Recent genetic, phenetic and ecological divergence across the Mesoamerican highlands: a study case with Diglossa baritula (Aves: Thraupidae)

The topographical, geological, climatic and biodiversity complexity of Mesoamerica has made it a primary research focus. The Mesoamerican highlands is a region with particularly high species richness and within-species variation. The Cinnamon-bellied Flowerpiercer, Diglossa baritula (Wagler, 1832), is a species endemic to the Mesoamerican highlands, with three allopatric subspecies currently recognized. To characterize divergence within this species, we integrated genomics, morphology, coloration and ecological niche modeling approaches, obtained from sampling individuals across the entire geographic distribution of the species. Our results revealed a clear genomic divergence between the populations to the east versus the west of the Isthmus of Tehuantepec. In contrast to the genomic results, morphology and coloration analyses showed intermediate levels of differentiation, indicating that population groups within D. baritula have probably been under similar selective pressures. Our morphology results indicated that the only sexually dimorphic morphological variable is the wing chord, with males having a longer wing chord than females. Finally, ecological data indicated that there are differences in ecological niche within D. baritula. Our data suggest that D. baritula could contain two or more incipient species at the intermediate phase of the speciation continuum. These results highlight the importance of the geographical barrier of the Isthmus of Tehuantepec and Pleistocene climatic events in driving isolation and population divergence in D. baritula. The present investigation illustrates the speciation potential of the D. baritula complex and the capacity of Mesoamerican highlands to create cryptic biodiversity and endemism.