Rapid, but limited, zooplankton adaptation to simultaneous warming and acidification

Predicting the response of marine animals to climate change is hampered by a lack of multigenerational studies on evolutionary adaptation, particularly to combined ocean warming and acidification (OWA). We provide evidence for rapid adaptation to OWA in the foundational copepod species, Acartia tonsa, by assessing changes in population fitness on the basis of a comprehensive suite of life-history traits, using an orthogonal experimental design of nominal temperature (18 °C, 22 °C) and $$p_{\mathrm{{CO}}_2}$$ (400, 2,000 µatm) for 25 generations (~1 year). Egg production and hatching success initially decreased under OWA, resulting in a 56% reduction in fitness. However, both traits recovered by the third generation, and average fitness was reduced thereafter by only 9%. Antagonistic interactions between warming and acidification in later generations decreased survival, thereby limiting full fitness recovery. Our results suggest that such interactions constrain evolutionary rescue and add complexity to predictions of the responses of animal populations to climate change. The authors investigate temperature and pH effects on fitness of an abundant marine crustacean (copepod) across 25 generations. Reduced fitness under combined warming and acidification was recovered rapidly, but incompletely, due to interactions between warming and acidification effects.