Sexual Dimorphism and Trophic Trait Evolution in the Carolina Bay Fundulus Complex

Abstract

Convergent evolution in similar environments is widely held to provide some of the strongest evidence for natural selection's role in evolution, and convergent or parallel evolution of reproductive isolation, best studied in some fish systems, has been interpreted as evidence of selection's role in speciation. Most such fish studies have emphasized the role of selection on trophic traits in explaining trait convergence and speciation, but lately the roles of sexual selection and sexual dimorphism have also been considered in the studies of speciation and adaptive radiation. In the present study I investigated a to date little studied system, the Carolina Bay Fundulus species complex, in which patterns of convergence and divergence of body shape (and even speciation) have been suggested to be driven largely by predation. I investigated this complex for the trophic trait evolution seen in other fish systems, and for evidence of sexual dimorphism in body shape that could be important to the interpretation of shape evolution. I found that gill raker length and density, key trophic traits in fish, exhibited similar patterns of divergence and convergence in Fundulus sp. from Carolina Bays and streams as are seen for body shape. I further found that body shape divergence between Lake Phelps (a Carolina Bay) and the adjacent Scuppernong River was uneven between the sexes, females diverged significantly whereas males did not. In a second lake-river pair, however, Lake Waccamaw and the Waccamaw River, sexual dimorphism in body shape was not statistically detectable. These results suggest that selection on trophic traits may also be important to the divergence of Carolina Bay Fundulus from populations in other habitats, and that shape divergence between habitats may involve sexual dimorphism.