Sexual Reproduction of Spiders

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 fro...

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...or her offspring. Sexual cannibalism is found to greatly benefit fertilization. That is, if after copulation, the female eats the male, the amount of clutch sired becomes twice as much as in the cases when he survives. Finally, males who are cannibalized by females have a higher share of paternity. However, the probability of being cannibalized makes most males willing to sometimes avoid copulation, which greatly reduces sexual competition.

The conflict of sexes remains unsolved, as female prefer to cannibalize males for benefits of the progeny, males always try to escape in order to fertilize more eggs of other females.

Bibliography:

Elgar, Mark A. and Schneider, Jutta M.. "Sexual cannibalism and sperm competition in the golden orb-web spider Nephila plumipes (Araneoidea): female and male perspectives." Behavioral Ecology, Vol. 12, No. 5, 2001. 547-552.