Resource Competition and Coevolution in Sticklebacks

Abstract

Threespine stickleback in young postglacial lakes provide a compelling example of coevolution between species that compete for resources. Coexisting pairs of stickleback species are highly divergent in habitat, diet, and body size and shape, whereas stickleback occurring alone in lakes are intermediate. We used experiments in ponds to test mechanisms of divergence between coexisting species. The results support the hypothesis of coevolution by resource competition between stickleback, but we found evidence that interactions with natural enemies also contribute to divergence. Natural selection arising from these interactions selects against intermediate phenotypes, included hybrids, and thus has contributed to the origin and persistence of stickleback species.