Temporal changes in the level of infestation of Simulium ornatum Meigen (complex) (Simuliidae: Diptera) larvae by the endosymbiotic fungus Harpella melusinae Lichtwardt (Harpellales: Trichomycetes)

The fungus Harpella melusinae (Harpellales: Trichomycetes) is obligately associated with the midguts of larval Simuliidae (Diptera). The level of infestation of a population of Simulium ornatum by H. melusinae was monitored at a stream in Hampshire, England. Significant temporal changes in the level of infestation were recorded during monthly and weekly collections; a twenty-fold increase being recorded over a nine-day period. Possible mechanisms by which these changes occur are discussed.     

Trichomycete symbiotes of Crozetia seguyi, a primitive black fly

Crozetia is a genus of black flies endemic to the Crozet Islands in the Indian Ocean. No internal symbiotes were previously known from Crozetia species. We report two species of trichomycete symbiotes Stachylina litoralis and Smittium culicisoides from Crozetia seguyi. Larvae of C. seguyi were examined from three sites. The infection rates for St. litoralis was 10.0-33.3% (n=47) of the larvae and Sm. culicisoides was 46.1-85.7% (n=47). No other symbiotes were discovered.     

Secondary spore formation in <Emphasis Type="Italic">Orchesellaria mauguioi</Emphasis> (Asellariales,Trichomycetes) and its taxonomic and ecological implications

Orchesellaria (Orc.) mauguioi (Asellariales) was detected from the hindguts of Isotomurus palustris (Collembola, Hexapoda) collected in Japan. The secondary spore formation on the exuviae of its host is described. When the host molted, its exoskelton including the ectoderm-originated hindgut cuticle to which Orc. mauguioi mycelia attaches was shed. Arthrospores of Orc. mauguioi germinated and penetrated the molt skin and produced secondary spores terminally. The secondary spore is a narrowly ovoid monosporangious sporangium accompanied by a capitate-lageniform terminal cell; these fall off together as a dispersive unit. The terminal cell is sterile and bears one to three fine filamentous extensions seven times as long as the length of the cell. In contrast to the appendages produced endogenously by other harpellids, the filament is produced exogenously and is similar to those of the genus Orphella (Harpellales). The taxonomic and ecological implications of the secondary spore formation of Orc. mauguioi are discussed by comparison with those of other Trichomycetes.     

Prevalence dynamics of two endosymbiont fungi (Orphella spp. Harpellales: Kickxellomycotina) and host shift among different Leuctra (Plecoptera) species in a stream community

This study was conducted to increase the understanding of the temporal dynamics of the plecopteran-associated endosymbiont species Orphella helicospora and Orphella catalaunica (Harpellales, Zygomycota) in the middle reaches of a stream in Montseny Natural Park (Barcelona, Spain). Previous studies addressing the temporal dynamics of Harpellales have focused on Diptera-related species. Statistical analyses revealed that the temporal dynamics of Plecoptera-associated Harpellales do not respond directly to environmental factors but are more directly dependent on biotic factors, such as the particular preference and fitness of each Orphella species towards a specific Leuctra host, the relative host abundance, and its annual cycle. We report that an in situ host shift linked to Leuctra species replacement occurred during the years 2012–2013, with a resulting decline of O. catalaunica in this environment. The ecological implications of the specificity range and fitness of the host are discussed. We also provide information about the possible causes of this macroinvertebrate shift and the effects on the associated endozoic community.     

Predicting occurrence of the fungal symbiote Harpella colonizing black fly larvae in coastal streams of Alabama and Mississippi, USA

The environmental conditions governing symbioses are poorly known in aquatic systems. Stream conditions associated with the distribution of the black fly (Simuliidae) midgut symbiote Harpella were investigated in southern Alabama and Mississippi streams. Stream conditions that were most useful in predicting the distribution of Harpella spp. in the study area were dissolved oxygen and water temperature. Presence of Harpella species in streams was associated with higher dissolved oxygen and decreased water temperature compared to streams where Harpella spp. was absent. Stream conditions associated with the distribution of Harpella spp. in other regions of the world vary according to conditions other than those elucidated here, indicating that geography, host species, and stream conditions play important roles in the spatial distribution of Harpella species.     

