approximately 85% of the estimated length of llp15. The predicted order of the gene loci used is cenMYODI- PTH-CALCA-ST5-RBTNI-HPX-HBB-RRMlTH/ INS!1GF2-H19-CTSD-MUC2-DRD4-HRAS-RNHtel. This map wiu allow higher resolution mapping of new Ilp15 markers, facilitate positional cloning of disease genes, and provide a framework for the physical mapping of llp15 in clone contigs.
PtK2 cells in which pore complex-mediated transport is blocked by microinjection early in mitosis of a monoclonal antibody (specific for an Mr 68000 pore complex glycoprotein) or of wheat germ agglutinin (WGA) complete cytokinesis. However, their nuclei remain stably arrested in a telophase-like organization characterized by highly condensed chromatin and the absence of nucleoli, indicating a requirement for pore-mediated transport for the reassembly of interphase nuclei. We have now examined this requirement more closely by monitoring the behavior of individual nuclear macromolecules in microinjected cells using immunofluorescence microscopy and have investigated the effect of microinjecting the antibody or WGA on cellular ultrastructure. The absence of nuclear transport did not affect the sequestration into daughter nuclei of components such as DNA, DNA topoisomerase I and the nucleolar protein fibrillarin that are carried through mitosis on chromosomes. On the other hand, lamins, snRNAs and the p68 pore complex glycoprotein, all cytoplasmic during mitosis, remained largely cytoplasmic in the telophase-arrested cells. Electron microscopy showed the nuclei to be surrounded by a doublelayered membrane with some inserted pore complexes. In addition, however, a variety of membranous structures with associated pore complexes was regularly noted in the cytoplasm, suggesting that chromatin may not be essential for the postmitotic formation of pore complexes. We propose that cellular compartmentalization at telophase is a two-step process. First, a nuclear envelope tightly encloses the condensed chromosomes, excluding non-selectively all macromolecules not associated with the chromosomes. Interphase nuclear organization is then progressively restored by selective pore complex-mediated uptake of nuclear proteins from the cytoplasm.
No abstract available
The arrangement of genes of precursor molecules for ribosomal RNA (pre-rRNA) in primary nuclei from two green algae species, Acetabularia mediterranea and A. major, has been analyzed in an electron microscope study. The pattern of transcriptional units in individual strands of nucleolar chromatin was investigated using spread and positively stained preparations. The rDNA pattern is not uniform but differs in different strands. The predominant type of nucleolar chromatin exhibits a high degree of homogeneity in the sequence of matrix units (intercepts covered with fibrilst hat contain the pre-rRNA) and fibril-free spacer intercepts. Substantial differences, however, are observed between the patterns in different strands. In addition, there is evidence in some strands for intraaxial heterogeneity of both spacer and matrix units. The following major types can be distinguished: type la, ca. 2 micrometer long matrix units, extremely short spacer intercepts in A. mediterranea (ca. 1 micrometer long ones in A. major), completely homogeneous distribution; type Ib, as type la but with intercalated, isolated, significantly shorter and/or longer matrix units; type lIa, matrix unit sizes as in type la, but much longer spacer intercepts, high degree of homogeneity; type Ill, largely heterogeneous arrangements of matrix and spacer units of varying sizes. The matrix unit data are compared with the sizes of pre-rRNA as determined by polyacrylamide gelelectrophoresis under denaturing and non-denaturing conditions. The findings are discussed in relation to recent observations in amphibia and insects and with respect to current concepts of the species-specificity of rDNA arrangements.
Antibody against tubulin from porcine brain was used to evaluate the immunological cross reactivity of tubulin from a variety of animal and plant cells. Indirect immunofluorescence microscopy revealed microtubule-containing structures including cytoplasmic microtubules, spindle microtubules, cilia and fIagella. Thus tubulin from diverse species of both mammals and plants show immunological cross-reactivity with tubulin from porcine brain. Results obtained by immunofluorescence microscopy are whenever possible compared with previously known ultrastructural results obtained by electron microscopy.
