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Drilus beetle larvae (Coleoptera: Elateridae) are specialized predators of land snails. Here, we describe various aspects of the predator-prey interactions between multiple Drilus species attacking multiple Albinaria (Gastropoda: Clausiliidae) species in Greece. We observe that Drilus species may be facultative or obligate Albinaria-specialists. We map geographically varying predation rates in Crete, where on average 24% of empty shells carry fatal Drilus bore holes. We also provide first-hand observations and video-footage of prey entry and exit strategies of the Drilus larvae, and evaluate the potential mutual evolutionary impacts. We find limited evidence for an effect of shell features and snail behavioral traits on inter-and intraspecifically differing predation rates. We also find that Drilus predators adjust their predation behavior based on specific shell traits of the prey. In conclusion, we suggest that, with these baseline data, this interesting predator-prey system will be available for further, detailed more evolutionary ecology studies.
The variant surface glycoprotein (VSG) of African trypanosomes plays an essential role in protecting the parasites from host immune factors. These trypanosomes undergo antigenic variation resulting in the expression of a single VSG isoform out of a repertoire of around 2000 genes. The molecular mechanism central to the expression and regulation of the VSG is however not fully understood.
Gene expression in trypanosomes is unusual due to the absence of typical RNA polymerase II promoters and the polycistronic transcription of genes. The regulation of gene expression is therefore mainly post-transcriptional. Regulatory sequences, mostly present in the 3´ UTRs, often serve as key elements in the modulation of the levels of individual mRNAs. In T. brucei VSG genes, a 100 % conserved 16mer motif within the 3´ UTR has been shown to modulate the stability of VSG transcripts and hence their expression. As a stability-associated sequence element, the absence of nucleotide substitutions in the motif is however unusual. It was therefore hypothesised that the motif is involved in other essential roles/processes besides stability of the VSG transcripts.
In this study, it was demonstrated that the 100 % conservation of the 16mer motif is not essential for cell viability or for the maintenance of functional VSG protein levels. It was further shown that the intact motif in the active VSG 3´ UTR is neither required to promote VSG silencing during switching nor is it needed during differentiation from bloodstream forms to procyclic forms. Crosstalk between the VSG and procyclin genes during differentiation to the insect vector stage is also unaffected in cells with a mutated 16mer motif. Ectopic overexpression of a second VSG however requires the intact motif to trigger silencing and exchange of the active VSG, suggesting a role for the motif in transcriptional VSG switching. The 16mer motif therefore plays a dual role in VSG in situ switching and stability of VSG transcripts. The additional role of the 16mer in the essential process of antigenic variation appears to be the driving force for the 100 % conservation of this RNA motif.
A screen aimed at identifying candidate RNA-binding proteins interacting with the 16mer motif, led to the identification of a DExD/H box protein, Hel66. Although the protein did not appear to have a direct link to the 16mer regulation of VSG expression, the DExD/H family of proteins are important players in the process of ribosome biogenesis. This process is relatively understudied in trypanosomes and so this candidate was singled out for detailed characterisation, given that the 16mer story had reached a natural end point. Ribosome biogenesis is a major cellular process in eukaryotes involving ribosomal RNA, ribosomal proteins and several non-ribosomal trans-acting protein factors. The DExD/H box proteins are the most important trans-acting protein factors involved in the biosynthesis of ribosomes. Several DExD/H box proteins have been directly implicated in this process in yeast. In trypanosomes, very few of this family of proteins have been characterised and therefore little is known about the specific roles they play in RNA metabolism. Here, it was shown that Hel66 is involved in rRNA processing during ribosome biogenesis. Hel66 localises to the nucleolus and depleting the protein led to a severe growth defect. Loss of the protein also resulted in a reduced rate of global translation and accumulation of rRNA processing intermediates of both the small and large ribosomal subunits. Hel66 is therefore an essential nucleolar DExD/H protein involved in rRNA processing during ribosome biogenesis. As very few protein factors involved in the processing of rRNAs have been described in trypanosomes, this finding represents an important platform for future investigation of this topic.
This study investigates the abundance and geographic distribution of the hawkmoth species (Lepidoptera: Sphingidae) of Southeast-Asia and analyses the resulting patterns of biodiversity, biogeography and macroecology. Data on the distribution of species were retrieved from published and unpublished faunal lists and museum collections (in close cooperation with the Natural History Museum, London). Over 34,500 records of the global distribution of the 380 species that occur in Southeast-Asia (including New Guinea and the Solomon Islands) were used for a GIS-supported estimate of distributional ranges, which can be accessed at http://www.sphingidae-sea.biozentrum.uni-wuerzburg.de, an Internet site that also provides pictures of the species and checklists for 114 islands of the Malesian region. The abundance of species in local assemblages was assessed from nightly collections at artificial light sources. Using a compilation of own samples as well as published and unpublished data from other sources, local abundance data on 93 sites were used for analysis, covering 159 species or 17,676 specimens.
