The evolution of Thermal Performance Curves and life-history traits in responses to thermal selection

Thermal performance curves (TPCs) capture how population growth depends on temperature. When temperatures increase, such as during global change, TPCs may evolve to match new environmental temperatures. While previous studies mostly focus on population growth rate TPCs, evolution can also be strongly trait-dependent and require a multi-trait analysis. Here, we empirically tested how TPCs and multiple demographic, life-history and movement traits evolve by selecting four freshwater protist species at increased temperatures starting from clonal populations. After ten months of selection, populations showed a signature of evolutionary responses to the highest selection temperatures in different traits depending on the species. Particularly, we found consistent evolutionary reductions in body size in the three species having the largest cells and evolved changes in movement behaviour in all species. In contrast, we observed few modifications in population growth rate TPCs. These results suggest that adaptation, via evolution of TPCs, might involve the concurrent evolution of several traits. However, this may be species-specific and difficult from de-novo mutation alone, suggesting that natural populations that do not have sufficient standing genetic variation might have to rely on other means of mitigating the effects of climate change, such as dispersal.