Metabolic compensation and behavioral thermoregulation of subtropical rhacophorid (Polypedates megacephalus) tadpoles in container habitats

We examined the relative importance of behavioral thermoregulation and metabolic compensation used by a subtropical rhacophorid (Polypedates megacephalus) tadpoles living in man-made container habitats to cope with thermal stress. We collected foam nests of P. megacephalus from man-made container habitats, and hatchlings were raised in 150 or 15 L of water (LWB and SWB containers, respectively). Water and air temperatures of containers were monitored using a datalogger. Tadpoles from both types of containers were acclimated at 22 and 32 degrees C for 10 d before measuring oxygen consumption (V(O2)) in a closed-system at 22, 27, and 32 degrees C. Thermal selection of tadpoles from two containers was determined using an aquatic thermal gradient. We observed daily stratification of temperature in the water column of LWB containers but not SWB containers. Tadpoles from LWB and SWB containers exhibited metabolic compensation so that tadpoles acclimated to 22 degrees C had significantly higher V(O2) than those acclimated to 32 degrees C. This was probably related to the variation of environmental temperature experienced by the tadpoles. Tadpoles of LWB and SWB containers selected similar water temperatures with low coefficient of variation, suggesting they are good thermal selectors. Results of this study suggest that P. megacephalus tadpoles use both behavioral thermoregulation and metabolic compensation to cope with the environmental temperature fluctuation, and this is, in part, due to the heterogeneity in the thermal regimes of breeding habitats. Even though metabolic compensation of tadpoles incurs a cost, P. megacephalus tadpoles that experience no daily thermal gradient in the man-made water bodies and/or seasonal variations in temperature over tadpole period evolve metabolic compensation to maintain physiological homeostasis under different thermal regimes.