Relationships between environmental gradients and geographic variation in the intraspecific body size of three species of frogs (Anura)

The relationship between environmental gradients and patterns of geographic variation in body size has been a controversial topic for ectothermic organisms globally. To examine whether the patterns that generally hold in more temperate species also hold for tropical ones, we examined the intraspecific body size variation in three species of Neotropical frogs, Dendropsophus minutus, Hypsiboas faber and Physalaemus cuvieri, along different environmental gradients (e.g. temperature, precipitation and topography). We analysed four competing hypotheses: (i) the water availability hypothesis that predicts a negative relationship between body size and precipitation; (ii) the heat balance hypothesis that predicts a negative relationship between body size and temperature; (iii) the topography hypothesis that predicts a negative relationship between body size and altitude; and (iv) the mixed-effect hypothesis that predicts that individuals occurring in wet and cold sites would be larger than individuals occurring in dry and warm sites. The spatial pattern of geographic variation in body size among populations of H.faber was associated with the mixed-effect hypothesis. In localities with low precipitation seasonality and cold conditions, H.faber individuals were larger than in localities with high precipitation seasonality and warm conditions. Variation in the body size of D.minutus was the opposite of that predicted by the heat balance hypothesis. Individuals in localities with high temperatures were larger than in localities with low temperatures. On the other hand, variation in the body size of P.cuvieri was not associated with the variables used in this study. Our results suggest that intraspecific variation in anuran body size is more dependent on species-specific response than on the region (i.e. temperate or tropical) where they occur.