Quantifying the Benefits of Water Conservation Posture for North Carolina Frogs

Dehydration is a constant risk for terrestrial animals. Due to the fact that amphibian skin is permeable, frogs lose large amounts of water via evaporative water loss (EWL). Frogs reduce EWL through a variety of physiological and behavioral factors. Treefrogs in particular exhibit a unique change in posture that reduces the amount of their skin that is exposed to air, therefore decreasing their individual EWL. This posture is aptly named water conservation posture (WCP). Using photogrammetry and 3D modeling, we accurately measured the surface area of Green Treefrogs (Hyla cineria) and Cope’s Gray Treefrogs (Hyla chrysoscelis). To find the difference in surface area between treefrogs displaying vs not displaying WCP, we photographed each treefrog in two postures: WCP and “splat,” where the frog’s legs were extended away from its body. On average, WCP reduced the surface area of treefrogs by 32%. In addition to finding their surface areas, we also calculated the volumes of each frog. Body size had a strong negative relationship with surface area to volume ratios, with larger frogs in WCP having a lower SA:V than smaller frogs in WCP. However, there was little correlation between body size and SA:V in frogs not displaying WCP. This research highlights the important role behavior plays in reducing water loss in frogs. Understanding how amphibians adapt to dry conditions can help us better understand how they survive extreme environmental conditions and respond to increasing drought and climate change.