The contribution of temperature and continental fragmentation to amphibian diversification

Aim Abiotic factors such as global temperature or continental fragmentation may favour speciation through the ecological and geographical isolation of lineages, but macroevolutionary quantifications of such effect with both fossil and phylogenetic data are rarely performed. Here, we propose to use biogeographical estimations and palaeo-environmental diversification models to estimate whether and how palaeotemperature and the sequential break-ups of Pangaea, Gondwana and Laurasia have affected the diversification of amphibians through time. Location Global. Methods Using a time-calibrated phylogeny for 3,309 amphibian species and a genus-level fossil record, we estimated the diversification rates of the group with birth-death models allowing rates to depend on the temporal variations of the environment. We used estimates of global palaeotemperature and an index of continental fragmentation through time to test the association between speciation and/or extinction rates and past temperature and fragmentation. We also estimated the biogeographical history based on a time-stratified parametric model informed by the global palaeogeography. We inferred whether vicariance or dispersal events explained the ancient and current geographical distribution of amphibians. Results The diversification analyses on the whole amphibians showed that temperature-dependent models are better supported than tectonic-dependent, time-dependent and constant-rate models for both the fossil and phylogenetic data. The best-fitting temperature-dependent model indicated a positive dependence of both speciation and extinction rates with the temperature through time. Biogeographical analyses indicated a Pangaean origin for amphibians and also showed that allopatric speciation (vicariance) explained important phases of the evolution of geographical ranges in the Mesozoic. Main conclusions Our results support that palaeotemperatures have positively impacted amphibian diversification. Our study provides additional insights into how to quantify the effect of the landmass fragmentation on the diversification processes and shows with biogeographical reconstruction that continental fragmentation is linked to allopatric speciation in the early history of the clade.