The taxonomy and phylogeny of the mycangial fungi from Dendroctonus brevicomis and D frontalis (Coleoptera: Scolytidae)
The mycangia of two closely related bark beetles, western pine beetle (Dendroctonus brevicomis, WPB) and southern pine beetle (D. frontalis, SPB), harbor similar fungi. Ceratocystiopsis brevicomi is described as new. It is the mycangial ascomycete of WPB. The new species is distinct from C. collifera and C. ranaculosus, a mycangial fungus of SPB, based on isozyme analysis, mating tests and growth rate. Molecular phylogenetic analyses using DNA sequences of the mitochondrial small subunit rRNA (mt-ssu-rRNA) region, the internal transcribed spacers and the integenic short spacer showed that the mycangial basidiomycetes of WPB and SPB are distinct but closely related to Entomocorticium dendroctoni, five undescribed Entomocorticium species associated with mountain pine beetle (D. ponderosae, MPB), and the mycangial fungus of Pityoborus comatus. The data further indicate that this group of bark beetle associates is recently derived from a Peniophora-like ancestor. Peniophora species have wind-disseminated basidiospores, whereas Entomocorticium species do not forcibly discharge their basidiospores and rely on bark beetle dispersal. Analysis of mt-ssu-rDNA sequences further showed that the mycangial basidiomycete of D. approximatus, a close relative of SPB and WPB, was closely related to Phlebiopsis gigantea, as was an arthroconidial basidiomycete associated with MPB. Gloeocystidium ipidophilum has been found associated with the bark beetle Ips typographus on Norway spruce. Although its phylogenetic placement is not clear, its mt-ssu-rDNA sequence was close to the mushroom forming fungi Pleurotus tuberregium and Lentinula boryana. The mycangial basidiomycete of the ambrosia beetle Xyleborus dispar was found to be most closely related to the brown rot fungus Antrodia carbonica. Thus, the mt-ssu-rDNA data indicated that bark and ambrosia beetle associations have evolved at least four times in the Holobasidiomycetes.