Biogeographic Studies on Trichomycete Gut Fungi in Winter Stonefly Nymphs of the Genus Allocapnia

ABSTRACT

Winter stoneflies of the genus Allocapnia (Plecoptera, Capniidae) have low vagility, and apparently first evolved in the Appalachian system from where they slowly dispersed and speciated at different times during the Pleistocene. Five described genera and species of Harpellales (Trichomycetes) live in the aquatic nymphs of Allocapnia. Two of these, Genistelloides hibernus and Simuliomyces spica, were found widely distributed in 53 stream sites in nine states that include the western and southern distribution limits of Allocapnia spp. This suggests that the fungi had already evolved in Allocapnia nymphs before major radiation pulses of the stoneflies during the Pleistocene. Two other fungi, Ejectosporus magnus and Capniomyces stellatus, were more limited in their distribution and might have evolved subsequent to early Allocapnia dispersals. One species, Orphella hiemalis, may be endemic to the Ozark Plateau and Ouachita Mountains. The presence of different extant species of Genistelloides and Orphella in the stonefly faunas of North America and Europe indicates that species of those two genera of fungi must have existed prior to the final separation of the two continents during the Lower Eocene. Isozymes were extracted and electrophoresed from 25 axenic cultures of G. hibernus obtained from six states. When grouped by geographic region, the greatest coefficient of similarity among fungal isozyme phenotypes was between the Ozarkian isolates and those from northeastern Texas. However, the similarities between central Tennessee and Kansas were greater than they were between eastern Tennessee and Alabama. This apparent disparity might be explained biogeographically by a southwestward Pleistocene dispersal into Alabama of G. hibernus-infcsted Allocapnia populations originally located between the Cumberland Plateau and the mountains to the east, and a separate westward dispersal of other populations of fungus-infested stoneflies that were situated to the west of the Cumberland Plateau. The isozyme data also suggest that G. hibernus may have moved with its hosts from northern Alabama into the Ozark Plateau.

Key Words:

• biogeography
• Capniidae
• gut fungi
• Harpellales
• isozymes
• Plecoptera
• Trichomycetes