Population differentiation and nuclear gene flow in the Dominican anole (Anolis oculatus)

Allele frequency data from nuclear microsatellite loci were used to investigate patterns of nuclear gene flow and population structure in the morphologically variable Dominican anole (Anolis oculatus). All six loci used proved to be highly polymorphic, with an average of 18.8 alleles per locus. Test for Hardy-Weinberg equilibrium revealed small numbers of heterozygote deficiencies at single loci in single populations and consistent patterns of increasingly significant heterozygote deficiency in global tests across populations and loci. No significant relationship between FST and patristic distances estimated from mitochondrial DNA sequences was detected and estimates of FIS were significantly higher in females than in males, indicating that gene flow may be sex-biased and mediated mainly by male migration. A highly significant correlation between linearized FST and loge (geographical distance) indicates that geographical proximity is a significant factor in the genetic structure of A. oculatus populations. However, levels of gene flow between morphologically differentiated parapatric populations are frequently seen to be relatively high. This supports the hypothesis of natural selection being the driving force behind the development and maintenance of morphological variation and shows that adaptive differentiation may be maintained despite the homogenizing influence of gene flow. Generally, the morphologically variable populations of A. oculatus are seen to be poor candidates for in situ speciation, but an exceptional case on the west coast of Dominica indicates that isolation resulting from vicariant events may lead to rapid differentiation at both mitochondrial and nuclear loci. This provides a possible mechanism for anole speciation on other Caribbean islands.