The organization of the extrachromosomal nucleolar material in oocytes of two insect species with different ovary types, the house cricket Acheta domesticus (panoistic ovary) and the water beetle Dytiscus marginalis (meroistic ovary), was studied with light and electron microscopic techniques. Stages early in oogenesis were compared with fully vitellogenic stages (mid-to-Iate diplotene). The arrangement of the nucleolar material undergoes a marked change from a densely aggregated to a dispersed state. The latter was characterized by high transcriptional activity. In spread and positively stained preparations of isolated nucleolar material, a high frequency of small circular units of transcribed rDNA was observed and rings with small numbers (1-5) of pre-rRNA genes were predominant. The observations suggest that the "extra DNA body" observed in early oogenic stages of both species represents a dense aggregate of numerous short circular units of nucleolar chromatin, with morphological subcomponents identifiable in ultrathin sections. These apparently remain in close association with the chromosomal nucleolar organizer(s). The observations further indicate that the individual small nucleolar subunit circles dissociate and are dispersed as actively transcribed rDNA units later in diplotene. The results are discussed in relation to principles of the ultrastructural organization of nucleoli in other cell types as well as in relation to possible mechanisms of gene amplification.
The morphology of two forms of transcription ally active chromatin, the nucleoli and the loops of lampbrush chromosomes, has been examined after fixation in situ or after isolation and dispersion of the material in media of low ionic strengths, using a variety of electron microscopic preparation techniques (e.g. spread preparations with positive or negative staining or without any staining at all, with bright and dark field illumination, with autoradiography, after pretreatment of the chromatin with specific detergents such as Sarkosyl NL-30; transmission and scanning transmission electron microscopy of ultrathin sections). Nucleolar chromatin and chromosomes from oocytes of various amphibia and insects as well as from green algae of the family of the Dasycladaceae were studied in particular detail. The morphology of transcriptional units that are densely packed with lateral ribonucleoprotein fibrils, indicative of great transcriptional activity, was compared with that of chromatin of reduced lateral fibril density, including stages of drug-induced inhibition. The micrographs showed that under conditions which preserve the nucleosomal organization in condensed chromatin studied in parallel, nucleosomes are not recognized in transcriptionally active chromatin. This holds for the transcribed regions as well as for apparently untranscribed (i.e. fibril-free) regions interspersed between ('spacer') and/or adjacent to transcribed genes and for the fibril-free regions within transcriptional units of reduced fibril density. In addition, comparison oflengths of repeating units of isolated rDNA with those observed in spread nucleolar chromatin indicated that this DNA is not foreshortened and packed into nucleosomal structures. Granular particles which were observed, at irregular frequencies and in variable patterns, in some spacer regions, did not result in a proportional shortening of the spacer axis, and were found to be resistant to detergent treatment effective in removing most of the chromatin associated proteins including histones. Thus, these particles behave like RNA polymerases rather than nucleosomes. It is suggested that structural changes from nucleosomal packing to an extended form of DNA are involved in the transcriptional activation of chromatin.
Available data on the occurrence and expression of somatic histone HI during oogenesis and early embryogenesis of Xenopus laevis are contradictory. In particular the reported presence of a large storage pool of histone HIA in oocytes is difficult to reconcile with the high transcriptional activity of all gene classes in this specific cell type. In the present study we have used polyclonal antibodies raised against somatic Xenopus histone HI (HIA and HIA/B) for combined immunoblotting experiments to quantitate HI pools and immunolocalization studies to visualize chromosome- bound HI. Both approaches failed to detect soluble or chromosomal histone HI in vitellogenic oocytes, eggs, and cleavage-stage embryos up to early blastula. In addition, chromatin assembled in Xenopus egg extract was also negative for histone HI as revealed by immunofluorescence microscopy. Lampbrush chromosomes not only lacked histone HI but also the previously identified histone HI-like B4 protein (Smith et al., 1988, Genes Dev. 2,1284-1295). In contrast, chromosomes of eggs and early embryos fluoresced brightly with anti-B4 antibodies. Our results lend further support to the view that histone HI expression is developmentally regulated during Xenopus oogenesis and embryogenesis similar to what is known from other species.
