Sexual cannibalism

Sexual cannibalism is when a female cannibalizes her mate prior to, during, or after copulation. It is a phenomenon characterized primarily by members of most arachnid orders, as well as several insect orders. The adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis are among the proposed theories to explain how sexual cannibalism evolved. This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ. In many species that exhibit sexual cannibalism, the female consumes the male upon detection. Females of cannibalistic species are generally hostile and unwilling to mate; thus many males of these species have developed adaptive behaviors to counteract female aggression.

Sexual cannibalism is common among insects, arachnids and amphipods. There is also evidence of sexual cannibalism in gastropods and copepods. Sexual cannibalism is common among species with prominent sexual size dimorphism (SSD); extreme SSD likely drove the evolution of sexual cannibalism in spiders.

Although females often instigate sexual cannibalism, reversed sexual cannibalism has been observed in Micaria sociabilisand Allocosa brasiliensis. In a laboratory experiment on M. sociabilis, males preferred to eat older females. This behavior may be interpreted as adaptive foraging, because older females have low reproductive potential and food may be limited. Reversed cannibalism in M. sociabilis may also be influenced by size dimorphism. Males and females are similar sizes, and bigger males were more likely to be cannibalistic. In A. brasiliensis males tend to be cannibalistic in between mating seasons, after they have mated, gone out of their burrows to search for food, and left their mates in their burrows. Any females they cross during this period likely have little reproductive value, so this may also be interpreted as adaptive foraging.

The adaptive foraging hypothesis is a proposed pre-copulatory explanation in which females assess the nutritional value of a male compared to the male's value as a mate. Starving females are usually in poor physical condition and are therefore more likely to cannibalize a male than to mate with him. Cannibalism by females of the Pseudomantis albofimriata species improves fecundity, overall growth, and body condition.Dolomedes triton females in need of additional energy and nutrients for egg development choose to consume the closest nutritional source even if this means cannibalizing a potential mate. In Agelenopsis pennsylvanica and Lycosa tarantula, a significant increase in fecundity, egg case size, hatching success, and survivorship of offspring has been observed when hungry females choose to cannibalize smaller males before copulating with larger, genetically superior males. This reproductive success was largely due to the increased energy uptake by cannibalizing males and investing that additional energy in the development of larger, higher-quality egg cases. In D. triton, post-copulatory sexual cannibalism was observed in the females that had a limited food source; these females copulated with the males and then cannibalized them.

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