Not just small, wet, and cold: effects of body size and skin resistance on thermoregulation and arboreality of frogs

We used simulations from a biophysical model that integrates interlinked exchanges of energy and water between frogs and their environments to address questions about the limits to thermoregulation and about adaptations for arboreality. Body size and cutaneous resistance (R-c) both significantly affected body temperature (T-b) and the time to desiccate to 70% of standard mass (an ecologically relevant metric of desiccation). Cutaneous resistances < 25 s/cm allow basking frogs to elevate their T-b several degrees above ambient, but R-c. above 25 had little additional effect on T-b. Small frogs (<10 g) are able to elevate their T-b above ambient while basking, even with small R-c. Large frogs must have greater skin resistances to be able to elevate body temperatures above ambient, yet large frogs take longer to desiccate to 70% of their standard mass. Frogs can avoid rapid desiccation with high R-c, a large body size, or some combination of these traits. Our literature survey indicates that frogs with a combination of R-c and body size that would result in long times to desiccate to 70% of standard mass tend to be arboreal, suggesting that those species may be selectively favored in a niche that often requires frogs to be away from water sources for extended periods of time.