Hyaloraphidium curvatum is not a green alga, but a lower fungus; Amoebidium parasiticum is not a fungus, but a member of the DRIPs

The unicellular heterotrophic protist Hyaloraphidium is classified with a family of green algae, the Ankistrodesmaceae. The only species that exists in pure culture and that is available for taxonomic studies is H. curvatum. Comparative 18S ribosomal RNA sequence analyses showed that H. curvatum belongs to the fungi rather than to the algae. Within the fungi, H. curvatum preferentially clustered with Chytridiomycetes. Unlike Chytridiomycetes, H. curvatum propagates by autosporulation, and the presence of flagella has never been reported. Transmission electron microscopy indicated that H. curvatum in some respects resembles Chytridiomycetes, but no elements of a flagellar apparatus were detected. The habitus of H. curvatum is unlike that of other fungi except the trichomycete Amoebidium parasiticum. The cell wall sugar composition of H. curvatum was unique, but to some extent resembled that of A. parasiticum. However, H. curvatum and A. parasiticum are not closely related to each other according to 18S rRNA sequence data. Moreover, A. parasiticum clustered with protistan animals, the Mesomycetozoa (DRIPs). Combined molecular, ultrastructural and chemical data do not allow assignment of H. curvatum to any recognized clade of fungi. This suggests that H. curvatum may represent an independent evolutionary lineage within the fungi.     

Morphological differences of symbiotic fungi Smittium culisetae (Harpellales: Legeriomycetaceae) in different Dipteran hosts

Harpellales (Legeriomycetaceae, Zygomycota) or ‘trichomycetes’ are fungi that inhabit the digestive tracts of arthropods such as insects, millipedes, and crustaceans. In the current study we examined changes in 5 morphological characters of Smittium culisetae (Harpellales: Legeriomycetaceae) between the two dipteran (mosquito, black fly) hosts reared under 3 different temperatures (17, 22, 30 °C). Both host and temperature had a pervasive effect on the linear dimension of trichospores, their generative cells and hyphae width. At 30 °C the mean size of all 5 morphological characters were consistently larger in fungus taken from the mosquito host than from the black fly host. At 17 °C and 22 °C, however, there were no consistent patterns. The effect of host was so pronounced that it could be accurately determined which host S. culisetae colonised based on differences in linear morphology. Such changes in fungal morphology between hosts have important ramifications for the morphologically based taxonomy of this group.     

Sterols synthesized by cultured trichomycetes

Desmosterol was synthesized by all but 2 of 14 isolates of the fungal genus Smittium (Harpellales) obtained from the hindguts of various Diptera larvae and grown axenically on a sterol-free medium. Also detected in some isolates of Smittium were cholesterol and ergosterol, and another, unidentified sterol with an apparent molecular ion of 470. Sterol content based on dry weight of fungal tissue was as high as 0.34%, but it was shown in one isolate that sterols vary both quantitatively and qualitatively during growth of the fungus. Two axenic cultures of the trichomycete Amoebidium parasiticum (Amoebidiales) isolated from the exoskeleton of a Cladocera contained cholesterol and ergosterol, but no desmosterol. Two soil fungi with possible phylogenetic affinities to Smittium, Linderina pennispora and Dipsacomyces acuminosporus (Kickxellales), produced cholesterol alone. The possible influence of the gut fungi on arthropod growth and development is discussed.Abbreviations TMS trimethylsilyl Based upon a Master of Arts thesis submitted by the senior author to the Department of Botany, University of Kansas. This research was partially supported by NSF grants BMS 72-02380-AO and DEB 77-16161 to R.W.L.