Ecological speciation in orchids: the contribution of mycorrhizal divergence to reproductive isolation

The major aim of this research project is to disentangle the absolute and relative contribution of specific adaptations to distinct habitats and mycorrhizal divergence to reproductive isolation in closely related Epipactis species. Adaptive divergence due to habitat differences is thought to play a major role in formation of new species. However the extent to which individual reproductive isolating barriers related to habitat differentiation contribute to total isolation is not clear yet. 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 a large number of related species of the orchid genus Epipactis. Our own research has recently shown strong variation in mycorrhizal communities between dune and forest ecotypes of the terrestrial orchid Epipactis helleborine, suggesting that mycorrhizal divergence may contribute to the process of speciation in orchids. Moreover, many species of the E. helleborine complex occupy largely different environments (dune slacks, closed forests), suggesting that  divergent selection arising from differences between species in environmental conditions has further contributed to reproductive isolation.