Genic Population Structure and Gene Flow in the Northern Flicker (Colaptes auratus) Hybrid Zone

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Abstract
The Yellow-shafted Flicker (Colaptes auratus auratus) and Red-shafted Flicker (C. a. cafer) form a stable, narrow hybrid zone on the western Great Plains of North America. Allozyme data were obtained from 31 structural gene loci for 33 samples representing 246 Northern Flickers from throughout the Great Plains. Flickers were approximately equivalent to other birds in terms of proportion of polymorphic loci (P̄ = 0.207) and average heterozygosity (H̄ = 0.056). There was no concordant variation between plumage characters and allelic frequencies. Gene-diversity analysis indicated that 92.5% of the genic variation occurred as within-deme heterozygosity(GD= 0.925),a pproximately 7% occurred among individual demes( GST= 0.07), and only 0.9% occurred among major river drainages (GST = 0.009). Even less diversity was found amongp arentala nd hybrid groups( GST= 0.002).T here is substantiaal llozymics tructuring of the Northern Flicker speciesp opulation, but the structuringis not associated with the hybrid zone, and there is, at most, very weak structuring into riparian zones of habitat. The electrophoretic data support the inference that gene flow among Northern Flicker populationsis high (Nm = 1.9-4.4/generation).I f the high gene-flowe stimatesa recorrect, then geographicasl electiong radientsw ould be the most likely mechanismm aintaining the narrow hybrid zone of plumage and morphometric traits.