Geographic body size variation of a Plateau anuran: evidence supporting the water availability and hibernation hypotheses

Body size influences ecological interactions between species as well as social interactions within species, eventually affecting the evolution of large-scale biodiversity patterns. Thus, macroecological investigations of body size can connect spatial variation in selection regimes and the evolution of organisms distributed through space. To better understand intra-specific body size variation in ectotherms, we considered eight hypotheses proposed in the literature, asking which best explain the geographical body size variation of Bufo minshanicus, an animal endemic to the eastern Tibetan Plateau, that is broadly distributed across high elevations (1700–3700 m). The body size of B. minshanicus from 4658 adult toads was obtained from 16 study sites, covering the majority of the distributional range of the species. We found that B. minshanicus had larger bodies and higher post-hibernation body condition in areas with greater seasonality (supporting the hibernation hypothesis). In addition, we found that individuals living in populations with lower precipitation and lower annual actual evapotranspiration, as well as high precipitation seasonality are larger (supporting the water availability hypothesis). Larger individuals tend to have an advantage when living in stressful environments due to energy consumption and desiccation rates. We conclude that multiple factors related to seasonality and humidity influence adult body size variation in B. minshanicus.