In Risky Times, "Desperado" Male Spiders Work Harder to Mate

How do you determine whether a spider is attractive? The researchers first measured the symmetry of the spiders’ front legs. After sorting the spiders into "hot or not," they performed two experiments to examine courtship behaviors. They first looked at the relationship between attractiveness and courtship behavior (which, for these spiders, means raising and lowering the front legs, among other such behaviors). The researchers were surprised to find in the first experiment that the less symmetrical spiders did fewer leg raises than the symmetrical ones. As a mating ritual, researchers posit that the leg raises serve to show off the symmetry (or lack thereof) of the spiders’ legs for the female spider. And the female spiders noticed: While not all of the spider pairs mated, all of those that did had symmetrical legs. The second experiment introduced signals that a predator was near. The more attractive males, believing that they had a good chance of finding a mate again in the future, did not court as aggressively when there was a threat present. This is an example of asset protection—the spiders upped their chances for survival in lieu of mating, explains Matt Persons, professor of biology at Susquehanna University in Selinsgrove, Pa. On the other hand, he says, the less attractive males did more leg raises, an example of the “desperado effect.” Realizing they will have difficulty attracting mates in the future and perceiving risky conditions, they seize the moment and flaunt what they can, hoping to attract a mate. “The more reproductive value a male has, the more cautious he is,” says Persons. “When males have low mating probabilities, they have little to lose. In fact, inferior males might gain a competitive advantage if higher-quality males aren’t willing to court as much under higher levels of risk.” The paper, "Cautious versus desperado males: predation risk affects courtship intensity but not female choice in a wolf spider,” was published online in the journal Behavioral Ecology on Dec. 31 and is forthcoming in print. It was co-authored by Ann L. Rypstra of Miami University and Sean E. Walker of California State University.