Mixed breeding and climate extremes: Flexibility or fatal flaw

Background/Question/Methods Global warming can cause flowering plants to bloom earlier, but the implications for mixed mating species are unclear because: 1) mixed breeding may give flexibility that buffers change, and 2) climate change co-occurs with other factors (invasion, pollinator declines) that may overwhelm or exacerbate climate effects. We tested both issues with a cleistogamous violet, Viola praemorsa, which produces facultatively outcrossing Chasmogamous (CH) flowers in the spring and obligately selfing cleistogamous (CL) flowers in the summer. We manipulated the vernal microclimate using open-topped-chambers (OTC's), and also quantified pollination dynamics including pollinator visitation. In addition, we examined resource allocation responses to warming, and the impacts of climate change on co-occurring dominant invasive grasses. Results/Conclusions Temperatures were increased by an average of 2.5°C but there was no effect on the biomass of the exotic dominant grasses. Both flower types bloomed significantly earlier when warmed, and the duration of flowering increased by 25% for CH flowers. Plants were also significantly larger, and produced more CL flowers and CL fruit. Warming had no effect on the production of CH flowers. Pollinator's visited infrequently and there was no difference in seed set among control plants that flowered early or late, but plants that flowered early were less likely to be fertilized. There was no evidence of reproductive tradeoffs, whereby the production of CH seeds was not negatively related to the subsequent production of CL flowers or seeds. Our results suggest that in the short-term vernal warming does not negatively affect fitness. Species responding plastically to the environment could be hindered by depleting stored resources affecting performance in subsequent years, when conditions may not be favorable. Further, increasing the production of autonomously self-fertilizing CL flowers, will reduce genetic variation, threatening future persistence.