Does temperature at local scale explain thermal biology patterns of temperate tadpoles?

Abstract

Most of the literature on temperature–organism interactions rely on mean temperature (mostly air), disregarding the real complexity of this variable. There is a growing consensus about the importance of considering the temperature fluctuations as a mechanism improving organism's performance. Tadpoles are small body size ectotherm organisms that behave isothermally with their environment. As such, are good models for studying their thermal biology relative to their immediate environment. We studied six anuran tadpole species in North Patagonia, Alsodes gargola, Hylorina sylvatica, Batrachyla taeniata, Pleurodema thaul, P. bufoninum and Rhinella spinulosa, distributed in a West-East altitudinal cline with different environments and thermal conditions. We evaluated the relationship between thermal descriptors at a local scale and the thermal biology patterns of these temperate tadpoles. We estimated thermal tolerance limits and thermal sensitivity of locomotion of each species. The different aquatic environments showed important differences in local thermal conditions, associated with observed differences in the thermal traits in these tadpoles. Species exposed to lower temperature fluctuations and lower environmental mean temperatures showed lower swimming optimal temperatures and narrower thermal tolerance ranges. We found greater variability in the upper than in the lower critical limits in these Patagonian anuran tadpoles. Minimum critical temperatures were close to freezing temperature, possibly in detriment of their tolerance to high temperatures. Overall, our results suggest that these species are adapted to low temperatures. Finally, warming tolerances and predicted thermal safety margins, show that none of the studied species appear to be under thermal stress that may compromise their survival at the present time or in the near future, under a moderate climate change scenario.