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.