Mitochondrial, morphological and environmental data partially support current subspecies designation in Amazilia yucatanensis hummingbirds

Abstract

Historical geological events and Pleistocene climatic fluctuations have played important roles in shaping distribution and population differentiation across taxa. The buff-bellied hummingbird (Amazilia yucatanensis) is widely distributed along the Gulf of Mexico slope and the Yucatan Peninsula. Here, we obtained measurements and sequenced two mitochondrial DNA fragments from currently recognized subspecies: Amazilia yucatanensis yucatanensis (YUC), Amazilia yucatanensis cerviniventris (CER) and Amazilia yucatanensis chalconota (CHA). Additionally, we tested for their genetic and morphological differentiation, demographic expansion, palaeoclimatic distribution and niche overlap. Our results reveal genetic differentiation between two groups of populations: (1) from the Yucatan Peninsula to Veracruz (YUC+CER); and (2) from Veracruz to Tamaulipas (CHA). Neutrality tests and Bayesian skyline plots suggest past demographic expansion without changes in the effective population size over time. The potential distribution was fragmented at the Trans-Mexican Volcanic Belt and expanded northwards during the Last Glacial Maximum and Mid-Holocene to current conditions. Niche overlap was higher between YUC and CER. The environmental space occupied by subspecies was more similar to each other than expected by chance but significantly non-equivalent. Our results provide new insight on the distribution of this widespread hummingbird species and suggest that fragmentation during glaciations and differences in habitat have played a role in the recent diversification.