![]() ![]() In the Pacific Northwest, the legacy of the last glacial maximum (LGM) combined with contemporary landscape features on population genetic structure is especially evident. The fragmentation of populations due to repeated habitat contractions and expansions led to many recent speciation events 7 and fragmented habitat including the separation of coniferous forests in western North America 8. One only has to look at the Pleistocene glaciations to see the historical impact of climate change on population genetic structure. Contemporary processes are especially important given the alarming rate that environments are changing and the effects of these changes on populations 4– 6. The greater signal of isolation by distance on mtDNA patterns likely reflects the strong effects of Pleistocene glaciations in shaping genetic patterns in western North America.Īlthough life history and historical processes are the primary factors shaping an organism’s evolutionary history, one must consider the role of contemporary processes on genetic variation 1– 3. Overall the isolation by distance signal was greater for mtDNA than microsatellite patterns. Finally, our study revealed a greater effect of isolation by distance than isolation by habitat for both mtDNA and microsatellite data. These results suggest the presence of a contact zone in Washington between the two mtDNA clades Coast Range/Cascades/Rocky Mountain and southern Oregon/California clades. In particular, Washington clustered with the Coast Range/Cascades/Rocky Mountain mtDNA group, but with populations in southern Oregon/California based on microsatellite data. Our analyses of populations in Oregon and Washington revealed a mismatch between patterns detected with mtDNA and microsatellite data. We found a near significant relationship between genetic diversity and latitude, however, our results indicate that overall, latitude is not a strong predictor of genetic diversity. In this study we used both mitochondrial control region (mtDNA) and microsatellite data to answer the following questions about genetic diversity and divergence in mountain chickadees ( Poecile gambeli) a resident bird species in western North America: (1) Do populations exhibit similar levels of genetic diversity across the range? (2) What is the genetic affinity of western populations in Oregon and Washington? (3) Do genetic patterns exhibit isolation by distance, or are genetic patterns more heavily influenced by habitat discontinuity? We tested the effects of isolation by distance and habitat distribution on genetic structure by analyzing 266 samples from 17 sites across western Canada and the United States. In particular habitat fragmentation and climate change are expected to influence the distribution and diversity of natural populations. Examining the factors that influence contemporary genetic patterns is important given the alarming rate at which natural environments are changing.
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