Virgin doves and mated hawks: contest behaviour in a spider

Theory predicts that the outcome and escalation level of animal contests will reflect the contestants' expected payoffs as well as their relative fighting ability. Although an individual's future prospects of reproduction are expected to be critical for the risk of injury that it should accept when contesting a given resource, previous empirical work has ignored the possibility that this factor may differ between individuals. We studied male-male contests in the golden orb spider Nephila fenestrata, where the potential for future reproduction is much lower in mated than virgin males. Males typically mate with only one female in their lifetime, and are subsequently functionally sterile because of damage to their mating organs. Nevertheless, they guard their mate against rival males. This leads to a situation where mated males, having nothing to lose, are predicted to fight with maximal force when facing an intruder. In line with this prediction, mated males usually won contests against virgin males, even when the latter were physically superior. Staged contests between mated males resulted in high frequencies of injury. Our results show that constraints on future reproduction can be critical for understanding a species' contest behaviour.