Geographic body size variation of a tropical anuran: effects of water deficit and precipitation seasonality on Asian common toad from southern Asia.

BACKGROUND

Two previous studies on interspecific body size variation of anurans found that the key drivers of variation are the species' lifestyles and the environments that they live in. To examine whether those findings apply at the intraspecific level, we conducted a study of the Asian common toad (Duttaphrynus melanostictus), a terrestrial anuran distributed in tropical regions. The body size of toads from 15 locations, covering the majority of their geographic range, and local environmental data were summarized from published literature. We used a model selection process based on an information-theoretic approach to examine the relationship between toad body size and those environmental parameters.

RESULTS

We found a positive correlation between the body size of the Asian common toad and the water deficit gradient, but no linkage between body size and temperature-related parameters. Furthermore, there was a positive correlation between the seasonality of precipitation and body size of females from different sampled populations.

CONCLUSIONS

As a terrestrial anuran, the Asian common toad should experience greater pressure from environmental fluctuations than aquatic species. It is mainly distributed in tropical regions where temperatures are generally warm and stable, but water availability fluctuates. Therefore, while thermal gradients are not strong enough to generate selection pressure on body size, the moisture gradient is strong enough to select for larger size in both males and females in dryer regions. Larger body size supports more efficient water conservation, a pattern in accordance with the prediction that lifestyles of different species and their local habitats determine the relationship between body size and environment. In addition, larger females occur in regions with greater seasonality in precipitation, which may happen because larger females can afford greater reproductive output in a limited reproductive season.