Data from: 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 mean
annual temperature and higher total annual precipitation. We also find
that both CL and CH flower phenology has advanced across this time period.
Conclusions: Our results suggest that V. sororia has responded to lower
temperatures and greater water availability by shifting reproductive
strategy allocation away from selfing and toward potential outcrossing.
This provides the first long term study of how climate change may affect
relative allocation to potential outcrossing in species with mixed mating
systems. By revealing that CL flowering is associated with low water
availability and high temperature, our results suggest the production of
obligately selfing flowers is favored in water limited environments.