A phylogeographic survey of a circumboreal polypore indicates introgression among ecologically differentiated cryptic lineages

Gloeoporus taxicola is a widespread saprotrophic polypore that occurs on a variety of coniferous substrata in the Northern Hemisphere. In this study a multi-locus sequencing approach was used, on an extensive worldwide sample, to investigate the phylogeography of G. taxicola with respect to substratum affinity. DNA sequences from two nuclear and one haploid mitochondrial marker gave a complex phylogeographic pattern that roughly divided the specimens into two evolutionary lineages, but some admixed and highly heterozygous sequences appeared as well in the diplophase data. To increase the resolution, cloning was performed and haplophase sequences obtained from the nuclear markers. This revealed three main clusters of haplotypes, one representing a European lineage associated with pine, while the other two had more northern circumboreal distributions, occurring on a wide number of substrata. Some specimens contained two highly divergent haplophase sequences, probably reflecting hybridization and further introgression between the separate evolutionary lineages. Despite the saprobic status of the fungus, there was a strong indication of different host affinity between the two main evolutionary lineages.