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Abstract

SYMPATRIC SPECIATION BY HYBRIDIZATION IN A MARINE FISH.

Luiz A. Rocha
University of Hawaii
Bio

Mechanisms that lead to speciation remain among the most debated topics in evolutionary biology, and sympatric speciation is especially difficult to demonstrate in nature. Because of their peculiar biogeography and their rare ability to produce sounds, fishes of the genus Haemulon serve as a great subject for tests of speciation hypotheses. Collectively known as grunts, the genus is comprised of 19 nominal species and occurs in tropical and subtropical reefs along both sides of the Americas. Aiming to elucidate the phylogenetic relationships among the species of Haemulon, a combined total of ~2,000 base pairs from two mitochondrial genes (cytochrome b and cytochrome oxidase I), one nuclear intron (TMO-4C4) and one nuclear gene (RAG2) were obtained from all nominal species. Our data also indicate that the trans-isthmian H. steindachneri is composed of two species, one in each side of the Americas, and we propose the revalidation of the Atlantic species. The closure of the Isthmus of Panama seems to have played a role in the diversification of Haemulon, however, many sister species pairs have completely overlapping geographical distributions, indicating that vicariance is not the only process driving speciation in this genus, and that sympatric speciation by sound recognition is possible. Finally, the species H. carbonarium seems to have originated through a hybridization event between H. macrostomum and H. flavolineatum. These three species form a strongly supported group in the phylogeny, however, mtDNA groups H. carbonarium with H. macrostomum, whereas nuclear DNA groups H. carbonarium with H. flavolineatum. A detailed morphological analysis shows that many morphological characters in H. carbonarium are intermediate between H. macrostomum and H. flavolineatum, indicating a probable hybrid origin for H. carbonarium. If supported by additional ongoing analyses, this will be the first case of sympatric speciation by hybridization in a vertebrate animal.