Growing a fin: wetland and upland effects on tadpole morphology of Scinax squalirostris (Anura: Hylidae)

Geographical patterns of phenotypic variation are the outcome of a complex array of evolutionary and environmental factors. Studies on the correlates of the geographic variation in morphological characters can be useful to understand the drivers of phenotypic differences and because intraspecific variation in morphology can impact either local adaptation of any given species or higher-level ecosystem processes. The morphology of larval amphibians responds to multiple factors, including wetland level and surrounding land use. However, understanding the relative influence of such environmental factors on the morphology of tadpoles remains challenging. We used geometric morphometrics to describe the intraspecific morphological variation in tadpoles of Scinax squalirostris (Anura: Hylidae) in freshwater wetlands ranging along the transition between the Pampa and Atlantic Forest biomes in southern Brazil. Specifically, we assessed the relative influence of spatial and environmental (aquatic predators, water chemistry and hydroperiod, crop area) factors to tadpole body size and shape. The size of S. squalirostris tadpoles was affected by spatial factors and pH. Smaller-sized tadpoles were observed in the Pampa-Atlantic Forest transition. Allometry-free changes in the shape of tadpoles were associated both to wetland and upland factors. Tadpoles in larger ponds showed globular bodies and higher ventral fins, while tadpoles in ponds with higher electrical conductivity showed smaller tails. Tadpoles in ponds surrounded by larger crop areas showed longer fins. Our results are useful to understand the importance of wetland and upland effects on the morphology of widely distributed aquatic species, especially given the ongoing scenarios of land cover modification and climate change.

Automated summary

This study used geometric morphometrics to analyze the intraspecific morphological variation in tadpoles of Scinax squalirostris in southern Brazil and assessed the relative influence of spatial and environmental factors on their body size and shape. The results showed that tadpole size was affected by spatial factors and pH, while tadpole shape changes were associated with both wetland and upland factors.