Seasonal changes in the thermal tolerances of the toad Rhinella arenarum (Bufonidae) in the Monte Desert of Argentina

We studied the thermal tolerances of Rhinella arenarum during the dry and wet seasons of the Monte Desert in San Juan Province, Argentina. This toad had differences in CTmax between dry and wet seasons, and the CTmax values were higher in the wet season (Austral summer). Operative temperature, body temperature, environmental maximal temperature, and relative humidity were related to CTmax, suggesting seasonal acclimatization of R. arenarum. Additionally, the CTmax recorded for R. arenarum was 36.2 °C, and the maximum ambient temperature recorded during the toads' activity time was 37 °C. Also, the CTmin recorded for R. arenarum was 5.3 °C and the minimum environmental temperature recorded was 7.2 °C. The wide thermal tolerance range recorded and the relationship between tolerance limits and the environmental extremes indicate that seasonal acclimatization is an effective mechanism by which toads can raise their thermal tolerance, allowing them to survive in the challenging conditions of the Monte Desert. Additional studies are needed to understand the relationship between the thermal tolerance of this desert amphibian and the environmental parameters that influence its thermal physiology.

R. arenarum showed differences in CTmax between dry and wet seasons, and the CTmax values were greater in the wet season (Austral summer). In addition, Te, Tb and Tmax were related to CTmax. This suggests that the acclimatization process, could be mainly regulated by environmental temperature. It has been suggested that the acclimatization of a species is not determined by only one factor, but by a combination of factors.Here, we found the CTmin of R. arenarum to be significantly different between wet and dry seasons. Excessive loss of body heat would be difficult to recover since a large body size would limit heat exchange with the environment. Although ectotherms lack mechanisms of internal heat production, they are still able to exploit low temperature environments by behaviorally thermoregulating and lowering their minimum temperature tolerance.Figure optionsDownload as PowerPoint slide