The impact of global warming on floral traits that affect the selfing rate in a high-altitude plant

Premise of research. Changes in the abiotic environment can influence plant mating systems through phenotypic changes in floral traits that affect selfing. Herkogamy (spatial separation of male and female functions within a flower), dichogamy (temporal separation), and total flower number affect within- (autogamy) and/or among- (geitonogamy) flower selfing. We examined the potential effects of environmental changes associated with global warming on herkogamy, dichogamy, and number of flowers per plant and discussed the impacts on the mating system in a high-altitude species, Aquilegia coerulea. Methodology. In the high-altitude habitats in which this species grows, global warming is expected to increase both temperature and spring precipitation in the form of rain. We grew plants from 17 families from each of three natural populations of A. coerulea at two temperature and two water treatments, leading to 692 experimental plants (2 temperature × 2 water × 3 populations × 17 families × 3-4 individuals per family). We measured herkogamy and dichogamy, recorded total flower number for each plant, and examined variation in floral traits due to genes and the environment. Pivotal results. Herkogamy, dichogamy, and total flower number-traits known to influence selfing rate- were all phenotypically plastic in response to changes in water or temperature. Genetic variation for all three traits was detected within and/or among populations. Conclusions. On the basis of our results, we predict that the increase in total flower number as a plastic response to global warming will have the strongest influence on the selfing rate and increase the level of geitonogamous selfing. Because inbreeding depression is high in A. coerulea, selection will act to reduce floral display in order to reduce inbreeding depression, but there will be a balance between the negative impact of inbreeding depression and the advantage provided by large floral displays in attracting pollinators.