Nach homoplastischer Transplantation von larvalen Gonaden mit Fettkiirper in die vordere Leibeshiihle wiichst nur der Fettkiirper an der Leber an, so daB die Gonade nur indirekt mit dem Wirtsgewebe verbunden ist. Die Differenzierung der Gametogonien folgt der Normogenese, bei Ovartransplantationen entwickeln sich Auxocyten. Nach spatestens 27 Tagen ist die Blutversorgung wiederhergestellt. Homo- und autoplastische Transplantationen von Gonaden oh ne Fettkiirper ergeben fUr die Gametogonien eine vollig andere Entwicklung. Sind die Gonaden mit breiter Fliiche angewachsen, liiBt si ch bereits 7 Tage p.o. im Bereich der Kontaktzone Gonade-Leber die Karyolyse der Gametogonienkerne feststellen. Nach 3--4 Wochen stellt das Transplantat eine bindegewebige Zyste ohne Geschlechtszellen dar. Erythrozyten zeigen die Vaskularisation an. 1st nur ein Teil der Gonade mit der Leber verwachsen, zeigt der frei gebliebene Abschnitt eine normale Struktur mit Mitosen der Gametogonien. Die Degeneration der Geschlechtszellen hiingt offenbar von ihrer Lage zum extragonadalen Gewebe ab.
Transcribed nucleolar chomatin, including the spacer regions interspersed between the rRNA genes, is different from the bulk of nontranscribed chromatin in that the DNA of these regions appears to be in an extended (B) conformation when examined by electron microscopy. The possibility that this may reflect artificial unfolding of nucleosomes during incubation in very low salt buffers as routinely used in such spread preparations has been examined by studying the influence of various ion concentrations on nucleolar chromatin structure. Amplified nucleolar chromatin of amphibian oocytes (Xenopus laevis, Pleurodeles waltlii, Triturus cristatus) was spread in various concentrations of NaCl (range 0 to 20 mM). Below 1 mM salt spacer chromatin frequently revealed a variable number of irregularly shaped beads, whereas above this concentration the chromatin axis appeared uniformly smooth. At all salt concentrations studied, however, the length distribution of spacer and gene regions was identical. Preparations fixed with glutaraldehyde instead of formaldehyde, or unftxed preparations, were indistinguishable in this respect. The observations indicate that (i) rDNA spacer regions are not compacted into nucleosomal particles and into supranucleosomal structures when visualized at chromatin stabilizing salt concentrations (e.g., 20 mM NaCl), and (ii) spacer DNA is covered by a uniform layer of proteins of unknown nature which, at very low salt concentrations (below 1 mM NaCl), can artificially give rise to the appearance of small granular particles of approximately nucleosome-like sizes. These particles, however, are different from nucleosomes in that they do not foreshorten the associated spacer DNA. The data support the concept of an altered nucleohistone conformation not only in transcribed chromatin but also in the vicinity of transcriptional events.
High sensitivity immunolocalization of double and single-stranded DNA by a monoclonal antibody
(1987)
A monoclonal antibody (AK 30-10) is described which specifically reacts with DNA both in double and single-stranded forms but not with other molecules and structures, including deoxyribonucleotides and RNAs. When used in immunocytochemical experiments on tissue sections and permeabilized cultured cells, this antibody detects DNA-containing structures, even when the DNA is present in very small amounts. Examples of high resolution detection include the DNA present in amplified extrachromosomal nucleoli, chromomeres of lampbrush chromosomes, mitochondria, chloroplasts and mycoplasmal particles. In immunoelectron microscopy using the immunogold technique, the DNA was localized in distinct substructures such as the "fibrillar centers" of nucleoli and certain stromal centers in chloroplasts. The antibody also reacts with DNA of chromatin of living cells, as shown by microinjection into cultured mitotic cells and into nuclei of amphibian oocytes. The potential value and the limitations of immunocytochemical DNA detection are discussed.
Using a monoclonal antibody (No-194) we have identified, in Xenopus laevis and other amphibia, an acidic protein of M, 40,000 (ribocharin) which is specifically associated with the granular component of the nucleolus and nucleoplasmic 65S particles. These particles contain the nuclear 28S rRNA and apparently represent the precursor to the large ribosomal subunit in nucleocytoplasmic transit. By immunoelectron microscopy ribocharin has been localized in the granular component of the nucleolus and in interchromatin granules. During mitosis ribocharin-containing particles are associated with surfaces of chromosomes and are recollected in the reconstituting nucleoli in late telophase. We suggest that ribocharin is a specific component of precursor particles of the large ribosomal subunit, which dissociates from the 65S particle before passage through the nuclear envelope, and is reutilized in ribosome biogenesis.
