right|thumb|The prevalence of sexual cannibalism gives several species of Latrodectus the common name "black widow spider".Сексуални канибализам је када животиња, обично женка, канибализује свог партнера пре, током или после копулације. То је особина која се примећује код многих редова паука, неколико врста инсеката и ракова, пужева и неких врста змија. Предложено је неколико хипотеза које објашњавају ово наизглед парадоксално понашање. Хипотеза адаптивног тражења хране, хипотеза агресивног преливања и хипотеза погрешног идентитетаGould, S. Only his wings remained. Natural History 93, 10-18 (1984). су међу предложеним хипотезама које објашњавају како је сексуални канибализам еволуирао. Верује се да је ово понашање еволуирало као манифестација сексуалног сукоба, који се јавља када се репродуктивни интереси мушкараца и жена разликују. Код многих врста које показују сексуални канибализам, женка конзумира мужјака након откривања. Женке канибалистичких врста су генерално непријатељски расположене и не желе да се паре; стога су многи мужјаци ових врста развили адаптивно понашање како би се супротставили агресији жена.
Преваленција 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 drives this trait of sexual cannibalism in spiders. It also sometimes occurs in some anacondas, especially the green anaconda (Eunectes murinus), where females are larger than the males.
Предложена објашњења thumb|Female Chinese mantis eats a male copulating with her.
Different hypotheses have been proposed to explain sexual cannibalism, namely adaptive foraging, aggressive spillover, mate choice, and mistaken identity.
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.Barry, K.L., Holwell, G.I. & Herberstein, M.E. Female praying mantids use sexual cannibalism as a foraging strategy to increase fecundity. Behavioral Ecology 19, 710-715 (2008). Starving females are usually in poor physical condition and are therefore more likely to cannibalize a male than to mate with him.Andrade, M.C.B. Female hunger can explain variation in cannibalistic behavior despite male sacrifice in redback spiders. Behavioral Ecology 9, 33-42 (1988). Among mantises, cannibalism by female Pseudomantis albofimbriata improves fecundity, overall growth, and body condition. A study on the Chinese mantis found that cannibalism occurred in up to 50% of matings. Among spiders, 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.Johnson, J.C. . Animal Behaviour 61, 905-914 . In Agelenopsis pennsylvanica and Lycosa tarantula, a significant increase in fecundity, egg case size, hatching success, and survivor-ship of offspring has been observed when hungry females choose to cannibalize smaller males before copulating with larger, genetically superior males.Berning, A.W. et al. . Animal Behaviour 84, 715-721 .Rabaneda-Bueno, R. et al. Sexual cannibalism: high incidence in a natural population with benefits to females. PLoS ONE 3, e3484 (2008). 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.Wilder, S.M. & Rypstra, A.L. Males make poor meals: a comparison of nutrient extraction during sexual cannibalism and predation. Oecologia 162, 617-25 (2010). 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.
The adaptive foraging hypothesis has been criticized because males are considered poor meals when compared to crickets; however, recent findings discovered Hogna helluo males have nutrients crickets lack, including various proteins and lipids.Kralj-Fišer, S. et al. Mate quality, not aggressive spillover, explains sexual cannibalism in a size-dimorphic spider. Behavioral Ecology and Sociobiology 66, 145-151 (2011). In H. helluo, females have a higher protein diet when cannibalizing males than when consuming only house crickets. Further studies show that Argiope keyserlingi females with high-protein/low-lipid diets resulting from sexual cannibalism may produce eggs of greater egg energy density (yolk investment).
Aggressive spillover The aggressive spillover hypothesis suggests that the more aggressive a female is concerning prey, the more likely the female is to cannibalize a potential mate. The decision of a female to cannibalize a male is not defined by the nutritional value or genetic advantage (courtship dances, male aggressiveness, & large body size) of males but instead depends strictly on her aggressive state. Aggression of the female is measured by latency (speed) of attack on prey. The faster the speed of attack and consumption of prey, the higher the aggressiveness level. Females displaying aggressive characteristics tend to grow larger than other females and display continuous cannibalistic behavior. Such behavior may drive away potential mates, reducing chances of mating. Aggressive behavior is less common in an environment that is female-biased, because there is more competition to mate with a male. In these female dominated environments, such aggressive behavior comes with the risk of scaring away potential mates.
Males of the Pisaura mirabilis species feign death to avoid being cannibalized by a female prior to copulation. When males feign death, their success in reproduction depends on the level of aggressiveness the female displays.Dougherty, L.R., Burdfield-Steel, E.R. & Shuker, D.M. Sexual stereotypes: the case of sexual cannibalism. Animal Behaviour 85, 313-322 (2013). Research has shown that in the Nephilengys livida species, female aggressiveness had no effect on the likelihood of her cannibalizing a potential mate; male aggressiveness and male-male competition determined which male the female cannibalized. Males with aggressive characteristics were favored and had a higher chance of mating with a female.
