Climate change is causing increases in thermal variability in addition to rises in global temperature averages. Organisms may utilize plasticity to respond to rapid thermal changes, but few studies have examined plasticity of early life stage as a mechanism to mediate the impacts of climate change. Using the dung beetle Onthophagus taurus, we investigated the potential of plasticity to buffer species from climate change by examining the effects of increasing temperature mean and variation during egg and larval development on the thermal responses of pupae, a later life stage. Beetles were reared at one of nine incubation treatments using a full factorial design including three average temperatures (22, 24, 26°C) and three amplitudes of fluctuation (±2, ±4, ±8°C). At pupation, we measured thermal sensitivity of metabolism (TSM), the relationship between temperature and carbon dioxide production, which influences energetic costs in thermally variable environments. TSM was quantified by measuring carbon dioxide production at 15, 20, 25, and 30°C using stop-flow respirometry. The relationship between carbon dioxide production and temperature provides an estimate of energetic costs at a given temperature (i.e. using the intercept) and costs incurred under thermal variability (i.e. using the slope).
Results/Conclusions
Onthophagus taurus exhibit plasticity in response to incubation temperatures that affects their ability to respond to temperature later in life. The relationship between temperature and metabolic rate was affected by developmental incubation; temperature mean and variation interact to influence pupae metabolic rates (p= <.0001). Onthophagus taurus reared in the warmest treatments (26°C), and the most thermally variable treatments (±8⁰C) had the lowest thermal sensitivity of metabolism, meaning they incurred the smallest energetic costs across thermal environments. This suggests that being reared in warm and/or variable temperatures may prime individuals for life in warm and variable environments by reducing energetic costs associated with fluctuating conditions. Beetles reared in cooler (22, 24°C) and less variable treatments (±4, ±2⁰C) expressed minimal thermal plasticity resulting in greater thermal sensitivity and energetic costs across temperatures. This could suggest a threshold of temperature mean and variability are required to stimulate plasticity and alter thermal physiology. These findings demonstrate that the temperatures experienced during development can affect how individuals cope with their thermal environments later in life, ultimately affecting responses to climate change.