Field body temperatures in Malagasy rainforest frogs

Temperature is one of the most prominent environmental factors influencing amphibian physiology and also an important life history trait for amphibian pathogens, such as the chytrid fungus Batrachochytrium dendrobatidis (Bd). This pathogen has been reported from wild amphibian communities on Madagascar, but it remains poorly known if field body temperatures (T_B) of wild Malagasy amphibians are in a range suitable for infection by this fungus. Here, we evaluated field T_B of 845 rainforest frogs from 38 species in two hyperdiverse amphibian communities in Madagascar during the warm-wet and cool-dry seasons, the first such comprehensive data set from the island. T_B of Malagasy rainforest frogs differed between habitat types and thus appears to correlate with ecological niche. In particular, frogs measured in pond habitats had a higher T_B across seasons than those sampled from streams, riparian zones, and terrestrial (including arboreal) habitats. Overall, T_B of the 38 frog species ranged between 9.3 and 33.5 across habitats and diel cycle. This temperature range matches the optimal temperature range for Bd growth (17–23°C). We hypothesize that susceptibility to Bd might differ between frogs occupying different habitats. Pond-dwelling frogs may have more opportunities to clear Bd infection by choosing warm operative temperatures in sun-heated pond water. Our results highlight the need for more studies evaluating the seasonal fluctuations of field body temperatures in the studied amphibian species to contribute to a more reliable disease risk assessment.