Wayne 9801704 As climates warm, natural selection can favor individuals within a population that have superior adaptations for the warmer temperatures; as a result the population will change in character over time. Alternatively, migration from warmer areas may supply more appropriately adapted individuals and the original inhabitants may be less fit. Whether migration or natural selection on pre-existing variation fuels evolutionary change in populations is a fundamental question in evolutionary biology. The debate also is relevant to concerns about global warming as habitat fragmentation greatly limits the ability of migration to supply appropriately adapted individuals. Research is proposed to assess if migration or genetic isolation has influenced evolutionary change over the last 3000 years in a population of pocket gophers (Thomomys talpoides) that were preserved in packrat middens in Lamar Cave in Yellowstone National Park. During this period, morphologic change has occurred in the population in response to changes in temperature. To assess if this change has occurred in genetic isolation, the investigators will use new molecular genetic techniques that allow for migration to be detected as the appearance of foreign mitochondrial DNA sequences. Initial results show that ancient and modern samples collected near Lamar Cave share mitochondrial cytochrome b sequences that are absent from surrounding localities suggesting that the population persisted and did not receive female migrants from elsewhere for 3000 years. The investigators will extend this analysis of Lamar Cave fossils to include a more extensive sampling of stratigraphic levels within the deposit. This analysis should definitively establish the degree of isolation of Lamar Cave and may be the first that directly assesses temporal isolation of a population over evolutionarily significant time periods. Results will be relevant to the debate about how rapidly and by which mechanisms populations respond to climate chang e.
