Forced copulation as a conditional alternative strategy in camel crickets

Abstract

In the animal kingdom, males typically acquire reproductive access to females through courtship, nuptial gifts, or combat. In many species, small or poor-condition males that are unable to produce an attractive display, proffer an adequate mating gift, or dominate in male–male competition may resort to forced copulation. Forced copulation has been previously demonstrated in the camel cricket Pristoceuthophilus marmoratus and is uniquely facilitated by male hind leg weaponry that functions in both intrasexual competition and sexual coercion. Because male leg armaments are positively allometric, the largest males would seem best equipped to force-copulate, although they might be the most attractive to females, and so least likely to adopt a forced copulation strategy. In order to resolve this potential paradox and determine which males are in fact most likely to force-copulate, we manipulated male body size using diet and performed mating trials. Results showed that (1) male size increased with diet quality, (2) females appear to prefer larger males, and (3) smaller males were more likely to attempt forced copulation. Our results thus suggest that forced copulation is a condition-dependent alternative mating tactic used by small males unattractive to females.