Rapid Adaption but Genetic Diversity Loss of a Globally Distributed Diatom in the Warmer Ocean.

Studies have demonstrated that marine phytoplankton can adapt to the warmer environment. However, the underlying mechanisms remain largely unknown. Here, we quantified the capacity of a globally distributed marine diatom Skeletonema dohrnii, for rapid evolution under the moderate (24°C) and severe (28°C) warming scenarios. Whole-genome resequencing analysis revealed that the evolutionary adaptation of S. dohrnii to moderate warming was slow (i.e., 700 generations), whereas it was rapid (i.e., 300 generations) under severe warming but suffered a substantial loss of genetic diversity within the population. Genes associated with energy production and lipid metabolism evolved rapidly, particularly under severe warming, suggesting their vital roles in thermal adaptation. Proteomic results also showed the enhanced expression of proteins involved in energy production and lipid metabolism, especially under severe warming. Furthermore, particulate organic carbon and nitrogen production was greatly enhanced in the moderate warming-selected population but increased insignificantly in the severe warming-selected population, indicating more rapid adaptation driven by severe warming. Our results provide molecular insights into the rapid but limited evolution of thermal adaptation in marine diatoms and highlight energy production and lipid metabolism as the most important adaptive strategy. Future warming will affect genetic diversity and population dynamics of diatoms in the ocean.