The development of all honey bee castes proceeds through three different life stages all of which encounter microbial infections to a various extent. We have examined the immune strength of honey bees across all developmental stages with emphasis on the temporal expression of cellular and humoral immune responses upon artificial challenge with viable Escherichia coli bacteria. We employed a broad array of methods to investigate defence strategies of infected individuals: (a) fate of bacteria in the haemocoel; (b) nodule formation and (c) induction of antimicrobial peptides (AMPs). Newly emerged adult worker bees and drones were able to activate efficiently all examined immune reactions. The number of viable bacteria circulating in the haemocoel of infected bees declined rapidly by more than two orders of magnitude within the first 4–6 h post-injection (p.i.), coinciding with the occurrence of melanised nodules. Antimicrobial activity, on the other hand, became detectable only after the initial bacterial clearance. These two temporal patterns of defence reactions very likely represent the constitutive cellular and the induced humoral immune response. A unique feature of honey bees is that a fraction of worker bees survives the winter season in a cluster mostly engaged in thermoregulation. We show here that the overall immune strength of winter bees matches that of young summer bees although nodulation reactions are not initiated at all. As expected, high doses of injected viable E.coli bacteria caused no mortality in larvae or adults of each age. However, drone and worker pupae succumbed to challenge with E.coli even at low doses, accompanied by a premature darkening of the pupal body. In contrast to larvae and adults, we observed no fast clearance of viable bacteria and no induction of AMPs but a rapid proliferation of E.coli bacteria in the haemocoel of bee pupae ultimately leading to their death.
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.
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.
Background
The metacestode larva of Echinococcus multilocularis (Cestoda: Taeniidae) develops in the liver of intermediate hosts (typically rodents, or accidentally in humans) as a labyrinth of interconnected cysts that infiltrate the host tissue, causing the disease alveolar echinococcosis. Within the cysts, protoscoleces (the infective stage for the definitive canid host) arise by asexual multiplication. These consist of a scolex similar to that of the adult, invaginated within a small posterior body. Despite the importance of alveolar echinococcosis for human health, relatively little is known about the basic biology, anatomy and development of E. multilocularis larvae, particularly with regard to their nervous system.
Results
We describe the existence of a subtegumental nerve net in the metacestode cysts, which is immunoreactive for acetylated tubulin-α and contains small populations of nerve cells that are labeled by antibodies raised against several invertebrate neuropeptides. However, no evidence was found for the existence of cholinergic or serotoninergic elements in the cyst wall. Muscle fibers occur without any specific arrangement in the subtegumental layer, and accumulate during the invaginations of the cyst wall that form brood capsules, where protoscoleces develop. The nervous system of the protoscolex develops independently of that of the metacestode cyst, with an antero-posterior developmental gradient. The combination of antibodies against several nervous system markers resulted in a detailed description of the protoscolex nervous system, which is remarkably complex and already similar to that of the adult worm.
Conclusions
We provide evidence for the first time of the existence of a nervous system in the metacestode cyst wall, which is remarkable given the lack of motility of this larval stage, and the lack of serotoninergic and cholinergic elements. We propose that it could function as a neuroendocrine system, derived from the nervous system present in the bladder tissue of other taeniids. The detailed description of the development and anatomy of the protoscolex neuromuscular system is a necessary first step toward the understanding of the developmental mechanisms operating in these peculiar larval stages.
Traps baited with attractive lures are increasingly used at entry-points and surrounding natural areas to intercept exotic wood-boring beetles accidentally introduced via international trade. Several trapping variables can affect the efficacy of this activity, including trap color. In this study, we tested whether species richness and abundance of jewel beetles (Buprestidae), bark and ambrosia beetles (Scolytinae), and their common predators (i.e., checkered beetles, Cleridae) can be modified using trap colors different to those currently used for surveillance of jewel beetles and bark and ambrosia beetles (i.e., green or black). We show that green and black traps are generally efficient, but also that many flower-visiting or dark-metallic colored jewel beetles and certain bark beetles are more attracted by other colors. In addition, we show that checkered beetles have color preferences similar to those of their Scolytinae preys, which limits using trap color to minimize their inadvertent removal. Overall, this study confirmed that understanding the color perception mechanisms in wood-boring beetles can lead to important improvements in trapping techniques and thereby increase the efficacy of surveillance programs.
