Sexual cannibalism in fishing spiders (Dolomedes triton): an evaluation oftwo explanations for female aggression towards potential mates

I manipulated food availability in juvenile and adult fishing spiders (Dolo medes triton) to test two hypotheses for sexual cannibalism. The adaptive f oraging hypothesis posits that sexual cannibalism is an economic, adaptive foraging strategy on the part of the adult female. In contrast, the aggress ive-spillover hypothesis suggests that precopulatory sexual cannibalism is misplaced aggression favoured in previous life-history phases. Several resu lts indicated support for the adaptive foraging hypothesis. First, increase d adult food availability produced marginally nonsignificant fecundity bene fits in female's first egg sacs and highly significant fecundity benefits i n female's second egg sacs. Second, while consumption of a male did not res ult in more offspring in either egg sac, it did significantly increase the probability a female would successfully hatch an egg sac. Finally, mating t rials revealed mixed support for the adaptive foraging hypothesis as, for t he most part, female mating behaviour (attack or mate) was not determined b y the adaptive value a male represented (food item or sperm donor). Specifi cally, the likelihood of it precopulatory attack was not determined by male size, date (an indirect estimate of male availability)or female nutrient l oad. However, mated females did tend to attack courting males more often th an virgin females. The aggressive-spillover hypothesis was supported by sev eral findings. For juveniles, food availability had a significant positive effect on fixed female size (cephalothorax area at final moult) which, in t urn, had a significant positive effect on fecundity. Thus, the spillover hy pothesis' assertion that strong fecundity selection acts on juvenile feedin g and fixed adult size was supported. The possibility that the spillover an d adaptive foraging hypotheses are not mutually exclusive is discussed, esp ecially in light of the presence of high levels of sexual cannibalism both before and after mating. (C) 2001 The Association for the Study of Animal B ehaviour.