Range dynamics, rather than convergent selection, explain the mosaic distribution of red-winged blackbird phenotypes
Article first published online: 7 NOV 2013
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Ecology and Evolution
Volume 3, Issue 15, pages 4910–4924, December 2013
How to Cite
Ecology and Evolution 2013; 3(15): 4910–4924
- Issue published online: 10 DEC 2013
- Article first published online: 7 NOV 2013
- Manuscript Accepted: 30 SEP 2013
- Manuscript Revised: 26 SEP 2013
- Manuscript Received: 31 AUG 2013
- Demographic expansion;
- mitochondrial DNA
Geographic distributions of genetic and phenotypic characters can illuminate historical evolutionary processes. In particular, mosaic distributions of phenotypically similar populations can arise from parallel evolution or from irregular patterns of dispersal and colonization by divergent forms. Two phenotypically divergent forms of the red-winged blackbird (Agelaius phoeniceus) show a mosaic phenotypic distribution, with a “bicolored” form occurring disjunctly in California and Mexico. We analyzed the relationships among these bicolored populations and neighboring typical populations, using ~600 bp of mitochondrial DNA sequence data and 10 nuclear short tandem repeat loci. We find that bicolored populations, although separated by ~3000 km, are genetically more similar to one other than they are to typical populations separated by ~400 km. We also find evidence of ongoing gene flow among populations, including some evidence of asymmetric gene flow. We conclude that the current distribution of bicolored forms represents incomplete speciation, where recent asymmetric hybridization with typical A. phoeniceus is dividing the range of a formerly widespread bicolored form. This hypothesis predicts that bicolored forms may suffer extinction by hybridization. Future work will use fine-scaled geographical sampling and nuclear sequence data to test for hybrid origins of currently typical populations and to more precisely quantify the directionality of gene flow.