Abstract
Cannibalism of females by males before, during or immediately following sex has been attributed to misidentification of females, rejection of females as mates and prioritisation of feeding over reproduction. In the gammarid amphipod Gammarus zaddachi, males demonstrate that they have identified a female and accepted her as a suitable mate by engaging in precopula pairing behaviour. However, a male may later decide to eat the female after pairing with her. Laboratory experiments were performed in which survival of females in precopula pairs of G. zaddachi was monitored after their male partners had been subjected to starvation, herbivorous diets or diets containing animal matter. These indicate that the female is less likely to survive when she is abnormally small relative to the male, when the male is at risk of death by starvation or when the male’s diet has lacked animal content. Decisions by males to forgo reproductive opportunities in favour of cannibalism, even after engaging in costly mate-guarding behaviour, emphasise the importance of carnivory in the trophic ecology of Gammarus species.
Highlights
Cannibalism of females by males before, during or immediately following sexual interactions occurs in several classes of crustacean, including amphipods (Dick 1995), decapods (Haddon 1995) and isopods (Tsai and Dai 2003)
A univariate General Linear Model (GLM) with female weight as a dependent variable, survival as a fixed factor and male weight as a covariate indicates that male weight was a significant predictor of female weight (F = 11.499, p \ 0.0001) (Fig. 3) but that there was no significant relation between female survival and female weight (F = 1.907, N.S.)
30/40 male Gammarus zaddachi survived the period of 21-day starvation
Summary
Cannibalism of females by males before, during or immediately following sexual interactions (reversed sexual cannibalism) occurs in several classes of crustacean, including amphipods (Dick 1995), decapods (Haddon 1995) and isopods (Tsai and Dai 2003). This behaviour is common in species where males are larger than females (Prenter et al 2006) and has been observed frequently in gammarid amphipods of the genus Gammarus (Dick 1995). Given that the post-moult period in which females are receptive to insemination is precisely the time at which they are most vulnerable to cannibalism (Dick 1995; Dick and Platvoet 1996; MacNeil et al 1997), a male guarding a recently moulted female must choose between inseminating the female and eating her
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