Genetic and Environmental Factors Shape Rates of Plasticity: The Temporal Dynamics of Opsin Gene Expression in Aquatic Environments.

Phenotypic plasticity enables organisms to adjust their traits in response to environmental changes, potentially enhancing survival under fluctuating conditions. While plastic capacity-the range of phenotypic change-has been extensively studied, the rate of plastic responses remains unexplored. The rate of plasticity is crucial, as prolonged mismatches between phenotype and environment reduce fitness. Nonetheless, evolutionary models typically do not investigate rates of plasticity. Here, we measure opsin gene expression to estimate the temporal changes in predicted visual sensitivity of Nicaraguan convict cichlids (Amatitlania siquia) from populations exposed to changes in light conditions. We show that rates of plasticity in single cone predicted sensitivity vary significantly among populations, developmental stages, and experimental light treatments, demonstrating that rates of plastic change are shaped by both genetic and context-dependent factors. Notably, great lake cichlids-native to predominantly turbid environments-responded more rapidly to red-shifted photic conditions than crater lake fish, but more slowly when returned to clear conditions. Additionally, younger individuals exhibited faster changes in opsin gene expression than older ones, highlighting the role of developmental stage in modulating plasticity. These findings challenge the assumption of constants rates of plasticity and suggest that selection could act not only on plastic capacity but also on the rate of plastic responses. Our results demonstrate that rates of plasticity are themselves evolvable traits. Incorporating this temporal dimension into models of plasticity will improve our understanding of how organisms respond to environmental heterogeneity, with broad implications for evolutionary biology and ecology.