Multigene phylogeny of Epichloe species, fungal symbionts of grasses

Epichloe species are fungal symbionts (endophytes) of grasses, many of whic h are benign or mutualistic and have a balance of horizontal (contagious) a nd vertical (seed-borne) transmission, whereas others mainly transmit horiz ontally and are more antagonistic. Over the past eight years several Epichl oe species have been described based largely on the biological species conc ept. We conducted a multi-gene phylogenetic analysis to evaluate these endo phytes as phylogenetic species, and thereby assess the relationship of phyl ogenetic and biological species. Variation mainly in introns of genes encod ing beta -tubulin (tub2), translation elongation factor 1-alpha: (tef1), an d actin (act1) provided robust phylogenetic signal distinguishing the descr ibed Epichloe species. Outgroup rooting split the genus into two major grou ps. One group included most species with balanced transmission strategy, an d in this group the phylogenetic and biological species concepts correspond ed well. In contrast, these species concepts poorly corresponded for the ot her group, the Epichloe typhina complex, with predominantly antagonistic, h orizontally transmitted endophytes. me suggest that the balance of vertical and horizontal transmission may promote ecological (host) specialization a nd subsequent genetic isolation as mechanisms promoting speciation; whereas strict horizontal transmission may select for broader host ranges, slow th e development of genetically isolated species, and thereby increase lineage sorting effects that cause conflicts between phylogenetic and biological s pecies.