Historical decline of genetic diversity in a range-periphery population of Spruce Grouse (Falcipennis canadensis) inhabiting the Adirondack Mountains

Isolation can affect genetic structure of populations near the edge of a species’ geographic range by reducing gene flow and allelic diversity, resulting in greater among-population differentiation. Spruce Grouse (Falcipennis canadensis), which are restricted to the boreal forest biome of North America, persist in small, disjunct lowland conifer patches at the southeastern extent of their range in the Adirondack Mountains of New York. This isolated peripheral population has declined since the early twentieth century and is considered highly vulnerable to extirpation. We examined haplotype diversity of mitochondrial control region sequences, comparing modern Spruce Grouse populations sampled from 2004 to 2013 in the Adirondacks and Algonquin Provincial Park, ca. 250 km to the northwest. Genetic diversity in the modern Adirondack population sample was very low compared to our smaller sample from Algonquin Park (three haplotypes vs seven). The modern Adirondack population shared no haplotypes with birds sampled from Algonquin, and these two populations are highly differentiated today (Fst = 0.632). We obtained shorter control region sequences from 18 museum specimens collected in the Adirondack from 1881 to 1986, in which we found six haplotypes, including five no longer found in the Adirondack Region. Some haplotypes that were once found in both regions have been lost from the Adirondacks as that population has declined demographically and shrunk geographically, indicating that the current differentiation is partly the result of these losses; when all 18 historical samples of Adirondack Spruce Grouse are included in the analysis, Fst between Adirondacks and Algonquin drops to 0.359. Haplotype diversity in Adirondack specimens collected prior to demographic decline (1881–1905, n = 10) was h = 0.778 compared to h = 0.245 in the modern Adirondack population, an over a three-fold decrease over period of ca. 130 years. These findings suggest that conservation measures that include supplementation of individuals from more diverse populations may restore genetic diversity in the Adirondack population to levels that existed a century ago.