Dehydration effects on the thermal biology and locomotor performance of the South American White-lipped Grassfrog, Leptodactylus fuscus

Abstract

Amphibians must constantly balance two vital physiological demands: maintaining adequate hydration and regulating body temperature. The behavioral adjustments required to support these needs often conflict, especially for terrestrial species, where performance-enhancing body temperatures typically increase the risk of dehydration. The complex interplay among these factors affects all aspects of amphibians' biology and is thought to be highly sensitive to changes in climate and environment. Herein, we investigated how dehydration affects aspects of the thermal biology of the ground-dwelling frog Leptodactylus fuscus, a species tightly associated with terrestrial habitats. We investigated the frog's locomotor performance across different combinations of temperatures (10, 15, 20, 25, 30 and 35 °C) and hydration levels (100, 90 and 80 %), focusing on traits such as optimal temperature, maximal performance, and thermal performance breadth. We also investigated how dehydration affected their preferred body temperature, critical thermal maximum and minimum, and the thermal tolerance breadth. We found that dehydration reduced maximal performance capacity but did not affect optimal temperature or thermal performance breadth. Dehydrated frogs reduced their critical thermal maximum but not the critical thermal minimum, and as a result, narrowed their thermal tolerance breadth. Dehydration did not affect the frog's preferred body temperature, a response thought to be convenient to water conservation, since it reduces the potential for evaporative water loss. In general, the interplay between performance, temperature, and hydration state in L. fuscus seems to reflect the more terrestrial habit of this species and the climatic features of its habitat. The deleterious effects of combined hot and dehydrating conditions on the absolute levels of maximal performance may bear important consequences to the fitness and persistence of the species, and predicted scenarios of extreme heat and intense drought events bear more concern in the light of these findings.