Long-term evolution experiments fully reveal the potential for thermal adaptation

Abstract

Climate change is leading to biodiversity decline at an unprecedented pace. Evolutionary responses may be crucial for organisms ability to cope with prolonged effects of climate change. It is thus fundamental to understand the dynamics of adaptation to warming environments in order to predict and mitigate the impacts of climate change on biodiversity. In particular, addressing how reproductive success evolves in deteriorating environments is extremely relevant, as this trait is more likely constrained at lower temperatures than upper physiological thermal limits. Experimental evolution udner a warming environment can illucidate the potential of populations to respond to rapid environmental changes. The few studies following such framework lack analysis of long-term response. We here focus on the long-term adaptive response of Drosophila subobscura populations evolving under a warming environemnt, analysing the reproductive success after 39 and 52 generations of thermal evolution. We found that long-term adaptation to higher temperatures can occur but the pace of such response is slow and likely dependent on low rates of environmental change. Furthermore, we observed that the magnitude of the response is relatively mild. In addition, the evolutionary dynamics differs between populations of distinct geographical origin, with the higher latitude populations only showing an adaptive response to the warming environment in a more advanced generation. This study reinforces the need for long-term evolution experiments to fully reveal the potential for thermal response. It also highlight that the scrutiny of several populations in this context is needed for a measure of variation within a species. Accounting for these sources of variation - both temporal and spatial - will allow for more robust assessments of climate change responses.