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

• Published in: The Auk 1987-10, Vol.104 (4), p.654-664
• Main Authors: Grudzien, Thaddeus A., Moore, William S., J. Richard Cook, Danilo Tagle
• Format: Article
• Language: English
• Subjects: Alleles; Animals; Biological and medical sciences; Dehydrogenases; Evolution; Evolutionary genetics; Fundamental and applied biological sciences. Psychology; Gene flow; Genetic loci; Genetic variation; Genetics of eukaryotes. Biological and molecular evolution; Hybridity; Plumage; Population genetics, reproduction patterns; Population structure; Vertebrata
• ISSN: 0004-8038; 1938-4254
• DOI: 10.1093/auk/104.4.654

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 ($G_{{\rm D}}=0.925$), approximately 7% occurred among individual demes ($G_{{\rm DT}}=0.07$), and only 0.9% occurred among major river drainages ($G_{{\rm ST}}=0.009$). Even less diversity was found among parental and hybrid groups ($G_{{\rm ST}}=0.002$). There is substantial allozymic structuring of the Northern Flicker species population, but the structuring is 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 populations is high (Nm = 1.9-4.4/generation). If the high gene-flow estimates are correct, then geographical selection gradients would be the most likely mechanism maintaining the narrow hybrid zone of plumage and morphometric traits.