TRACY, Christopher R.*; CHRISTIAN, Keith A.; BETTS, Greg; TRACY, C. Richard; Charles Darwin University; Charles Darwin University; Charles Darwin University; University of Nevada Reno: Interactions between water balance, temperature regulation and arboreality in frogs

Many amphibians evaporate water freely across their skin. This creates a challenge to thermoregulation: how to simultaneously regulate water and temperature balances when thermoregulatory behaviors may simply result in changes in rates of water loss rather than changes in body temperature. The apparent conflict between predictions based upon the physics of heat exchange, and observations of apparent thermoregulatory behaviors (e.g. basking), and physiology (e.g. increased water loss at high temperatures) has resulted in a debate for many years. It is likely that frogs with extreme resistance to water loss have the capacity to thermoregulate and to be partially emancipated from the need to find free water, and therefore have the means to become arboreal. Controlling rates of desiccation in frogs appears to be accomplished by three mechanisms: (1) having cutaneous resistance to water vapor transport (e.g. Litoria bicolor), (2) having a large body size which effectively reduces the surface area to volume ratio, and thus, reduces the rate dehydration (e.g. L. caerulea), and (3) behavioral or ecological selection of wet environments (such as rainforests or stream sides; e.g. Platymantis vitiensis). We have developed biophysical models to calculate water loss in frogs in relation to cutaneous resistance to water vapor loss and body size, and the simulations from this modeling shows that it is possible to achieve the same resistance to loss of hydration level by having a high cutaneous resistance, or by having large body size. This is consistent with the hypothesis that there is more than one means by which the ability to avoid desiccation can evolve, thereby providing potential for thermoregulation.