Stochastic processes and human activity are important drivers in mycorrhizal evolution.
Søren Rosendahl
Department of Biology, University of Copenhagen, Denmark
The plant root symbiotic arbuscular mycorrhizal fungi are common in most ecosystems. Several cosmopolitan species are found on all continents except the Antartica. Three hypotheses may explain this worldwide distribution. Either speciation occurred before the continents separated 120 mill yr ago, or the distribution is a result of human mediated dispersal related to agriculture. Finally, morphologically defined species may encompass several local endemic species. To test these hypotheses three genes were sequenced from 82 isolates of Glomus mosseae originating from six continents. Sequences were analyzed for geographic subdivision and estimation of migration between continents. Coalescent analyses estimated divergence and age of mutations. Baysian coalescent modeling was used to reveal important past population changes in the global population. The sequence data showed no geographical structure, with identical genotypes found on different continents. Coalescence analyses indicated a recent diversification in the species, and the data could be explained by a recent population expansion in G.mosseae. The results suggest that speciation and the range expansion happened much later than continental spread and that human activity may have had a major impact on the dispersal and the population structure of the fungus. At the local scale analyses of haplotype networks suggested a subdivision of G. mosseae haplotypes between fields with different land use history. The results show that agricultural practices differently affect both the abundance and the population genetic structure of arbuscular mycorrhizal fungi.
