Female Spiders Benefit From Killing And Consuming Males In Nature

Main Category: Biology / Biochemistry
Also Included In: Veterinary
Article Date: 21 Oct 2008 - 4:00 PDT

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A team of researchers from Spain and the US led an investigation to reveal the extent to which sexual cannibalism occurs in nature and whether this behavior benefits female spiders. According to their results, in a natural population of burrowing wolf spiders, one third of the females kill males rather than mating with them, and the females accrue substantial benefits from consuming their kill. These results will appear in the October 22 issue of the open-access journal PLoS ONE.

The extent to which sexual cannibalism (females killing and consuming males) occurs in nature, and whether females benefit from cannibalism, have been two largely unanswered questions until now, primarily because so far no experiments had been conducted under natural or semi-natural conditions.

Intrigued by previous field data which suggested that females of the burrowing wolf spider Lycosa tarantula (the Mediterranean tarantula) may substantially benefit from killing and consuming males, a team of ecologists from the Estación Experimental de Zonas Áridas (CSIC, Almería) in Spain, joined by researchers from the University of Illinois at Chicago and the Autonomous University of Madrid (also from Spain), conducted a series of field experiments with this species in order to answer some basic questions about the evolution and possible adaptive significance of sexual cannibalism.

The researchers found that in an experimental population established at natural density, a substantial fraction (one third) of females kill a potential mate instead of mating with him. The investigators also manipulated the availability of males in this population and discovered that female propensity to attack and consume a male, rather than mating with him, increased if males were more abundant. They also found that previous mating history influences female behaviour; already mated females, which had stored sperm for offspring production, were more likely to kill a potential mate. In another experiment, in which all females were given a superabundance of natural prey species, females that were also allowed to feed on a male L. tarantula had more offspring, and of higher quality, than females that were allowed to feed only on natural prey. Previous studies on the benefit that accrue to females from sexual cannibalism are scant and very difficult to interpret, since cannibalism occurred under laboratory conditions and/or under a non-natural food supply.

"Now we know that, at least in one species, sexual cannibalism benefitting females occurs in nature," says Dr. Jordi Moya-Laraño from Spain, the principal investigator on this project.

For Prof. David H. Wise, a well-known ecologist from the University of Illinois at Chicago and co-author of the study, "the results of these field experiments are incredibly important, because they demonstrate that pre- mating sexual cannibalism is a frequently expressed adaptive behaviour in a species that is an excellent model for understanding the ecological and evolutionary significance of sexual cannibalism in generalist predators."

Rubén Rabaneda-Bueno, PhD student and lead author of the paper, adds: "After four manipulative experiments involving thousands of hours of field work, we could reach a robust conclusion: in these wolf spiders sexual cannibalism benefits females while males do not obtain any benefit, since they do not get to mate with the female that kills them."

These results also show that cannibalistic females do not indiscriminately kill males, as some investigators of pre-mating sexual cannibalism in other spider species have suggested, but rather that females behave adaptively, with the majority of cannibalistic females waiting until they have sperm to fertilize their eggs before they start attacking males.

"Sexual Cannibalism: High Incidence in a Natural Population with Benefits to Females."
Rabaneda-Bueno R, Rodríguez-Gironés MÁ, Aguado-de-la-Paz S, Fernández-Montraveta C, De Mas E, et al. (2008)
PLoS ONE 3(10): e3484. doi:10.1371/journal.pone.0003484
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