What can physiological capacity and behavioral choice tell us about thermal adaptation?

To date, behavioral responses and their role for thermal adaptation have been largely overlooked in small ectotherms. Here, we measure reproductive output using four adult acclimation temperatures in Drosophila melanogaster and quantify egg-laying at restricted temperatures (thermal capacity) and across a thermal gradient (thermal preference). We demonstrate that different conclusions about insect responses to changing environmental temperatures can be drawn based on whether individuals were temperature restricted or were allowed a behavioral choice of temperature. When measuring physiological capacity at forced temperatures, we find an acclimation response to increasing temperatures. In contrast, when measuring behavioral choice, we find limited variation in thermal preference regardless of the acclimation temperature. Even though flies are physiologically capable of increased performance at higher temperatures, these benefits may not be realized in heterogeneous environments. Our data serve as an example as to why it is important to understand how behavior and physiology contribute to thermal biology and ultimately the ecology of organisms. To do this, we should consider the behavioral avenues available to the organism when estimating ecologically relevant fitness consequences in varying thermal environments