Ecological niche variation drives morphological differentiation in tropical stream-dwelling newts from Indochina

Morphological diversity within organisms can arise from factors other than genetic diversity alone. Local adaptations and combinations of various factors are also involved in shaping morphology. We investigated the relationship between morphological diversity and ecological niche divergence within two related tropical stream-dwelling newt species from Indochina: Paramesotriton deloustali and P. guangxiensis. We identified sexual dimorphism within both species and a significantly larger body size in P. deloustali than in P. guangxiensis. Our findings highlighted that climatic variables strongly influence Asian warty newt distribution, indicating the potential effects of climate change on tropical newt populations. Furthermore, we identified significant intra- and interspecific morphological and niche differentiation across five populations of the two newt species, suggesting that newt morphology is responsive to environmental factors. A significant negative relationship was observed only between ecological niche similarity and geographic distance among various combinations of factors, indicating that the distinct morphology of the study species mirrors ecological adaptation.