Molecular phylogenetics and the evolution of courtship behavior, body shape, and coloration in the livebearing fish genus Limia

This project addressed the question of why there are differences in the body shape and color patterns of closely-related species, with a focus on the hypothesis that female choice was the most influential form of sexual selection in these animals. The research combined molecular systematics on a group of Caribbean poeciliid fish with a morphometric analysis of body shape and a comparative study of courtship behavior and coloration patterns. The first well-resolved phylogeny for Limia was estimated using the mitochondrial ND2 gene which revealed the relationships between the species. The phylogeny was used to confirm or refute several proposed species groups within Limia and look for the closest relatives of the genus; the closest mainland relative remained unclear although the Hispaniolan Poecilia elegans was found to be the sister-taxon to Limia . The analysis of body shape variation in Limia revealed that all of the tested species were sexually dimorphic, not just those with male courtship displays predicted to be the most likely to show dimorphism. Both males and females were found to be distinct between species, meaning that the explanation for body shape evolution in Limia would have to account for interspecific changes in both sexes, as well as the sexual dimorphism within each species. A phylogenetic comparative analysis was used to evaluate a hypothesis linking female choice to dimorphism in color. The results showed that courtship display behavior evolved independently at least twice within Limia and perhaps three times. Some color patterns were phylogenetically correlated with courtship and by implication were likely to have been primarily elaborated by female choice; these included black markings on the edge of the caudal fin and underside of the body. However, vertical bars on the body of the male and yellow (carotenoid) coloration on the caudal fin appeared to predate the appearances of courtship. Although female preferences may have developed for these traits, an alternative hypothesis for the origin of those color patterns would be that male aggressive confrontations (including a blocking maneuver common in Limia) may have a greater selective role in modifying the appearance of poeciliid fish than generally thought.