Abstract
Species may persist through the unprecedented changes in global conditions using genetic adaptation or physiological plasticity. However, few empirical studies have revealed the relationship between adaptation and plasticity or addressed the long-standing debate on whether plasticity impedes or facilitates adaptive evolution. Here, we used experimental evolution and reciprocal transplantation of the marine coastal copepod, Acartia tonsa, to present-day and future greenhouse conditions (high temperature, high CO2). Despite the presence of plasticity in ambient conditions, twenty generations of selection resulted in highly parallel genetic adaptation to greenhouse conditions where genes related to stress response, actin regulation, developmental processes, and energy production diverged between conditions. Genetic adaptation, however, reduced fecundity and population growth when greenhouse animals were returned to ambient conditions or reared in low food conditions. Concurrently, adaptation reduced gene expression plasticity by 12.7 fold. Despite the loss of plasticity, across three successive transplant generations, greenhouse-adapted animals were able to match the ambient-adaptive transcriptional profile through genetic adaptation, which in turn eroded nucleotide diversity in greenhouse-adaptive genes. These results demonstrate the power of experimental evolution from natural populations to reveal the mechanisms, timescales of responses, consequences, and reversibility of complex, physiological adaptation. While plasticity facilitated initial survival in global change conditions, it eroded after 20 generations as populations genetically adapted, limiting resilience to new stressors and previously benign environments.
Competing Interest Statement
The authors have declared no competing interest.