Climatic niche shifts and ecological sky-island dynamics in Mesoamerican montane birds.

An ongoing challenge in evolutionary and ecological research focuses on testing biogeographic hypotheses for the understanding of both species' distributional patterns and of the factors influencing range limits. In this study, we described the climatic niches of Neotropical humid montane forest birds through the analysis of factors driving their evolution at inter- and intraspecific levels; and tested for differences among allopatric lineages within Aulacorhynchus, Chlorospingus, Cardellina, and Eupherusa. We employed ecological niche models (ENMs) along with an ordination approach with kernel smoothing to perform niche overlap analyses and test hypotheses of niche equivalence/similarity among lineages. In addition, we described the potential distributions of each lineage during the Late Pleistocene climate fluctuations, identifying historical range expansions, connectivity, and stability. Overall, we observed differences in environmental variables influencing climatic requirements and distributional patterns for our selected species. We detected the highest values of niche overlap mainly between Eupherusa and some Chlorospingus lineages. At both interspecific and intraspecific levels, sister lineages showed non-identical environmental niches. Our results offer weak support to a moist forest model, in which populations followed the expansion and contraction cycles of montane forests, leading to a lack of niche conservatism among lineages (they tend to occupy not identical climatic environments) throughout Mesoamerica. Therefore, historical climatic conditions may act as ecological barriers determining the distributional ranges of these species.

The geography of evolutionary divergence in the highly endemic avifauna from the Sierra Madre del Sur, Mexico.

BACKGROUND: Mesoamerica is a remarkable region with a high geological and ecological complexity. Within northern Mesoamerica, the biotic province of the Sierra Madre del Sur (SMS) in southwestern Mexico harbors exceptionally high avian endemism and diversity. Herein, we searched for spatially and temporally concordant phylogeographic patterns, in four bird genera from three distinct avian orders co-distributed across Mesoamerica and investigated their causes through hypothesis testing regarding historical processes. Selected species include endemic and differentiated populations across the montane forests of Mesoamerica, and particularly within the SMS. RESULTS: We gathered mitochondrial DNA sequences for at least one locus from 177 individuals across all species. We assessed genetic structure, demographic history, and defined a framework for the coalescent simulations used in biogeographic hypothesis testing temporal and spatial co-variance. Our analyses suggested shared phylogeographic breaks in areas corresponding to the SMS populations, and between the main montane systems in Mesoamerica, with the Central Valley of Oaxaca and the Nicaragua Depression being the most frequently shared breaks among analyzed taxa. Nevertheless, dating analyses and divergence patterns observed were consistent with the hypothesis of broad vicariance across Mesoamerica derived from mechanisms operating at distinct times across taxa in the SMS. CONCLUSIONS: Our study provides a framework for understanding the evolutionary origins and historical factors enhancing speciation in well-defined regions within Mesoamerica, indicating that the evolutionary history of extant biota inhabiting montane forests is complex and often idiosyncratic.

Phylogeography indicates incomplete genetic divergence among phenotypically differentiated montane forest populations of Atlapetesalbinucha (Aves, Passerellidae).

The White-naped Brushfinch (Atlapetesalbinucha) comprises up to eight allopatric subspecies mainly identified by the color of the underparts (gray vs. yellow belly). Yellow and gray bellied forms were long considered two different species (A.albinucha and A.gutturalis), but they are presently considered as one polytypic species. Previous studies in the genus Atlapetes have shown that the phylogeny, based on molecular data, is not congruent with characters such as coloration, ecology, or distributional patterns. The phylogeography of A.albinucha was analyzed using two mitochondrial DNA regions from samples including 24 different localities throughout montane areas from eastern Mexico to Colombia. Phylogeographic analyses using Bayesian inference, maximum likelihood and haplotype network revealed incomplete geographic structure. The genetic diversity pattern is congruent with a recent process of expansion, which is also supported by Ecological Niche Models (ENM) constructed for the species and projected into three past scenarios. Overall, the results revealed an incomplete genetic divergence among populations of A.albinucha in spite of the species' ample range, which contrasts with previous results of phylogeographic patterns in other Neotropical montane forest bird species, suggesting idiosyncratic evolutionary histories for different taxa throughout the region.