Phylogeny of Fomitopsis pinicola: a species complex

Abstract

Fomitopsis pinicola sensu lato is a common, saprotrophic fungal species occurring over the large circumpolar region covering Eurasia and North America, and extending south along areas of high elevation. It colonizes hardwood and softwood substrates, causing brown rot decay of wood, and exhibits a wide variety of morphological types and colors. Since the late nineteenth century, attempts have been made to determine how many species were in the genus Fomitopsis. Early attempts described two to three species based on host specificity and morphology. By the mid twentieth century, extensive mating studies among single spore isolates had been completed revealing three intersterility groups: two in North America and one in Europe. Partial fertility of both North American groups with the European group led researchers to describe F. pinicola as one biological species within which there was variation in host specificity and morphology. Further research was required using powerful molecular techniques to determine if a cryptic species complex was indeed present. This study was undertaken to delimit phylogenetic species in Fomitopsis pinicola sensu lato using phylogenetic and population genetic methods. Specimens of F. pinicola were collected throughout its range and gene sequences were obtained for three nuclear genes: EF I A, ITS and RPB2. Concatenated, partitioned Bayesian analyses were performed and gene tree topologies were compared to identify common Glades with high posterior probability support. In addition to phylogenetic methods, coalescent analyses were performed to develop a coalescent species tree, and DNA sequence polymorphism was evaluated to determine several measures of genetic variation for comparison among the clades. These data confirmed results of the historic mating studies and supported the existence of four phylogenetic species complex: Fomitopsis pinicola restricted to Eurasia, Fomitopsis ochracea restricted to North America, and two previously undescribed North American species of Fomitopsis.