Evolutionary Potential of Herkogamy

AbstractHerkogamy, the spatial separation of male and female sexual functions in flowers, is an important floral trait mediating variation in plant mating systems. Understanding the evolutionary potential of herkogamy may, therefore, yield insights into the evolutionary potential of the mating system itself. Herkogamy differs from typical floral traits in being a composite trait determined by the relative positions of anthers and stigmas. This feature creates challenges for measuring the evolvability of herkogamy but may also contribute to comparatively high evolvability. Empirical studies have demonstrated substantial evolvability of herkogamy, and that selection on herkogamy can be strong in the event of rapid environmental change such as the decline of pollinators. These results suggest that the evolutionary potential of herkogamy is high, and that detectable evolutionary change can be expected within a few generations following changes in the reproductive environment.Key ConceptsHerkogamy is a key floral trait associated with variation in plant mating systems and often varies widely among populations and species.Herkogamy is a composite trait determined by the relative positions of anthers and stigmas within flowers, and the evolution of herkogamy may involve changes in the positions of anthers and stigmas, the variances in anther and stigma positions or both.Evolution by natural selection is a two‐step process, the rate of which depends on the strength and direction of natural selection and the potential of traits to evolve (i.e. evolvability).Compared to other floral traits, and morphological traits in general, herkogamy can evolve rapidly in percentage of the trait mean.Natural selection on herkogamy is often weak when cross‐pollination is reliable, but strong when cross‐pollination is unreliable.Strong selection combined with high evolvability means that herkogamy can evolve rapidly in response to environmental change.