The Common Raven (Corvus corax) is widespread at high latitudes and a noted disperser to remote islands. We hypothesized that, given their dispersal abilities, Alaskan populations would be genetically similar and maintain genetic diversity across thousands of kilometers. We sampled 134 ravens from 9 areas in Alaska, including 6 populations we considered as mainland and 3 as island (Kodiak, Adak, and Attu islands). Using 8 microsatellite loci, we found that in most Alaskan populations gene flow is sufficient to counter population divergence due to genetic drift. Our dataset suggests that conservatively there are just 2 raven populations in Alaska (K = 2), although the second Aleutian population, from Adak Island, was significantly differentiated, too. The Attu Island population was quite different from the other sampled populations, and it was the only location that neither received immigrants nor sent emigrants to other sampled locations. In addition, a comparison of gene flow models using a Bayesian coalescent approach most strongly supported an Attu Island isolation model. Prior work suggested that the uniqueness of the Attu Island population is due to isolation in a glacial refugium during the last glacial maximum. Postglacial dispersal from the Alaskan mainland has not erased this signal, suggesting that there could be limits to the species' dispersal abilities (i.e. remote colonization is rare). The isolated Attu Island population underwent a substantial decline ∼4 Kya, which roughly coincides with the arrival of the ultimate invasive species, humans. Traditional cultural values suggest that any surmised effect of humans would likely be indirect rather than direct.
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Vol. 135 • No. 4