Phylogenetic analyses of Nematoctonus and Hohenbuehelia (Pleurotaceae)

Abstract

Hohenbuehelia (Agaricales, Pleurotaceae) and Nematoctonus (Hyphomycetes) are the names for the sexual and asexual stages of a genus of nematode-destroying fungi (Basidiomycota). We obtained partial sequences of nuclear ribosomal DNA, including the internal transcribed spacer region and the 5′ end of the large subunit, of 37 isolates of Hohenbuehelia and Nematoctonus representing 13 of the 16 described species in Nematoctonus. Phylogenetic analyses support Hohenbuehelia–Nematoctonus as a monophyletic clade of the Pleurotaceae, within which the species were placed in five main subclades. Exclusively predatory species ( Nematoctonus brevisporus Thorn & G.L. Barron, Nematoctonus campylosporus Drechsler, Nematoctonus robustus F.R. Jones, and Nematoctonus sp. UAMH 5317) appear to be basal. In these species, adhesive knobs to capture prey are produced on their hyphae but not on their conidia. A single mycelial individual may feed on many nematodes. From these have arisen both exclusively parasitoid species ( Nematoctonus cylindrosporus Thorn & G.L. Barron, Nematoctonus leiosporus Drechsler, Nematoctonus leptosporus Drechsler, Nematoctonus pachysporus Drechsler, Nematoctonus tylosporus Drechsler), and species that we call intermediate predators ( Nematoctonus angustatus Thorn & G.L. Barron, Nematoctonus concurrens Drechsler, Nematoctonus geogenius Thorn & GL. Barron, Nematoctonus hamatus Thorn & G.L. Barron, and Nematoctonus subreniformis Thorn & G.L. Barron). Exclusively parasitoid species have conidia that germinate to form sticky knobs that attach to passing nematodes but lack adhesive knobs on the hyphae. Each mycelial individual feeds on only one nematode. Intermediate predators have adhesive knobs both on hyphae and on germinated conidia and can act in both predatory and parasitoid modes. Most morphospecies are resolved as monophyletic, but sequences of additional gene regions are required to clarify species limits within the N. angustatus – N. geogenius group.