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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.
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.
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.
No abstract available
No abstract available
The desert isopod, Hemilepistus reaumuri, extremely common in the arid regions of North Africa and Asia Minor, depends upon the burrows it itself digs for survival during the hotter parts of the year. The dig-ging of new burrows is limited by chmatic conditions to a short period during the spring. Burrows must be constantly defendet - especially against roving eonspecifics. The decisive problem of a connnuous burrow defense is solved through cooperative behavior: the adult woodlice form monogamous pairs whose partners recognize one another individually. Here, questions on the binding of partners, especially the problem of the binding of male to female will be treated upon, along with questions on the evolution of monogamy, wherein the purely maternal families of Porcellio species will be taken as models for intermediäre stages. At first, males olHemilepistus are not permitted to copulate at all; later, for a relatively long period, they are only permitted incomplete copulations, the females alone have control over the partunal ecdysis; they alone determine the moment of final copulations. Under the thermal conditions prevalent during the season of pair formation, a female irreversibly induces a parturial ecdysis only when it has spent a minimum of sev-eral days in her own burrow with a specific male. At higher average temperatures, the number of females which undergo parturial ecdyses without these preconditions increases sharply. Males cannot greatly lnrlu-ence the willingness of females to reproduce with the investment they make in the digging of burrows; the factors deciding this are the male's presence and its role as guard. The first condition necessary for the genesis of monogamy might have been the evolution of a stncüy lo-cation-dependent copulatory behavior, which guaranteed the male exclusive mating pnveliges with the female whose location - the burrow - he acheived control of. A male must, under these conditions, serve guard duty in his own interest, and defend the burrow against competitors (Cf or 2) seeking an already-dug burrow. The decisive advantage for the female in the beginning of the development was probably that she could leave the burrow for extended feeding excursions, whereas alone it would have to either completely forego nourishment or, as is the case with the Porcellio species mentioned, must greatly restrict the spectrum of food that it can use (to that which is to be found only a short distance from the burrow and which can eas-ily be carried inside the burrow). This could be a disadvantage, especially during egg production. Necessary to the male's successful defense of the burrow is that he recognises his female. Studies of the Canary Island Porcellio species have shown over which pathways and under what selection pressures the recopinon of individuals, as is realized mHemilepistus, could have evolved. Females can bind males longer, the longer the period of their attraction is extended: Females olHemilepistus reaumuri have been proven to be al·ready att-ractive before they are ready to copulate and still remain attractive after they have copulated. The conse-quences of the last fact will be discussed. The question of why the males remain with the females after the parturial ecdysis will also be discussed: The great danger to the male's investment resulting from a tooi early abandoning, and the low probability of successfully finding another partner after a later abandomng should prevent a positive balance in the males' cost-effecriveness calculations.
Individual recogmtlon in the non-eusocial arthropods is, according to our present knowledge, predominantly found in the frame of permanent or temporary monogamy. In some cases, e. g. in stomatopods and possibly other marine crustaceans too, individual recognition may serve to allow identification of (i) individuals within dominance hierarchies or (ii) neighbours in territorial species thus helping to avoid the repetition of unnecessary and costly fights. Kin recognition is experimentally proven only in some isopod species (genera Hemilepistus and Porcel/io) and in the primitive cockroach (termite?) Cryptocercus. The «signatures» or «discriminators» used in the arthropods are chemical. It is assumed that the identifying substances are mainly genetically determined and in this paper I shall discuss possible evolutionary origins. The main part of this account is devoted to the presentation of some aspects of the highly developed individual and kin identification and recognition system in the desert isopod Hemilepistus reaumuri - a pure monogamous species in which pairs together with their progeny form strictly exclusive family units. Amongst other things problems of (i) mate choice, (ii) learning to recognize a partner, (iii) avoiding the un adaptive familiarization with aliens are treated. Monogamy under present conditions is for both sexes the only suitable way of maximizing reproductive success; an extremely strong selection pressure must act against every attempt to abandon monogamy under the given ecological conditions. The family «badges» which are certainly always blends of different discriminator substances are extremely variable. This variability is mainly due to genetical differences and is not environmentally caused. It is to be expected that intra-family variabiliry exists in respect of the production of discriminator substances. Since the common badge of a family is the result of exchanging and mixing individual substances, and since the chemical nature of these discriminators requires direct body contacts in order to acquire those substances which an individual does not produce itself, problems must arise with molting. These difficulties do indeed exist and they are aggravated by the fact that individuals may produce substances which do not show up in the common family badge. An efficient learning capability on the one hand and the use of inhibiting properties of newly molted isopods help to solve these problems. In the final discussion three questions are posed and - partly at least - answered; (i) why are families so strictly exclusive, (ii) how many discriminator substances have to be produced to provide a variability allowing families to remain exclusive under extreme conditions of very high population densities, (iii) what is the structure of the family badge and what does an individual have to learn apart from the badge in order not to mistake a family member for an alien or vice versa.
