A resurrection experiment reveals reduced adaptive potential in a common agricultural weed.

Adaptive evolution is critical to population responses under accelerating anthropogenic global change. Although theory and some empirical work suggest that contemporary rates of environmental change can be met by equally rapid evolutionary shifts, mismatches between expected and realized evolution remain common in natural systems. Using a resurrection approach, we demonstrate that the structure of genetic covariances among pollination and mating-system traits in the common morning glory (Ipomoea purpurea) is increasingly constraining evolutionary trajectories. Pollinator-attracting traits evolved or became more favored on a rapid time scale of less than 10 years, but genetic covariances between traits limited the adaptive rate and evolutionary trajectory of flowering phenology, a trait with widely recognized importance in adapting to climatic shifts. Our results show that changing patterns of genetic constraint can substantially reduce adaptive potential even when selection favors rapid trait evolution.