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

Abstract

Abstract To date, behavioural responses and their role in thermal adaptation have largely been 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 are temperature restricted or allowed a behavioural choice of temperature. When measuring physiological capacity at forced temperatures, we find an acclimation response to increasing temperatures. In contrast, when measuring behavioural choice, we find limited variation in thermal preference regardless of the acclimation temperature. Although flies are physiologically capable of increased performance at higher temperatures, these benefits might not be realized in heterogeneous environments. Our data serve as an example to illustrate why it is important to understand how behaviour and physiology contribute to thermal biology and, ultimately, the ecology of organisms. To do this, we should consider the behavioural avenues available to the organism when estimating ecologically relevant fitness consequences in varying thermal environments.