Mate choice
Females exercise mate choice, rejecting unwanted and unfit males by cannibalizing them. Mate choice often correlates size with fitness level; smaller males tend to display a low level of fitness; smaller males are therefore eaten more often because of their undesirable traits. Males perform elaborate courtship dances to display fitness and genetic advantage.Maklakov, A. a., Bilde, T. & Lubin, Y. Vibratory courtship in a web-building spider: signalling quality or stimulating the female? Animal Behaviour 66, 623-630 (2003). Female orb-web spiders (Nephilengys livida) tend to cannibalize males displaying less aggressive behavior and mate with males displaying more aggressive behavior, showing a preference for this trait, which, along with large body size that indicates a strong foraging ability, displays high male quality and genetic advantage.Prenter, J., MacNeil, C. & Elwood, R.W. . Animal Behaviour 71, 481-490 .
Indirect mate choice can be witnessed in fishing spiders, Dolomedes fimbriatus, where females do not discriminate against smaller body size, attacking males of all sizes. Females had lower success rates cannibalizing large males, which managed to escape where smaller males could not. It was shown that males with desirable traits (large body size, high aggression, and long courtship dances) had longer copulation duration than males with undesirable traits. In A. keyserlingi and Nephila edulis females allow longer copulation duration and a second copulation for smaller males.Elgar, M. a, Schneider, J.M. & Herberstein, M.E. . Proceedings: Biological Sciences 267, 2439-43 . The gravity hypothesis suggests that some species of spiders may favor smaller body sizes because they enable them to climb up plants more efficiently and find a mate faster.Moya-Laraño, J., Halaj, J. & Wise, D.H. . Evolution; international journal of organic evolution 56, 420-5 (2002). Also smaller males may be favored because they hatch and mature faster, giving them a direct advantage in finding and mating with a female.Vollrath, F. & Parker, G. Sexual Dimorphism and Distorted Sex Ratios in Spiders. Nature 350, 156-159 (1992). In Leucauge mariana females will cannibalize males if their sexual performance was poor. They use palpal inflations to determine sperm count and if the female deems sperm count too low she will consume the male. In Latrodectus revivensis females tend to limit copulation duration for small males and deny them a second copulation, showing preference for larger body size. Another form of mate choice is the genetic bet-hedging hypothesis in which a female consumes males to prevent them from exploiting her. It is not beneficial for a female exploited by multiple males because it may result in prey theft, reduction in web, and reduced time of foraging. Sexual cannibalism might have promoted the evolution of some behavioral and morphological traits exhibited by spiders today.
Mistaken identity The mistaken identity hypothesis suggests that sexual cannibalism occurs when females fail to identify males that try to court. This hypothesis suggests that a cannibalistic female attacks and consumes the male without the knowledge of mate quality. In pre-copulatory sexual cannibalism, mistaken identity can be seen when a female does not allow the male to perform the courtship dance and engages in attack. There is no conclusive evidence for this hypothesis because scientists struggle to distinguish between mistaken identity and the other hypotheses (aggressive spillover, adaptive foraging, and mate choice).Aisenberg, A., Costa, F.G. & González, M. Male sexual cannibalism in a sand-dwelling wolf spider with sex role reversal. Biological Journal of the Linnean Society 68-75 (2011).
Male adaptive behaviours In some cases, sexual cannibalism may characterize an extreme form of male monogamy, in which the male sacrifices itself to the female. Males may gain reproductive success from being cannibalized by either providing nutrients to the female (indirectly to the offspring), or through enhancing the probability that their sperm is used to fertilize the female's eggs. Although sexual cannibalism is fairly common in spiders, male self-sacrifice has only been reported in six genera of araneoid spiders. However, much of the evidence for male complicity in such cannibalistic behavior may be anecdotal, and has not been replicated in experimental and behavioural studies.
Male members of cannibalistic species have adapted different mating tactics as a mechanism for escaping the cannibalistic tendencies of their female counterparts. Current theory suggests antagonistic co-evolution has occurred, where adaptations seen in one sex produce adaptations in the other. Adaptations consist of courtship displays, opportunistic mating tactics, and mate binding.
Opportunistic mating The risk of cannibalism becomes greatly reduced when opportunistic mating is practiced. Opportunistic mating has been characterized in numerous orb-weaving spider species, such as Nephila fenestrata, where the male spider waits until the female is feeding or distracted, and then proceeds with copulation; this greatly reduces the chances of cannibalization. This distraction can be facilitated by the male's presentation of nuptial gifts, where they provide a distracting meal for the female in order to prolong copulation and increase paternity.
Altered sexual approach