| Summary: | Climate cycling during the Quaternary played a critical role in the diversification of avian lineages in North America, greatly influencing the genetic characteristics of contemporary populations. To test the hypothesis that North American Northern Goshawks (Accipitergentilis) were historically isolated within multiple Late Pleistocene refugia, we assessed diversity and population genetic structure as well as migration rates and signatures of historical demography using mitochondrial control-region data. On the basis of sampling from 24 locales, we found that Northern Goshawks were genetically structured across a large portion of their North American range. Long-term population stability, combined with strong genetic differentiation, suggests that Northern Goshawks were historically isolated within at least three refugial populations representing two regions: the Pacific (CascadesSierra-Vancouver Island) and the Southwest (Colorado Plateau and Jemez Mountains). By contrast, populations experiencing significant growth were located in the Southeast Alaska-British Columbia, Arizona Sky Islands, Rocky Mountains, Great Lakes, and Appalachian bioregions. In the case of Southeast Alaska-British Columbia, Arizona Sky Islands, and Rocky Mountains, Northern Goshawks likely colonized these regions from surrounding refugia. The near fixation for several endemic haplotypes in the Arizona Sky Island Northern Goshawks (A. g apache) suggests long-term isolation subsequent to colonization. Likewise, Great Lakes and Appalachian Northern Goshawks differed significantly in haplotype frequencies from most Western Northern Goshawks, which suggests that they, too, experienced long-term isolation prior to a more recent recolonization of eastern U.S. forests.
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