Abstract
Population structure and gene flow were inferred from isozyme variation at 26 loci among five populations of Limnothlypis swainsonii (Swainson's Warbler; Parulidae), a Nearctic-Neotropic migrant songbird breeding in the unglaciated southeastern U.S.A. These populations exhibit relatively high levels of heterozygosity (Ho = 0.083), and 16 of 26 loci were polymorphic in at least one population (P = 0.385). Allelic frequencies were significantly heterogeneous at five loci, indicating a surprising degree of population structure for a migratory bird with no recognized subspecies (FST = 0.043). Moderate levels of gene flow are inferred (Nm = 1.5 to 11.7), yet population structure does not fit an isolation-by-distance model. Genetic heterogeneity is mostly due to differentiation between an Arkansas population and four populations from the coastal plain (from Louisiana to Virginia). Genetic drift may be responsible for much of the observed structure, but the lack of obvious barriers to dispersal between Arkansas and the coastal plain suggests that differentiation has been maintained by some other mechanism(s). Vicariance events on the breeding range, a split wintering range, or both could contribute to the pattern of differentiation observed.
Published Version
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