Most organisms live in thermally variable environments and climate change stands to increase this variation. However, studies often utilize constant temperatures and focus on a single life stage. This is problematic because fluctuating temperatures differentially affect performance compared to constant temperatures. Further, we do not know how life stages are affected by thermal variability or the capacity of different life stages to respond plastically to changing temperatures. Climate change predictions that are not based on the most critical life stage may overestimate the likelihood of persistence. Using Onthophagus taurus dung beetles, we determined if life stages 1) differ in the degree of thermal plasticity in response to temperature fluctuations, and 2) incur different costs associated with experiencing thermally variable conditions. Using a full-sibling design, we exposed individual O. taurus to high (24 ± 8°C) or low (24 ± 4°C) temperature fluctuation treatments from the egg to adult life stages. We then measured CO2 production across a range of temperatures (15, 20, 25, 30 °C) in pupae and adults to quantify the thermal sensitivity of metabolism. Thermal sensitivity of metabolism was used to estimate the plasticity across life stages and the energetic costs of living under temperature fluctuations.
Results/Conclusions
Life stages of O. taurus vary in the degree of thermal plasticity expressed and the thermal sensitivity of metabolism, which can affect the energetic costs incurred in a thermally variable environment. Adults expressed higher magnitudes of thermal plasticity than pupae (p=0.01). Adults reared in the high temperature fluctuation treatment (24 ± 8 °C) had lower thermal sensitivity of metabolism than their full siblings from the low temperature fluctuation treatment (24 ± 4 °C). Comparatively, full sibling pupae reared in the low and high fluctuation treatments exhibited limited thermal plasticity. Overall, beetles in the high flux group exhibit decreased thermal sensitivity of metabolism compared to the low flux group (p=0.014), and adults exhibit increased thermal sensitivity of metabolism compared to pupae (p=0.001). Taken together, these data suggest that life stages differ in their responses to increased thermal variability and accounting for these differences may be crucial for accurate predictions of species persistence under climate change.