BIOGEOGRAPHIC STUDIES ON TRICHOMYCETE GUT FUNGI IN WINTER STONEFLY NYMPHS OF THE GENUS ALLOCAPNIA

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 duri ng 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 dis tributed in 53 stream sites in nine states that include the western an d southern distribution limits of Allocapnia spp. This suggests that t he fungi had already evolved in Allocapnia nymphs before major radiati on pulses of the stoneflies during the Pleistocene. Two other fungi, E jectosporus magnus and Capniomyces stellatus, were more limited in the ir distribution and might have evolved subsequent to early Allocapnia dispersals. One species, Orphella hiemalis, may be endemic to the Ozar k Plateau and Ouachita Mountains. The presence of different extant spe cies of Genistelloides and Orphella in the stonefly faunas of North Am erica and Europe indicates that species of those two genera of fungi m ust have existed prior to the final separation of the two continents d uring the Lower Eocene. Isozymes were extracted and electrophoresed fr om 25 axenic cultures of G. hibernus obtained from six states. When gr ouped by geographic region, the greatest coefficient of similarity amo ng fungal isozyme phenotypes was between the Ozarkian isolates and tho se from northeastern Texas. However, the similarities between central Tennessee and Kansas were greater than they were between eastern Tenne ssee and Alabama. This apparent disparity might be explained biogeogra phically by a southwestward Pleistocene dispersal into Alabama of G. h ibernus-infested Allocapnia populations originally located between the Cumberland Plateau and the mountains to the east, and a separate west ward 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 nort hern Alabama into the Ozark Plateau.