A non-radioactive in situ hybridization method is described for the localization of transcription units of defined genes to lateral loops of Xenopus laevis lampbrush chromosomes. Two Xenopus cONA probes were used encoding the nucleolar protein N038/ B23 and cytokeratin 1(8). Both proteins are known to be synthesized in Xenopus oocytes, and Northern blot analysis revealed the presence of the corresponding mRNAs in different oogenic stages. The probes were enzymatically labeled with biotin-dCTP and hybridized to lampbrush chromosomes. The sites of hybridization were detected either by indirect immunofluorescence microscopy using rabbit antibodies against biotin and fluorescein-conjugated antirabbit IgG or enzymatically using peroxidase-conjugated streptavi din. The probe encoding the nucleolar protein hybridized to two sets of lateral loops on different bivalents, the cytokeratin probe to at least four. Our finding that each probe hybridized to more than one chromosomal locus may reflect the tetraploid nature of the Xenopus laevis genome or results from cross-hybridization to other transcriptionally active members of the N038/ B23-nucleoplasmin or the cytokeratin-Iamin gene families. The method described should facilitate further in situ hybridization studies with appropriate genomic clones in order to map specific DNA sequences to defined loop regions and to come to a better understanding of the relationship between loop organization and gene transcription unit.
Many nuclear proteins are released into the cytoplasm at prometaphase and are transported back into the daughter nuclei at the end of mitosis. To determine the role of this reentry in nuclear remodelling during early interphase, we experimentally manipulated nuclear protein uptake in dividing cells. Recently we and others have shown that signal-dependent, pore complex-mediated uptake of nuclear protein is blocked in living cells on microinjection of the lectin wheat germ agglutinin (WGA), or of antibodies such as PI1 that are directed against WGA-binding pore complex glycoproteins. In the present study, we microinjected mitotic PtKz cells with WGA or antibody PIt and followed nuclear reorganization of the daughter cells by immunofluorescence and electron microscopy. The inhibitory effect on nuclear protein uptake was monitored by co-injection of the karyophilic protein nucleoplasmin. When injected by itself early in mitosis, nucleoplasmin became sequestered into the daughter nuclei as they entered telophase. In contrast, nucleoplasmin was excluded from the daughter nuclei in the presence of WGA or antibody PI1 . Although PtKz cells with blocked nuclear protein uptake completed cytokinesis, their nuclei showed a telophaselike organization characterized by highly condensed chromatin surrounded by a nuclear envelope containing a few pore complexes. These findings suggest that pore complexes become functional as early as telophase, in close coincidence with nuclear envelope reformation. They further indicate that the extensive structural rearrangement of the nucleus during the telophase-G1 transition is dependent on the influx of karyophilic proteins from the cytoplasm through the pore complexes, and is not due solely to chromosome- associated components.
In order to investigate the DNA localization within Ehrlich tumor cell nucleoli during mitosis, two recent immunocytochemical methods using either an anti-DNA or an anti-bromodeoxyuridine (BrdU) monoclonal antibody have been applied. In both cases, the immunogold labeling has been performed on ultrathin sections of cells embedded either in Lowicryl K4M or in Epon, respectively. Identical results are observed with both immunocytochemical approaches. In the interphase nucleolus, besides the labeling of the perinucleolar chromatin shell and of its intranucleolar invaginations which penetrate into the nucleolar body and often terminate at the fibrillar centers, a few gold particles are also preferentially found towards the peripheral region of the fibrillar centers. In contrast, the dense fibrillar component and the granular component are never labeled. During mitosis, the fibrillar centers persist at the chromosomal nucleolus organizing regions (NOR's) and can be selectively stained by the silver method. However, these metaphase fibrillar centers are no longer decorated by the DNA- or BrdU antibodies. These results indicate that until the end of prophase, rRNA genes are present inside the fibrillar center material, disappear during metaphase and reappear in reconstituting nucleoli during telophase. Thus, fibrillar centers appear to represent structures sui generis, which are populated by rRNA genes only when the nucleolus is functionally active. In segregated nucleoli after actinomycin D treatment, the DNA labeling is exclusively restricted to the perinucleolar chromatin blocks. These findings also suggest that the DNA content of the fibrillar center material varies according to the rRNA transcription level of the cells. The results are discussed in the light of the present knowledge of the functional organization of the nucleolus.
