Sexual cannibalism
[1] This trait is observed in many arachnid orders, several insect and crustacean clades,[2] gastropods, and some snake species.
[5] This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ.
[11] Different hypotheses have been proposed to explain sexual cannibalism, namely adaptive foraging, aggressive spillover, mate choice, and mistaken identity.
[14] 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.
[17][22] Males of the Pisaura mirabilis species feign death to avoid being cannibalized by a female prior to copulation.
[28] 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.
[29] Also smaller males may be favored because they hatch and mature faster, giving them a direct advantage in finding and mating with a female.
[27] Another form of mate choice is the genetic bet-hedging hypothesis in which a female consumes males to prevent them from exploiting her.
[32] 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.
[27] The mistaken identity hypothesis suggests that sexual cannibalism occurs when females fail to identify males that try to court.
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.
[15] 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).
This is evident in the mantid species, Tenodera aridifolia, where the male alters his approach utilizing the surrounding windy conditions.
[7] While both chemical and tactile cues are important factors for reducing cannibalistic behaviors, the latter functions as a resource to calm the female, exhibited in the orb-weaver spider species, Nephila pilipes.
Subsequent copulatory bouts are imperative for the male's ability to copulate due to prolonged sperm transfer, therefore increasing his probability of paternity.
[8] Subsequent improvements in male adaptive mating success include web reduction, as seen in the Western black widow, Latrodectus hesperus.
[42] In some species of spiders, such as Agelenopsis aperta, the male induces a passive state in the female prior to copulation.
[43] The chemical structure of the pheromone utilized by the male A. aperta is currently unknown; however, physical contact is not necessary for the induced passive state.
For example, in Pisaurina mira, also known as the nursery web spider, the male wraps the legs of the female in silk prior to and during copulation.
In the Paratrechalea genus, males silk wrap nutritive or worthless gifts to avoid being cannibalized by the female spider.
The physiological impacts of cannibalism on male fitness include his inability to father any offspring if he is unable to mate with a female.
[38] In the species of orb-weaving spider, Argiope arantia, males prefer short copulation duration upon the first palp insertion in order to avoid cannibalism.
[48] Occasionally (in 12% of cases in a 2012 study on Nephilidae spiders) palp severance is only partial due to copulation interruption by sexual cannibalism.
[48] Some males, as in the orb-weaving spider, Argiope arantia, have been found to spontaneously die within fifteen minutes of their second copulation with a female.
In this "programmed death", the male is able to utilize his entire body as a genital plug for the female, causing it to be much more difficult for her to remove him from her copulatory ducts.
[45] In other species males voluntarily self-amputate a pedipalp prior to mating and thus the mutilation is not driven by sexual cannibalism.
Male reproductive success can be determined by their number of fathered offspring, and monogyny is seen quite often in sexually cannibalistic species.
This behavior may be interpreted as adaptive foraging, because older females have low reproductive potential and food may be limited.
This behavior may occur due to their opportunistic feeding habits, lack of availability of prey, or competition for resources among the individuals of the species.
As this species exhibits male-biased sexual dimorphism, it is easier for male Montpellier snakes to attack and cannibalize the females.
