The relative importance of male-male competition and female mate preference in determining reproductive success has been studied in a variety of species, including freshwater guppies. Dr. Bruce's preliminary observations indicate that male guppies appear to adjust their courtship displays depending on the presence or absence of the highest-ranking male of their social group. These observations suggest that the roles of male-male competition and alternative mating strategies deserve further investigation. Dr. Bruce will investigate the effects of social structure on courtship displays of male guppies. Social groups of three male and three female guppies will be observed to determine male social rank; the highest-ranking (alpha) male will then be removed from the group and the behavior of the subordinate males monitored. The alpha male will then be reintroduced and all males' courtship behavior observed. Subordinate males' sexual behavior is expected to increase when the alpha male is absent and decrease after his reintroduction. In a subsequent study, the behavior of males in a stable social group will be monitored before and after the introduction of a novel male. The resident males' sexual behavior is expected to remain high or increase and inhibit the novel male's courtship displays to females. If competition affects the courtship displays of male guppies, then male-male competition may affect reproductive success not only directly, by removing some males from contention, but also indirectly, by influencing males' communication with females and thereby the females' preference for mates. Dr. Bruce's research thus has the potential for contributing to our understanding of the behavioral factors in reproductive success.