After microinjection of antibodies against RNA polymerase I into the nuclei of cultured rat kangaroo (PtKz) and rat (RVF-SMC) cells alterations in nucleolar structure and composition were observed. These were detected by electron microscopy and double-label immunofluorescence microscopy using antibodies to proteins representative of the three major components of the nucleolus. The microinjected antibodies produced a progressive loss of the material of the dense fibrillar component (DFC) from the nucleoli which, at 4 h after injection, were transformed into bodies with purely granular component (GC) structure with attached fibrillar centers (FCs). Concomitantly, numerous extranucleolar aggregates appeared in the nucleoplasm which morphologically resembled fragments of the DFC and contained a protein (fibrillarin) diagnostic for this nucleolar structure. These observations indicate that the topological distribution of the material constituting the DFC can be experimentally influenced in interphase cells, apparently by modulating the transcriptional activity of the rRNA genes. These effects are different from nucleolar lesions induced by inhibitory drugs such as actinomycin D-dependent "nucleolar segregation". The structural alterations induced by antibodies to RNA polymerase I resemble, however, the initial events of nucleolar disintegration during mitotic prophase.
The ultrastructure of twO kinds of transcription ally active chromatin, the lampbrush chromosome loops and the nucleoli from amphibian oocytes and primary nuclei of the green alga Acetabularia, has been examined after manual isolation and dispersion in low salt media of slightly alkaline pH using various electron microscopic staining techniques (positive staining, metal shadowing, negative staining, preparation on positively charged films, etc.) and compared with the appearance of chromatin from various somatic cells (hen erythrocytes, rat hepatocytes, ClIltured murine sarcoma cells) prepared in parallel. While typical nucleosomes were revealed with all the techniques for chromatin from the latter three cell system, no nucleosomes were identified in either the lampbrush chromosome structures or the nucleolar chromatin. Nucleosomal arrays were absent not only in maximally fibril-covered matrix units but also in fibril-free regions between transcriptional complexes, including the apparent spacer intercepts between different transcriptional units. Moreover, comparisons of the length of the repeating units of rDNA in the transcribed state with those determined in the isolated rDNA and with the lengths of the first stable product of rDNA transcription, the pre-rRNA, demonstrated that the transcribed rDNA was not significantly shortened and/or condensed but rather extended in the transcriptional units. Distinct granules of about nucleosomal size which were sometimes found in apparent spacer regions as well as within matrix units of reduced fibril density were shown not to represent nucleosomes since their number per spacer unit was not inversely correlated with the length of the specific unit and also on the basis of their resistance to treatment with the detergent Sarkosyl NL-30. It is possible to structurally distinguish between transcriptionally active chromatin in which the DNA is extended in a non-nucleosomal form of chromatin and condensed, inactive chromatin within the typical nucleosomal package. The characteristic extended structure of transcriptionally active chromatin is found not only in the transcribed genes but also in non-transcribed regions within or between ("spacer") transcriptional units as well as in transcriptional units that are untranscribed amidst transcribed ones and/or have been inactivated for relatively short time. It is hypothesized that activation of transcription involves a transition from a nucleosomal to an extended chromatin organisation and that this structural transition is not specific for single "activated" genes but may involve larger chromatin regions, including adjacent untranscribed intercepts.
Thin section electron microscopy of Actinomycin D treated Tetrahymena cells and amphibian oocytes (Xenopus laevis, Triturus aZpestris) reveal no reduction in the central granules in the nuclear pore complexes. Possible reasons for the diversity between these results and earlier observations using negatively stained isolated nuclear envelopes from the same objects are discussed. The results clearly show that the presence of central granules within the nuclear pores does neither depend on nuclear RNA synthesis nor does indicate nucleocytoplasmic RNA transport. This conclusion leads to a reconsideration of the nature of the central granule. The functioning of the central granule of the nuclear pore complexes is further discussed in connection with recent studies on the ultrastructure of various types of cisternal pores.
