Seasonality drives body size variation in a widely distributed Neotropical treefrog

Abstract

It is well known that body size variation can be related to genetic and environmental factors and that this variation may occur among species, and among and within populations. Scinax fuscomarginatus is a widely distributed Neotropical anuran that occurs in open areas of several South American ecoregions, exposed to different climatic conditions and showing high levels of body size variation. We tested if this variation in body size is related to phylogeny or to any climatic condition to which populations are subjected. We measured the snout-vent length (SVL) of 285 individuals of S. fuscomarginatus from 37 populations, covering virtually all the known geographic distribution of the species. We constructed a phylogenetic tree under Bayesian inference based on mtDNA sequences to test for the existence of phylogenetic signal in body size variation and performed a multiple linear regression to examine the relationship between body size and environmental variables. Although S. fuscomarginatus shows a deep genetic structure, body size variation was randomly distributed across the phylogeny, indicating no phylogenetic signal. On the other hand, we found evidence that support some influence of climatic conditions in body size variation, being the precipitation seasonality and the temperature seasonality the most important variables. Our results are in accordance with the water conservation hypothesis, which predicts an increase in body size towards drier regions assuming that lower surface-to-volume ratio of larger bodies minimizes water loss by evaporation.