Adaptation: The question of ‘adaptive value’ or ‘function’ describes what value the behavior contributes to the animals overall fitness, explaining how the behavior was preserved through time.

Numerous hypotheses for the adaptive value have been posed and studied by biologists interested in manifestations of sexual cannibalism in different species, primarily arthropods. The proposed adaptive value of these behaviors depends on the time at which the cannibalistic behavior (by females) occurs relative to fertilization, with pre-copulatory cannibalism benefitting the female and post-copulatory cannibalism potentially benefitting both sexes.

The precopulatory cannibalization of males may occur in mating provides no possible reproductive advantages to the male involved, as he loses the specific reproductive opportunity and the potential for any reproductive success to follow. For females, multiple explanations of the adaptive value of this early cannibalization have been researched. Precopulatory sexual cannibalism was suggested to act as a form of sexual selection, demonstrated by studies of the behavior in garden sWolf Spiderpiders where smaller males were more likely to be cannibalized by their females (Elgar & Nash 1988). In this case, the larger body size is selected for as males of this kind go on to successfully mate with the female. Another proposed explanation for the occurrence of precopulatory cannibalism by females is the behavior’s tangential relationship to the truly adaptive behavior of highly aggressive behavior in females. Following the observation of varying food conditions’ insignificant effects on the frequency of sexual cannibalism by female fishing spiders, the cannibalizing behavior was predicted to be unrelated to foraging and instead suggested to be a side effect of a selection for aggressive female behavior in female fishing spiders (Arnqvist & Hendriksson 1997). Other studies interested in foraging and sexual cannibalism have demonstrated the nutritional gain provided by the precopulatory consumption of males. Female cannibalism in female praying mantids was shown to be an adaptive foraging behavior as cannibalistic females benefitted from an increase and body condition, followed by increases in egg condition where their non-cannibalistic counterparts of the same species did not (Barry et al 2008).

Post-copulatory cannibalism by females has been suggested to offer adaptive value (in terms of increased reproductive success) to both participating mates. Comparison among species with varying rates of male lifetime matings and varying nutritional strains imposed by mating and gamete production, indicates a model where the occurrence of sexual cannibalism increases as males tend to have fewer matings in their lifetimes and as the costs of each mating increase (Buskirk et al 1984). This indicates the increased reproductive success of sexual cannibalism under these favorable conditions.

In orb-web spider (Argiope brownish), the adaptiveness of cannibalism by females was illustrated in a study that measured the offspring survival times of cannibalistic females when they were allowed to cannibalize their mates and when they were prevented from doing so. The females engaging in the cannibalistic behavior showed offspring with increased survival times (and healthier broods), indicating the lifetime fitness gains for both mother and father of offspring resulting from matings where sexual cannibalism occurred (Welke & Schneider 2012).