Evolution of thermal tolerance in marine diatoms: Metabolic strategies under heat stress.

In the last decade, numerous laboratory experiments have demonstrated that when marine phytoplankton are exposed to thermal stress, they can evolve high temperature tolerance in a short time (weeks to months). This evolutionary potential may ensure the persistence of marine phytoplankton species under current and future global warming. However, the effect of such adaptation on the phytoplankton interaction with the environment and other organisms depends on how cellular metabolism shifts during the evolutionary process. In order to elucidate which cellular strategies allow the emergence of thermo-tolerant populations, we analyzed the proteomics response of a marine diatom (Chaetoceros simplex) to both thermal acclimation and evolutionary adaptation. We found that high temperature-tolerant populations exhibit a conservative cellular strategy when acclimated to high, above-optimal temperature, where recycling and reallocation is favored at the expense of new structures biosynthesis. While this strategy gives the populations that evolved high temperature tolerance an advantage under thermal stress, the shift to resource reallocation may explain the absence of high-temperature adaptation when cells are exposed to low nitrate availability.