Futuyma 9801284 The proposed research uses molecular analyses to gain insight into the origin of species in the relatively recent geological past, and into the biological consequences of major changes in climate. The mountains of western North America constitute an unusual archipelago of sky islands for high-altitude species. Closely related species, including Melanoplus grasshoppers as well as other animals and plants, occupy different mountain ranges and peaks, in a pattern that suggests recent evolutionary diversification. It as often been suggested that such species originated by isolation and colonization during the Pleistocene glaciations that ended about 10,000 years ago. However, it is not certain which regions remained free of ice, or how habitats such as grasslands were distributed during the alternating glacial and interglacial periods. Thus the exact history by which organisms came to occupy different mountain ranges and differentiated into distinct species is very uncertain. For instance, species may have colonized progressively more northern areas from southern refuges as the glaciers retreated. Alternatively, ancestral species may have persisted at low altitudes, and have given rise to new species, as their habitats became restricted to isolated mountaintops when the climate became warmer. The proposed research uses Melanoplus grasshoppers to determine more fully the history by which biodiversity has originated in the western mountains. Comparisons of DNA sequences among populations and species from different mountain ranges can provide dates for divergence, and thus test the hypothesis that many species formed during or since the Pleistocene glaciations. Evolutionary relationships among species as reconstructed from DNA sequences, will be used to determine whether species formed by fragmentation or by progressive northward colonization. This research will provide one of the few comprehensive views of an evolutionary radiation. Using modern phylogenetic techniques and population genetic models, it will test hypotheses about species formation, and thus provide insights into the origin of diversity. And it will cast light on how past changes in climate have affected the distribution and diversity of organisms - information that may help to predict effects of future global changes in climate.
