Striped marsh frog (Limnodynastes peronii) tadpoles do not acclimate metabolic performance to thermal variability

Human-induced climate change is predicted to affect not only the mean temperature of the environment but also the variability and frequency of extreme climatic events. Variability in an organism's developmental environment has the potential to markedly affect an individual's growth trajectory and physiological function, leading to impacts on individual fitness and population dynamics. Thus, it is important to consider the consequences of thermal variability on developing organisms and understand their capacity to respond to such increased variation. We investigated the capacity of larval striped marsh frogs (Limnodynastes peronii) to initiate a response to increases in the thermal variability of their developmental environment by reducing the sensitivity of their physiological rate functions to changes in temperature. In variable environments, we expected the thermal sensitivity of rate functions to decrease and their performance breadth to widen so as to buffer the effect of thermal variability. We raised larvae in stable (24°C), narrowly variable (22-26°C; mean 24°C) and widely variable (14-34°C; mean 24°C) thermal environments and measured the thermal sensitivity of their locomotor performance, heart rate, oxygen consumption and activities of two metabolic enzymes, lactate dehydrogenase and cytochrome c oxidase. We found that the temperature-dependent relationships of these physiological functions did not differ between tadpoles raised in stable or variable thermal conditions. Furthermore, the Q(10) values of each response variable were virtually unaffected by treatment when measured over the entire thermal range. Our results reveal that larval amphibians exhibit little plasticity in metabolic traits to thermal variability. This lack of plasticity may have important implications for the growth and population dynamics of organisms in environments that are beginning to experience increased thermal variability.