Genetic, phenotypic and ecological divergence with gene flow at the Isthmus of Tehuantepec: the case of the azure-crowned hummingbird (Amazilia cyanocephala)
amazilia cyanocephala, Gene Flow, genetic differentiation, Isthmus of Tehuantepec, Mexico, morphological variation, niche divergence, Pleistocene, selection
Aim We test whether populations of the Mesoamerican azure-crowned hum- mingbird, Amazilia cyanocephala (Trochilidae), located east and west of the Isthmus of Tehuantepec are genetically, morphologically and environmentally differentiated and examine the relative role of drift and selection in driving diversification. Location Mexico. Methods We sequenced the mitochondrial ATPase-6 and ATPase-8 genes and the control region of 130 individuals collected throughout the range of the spe- cies in Mexico. Population genetic methods and coalescent tests were used to reconstruct the phylogeography of the species. Morphological and niche varia- tion between genetic groups of A. cyanocephala were assessed. Results The data revealed two genetic groups separated by the Isthmus of Tehuantepec in the late Pleistocene (49,300–75,800 years ago), with the split occurring in the presence of gene flow. Deviations from demographic equilibrium were detected for the two genetic groups, indicating more recent population expansions. Amazilia cyanocephala individuals from populations on either side of the Isthmus of Tehuantepec differed in mor- phology and were distributed in unique environmental space. A coalescent- based test indicated that selection is driving the observed morphological differentiation. Main conclusions Our findings implicate the Isthmus of Tehuantepec as a permeable barrier driving recent diversification of A. cyanocephala in the pres- ence of gene flow. The two A. cyanocephala mitochondrial DNA (mtDNA) groups corresponding with morphological and environmental niche differences, in concert with the results of a coalescent-based test, suggest that selection has been strong enough to counteract the effects of gene flow.