Final Report Summary - MYCASOR (Speciation through fungi? - The role of mycorrhizal associations in orchid diversification) Although it is known for more than a century that orchids are critically dependent on mycorrhizal fungi for completion of their life cycle, very little is known about the ecology and spatial distribution of fungi and how they affect the population dynamics, spatial distribution and ultimately gene flow and speciation in orchids. In this project, we have investigated various aspects related to the ecology and spatial distribution of orchid mycorrhizal fungi and how they are related to the population dynamics and spatial distribution of orchids. Our results showed that co-occurring orchid species tend to associate with different sets of mycorrhizal fungi and occupy distinct regions within natural settings. Using both direct and indirect assessments of the spatial distribution of fungi in natural orchid populations, we further showed that fungal abundance and similarity in fungal community composition quickly decline with increasing distance from established plants. Concomitantly, our results showed that seed germination and seedling establishment decrease with increasing distances from established plants, suggesting that mycorrhizal fungi are important drivers of the recruitment dynamics of orchid populations and thus strongly determine where new plants will establish in existing populations. When multiple species coexist at a given site, divergent mycorrhizal communities and distance-dependent decline of seed germination may result in the strong spatial segregation of orchids that is typically observed in species-rich orchid sites and therefore present a prime mechanism determining coexistence of orchids. Our research further showed that recently diverged orchid species also associated with highly different mycorrhizal communities, suggesting that mycorrhizal fungi can act as a reproductive barrier and therefore affect speciation. Overall, these results indicate that mycorrhizal fungi play a pivotal role in determining the distribution of orchid species and as a result may contribute to diversification.
