Temperature variation and average temperature differ in their effects on body size and corticosterone across...

Global temperatures are rising, and temperature variation is rapidly becoming more extreme and less predictable with anthropogenic climate change. Ectotherms, organisms that rely on environmental conditions to regulate processes such as development and metabolism, are particularly susceptible to changes in temperature regimes. This is especially true for amphibians, which have low tolerance for heat stress in larval stages. We monitored natural ponds with larval spotted salamanders (Ambystoma maculatum) and tested whether temperature variation and average temperature impacted salamander size and corticosterone (CORT) levels at (a) a single time point in early larval stages and (b) across time until metamorphosis. We also assessed additional factors with the potential to impact larval size and CORT levels, including prey abundance and larval development stage. At the early larval stage, both higher temperature variation and lower average temperatures predicted larger larval size. Through development to metamorphosis, higher mean temperatures predicted larger larvae, while the effect of temperature variation on larval size differed between ponds. Across development until metamorphosis, CORT levels increased with temperature variation and average temperature, but future experimental work is needed to identify the causal mechanisms. Our results demonstrate that even moderate changes in environmental temperature regimes can affect amphibian development at both early larval stages and through development until metamorphosis, which emphasizes the need for future work to identify both the underlying mechanisms of response to temperature as well as population consequences of shifts in growth and hormonal expression.