Many studies propose that Quaternary climatic cycles contracted and/or expanded the ranges of species and biomes. Strong expansion-contraction dynamics of biomes presume concerted demographic changes of associated fauna. The analysis of temporal concordance of demographic changes can be used to test the influence of Quaternary climate on diversification processes. Hierarchical approximate Bayesian computation (hABC) is a powerful and flexible approach that models genetic data from multiple species, and can be used to estimate the temporal concordance of demographic processes. Using available single-locus data, we can now perform large-scale analyses, both in terms of number of species and geographic scope. Here, we first compared the power of four alternative hABC models for a collection of single-locus data. We found that the model incorporating an a priori hypothesis about the timing of simultaneous demographic change had the best performance. Second, we applied the hABC models to a data set of seven squamate and four amphibian species occurring in the Seasonally Dry Tropical Forests (Caatinga) in northeastern Brazil, which, according to paleoclimatic evidence, experienced an increase in aridity during the Pleistocene. If this increase was important for the diversification of associated xeric-adapted species, simultaneous population expansions should be evident at the community level. We found a strong signal of synchronous population expansion in the Late Pleistocene, supporting the increase of the Caatinga during this time. This expansion likely enhanced the formation of communities adapted to high aridity and seasonality and caused regional extirpation of taxa adapted to wet forest.

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Two main hypotheses have been proposed to explain the diversification of the Caatinga biota. The riverine barrier hypothesis (RBH) claims that the São Francisco River (SFR) is a major biogeographic barrier to gene flow. The Pleistocene climatic fluctuation hypothesis (PCH) states that gene flow, geographic genetic structure and demographic signatures on endemic Caatinga taxa were influenced by Quaternary climate fluctuation cycles. Herein, we analyse genetic diversity and structure, phylogeographic history, and diversification of a widespread Caatinga lizard (Cnemidophorus ocellifer) based on large geographical sampling for multiple loci to test the predictions derived from the RBH and PCH. We inferred two well-delimited lineages (Northeast and Southwest) that have diverged along the Cerrado-Caatinga border during the Mid-Late Miocene (6-14 Ma) despite the presence of gene flow. We reject both major hypotheses proposed to explain diversification in the Caatinga. Surprisingly, our results revealed a striking complex diversification pattern where the Northeast lineage originated as a founder effect from a few individuals located along the edge of the Southwest lineage that eventually expanded throughout the Caatinga. The Southwest lineage is more diverse, older and associated with the Cerrado-Caatinga boundaries. Finally, we suggest that C. ocellifer from the Caatinga is composed of two distinct species. Our data support speciation in the presence of gene flow and highlight the role of environmental gradients in the diversification process.

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Aim Amphibians exhibit two basic reproductive modes, terrestrial and aquatic, each with different ecophysiological constraints related to evaporative water loss. We hypothesize that these fundamental niche differences will generate strong geographical patterns at the global scale in response to spatial heterogeneity in temperature and water availability. Location Global. Time period Present. Major taxa studied Amphibians. Methods We used global distribution maps of 5,434 amphibian species, classified into terrestrial or aquatic breeders, to estimate the occurrence and proportion of terrestrial breeding species per 1° cell. We used multiple regression models to test the relative importance of seven abiotic variables: annual precipitation, annual mean temperature, annual mean relative air humidity, annual mean actual evapotranspiration, availability of lotic and lentic environments and slope. We used residuals autocovariate (RAC) generalized multiple regression models to control for spatial autocorrelation and a spatial vector based on amphibian phylogeny to account for phylogenetic dependencies among cells. Model generality was evaluated by contrasting results between 11 widely recognized world zoogeographical realms. Results Globally, the occurrence of terrestrial breeding species was better explained by temperature followed by total annual rainfall, relative air humidity and terrain slope. In contrast, the proportion of terrestrial breeders was better explained by terrain slope, followed by total rainfall, temperature and relative air humidity. Actual evapotranspiration and the extension of large lotic and lentic water bodies played a minor role. However, the relative importance and even the sign of the regression coefficients varied among realms, revealing different evolutionary pressures. Main conclusions Niche differences among terrestrial and aquatic breeding amphibian species are reflected in their distinct geographical distribution across the globe. Adequate conditions for terrestrial reproduction to evolve and thrive are reached in distinct ways in different realms. Temperature constraints and slope suggest that reproductive modes will be impacted differently by climate change.