Dissertation Research: Systematics, Secondary reproductive characteristics, and Biogeography of the Poeciliid Fish genus Limia

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0073231Springer and Hamilton Limia is a genus of Caribbean freshwater fishes related to the guppies and sailfin mollies (Poecilia) and swordtails (Xiphophorus). Poeciliid fish are important model organisms for studying the effects of sexual selection (especially female choice) on the behavior and appearance of animals. The 20 species of Limias are very diverse in sexual behaviors and coloration, but have rarely been studied until recently. Some species have elaborate male courtship displays while others do not; in some species males have colorful fin and body markings while in others males and females both appear plain. There are hypotheses for why such differences between species would arise, and it is thought that behavior and coloration may each influence the evolution of the other. To assess these ideas, it is necessary to find out how the different species of Limia are related to each other phylogenetically (or genealogically). Knowing the phylogeny of the genus will help determine the sequence and directionality of evolution of these characteristics. Graduate student Aaron Hamilton, under the direction of Drs. Mark Springer and David Reznick, is evaluating the relationships of the twenty species in the genus Limia using DNA sequencing of two genes, one nuclear and one mitochondrial. The results can then be applied to two different fields of research, sexual selection theory and biogeography. A comparative analysis of the courtship behavior and coloration of Limia species will seek to determine if there is a correlation between the presence of a display and the elaboration of male color patterns, whether display behaviors are ancestral or evolved within Limia, and whether any traits evolved more than once in the genus. The phylogenetic tree can also be compared to those of other Caribbean animals to look for common biogeographic patterns, which may match hypotheses for the geologic history of the Caribbean islands. The Caribbean islands have been a focus of biogeographers debating whether the distribution of animal species on these islands has been influenced primarily by vicariant events (such as plate tectonics) or by over-seas dispersal of the organisms. A robust phylogenetic tree for the 20 freshwater Limia species will contribute to the ongoing synthesis of knowledge bearing on this problem.