Isozyme patterns in cultured Harpellales

Abstract

Trichomycetes (Zygomycota) are arthropod-associated fungi consisting of three orders, only one of which, the Harpellales, contains cultured species. Isozyme patterns were studied using starch gel electrophoresis of 108 isolates representing 18 described species from six genera of Harpellales (Capniomyces, Furculomyces, Genistelloides, Simuliomyces, Smittium, and Trichozygospora), and some undescribed species of Smittium, as well as three isolates of Amoebidium parasiticum (Amoebidiales) and three species of nontrichomycetous fungi. A total of 176 different band positions for 13 loci in 11 enzyme systems were produced. The banding patterns were consistent with haploidy. Numerical taxonomic and principal coordinate analyses of Trichomycetes compared isozyme variation within and among described and undescribed species, including three named isolates of uncertain identity. There was no discernible pattern among the cultures attributable to geographic origin or type of insect host family. Isolates of described species produced similarity clusters that generally correlated well with morphologically defined genera and species. Based on isozyme patterns, one isolate tentatively identified as G. hibernus was re-examined and reclassified as C. stellatus. Thirty-six undescribed isolates of Smittium produced seven clusters that probably represent new species. Other undescribed Smittium isolates grouped with described species and may be conspecific. Cophenetic correlation coefficients for 13 clusters of Harpellales species were ≥0.90, but for A. parasiticum it was only 0.87; the latter may represent a species complex. Thirty-two isolates of Sm. culisetae originating from France, Australia, Japan, and six USA states (including Hawaii) were isozymically very similar or identical to each other, despite differences in their geographic origins and dipteran host families. A phenogram based on isozyme patterns generally corresponded with one from a previous immunological study.

Key Words:

• aquatic insects
• fungi
• isozymes
• Smittium
• Trichomycetes