PhDâ€theses - Ethologische Gesellschaft

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SEXUAL CANNIBALISM: WHAT DO MALES HAVE TO OFFER? Sarah Deventer sari_australia@hotmail.com Research Update Diploma thesis, supervised by Prof. Dr. J.M. Schneider & Prof. M.E. Herberstein, Department of Biology, Zoological Institute & Museum, University of Hamburg The occurrence of sexual cannibalism is well documented, but why this extreme behaviour evolved in the first place is only partially known, and explanations are often species specific and not mutually exclusive. Some hypotheses incorporate the nutritional aspect of consumption of males. It is conceivable that conspecific males constitute a higher quality food for females than their usual diet due to the fact that males should hold nutrients which females of the same species also need, already in the right proportions. Moreover, males could contain essential nutrients that are absent in alternative prey or at least hold higher amounts of these desirable nutrients. A number of studies showed a positive effect of sexual cannibalism on female fecundity. However, it is not clear if this increased fecundity is only due to the fact that cannibalistic females gained additional food in those studies. Thus the question arises if females still retain a fecundity advantage when cannibalising a male compared to ingestion of a comparably sized other prey. The aim of this study was to compare female feeding rate between a sexual cannibalistic and a non‐cannibalistic feeding event, and, importantly, to assess how this translates into the eggs and spiderlings. We predicted a fecundity benefit (in terms of number and/or quality of offspring) from sexual cannibalism compared to consumption of comparably sized other prey. We found that spiderlings from females that consumed a male hatched slightly earlier, and started web construction sooner than from the control group. Three further offspring parameters (size, mass and survival duration under food deprivation) were positively and exclusively correlated to spiderlings’ lipid content. Although crickets hold more lipids than males and females took advantage of that, those three mentioned lipid‐dependent offspring parameters were not affected by whether the female consumed a male or a cricket. These results can be interpreted against, or in favour of the hypothesis that conspecific males constitute a high quality food for females. Nevertheless, these results show that males contain a different nutritional aspect than crickets (besides their lack of lipids) that influenced offspring. These differential effects are quite subtle, and not detectable in the commonly quantified measures of fecundity (egg sac weight or number of offspring). To our knowledge, this is the first study directly comparing the consequences of sexual cannibalism and a heterospecific feeding event on offspring, looking at offspring quality and behaviour. The results of this study extend the foraging hypothesis in relation to sexual cannibalism by adding the aspect of male nutritional content, and highlight the need for more research on the nutritional value of cannibalism, not (only) as an additional food source, but more specifically in comparison to the usual prey of females. 11
Research Update THE INFLUENCE OF FEMALE BODY CONDITION AND PREDATOR THREAT ON THE BROOD CARE BEHAVIOUR OF MOUTHBROODING CICHLIDS Barbara Gerber gerberb1@hotmail.com Master Thesis, 2010, supervised by PD Dr. Barbara Taborsky, Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Switzerland When parental environmental conditions affect brood care decisions they can have a trans‐ generational impact on offspring phenotype and survival. Parental energetic needs and offspring predation pressure have both been recognized as important factors influencing the quality of parental care, but surprisingly they are rarely manipulated simultaneously to investigate how parents adjust care to these potentially conflicting demands. In the maternally mouthbrooding cichlid Simochromis pleurosplius, we manipulated female body condition before spawning by different rations and perceived offspring predation risk by visual presentation of a natural predator during brood care in a two‐by‐two factorial experiment. We found that females on a low body condition produced smaller, but more young and engaged less in brood care behaviour than females with a high body conditons. Final clutch size and, related to this, female protective behaviour, was interactively determined by maternal nutrition and predator exposure. Surprisingly, high food females without a predator experience had smaller clutches than all other females. Our results highlight the importance to investigate the critical selective forces on parents and offspring in combination, if we aim to understand reproductive strategies. 12
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PhDâ€theses - Ethologische Gesellschaft