DISSERTATION RESEARCH: Phylogeny of the Genus Microlophus (Squamata: Tropiduridae): A History of Colonization and Dispersal

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A grant has been awarded from the National Science Foundation to Dr. Jack Sites and Mr. Edgar Benavides, Brigham Young University, to study the "Phylogeny of the South American lizard genus Microlophus." This genus consists of 22 recognized species with an extremely unusual geographic distribution; 9 species are found only in the Galapagos islands, ~ 1000 km off the west coast of Ecuador in the eastern Pacific, while the remaining 13 species occur in western South America from southern Ecuador to central Chile. Most of the mainland species are confined to the Atacama Desert within a few km of the coast, and thus occupy a linear 'strip' of habitat almost 5000 km long. This distribution is absolutely unique among land vertebrates. The main objective of the study will be to reconstruct the evolutionary relationships of all species in this group using DNA sequences from seven different gene regions, and computer-assisted tree-building algorithms to test the strength of support for specific genealogical groups identified in the trees. The project is broadly significant for two reasons. First, earlier studies have suggested that ancestors of the mainland species of this group have colonized the Galapagos independently on two occasions, but none of these studies have been based on sampling of all mainland species, so results can be explained as possibly spurious consequences of incomplete sampling. Benavides has now collected all recognized mainland species, and can overcome this criticism with more statistically powerful analyses that were not available to earlier investigators. Second, there are at least three alternative scenarios for the sequence of coloniazation of islands within the Galapagos Archipelago, but again sampling limitations have not permit a rigorous evaluation of alternatives. Sites and Benavides have obtained all but two of the Galapagos taxa, and will collect the missing species during this study; this more complete sampling design coupled with extensive molecular data will give a clearer picture, based on statistically robust hypotheses, for the assembly and evolution of the unique Galapagos fauna.