Sexual coercion and the opportunity for sexual selection in guppies

The operational sex ratio (OSR) is believed to play a major role in determining the opportunity for sexual selection. Most studies that investigate the effects of OSR on the opportunity for sexual selection, however, ignore the important effects that OSR has on sexual coercion. Sexually coercive behaviour by males, including forceful or subversive mating tactics and sexual harassment, may cause females to mate suboptimally and thus have important consequences for the opportunity for sexual selection. We investigated how variation in OSR affects sexual coercion in guppies, Poecilia reticulata, and examined the costs of this coercion to females. Males did not change mating tactics nor did individuals perform more coercive acts in the male-biased treatment, but the net rate of coercive intersexual interactions was higher simply because there were more males present. Increased sexual coercion did not affect direct fitness components (including number, weight and survival of offspring) or the proportion of courtship displays to which females responded positively. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.