Boiling the frog: thermal adaptation in mountain tropical frogs

Pol Pintanel Costa

Global warming is seriously threatening amphibians. One of the main causes is the direct effect of the increase in average and extreme  temperatures, in addition to the indirect consequences that entail the  destruction and fragmentation of their terrestrial and aquatic  habitats. On the other hand, we have very little information of the  traits associated with thermal physiology, especially in tropical  species that constitute more than 85% of amphibian species. A thorough  knowledge of the features associated with tolerance and thermal  sensitivity, that define the fundamental thermal niche of these species, and the description of the climatic features both micro and  macroclimatic of their habitats, are essential to predict the  responses of amphibians to address climate change consequences on  amphibian communities.
We have analysed the interspecific variation in thermal tolerance  limits (CTmax, CTmin and thermal breath) and thermal performance  curves (optimum temperature (Top), thermal breadth (B80)) of an amphibian community along an altitudinal gradient in Ecuador. This  allowed us to estimate the vulnerability to suffer acute and chronic  thermal stress based on the temperatures measured at the micro  (dataloggers) and macroenvironmental level (WorldClim) in different  species of tadpoles (75) and adults of the genus Pristimantis (20),  collected from lowlands either from the Pacific coast and the Amazon  basin to the Andean highlands (5m – 4200 m).
We found a decrease in the thermal limits along the altitudinal  gradient, being greater the decline in cold tolerance values. This  asymmetric reduction of the thermal limits determined that high  elevation species have greater thermal ranges. In addition, we found  that species of open or deforested biomes, which are exposed to a  higher level of climate variability, have greater thermal tolerance  ranges. We also tested the hypothesis of climate variability in  altitude, which predicts that increased thermal tolerance range in ectotherms correlates with a wider distribution on altitude. Finally,  our results suggest that lowland species are more vulnerable to heat  stress which could determine in the worse cases an increased risk of  extinction due to global warming.