Behavioural adaptations have made the desert isopod Hemilepistus reaumuri the most successful herbivore and detritivore of the macrofauna of many arid areas in North Africa and Asia Minor. For survival and reproduction Hemilepistus is dependent on burrows. New burrows can only be dug during spring. With the time-consuming digging of a burrow, Hemilepistus has only made the first step towards solving its ecological problems. The burrows are vital and have to be continuously defended against competitors. This requirement is met by co-operation of individuals within the framework of a highly developed social behaviour. In spring adults form monogamous pairs in which partners recognize each other individually and later form, with their progeny, strictly closed family communities. Hemilepistus is compared with a Porcellio' sp. which has developed, convergently, a social behaviour which resembles that of Hemilepistus in many respects, but differs essentially in some aspects, partly reflecting differences in ecological requirements. This and a few other Porcellio species demonstrate some possible steps in the evolution of the social behaviour of Hemilepistus. The female Hemilepistus is-in contrast to Porcellio sp. - semelparous and the selective advantages of monogamy in its environment are not difficult to recognize. This chapter discusses how this mating system could have evolved and especially why monogamous behaviour is also the best method for the Hemilepistus male to maximize its reproductive success. The cohesion of pairs and of family communities in Hemilepistus is based on a highly developed chemical communication system. Individual- and family-specific badges owe their specificity to genetically determined discriminating substances. The nature of the badges raises a series of questions: e.g. since alien badges release aggression, how do parents avoid cannibalizing their young? Similar problems arise from the fact that family badges are mixtures of chemical compounds of very low volatility with the consequence that they can only be transferred by direct contact and that during moulting all substances are lost which an individual does not produce itself. It is shown that in solving these problems inhibiting properties (presumably substances) and learning play a dominant role.
During the past 50 to over 100 million years communities evolved in the tropics which attained unprecedented levels of biodiversity, strikingly represented by evergreen lowland rain forests offering home to more than 50% of all the world's extant species. Within only some 30 years human action reduced the area covered with tropical rain forests to about half of its former size, thereby negatively affecting local and global functions of the biosphere and exterminating an unknown number of species. With an exponentially increasing rate we are throwing away our and all future generations' biological heritage. We destroy the most complicated, scientifically most interesting living systems before we have gained any knowledge of their structures ,and dynamics. To understand the particular structures and dynamics of tropical communities means in the first place to understand the causes and consequences of their ten- to more than hundredfold higher alphadiversity (as compared to temperate systems). This problem has a historical dimension and a functional side requiring answers as to the nature of the proximate mechanisms of its maintenance. My review is only concerned with the latter aspect, and its maIn emphasis is on the gaps in our knowledge. Two sets of hypotheses have been developed for explaining the high within-commUnIty diversity. (1) According to the classical concept interspecific niche competition and subsequent niche separation are the main forces determining the structure of the community. These so-called equilibrium models have been contrasted in recent times with (2) non-equilibrium models. These models do not attribute the decisive role to interspecific competition. Strong niche overlaps are presumed to be very common within species-rich communities. Continuous stochastic local disturbances are assumed to prevent the achievement of any long-term equilibrium (climax) state. Being on the right spot at the right time is regarded as most important. Whether oneor a combination of both models provide the best key for understanding the structure of a special section within a community will certainly depend on many properties of the species at debate (mobility, disr.ersal, fertility etc.). For the vast majority of tropical organisms all such information is at present unavailable. The principles governing the structure of communities is just one of the very ,basic open problems. Another very prominent question is how the qualitatively very rich, however quantitatively poor resources are distributed among the members of highly diverse guilds of consumers and decomposers. Does the scarcity rather favour generalists or specialists, are small species overrepresented, are resources more extensively used than in temperate communities? One important property is fairly well established: Populations of most tropical species seem to be very small. Since a) in very many' cases distribution range is obviously very limited, since b) predator pressure is generally assumed to be higher in the tropics and c) recent - perhaps unduely generalized - results claim abundance fluctuations in the tropics fully comparable in their dimensions to those in the temperate zone, the question arises as to how these small populations can persist for seemingly long periods of time and avoid rapid extinction. Additionally treated PoInts concern detritivore communities, plant animal Interactions, key stone groups. Saving biodiversity in general and the tropical species and community richness in particular is one of the most urgent tasks of our generation, and biologists have to play a still more prominent role in this extremely important endeavor than they have in the past decades.