Plant communities in the European Alps are assumed to be highly affected by climate change since temperature rise in this region is above the global average. It is predicted that higher temperatures will lead to advanced snowmelt dates and that the number of extreme weather events will increase. The aims of this study were to determine the impacts of extreme climatic events on flower phenology and to assess whether those impacts differed between lower and higher altitudes. In 2010 an experiment simulating advanced and delayed snowmelt as well as drought event was conducted along an altitudinal transect ca. every 250m (600-2000 m a.s.l.) in the Berchtesgaden National Park, Germany. The study showed that flower phenology is strongly affected by altitude; however there were few effects of the manipulative treatments on flowering. The effects of advanced snowmelt were significantly greater at higher than at lower sites, but no significant difference was found between both altitudinal bands for the other treatments. The response of flower phenology to temperature declined through the season and the length of flowering duration was not significantly influenced by treatments. The stronger effect of advanced snowmelt at higher altitudes might be a response to differences in treatment intensity across the gradient. Consequently, shifts in the date of snowmelt due to global warming may affect species more at higher than at lower altitudes since changes may be more pronounced at higher altitudes. Our data indicate a rather low risk of drought events on flowering phenology in the Bavarian Alps.
One of the fascinating features of meiotic prophase I, is the highly conserved
vigorous movements of homologous chromosomes. These movements are
critical for the success of essential events as homologs alignment, synapsis and
recombination. Several organisms studied so far, including mammals, worms,
yeast and plants achieve these movements by anchoring the chromosome ends
to specialized sites in the nuclear envelope (NE). This attachment requires
telomere adaptor proteins which have to date been identified in fission yeast
and mice.
The mouse meiosis-specific telomere adaptor proteins TERB1, TERB2, and
MAJIN are involved in the attachment of ubiquitous shelterin telomere to the
LINC complex, in an analogous mechanism as those described in fission yeast.
Despite the essential role of meiosis-specific telomere adaptor proteins, the
precise mechanism of anchorage of telomeres to the nuclear envelope, as well
as their evolutionary history, are still not well understood. Therefore, the main
aim of this thesis is to investigate the organization of the mouse meiosis-specific
telomere adaptor complex TERB1-TERB2-MAJIN and its evolutionary history.
In the first part of this thesis high-resolution Structured Illumination Microscopy
(SIM), indirect immunofluorescence and Telo-FISH on mouse spermatocytes
were used to determine precisely how the telomere complex proteins are
localized with relation to the shelterin telomeric TRF1 protein and telomeric
DNA. During zygotene and pachytene stages staining patterns revealed
extensively overlapping of meiotic telomere complex proteins distributions in
which TERB2 organization is more heterogeneous than TERB1 and MAJIN at
the chromosome ends. Further, TRF1 localization was shown at the side of
lateral elements (LEs) ends with grasp-like distribution surrounding the TERB1
and MAJIN signals in zygotene and pachytene stages. Interestingly, telomeric
DNA was shown to be laterally distributed and partially overlapping with the
more central distribution displayed by meiotic telomere complex proteins of LEs
ends. The combination of these results allowed to describe an alternative model
of the telomere attachment to the NE during meiotic prophase I. The second part of this thesis, analyses mouse TERB1, TERB2, and MAJIN
evolutionary history. The lack of similarity between mouse and fission yeast
meiotic-specific telomere adaptor proteins has raised the question about the
origin of this specific complex through evolution. To identify mouse TERB1,
TERB2, and MAJIN putative orthologues, computational approaches and
phylogenetic analyses were performed. Besides, to test their potential function
during meiosis, expression studies were conducted. From these analyses, it was
revealed that mouse meiosis-specific telomere complex is ancient, as it
originated as early as eumetazoans pointing to a single origin. The absence of
any homologs in Nematoda and only a few candidates detected in Arthropoda
for meiosis-specific telomere complex, seemed, that these proteins have been
lost/replaced or highly diversified in these lineages. Remarkably, TERB1, TERB2,
and MAJIN protein domains involved in the formation of the complex as well as
those required for the interaction with the telomere shelterin protein and the
LINC complexes revealed high sequence similarity across all clades. Finally,
gene expression in the cnidarian Hydra Vulgaris provided evidence that the
TERB1-TERB2-MAJIN complex is selectively expressed in the germline
suggesting conservation of meiotic functions across metazoan evolution.
In summary, this thesis provides significant insights into the meiosis-specific
telomere complex mechanism to engage telomeres to the nuclear envelope and
the elucidation of its origin in metazoans.