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Mitochondrial DNA Homogeneity in the Phenotypically Diverse Redpoll Finch Complex (Aves: Carduelinae: Carduelis flammea-hornemanni)

Gilles Seutin, Laurene M. Ratcliffe and Peter T. Boag
Evolution
Vol. 49, No. 5 (Oct., 1995), pp. 962-973
DOI: 10.2307/2410418
Stable URL: http://www.jstor.org/stable/2410418
Page Count: 12
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Mitochondrial DNA Homogeneity in the Phenotypically Diverse Redpoll Finch Complex (Aves: Carduelinae: Carduelis flammea-hornemanni)
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Abstract

Breeding redpoll finches (Aves: Carduelinae) show extensive plumage and size variability and, in many cases, a plumage polymorphism that is not related to age or sex. This has been ascribed to extreme phenotypic variation within a single taxon or to moderate variability within distinct taxa coupled with hybridization. The predominant view favors the recognition of two largely sympatric species: Carduelis flammea, comprised of four well-marked subspecies-flammea, cabaret, islandica, and rostrata; and C. hornemanni, comprised of two subspecies-hornemanni and exilipes. We studied representative samples of these putative subspecies (except islandica) for variation in mitochondrial DNA (mtDNA). Using 20 informative restriction enzymes that recognized 124 sites (642 base pairs \[bp\] of sequence or ≈ 3.7% of the molecule), we identified 17 RFLP haplotypes in the 31 individuals surveyed. The haplotypes formed a simple phylogenetic network with most clones diverging by a single site difference from a common haplotype found in almost half of the individuals. Within populations and taxa, levels of mtDNA diversity were similar to those observed in other avian species. The pattern of mtDNA divergence among populations was statistically unrelated to their geographic or traditional taxonomic relationships, and the estimated distance between the two traditionally recognized species was very small relative to those typically observed among avian sister species. Redpolls are highly vagile and have very large effective population sizes that may be relatively stable over the long term. Under these conditions, an absence of mtDNA differentiation between reproductively isolated, but recently diverged, taxa is not necessarily surprising. Hybridization between imperfectly isolated taxa might also have impeded mtDNA differentiation or contributed to its loss. Other explanations for the conflicting patterns of genetic homogeneity and phenotypic polymorphism in redpolls include models of genetic polymorphism at a major locus having broad pleiotropic or epistatic effects, and various ecophenotypic models (e.g., niche polymorphism, threshold response mechanisms, phenotypic modulation, developmental conversion). Distinguishing among these possibilities will require detailed knowledge of the genetic or ecophenotypic basis of phenotypic variation in redpolls.

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