Sexual cannibalism in fishing spiders (Dolomedes triton): An evaluation of two explanations for female aggression towards potential mates

I manipulated food availability in juvenile and adult fishing spiders (Dolomedes triton) to test two hypotheses for sexual cannibalism. The adaptive foraging hypothesis posits that sexual cannibalism is an economic, adaptive foraging strategy on the part of the adult female. In contrast, the aggressive-spillover hypothesis suggests that precopulatory sexual cannibalism is misplaced aggression favoured in previous life-history phases. Several results indicated support for the adaptive foraging hypothesis. First, increased adult food availability produced marginally nonsignificant fecundity benefits in female's first egg sacs and highly significant fecundity benefits in female's second egg sacs. Second, while consumption of a male did not result in more offspring in either egg sac, it did significantly increase the probability a female would successfully hatch an egg sac. Finally, mating trials revealed mixed support for the adaptive foraging hypothesis as, for the most part, female mating behaviour (attack or mate) was not determined by the adaptive value a male represented (food item or sperm donor). Specifically, the likelihood of a precopulatory attack was not determined by male size, date (an indirect estimate of male availability) or female nutrient load. However, mated females did tend to attack courting males more often than virgin females. The aggressive-spillover hypothesis was supported by several findings. For juveniles, food availability had a significant positive effect on fixed female size (cephalothorax area at final moult) which, in turn, had a significant positive effect on fecundity. Thus, the spillover hypothesis' assertion that strong fecundity selection acts on juvenile feeding and fixed adult size was supported. The possibility that the spillover and adaptive foraging hypotheses are not mutually exclusive is discussed, especially in light of the presence of high levels of sexual cannibalism both before and after mating.