Mitochondrial DNA sequences and nuclear microsatellites reveal population genetic structure of the range-restricted hummingbird Phaeoptila sordida in the Balsas Basin


 The Dusky Hummingbird Phaeoptila sordida (= Cynanthus sordidus), occurs in the Balsas Basin, a region with a complex biogeographical history, and in the Tehuacán-Cuicatlán Valley and Valles Centrales in Puebla and Oaxaca, Mexico. However, the biogeographical and evolutionary history of these two regions of Mexico is poorly understood. We aimed to understand the genetic structure and phylogeographic history of Phaeoptila sordida, a range-restricted hummingbird to these two regions, as a proxy to study the evolutionary history of the Balsas Basin, by using mitochondrial DNA (mtDNA) sequences and nuclear microsatellites. Geographic structure was evident for both markers; however, some discordance was observed between the mitochondrial and nuclear markers. Based on mtDNA, samples from the Balsas Basin form one haplogroup, well separated from the Tehuacán-Cuicatlán Valley and Valles Centrales samples. In contrast to this, nuclear microsatellites uncovered two slightly different genetic clusters restricted to different habitats: samples from the Western Balsas restricted to the seasonally deciduous tropical dry forest, and samples from the Eastern Balsas-Tehuacán/Cuicatlán-Tehuantepec area in shrub and dry forested habitats. As expected by the interglacial refugia hypothesis, ENM predicted that the distribution of P. sordida was more contracted and fragmented during the Last Inter Glacial and more expanded at the Last Glacial Maximum. Consistent with that observed for other range-restricted hummingbird species, ENM predictions and a strong signal of population expansion indicate that the geographical range and population size are unstable over time, as compared to widespread hummingbird species, and that ecological and climatic factors possibly impacted its diversification. This study contributes to the debate that disputes the integrity of the Balsas Basin as a biogeographical unit and urges for the conservation of endemic species in the Balsas region and interior Oaxaca.