Feeding regime, adult age and sexual size dimorphism as determinants of pre-copulatory sexual cannibalism in virgin wolf spiders

Abstract

Pre-copulatory sexual cannibalism (Pre-SC), where females attack and consume courting males, is considered an extreme case of sexual conflict. Different ultimate causes underlying this phenomenon have been proposed for more than a century and still remain unclear. The main objective of this research was to test the ‘adaptive foraging hypothesis’ in females of the non-burrowing wolf spider Lycosa fasciiventris. We exposed virgin adult females to either rich or poor diet treatments (differing in prey quality and availability) and offered them males at different adult female ages (a proxy of mate availability during adulthood). The analysis of correlative data served to evaluate other hypotheses/predictions. In order to test the ‘mate choice hypothesis’ and the ‘sexual size dimorphism hypothesis’, we tested how male absolute and relative (to the female) body size, respectively, affected the probability of Pre-SC. Finally, we asked if the female body size predicts the rate of Pre-SC as proposed by the ‘aggressive spillover hypothesis’. Females from the poor diet treatment and females that were offered a mate shortly after reaching maturity more likely engaged in Pre-SC than females from the rich diet treatment and females that were deprived of males for longer periods. While females more likely cannibalized courting males of relatively or absolutely smaller body size, female absolute body size did not predict Pre-SC. Thus, our results support the ‘adaptive foraging hypothesis’, the ‘mate choice hypothesis’ and the ‘sexual size dimorphism hypothesis’ and failed to find support for one of the predictions of the ‘aggressive spillover hypothesis’. Pre-copulatory sexual cannibalism, where females kill and devour courting males, may be costly for both sexes raising questions about its adaptive aspects and evolution. We used wolf spider Lycosa fasciiventris to test several existing hypotheses aiming to explain the phenomenon. Pre-copulatory cannibalism in virgin females was predicted by their food availability during adulthood, age at first male encounter and the relative body size of the courting male. Females more likely engaged in pre-copulatory cannibalism if they were poorly fed, young at first male encounter and relatively larger than their courting males. Thus, our data may simultaneously support the ‘adaptive foraging’, the ‘sexual size dimorphism’ and the ‘mate choice’ hypotheses as the explanations for pre-copulatory cannibalism occurrences in L. fasciiventris.