Simple characterizations of symbiotic interactions i.e., parasitism, mutualism, and commensalism, might not be possible without proper reference to the conditions under which these interactions occur. We suggest that in many cases, parasitism and commensalism are endpoints of a continuum of effects that two species may experience when living in close association with one another. Using a Trichomycetes (fungus)-larval Simuliidae (aquatic dipteran) model, we investigate the context-dependent nature of symbiotic associations. In the black fly larval stage, the association of fungus and flies varied from commensalistic to mutualistic. In the adult stage, the eggs of the female fly can be replaced by ovarian cysts. Hence the relationship between adult flies and trichomycetes is parasitic. Accordingly, all three types of symbiosis are seen between black fly hosts and trichomycete symbionts.
Species 1: Diptera Simuliidae Simulium (Black fly)
Species 2: Harpellales Legeriomycetaceae Smittium (trichomycetes)
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