FACULTY NEWS

David Wise

In Wolf Spiders, the Way to a Woman’s Heart is Through her Stomach

What causes female tarantulas to eat males rather than mate with them? Biological Sciences Professor David Wise traveled to Spain to find out.

Wise teamed up with ecologists from the Estación Experimental de Zonas Áridas (CSIC, Almería) in Spain and researchers from the Autonomous University of Madrid to study the way sexual cannibalism works in natural populations of the burrowing wolf spider Lycosa tarantula, also called the Mediterranean tarantula. "The research was conducted in southern Spain, near the city of Almería in Andalucía," Wise reports.

The researchers found that in an experimental population established at natural density, a substantial fraction—about one third—of females kill a potential mate instead of mating with him. It seems that this behavior is highly beneficial to the females. "There is strong evidence for a fitness advantage to genes that promote cannibalistic behavior in this species, because male Lycosa tarantula wolf spiders are high-quality prey. Females that have fed on a male have more offspring than females that have not dined on their potential mate," says Wise. In fact, the higher the number of males in the population, the more likely the females were to feed on the males.

Arachnophobics need not click
to enlarge this image of a male
wolf spider entering a female’s
burrow.

Wise had several reasons for being interested in this project, not the least of which was inspiration from Charles Darwin's original work on the theory of evolution. When asked what made him pursue this project, he responded, "There were several things: the keen interest of biologists in sexual selection ever since the work of Charles Darwin; the fact that cannibalism of all types is widespread among generalist predators, particularly among spiders; and ongoing controversies over whether or not sexual cannibalism occurs frequently in natural populations and is not a laboratory curiosity. Also whether or not females that cannibalize males are displaying behavior that is non-adaptive, that is to say behavior that is coded for genetically and that is adaptive in other contexts, but that is maladaptive during courtship."

This research is also a kind of multi-generational project. Wise explains: "This project was conducted by a team of many researchers led by Jordi Moya-Laraño, whom I co-mentored for his PhD, which he earned through the Autonomous University of Barcelona when I was on the faculty at the University of Kentucky. Jordi is the doctoral mentor of the lead author of the paper, Rubén Rabaneda-Bueno, which makes Rubén my academic grandson. So this publication is a three-generation production." It is also an example of highly collaborative and successful international research.

The results of the study show conclusively that females do not indiscriminately kill males, or kill them territorially as they have been known to do to other females. "The results of these field experiments are incredibly important," says Wise, "because they demonstrate that pre-mating sexual cannibalism is a frequently expressed adaptive behavior in a species that is an excellent model for understanding the ecological and evolutionary significance of sexual cannibalism in generalist predators."

The academic paper on this research appeared in the October 22 issue of the open-access journal PLoS ONE.

"Sexual Cannibalism: High Incidence in a Natural Population with Benefits to Females." Rabaneda-Bueno R, Rodriguez-Girones MA, Aguado-de-Ia-Paz S, Fernandez-Montraveta C, De Mas E, et al. (2008) PLoS ONE 3(1 0): e3484. doi:1 0.1371 /journal.pone.0003484