Patterns of niche diversification in south-east Asian crocodile newts

Niche conservatism underlies the process of speciation in amphibians on the global scale. However, high tropical diversity is partly attributable to niche shifts within evolutionary lineages. Crocodile newts (genera Echinotriton and Tylototriton) are a monophyletic group endemic to south-east Asia, and are one of the few lineages of urodeles that appear in tropical regions. Here, we examined the patterns of ecological diversification within the crocodile newts based on 207 records of 23 species. The niche space was described according to topographic, climatic variables (temperature, rainfall, and seasonality) and forest cover. Our analysis showed that the occurrence of most of these species was strongly associated with the precipitation regime and seasonality. The diversification patterns of the crocodile newts are complex, showing both conservatism and divergence. These patterns can be related to the Tibetan uplift phase during the Neogene, resulting in the emergence of new montane habitats and subsequent changes in the palaeo-drainage system and climate. The range of ecological diversification within a lineage is possibly the result of several interacting processes, including environmental heterogeneity, the regional climatic history, and physiological constraints on species.