Molecular and climate data reveal expansion and genetic differentiation of Mexican Violet-ear Colibri thalassinus thalassinus (Aves: Trochilidae) populations separated by the Isthmus of Tehuantepec

Abstract

The present day distribution and spatial genetic diversity of Mesoamerican biota reflect a long history of responses to complex topography, geological history and climate changes. The hummingbird Colibri thalassinus thalassinus is distributed in northern Mesoamerica, with geographically disjunct populations mainly separated by the Isthmus of Tehuantepec (IT). Based on sampling across the species range in Mexico, we use mitochondrial DNA (mtDNA) sequences and distributional projections derived from ecological niche modeling (ENM) to test whether (1) populations are genetically differentiated according to the fragmented distribution of C. thalassinus thalassinus in Mexico, and (2) historical demographic patterns of these hummingbird populations correspond to those of expanded populations during the Last Glacial Maximum (LGM). Analysis of genetic variation revealed two main mtDNA lineages: populations west of the IT along the Sierra Madre Oriental, Trans-Mexican Volcanic Belt and Sierra Madre del Sur and populations east of the isthmus in Chiapas and Guatemala. A significant signal of genetic differentiation, demographic expansion near the LGM, and contractions/expansions of suitable environmental conditions during the LGM fit a model of lineage divergence west of the isthmus after the LGM, and that the species’ suitable habitat was continuous connecting populations on either side of the isthmus. We conclude that the genetic differentiation of C. thalassinus thalassinus in Mexico resulted from recent geographical isolation of populations separated by the IT. In addition, this scenario is supported by the modeled paleodistribution that suggests that populations expanded during the LGM, and that the spread of the species into the highlands caused habitat fragmentation and population isolation for C. thalassinus thalassinus during the interglacial periods. The findings corroborate the profound effects of Pleistocene climatic fluctuations on the genetic differentiation of C. thalassinus thalassinus in Mexico but challenge the generality of glacial refugia.