SOCIAL FACILITATION OF MALE SEXUAL BEHAVIOR, INTRASEXUAL COMPETITION, AND SEXUAL SELECTION IN THE GUPPY, POECILIA RETICULATA (PISCES: POECILIIDAE)

Abstract

Intrasexual competition among male guppies, P. reticulata, manifested itself partially as a social facilitation of courtship display rate. Single males in the presence of females displayed at a much lower rate than did males in the presence of females and other males. Furthermore, males in monomorphic populations displayed at a lower rate than males in dimorphic populations. Assuming that display rate is related to success in copulation, the following conclusions were drawn. A single male has a high probability of mating with a female when she is receptive. However, as the number of males increases, the probability of success becomes lower, so selection favors those males which increase their display rate when in the presence of other males. Finally, if all males in a population are identical in secondary sexual coloration, there is a high probability they are related; so, invoking an argument of kin selection, it is not entirely disadvantageous for a male to be unmated if his kin are successful. However, where males are different in coloration, the degree of relationship is probably less, so selection favors a further increase in display rate.