Joint evolution of mycorrhizal type, pollination, and seed dispersal mode in trees

Although tree diversity is fundamental to terrestrial ecosystems, the processes that generate it remain uncertain. Mycorrhizal type, pollination mode, and seed dispersal mode may be key drivers of tree diversity. We predicted that mycorrhizal symbiosis drove evolution of pollination and seed dispersal modes because arbuscular mycorrhizal (AM) associations would favour long-range seed or pollen dispersal owing to their negative plant–soil-feedback effects on conspecific individuals, and ectomycorrhizal (EcM) associations would favour short-range dispersal owing to their positive effects. We analysed evolutionary relationships among mycorrhizal type, seed dispersal mode, and pollination mode in 704 tree species and conducted a meta-analysis of the dispersal distances of the various seed dispersal and pollination modes. We found evidence of joint evolution of all three features. Most AM-associated trees had endozoochorous seed dispersal and biotic pollination and these dispersal modes had long dispersal distances, whereas most EcM-associated trees had anemochorous seed dispersal and wind pollination and these dispersal modes had relatively shorter dispersal distances. Overall, evolution of mycorrhizal type, seed dispersal mode, and pollination mode were linked, strongly suggesting that mycorrhizal symbiosis drives the evolution of seed and pollination modes and contributes to tree diversification.