Position specificity in Chitonomyces (Ascomycota, Laboulbeniomycetes) on Laccophilus (Coleoptera, Dytiscidae): a molecular approach resolves a century-old debate.

The occurrence of Laboulbeniomycete species consistently on a precise portion of beetle integument was investigated in 13 species of Chitonomyces ectoparasitic on the aquatic diving beetle Laccophilus maculosus (Coleoptera, Dytiscidae). The phenomenon was called "position specificity" by Roland Thaxter in 1896, yet the mechanism has remained unknown. By using molecular analysis of the nucSSU rRNA gene and the 5.8S and partial ITS1 rRNA regions, 13 species of Chitonomyces reported to exhibit position specificity on Laccophilus maculosus were placed neatly into pairs of morphotypes, resulting in synonomies and recognition of six phylogenetic species (one species is a triplet). Each phylogenetic species was located at corresponding positions on male and female beetles that make contact during mating. In addition, ecological data and video footage of the mating behaviors of Laccophilus confirmed that sexual transmission is the mechanism behind this enigmatic phenomenon.