The latitudinal variation in amphibian speciation rates revisited

Speciation can increase regional species richness, however, our knowledge of how and why speciation rates vary across space is still incomplete. Using comprehensive information on species distributions and their phylogenetic relationships, we describe the global spatial patterns of variation in amphibian speciation rates and explore their ecological determinants. We find that overall mean speciation rates in amphibians increase with latitude. This pattern is largely determined by anurans, the most diverse amphibian order. Salamanders, nevertheless, speciate faster in the tropics, whereas caecilians did not exhibit any relationship with latitude. Despite the overall inverse latitudinal trend in mean speciation rates of amphibians, tip-level maximum speciation rates are not necessarily restricted to higher latitudes and can be found in different regions across the globe. Among bioregions, higher mean speciation rates are associated with high past climatic velocity and topographic complexity, both factors potentially promoting isolation, an important primer for speciation. Our results suggest that the emerging inverse pattern of speciation rates in amphibians is likely driven by the combination of a few rapidly speciating clades distributed in higher latitudes and numerous clades in lower latitudes showing heterogeneous rates that, when averaged, pull down the estimations of mean speciation in the areas where they occur.