One of the largest issues in animal sexual reproduction is the conflict of interests between the female and the male of the species. For example, multiple mating has been shown to greatly increase the fertilization rate for the male, but recent studies have shown that multiple mating also benefits the female.
The demonstrated benefit to the female is “sequential female choice;” that is, the ability (on the part of the female) to allow the fertilization of her egg clutch with more viable offspring. However, this presents an inherent conflict of interest in that sperm competition may lower the fertilization success rates of the species.
Sexual cannibalism (when the female consumes the male near the time of copulation) is a striking manifestation of a sexual conflict of interest. If the female consumes the male prior to insemination, she gains the nutritional benefits but the male loses his ability to reproduce. However, if the female consumes the male after insemination, the costs and benefits to each party are not so clear. It is beneficial to both the male and female to increase the fecundity of the female, increasing the reproductive chances of the male as well, but if the female mates again the male loses any apparent benefit.
Some spiders seem to have resolved this problem in favor of both sexes such as the redback spider, Latrodectus hasselti. Experiments involving polygamy in this species revealed that cannibalized males had greater fertilization success because these males mated longer and the cannibalistic females tended not to mate again. This shows that a compromise is struck between the two sexes. The female gains the benefit of the nutrition from the stoma of the male while the male limits the competition from other males. The Argiope kerserlingi do not follow this general pattern, however, and thus more study is needed.
In order to properly study the adaptive significance of sexual cannibalism, both the female and male perspectives should be considered. It is possible that sexual cannibalism increases the female's fecundity so females in poor health could possibly cannibalize males more aggressively than other females. Moreover, larger males may be more frequently cannibalized because they provide a more attractive prey. If there is an association between cannibalism, the duration of mating, and paternity it could be said that the female uses cannibalism to control the paternity of her offspring. From the male perspective, if a female cannibalizes a male and only mates once or the male is allowed to fertilize most of her eggs, then it could be said that cannibalized males should have a higher fertilization rates than non-cannibalized males. Conversely, sexual cannibalism may always be against the reproductive interests of the male and therefore he will always try to escape.
This experiment will use the golden orb-web spider (Nephila plumipes). The females of this species cannibalize males before and during mating....