Ecological reproductive isolation in forest and grassland populations of the distylous Primula veris.

Adaptive divergence due to habitat differences is thought to play a major role in the formation of new species. However the extent to which individual reproductive isolating barriers related to habitat differentiation contribute to total isolation is not very clear. Furthermore, it is often difficult to determine the specific environmental variables that drive the evolution of those ecological barriers, and the geographic scale at which habitat-mediated speciation occurs. Here, we address these questions through an in-depth analysis of the population structure and reproductive isolation between grassland and forest forms of the distylous Primula veris. Recent research has revealed remarkable variation in anther-stigma separation in forest populations, but not in grassland populations. Concomitant to changes in floral morphology forest populations consistently flowered one month earlier than grassland populations. Imperfect positioning of the sexual organs combined with differences in flowering time can be hypothesized to constitute important reproductive barriers that hamper gene flow and lead to reproductive isolation. Moreover, differences in shade and drought tolerance can be expected to contribute further to reproductive isolation. To test the hypothesis that adaptations to distinct habitats are sufficient to lead to the formation of reproductively isolated species, we will combine molecular genetic analyses with detailed pollination and translocation experiments.