A small fraction of HeLa cells within an exponentially growing culture showed cisternal differentiations, such as cytoplasmic as well as intranuclear annulate lamellae and special smooth surfaced endoplasmic reticulum aggregates with a typical "Cotte de maillet" appearance. Additionally, clusters of dense granules were observed in the cytoplasm which were often associated with polysomes and strongly resembled the so-called "heavy bodies" known in particular in diverse oocytes. The functional meaning of these structures is discussed. Moreover, it is deduced from the ultrastructural identity of the pore complexes in the nuclear envelope and the cytoplasmic and intranuclear annulate lamellae that the pore complex material with its highly ordered arrangement is not a structure characteristic for nucleocytoplasmically migrating material, but rather is a general structural expression of a tight binding of ribonucleoprotein (RNP) to cisternal membranes. The pore complexes are thought of as representing sites of a RNP-storage. A similar functioning is hypothesized for the "heavy body"like aggregates. To the current hypotheses on the formation of annulate lamellae and the nuclear envelope, which are based on the concept of membrane continuities and constancies, the alternative view of a self assembly mechanism of membrane constituents on nucleoprotein structures is added.
Primary (giant) nuclei of the green algae Acetabularia mediterranea and A. major were studied by light and electron microscopy using in situ fixed material as well as manually isolated nuclear components. In addition, cytochemical reactions of nuclear structures and biochemical determinations of nuclear and cytoplasmic RNA and of genome DNA content were performed. The data obtained and the structures observed are interpreted as demonstralions of transcriptional activities of different gene classes. The most prominent class is the nucleolar cistrons of precursors of ribosomal RNA which occur highly repeated in clusters in the form of regularly alternating intercepts on deoxyribonucleoprotein axes of transcribed rDNA, the fibril-covered matrix units, and the fibril-free "spacer" segments. A description and a classification of the various structural complexes which seem to represent transcriptional activities is given. Quantitative evaluations of these arrangements are presented. The morphology and the dimensions of such structures are compared with the RNA molecular weight determinations and with the corresponding data reported from various animal cell systems. It is suggested that the formation of the giant nucleus is correlated with, and probably due to, an enormous amplification of transcriptionally active rDNA and packing of the extrachromosomal copies into the large nucleolar aggregate bodies.
Electron-opaque material is shown in the perinuclear cisternae of various cell types to connect the inner and outer nuclear membrane faces. Similar bridges were observed between the outer nuclear membrane and the outer mitochondrial membrane. The intracisternal bridges of the nuclear envelope appear to be important for the structural stability of the perinuclear cisterna. Stable structural linkage of mitochondria to the outer nuclear membrane might be relevant to the understanding of the characteristic juxtanuclear accumulation of mitochondria and also provide arguments for the discussions of certain biochemical activities found in nuclear and nuclear membrane fractions.
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No abstract available
So me species of the paleotropical tree genus Macaranga (Euphorbiaceae) live in elose association with ants. Thc genus comprises the full range of species from those not regularly inhabited by ants to obligate myrmecophytes. In Malaysia (peninsular and Borneo) 23 ofthe 52 species areknown to be ant-associated (44%). The simplest structural adaptation of plants to attract ants are extrafloral nectaries. We studied the distribution of extraflural nectaries in the genus Macaranga to assess the significance of this character as a possible predisposition for the evolution of obligate myrmecophytism. All species have marginal glands on the leaves. However, only the glands of nonmyrmecophytic species function as nectaries, whereas liquids secreted by these glands in myrmecophytic species did not contain sugar. Some non-myrmecophytic Macaranga and transitional Macaranga species in addition have extrafloral nectaries on the leaf blade near the petiole insertion. All obligatorily myrmecophytic Macaranga species, however, lack additional glands on the lamina. The non-myrmecophytic species are visited by a variety of different ant species, whereas myrmecophytic Macaranga are associated only with one specific ant-partner. Since these ants keep scale insects in the hollow sterns, reduction of nectary production in ant-inhabited Macaranga seems to be biologically significant. We interpret this as a means of (a) saving the assimilates and (b) stabilization of maintenance of the association's specificity. Competition with other ant species for food rewards is avoided and thereby danger ofweakening the protective function ofthe obligate antpartner for the plant is reduced. A comparison with other euphorb species living in the same habitats as Macaranga showed that in genera in which extrafloral nectaries are widespread, no myrmecophytes have evolved. Possession of extrafloral nectaries does not appear to be essential for the development of symbiotic ant-plant interactions. Other predispositions such as nesting space might have played a more important role.
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No abstract available