Hybridization among cryptic species of the cellar fungus Coniophora puteana (Basidiomycota)

In this study we have analysed the genetic variation and phylogeography in a global sample of the cellar fungus Coniophora puteana, which is an important destroyer of wooden materials indoor. Multilocus genealogies of three DNA regions (beta tubulin, nrDNA ITS and translation elongation factor 1 alpha) revealed the occurrence of three cryptic species (PS1-3) in the morphotaxon C. puteana. One of the lineages (PS3) is apparently restricted to North America while the other two (PS1-2) have wider distributions on multiple continents. Interspecific hybridization has happened between two of the lineages (PS1 and PS3) in North America. In three dikaryotic isolates, two highly divergent beta tubulin alleles coexisted, one derived from PS1 and one from PS3. Furthermore, one isolate included a recombinant ITS sequence, where ITS1 resembled the ITS1 version of PS3 while ITS2 was identical to a frequent PS1 ITS2 version. This pattern must be due to hybridization succeeded by intralocus recombination in ITS. The results further indicated that introgression has happened between subgroups appearing in PS1. We hypothesize that the observed reticulate evolution is due to previous allopatric separation followed by more recent reoccurrence in sympatry, where barriers to gene flow have not yet evolved. A complex phylogeographical structure is observed in the morphotaxon C. puteana caused by (i) cryptic speciation; (ii) the interplay between natural migration and distribution patterns and probably more recent human mediated dispersal events; and (iii) hybridization and introgression.