Scorpions, living in North African semideserts are - in spite of disrupting experimental interferences - able to maintain a certain direction in their natural environment in the dark on a plane surface. Under comparable laboratory conditions, excluding the possibility of light or gravity orientation, they can orient themselves if a directed air current passes over the "arena." In most cases the scorpions do not run necessarily with or against the wind, but rather maintain constant angles to the air current for anywhere from minutes to many hours. They are running anemomenotactically (ref. 1). Under identical conditions many species of beetles also orient themselves to air currents (refs. 2 to 4). The main problems to be solved in the study of anemomenotactic orientation are: (1) Which physical qualities of the air current have an influence on the anemomenotaxis? (2) With which sense organs do beetles and scorpions perceive wind directions? (3) Which physiological mechanism is the basis of anemomenotactic orientation? (4) What is the biological significance of anemomenotaxis in beetles and scorpions? With respect to these problems, more study has been done on beetles than on scorpions. Therefore, due to lack of space, I shall discuss mainly some of the results obtained in experiments with dung beetles (Geotrupes silvaticus, G. ,Stercorarius, G. armifrons, G. niger, Scarabaeus variolosus) and tenebrionid beetles (Tenebrio molitor, Pimelia grossa, P. tenuicomis, Scaurus dubius).
No abstract available
No abstract available
Reed frogs of the superspecies Hyperolius viridiflavus occur throughout the seasonally very dry and hot African savannas. Despite their small size (300-700 mg), estivating reed frogs do not avoid stressful conditions above ground by burrowing into the soil, but endure the inhospitable climate relatively unprotected, clinging to mostly dry grass sterns. They must have emcient mechanisms to enable them to survive e.g. very high temperatures, low relative hurnidities, and high solar radiation loads. Mechanisms must also have developed to prevent poisoning by the nitrogenous wastes that inevitably result from protein and nucleotide turnover. In contrast to fossorial amphibians, estivating reed frogs do not become torpid. Reduction in metabolism is therefore rather Iimited so that nitrogenous wastes accumulate faster in these frogs than in fossorial amphibians. This severely aggravates the osmotic problems caused by dehydration. During dry periods total plasma osmolarity greatly increases, mainly due to urea accumulation. Of the total urea accumulated over 42 days of experimental water deprivation, 30% was produced during the first 7 days. In the next 7 days rise in plasma urea content was negligible. This strong initial increase of urea is seen as a byproduct of elevated amino acid catabolism following the onset of dry conditions. Tbe rise in total plasma osmolarity due to urea accumulation, however, is not totally disadvantageous, but enables fast rehydration when water is available for very short periods only. Voiding of urine and feces eeases once evaporative water loss exceeds 10% of body weight. Tberefore, during continuous water deprivation, nitrogenous end products are not excreted. After 42 days of water deprivation, bladder fluid was substantially depleted, and urea coneentration in the remaining urine (up to 447 mM) was never greater than in plasma fluid. Feces voided at the end of the dry period after water uptake contained only small amounts of nitrogenous end products. DSF (dry season frogs) seemed not to be uricotelic. Instead, up to 35% of the total nitrogenous wastes produced over 42 days of water deprivation were deposited in an osmotically inert and nontoxic form in iridophore crystals. The increase in skin purine content averaged 150 µg/mg dry weight. If urea had been the only nitrogenous waste product during an estivation period of 42 days, lethal limits of total osmolarity (about 700 mOsm) would have been reached 10-14 days earlier. Thus iridophores are not only involved in colour change and in reducing heat load by radiation remission, but are also important in osmoregulation during dry periods. The seIective advantages of deposition of guanine rather than uric acid are discussed.
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.
The karyotype of D. elongatus was investigated by means of C-banding, silver staining, and mithramycinand quinacrine fluorescent staining. The diploid chromosome number is 2n = 50. C-banding shows pericentromerically localized constitutive heterochromatin in every chromosome. Two of the chromosome pairs carry two telomeric nucleolus organizer regions each. No heteromorphic sex chromosomes were found.