Diversification in the Andes: theAtlapetesbrush-finches

Evolutionary history of a cold-adapted limnephilid caddisfly: Effects of climate change and topography on genetic structure

The distribution of organisms is influenced by complex factors such as the phylogenetic evolutionary histories of species, the physiological and ecological characteristics of organisms, climate, and geographical and geohistorical features. In this study, we focused on a caddisfly, Asynarchus sachalinensis (Trichoptera: Limnephilidae), which has adapted to cold habitats. From phylogeographic analyses based on the mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I (COI) and 16S rRNA regions and the nuclear DNA (nDNA) 18S rRNA, 28S rRNA, carbamoyl-phosphate synthetase (CAD), elongation factor-1 alpha (EF1-α), and RNA polymerase II (POLII) regions, two distinct genetic clades were detected. Clade I was shown to be widely distributed from Sakhalin to Honshu, whereas Clade II was only distributed within Honshu. The distributions of these clades overlapped in Honshu. The habitats were located at relatively lower altitudes for Clade I and higher altitudes for Clade II. The divergence time of these clades was estimated to be during the Pleistocene, indicating that repeated climatic changes facilitated distributional shifts. Haplotype network and demographic analyses based on the mtDNA COI region showed contrasting genetic structures in the two clades. It was indicated that the population sizes of Clade I had expanded rapidly in a recent period, whereas Clade II had maintained stable population sizes. The habitats of Clade II were typically isolated and scattered at high altitudes, resulting in restricted migration and dispersal because of their discontinuous "Sky Island" habitats. The habitats of Clade I were located at relatively low altitudes, and it was assumed that the populations were continuous, which resulted in a higher frequency of migration and dispersal between populations. Thus, differences in the spatial scale of the adapted habitats of each clade may have resulted in different patterns of population connectivity and fragmentation associated with repeated climatic changes during the Pleistocene. Our study provided new insight into the distributional patterns of cold-adapted aquatic insects in the Japanese Archipelago. Furthermore, the distributional shifts predicted by ecological niche modeling under future climatic change conditions were different for each clade. Therefore, different principles are required in the assessment of each clade to predict temporal changes in their distributions.

Idiosyncratic patterns of local species richness and turnover define global biodiversity hotspots

Tropical mountains are global biodiversity hotspots, owing to a combination of high local species richness and turnover in species composition. Typically, the highest local richness and turnover levels are implicitly assumed to converge in the same mountain regions, resulting in extraordinary species richness at regional to global scales. We investigated this untested assumption using high-resolution distribution data for all 9,788 bird species found in 134 mountain regions worldwide. Contrary to expectations, the mountain regions with the highest local richness differed from those with the highest species turnover. This finding reflects dissimilarities in the regions' climates and habitat compositions. Forest habitats and humid tropical climates characterize the mountain regions with the highest local richness. In contrast, mountain regions with the highest turnover are generally colder with drier climates and have mostly open habitat types. The highest local species richness and turnover levels globally converge in only a few mountain regions with the greatest climate volumes and topographic heterogeneity, resulting in the most prominent global hotspots for avian biodiversity. These results underline that species-richness hotspots in tropical mountains arise from idiosyncratic levels of local species richness and turnover, a pattern that traditional analyses of overall regional species richness do not detect.

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.

Biogeographic regions and events of isolation and diversification of the endemic biota of the tropical Andes

Understanding the spatial and temporal evolution of biota in the tropical Andes is a major challenge, given the region's topographic complexity and high beta diversity. We used a network approach to find biogeographic regions (bioregions) based on high-resolution species distribution models for 151 endemic bird taxa. Then, we used dated molecular phylogenies of 14 genera to reconstruct the area history through a sequence of allopatric speciation processes. We identified 15 biogeographical regions and found 26 events of isolation and diversification within their boundaries that are independently confirmed with disjunct distributions of sister taxa. Furthermore, these events are spatially congruent with six geographical barriers related to warm and/or dry river valleys, discontinuities in elevation, and high peaks separating fauna from different range slopes. The most important barrier is the Marañon River Valley, which limits the boundaries of four bioregions and is congruent with eight phylogenetic distribution breaks, separating the Central and Northern Andes, where the most bioregions are found. We also show that many bioregions have diffuse and overlapping structures, with contact and transition zones that challenge previous conceptions of biogeographical regions as spatially simple in structure. This study found evidence that the drivers of our identified bioregions were processes of Andean uplift and mountain dispersal facilitated by temperature oscillations of the Pleistocene. Therefore, Andean bioregions were not formed from one simple biogeographical event in a certain time frame, but from a combination of vicariance and dispersal events, which occurred in different time periods.

Social selection parapatry in Afrotropical sunbirds

The extent of range overlap of incipient and recent species depends on the type and magnitude of phenotypic divergence that separates them, and the consequences of phenotypic divergence on their interactions. Signal divergence by social selection likely initiates many speciation events, but may yield niche-conserved lineages predisposed to limit each others' ranges via ecological competition. Here, we examine this neglected aspect of social selection speciation theory in relation to the discovery of a nonecotonal species border between sunbirds. We find that Nectarinia moreaui and Nectarinia fuelleborni meet in a ∼6 km wide contact zone, as estimated by molecular cline analysis. These species exploit similar bioclimatic niches, but sing highly divergent learned songs, consistent with divergence by social selection. Cline analyses suggest that within-species stabilizing social selection on song-learning predispositions maintains species differences in song despite both hybridization and cultural transmission. We conclude that ecological competition between moreaui and fuelleborni contributes to the stabilization of the species border, but that ecological competition acts in conjunction with reproductive interference. The evolutionary maintenance of learned song differences in a hybrid zone recommend this study system for future studies on the mechanisms of learned song divergence and its role in speciation.