Ontogenetic variation of thermal tolerance in two anuran species of Ecuador: Gastrotheca pseustes (Hemiphractidae) and Smilisca phaeota (Hylidae) and their relative vulnerability to environmental temperature change

Abstract

Thermal tolerance and morphological plasticity have allowed amphibians to survive in many unusual habitats. Amphibians show a particular life cycle, presenting different ranges of thermal regimes in their different ontogenetic stages. In this study we show the critical thermal maximum (CTmax) and critical thermal minimum (CTmin) of three different developmental stages: larvae, metamorphic and post-metamorphic for two species of frog Gastrotheca pseustes, a high altitude species and Smilisca phaeota, a low altitude species of Ecuador. The CTmax values were similar for both species and higher in larvae: 37.9oC for Gastrotheca psesutes and 44.0oC for Smilisca phaeota. A decrease was observed at metamorphosis climax (stages 43-44): 37.6oC for Gastrotheca pseustes and 36.4oC for Smilisca phaeota. The data showed that after metamorphosis thermal limit decrease gradually. The high altitude species showed very low CTmin (lowest value for metamorphic: -3.4oC) and consequently a wider thermal tolerance range for the three ontogenetic stages (wider range for larvae: 41.5oC). The comparison between CTmax and maximum exposure temperature (Te) showed that metamorphic and post-metamorphic stages of Smilisca phaeota are the most vulnerable specie to change in environmental temperature living apparently over their upper thermal limit. According to this study the conservation strategies should focus on amphibian species of low altitude, in order to mitigate the effects of climate change in this group of animals.