Patterns of genetic differentiation within species are influenced by both current dispersal and historical processes such as geographic isolation and subsequent recolonization. To gauge the relative importance of these factors, Shafer et al. examined spatial variation in genetic diversity across the natural range of the North American mountain goat (Oream-nos amerkanus). Fossil evidence supports the existence of a southern geographic refuge during the Last Glacial Maximum. Had mountain goats simply spread back from this region, one would expect a northward decrease in genetic heterozygosity and a nested phytogeny. Instead, analyses of microsatellite DNA reveal the presence of a second core area of elevated genetic diversity in northern British Columbia and southeastern Alaska. AAitochondrial DNA offers strong support for the separation of northern and southern clades, which molecular dating suggests split before the onset of the last glaciation. High gene flow links contiguous mountain ranges, and there are signs of contemporary long-distance dispersal. Similar considerations of population differentiation will be important for efforts to conserve alpine biota and ecosystems in the face of climate change.
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