PhD‐theses - Ethologische Gesellschaft

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.
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