The Dry‐Climate Hypothesis: Identifying the Environmental Drivers of Terrestrial Viviparous Salamanders

ABSTRACT Aim The evolution of adaptive innovations carries strong eco‐evolutionary implications, allowing organisms to explore novel ecological opportunities, which facilitates lineage diversification. The remarkable diversity of reproductive strategies in amphibians provides a natural laboratory for identifying ecological mechanisms driving evolutionary novelties. In viviparous salamanders, the transition from larviparous (i.e., live bearing of aquatic larvae) to pueriparous (i.e., live bearing of fully terrestrial juveniles) reproduction is hypothesized to represent an adaptation to the absence of water for larval deposition, in what is known as the dry‐climate hypothesis. This work aimed to identify the ecological drivers of independent evolutionary transitions to pueriparity and test the dry‐climate hypothesis. Location Western Palearctic. Taxon Salamanders of the Salamandra and Lyciasalamandra genera. Methods A comparative ecological niche‐based framework spanning the entire known distribution of larviparity and pueriparity in salamanders was used to identify the ecological drivers of this reproductive transition. Niche divergence was tested between (a) viviparous modes and (b) independent origins of pueriparity to assess the existence of ecological differentiation between groups. The relative contribution of environmental factors to niche divergence was assessed by regression analysis. Results We found that independent transitions from larviparity to pueriparity are consistently associated with ecological differentiation driven primarily by steep topography and karstic geology. Main Conclusions Reproductive transitions to pueriparity in salamanders were consistently associated with scarcity of surface water driven by steep topography and karstic geology, providing the most unambiguous support for the dry‐climate hypothesis to date and supporting convergent evolution of terrestrialisation in salamanders for most pueriparous lineages. Climatic, hydrological (i.e., soil moisture and vapour pressure deficit) and habitat factors appear to be comparatively less relevant drivers of reproductive shifts, yet may have played a role in specific transitions to pueriparity, especially at the intraspecific level. We also found key differences in the use of available habitat between reproductive modes, with pueriparity representing a more specialised strategy likely restricted to areas with strong selective pressure against aquatic breeding.