Climate change is associated with increased allocation to potential outcrossing in a common mixed mating species

Premise: The balance between cross- and self-fertilization is driven by the environment. Yet no long-term study has documented whether anthropogenic climate change is affecting reproductive strategy allocation in species with mixed mating systems. Here, we test whether the common blue violet (Viola sororia; Violaceae) has altered relative allocation to the production of potentially outcrossing flowers as the climate has changed across the 20th century. Methods: Using herbarium records spanning 1875 to 2015 from the central United States, we quantified production of obligately selfing cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers by V. sororia, coupled these records with historic temperature and precipitation data, and tested whether changes to the proportion of CL flowers correlate with temporal climate trends. Results: We find that V. sororia progressively produced lower proportions of CL flowers across the past century and in environments with lower ...