Journal
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 365, Issue 1543, Pages 1041-1052Publisher
ROYAL SOC
DOI: 10.1098/rstb.2009.0314
Keywords
sympatric speciation; ecological speciation; disruptive selection; reproductive isolation; gene flow; Darwin's finches
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Funding
- Secretaria Nacional de Ciencia
- Tecnologia e Innovacion and El Instituto para la Formacion y Aprovechamiento de los Recursos Humanos, Panama (L.F.d.L.)
- US National Science Foundation (J.P.)
- Natural Sciences and Engineering Research Council of Canada (A.P.H.)
- Smithsonian Tropical Research Institute (E.B.)
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Divergence and speciation can sometimes proceed in the face of, and even be enhanced by, ongoing gene flow. We here study divergence with gene flow in Darwin's finches, focusing on the role of ecological/adaptive differences in maintaining/promoting divergence and reproductive isolation. To this end, we survey allelic variation at 10 microsatellite loci for 989 medium ground finches (Geospiza fortis) on Santa Cruz Island, Galapagos. We find only small genetic differences among G. fortis from different sites. We instead find noteworthy genetic differences associated with beak. Moreover, G. fortis at the site with the greatest divergence in beak size also showed the greatest divergence at neutral markers; i.e. the lowest gene flow. Finally, morphological and genetic differentiation between the G. fortis beak-size morphs was intermediate to that between G. fortis and its smaller (Geospiza fuliginosa) and larger (Geospiza magnirostris) congeners. We conclude that ecological differences associated with beak size (i.e. foraging) influence patterns of gene flow within G. fortis on a single island, providing additional support for ecological speciation in the face of gene flow. Patterns of genetic similarity within and between species also suggest that interspecific hybridization might contribute to the formation of beak-size morphs within G. fortis.
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