Plasticity masks and mediates evolution in warming environments

Harvest-induced evolution has been linked to many documented declines in fish size at maturity, size-at-age, and harvest yields. Predicting the course of harvest-induced evolution to address scientific questions and design policy interventions is complicated by plastic relationships between temperature and growth in many species. We built an individual-based eco-genetic model incorporating growth plasticity in response to harvest via a temperature-inclusive biphasic growth model to ask how plastic responses to temperature affect the evolution of fish life-histories in response to harvest. We found that intensive harvest resulted in rapid evolution; catch rate of vulnerable fish was associated with increasingly rapid evolution of reduced genetic length at maturity and increased gonadal-somatic index. We additionally found that plasticity masked and mediated evolution. Populations subjected to the hot temperature regime evolved increased growth capacity whereas cool populations evolved reduced growth capacity, with the consequence that hot populations exhibited relatively little phenotypic response to harvest. Though hot populations exhibited marked genotypic changes, complementary trait evolution resulted in little decline in length at maturity or emergent patterns of growth compared to the cool populations. However, hot populations did experience declining harvest rates relative to cool populations, demonstrating that the application of evolutionary models to management on a warming planet demands an examination of how plasticity affects the strength of evolution and our ability to observe it.