Are communities of microbial symbionts more diverse than communities of macrobial hosts?

In this study, fungal viruses (mycoviruses) of plant-associated fungi were used to test the general assertion that communities of parasitic and mutualistic symbionts may be more species-diverse than communities of their hosts. Mycoviruses are poorly studied in general, but can affect the fitness and ecology of the fungi and plants with which they associate. To date, mycovirus incidence and diversity in natural communities remain largely unaddressed. Here, we compared the incidence and diversity of fungi associated with tallgrass prairie plants to the diversity and incidence of mycoviruses within those fungi. Specifically, we sampled viruses from fungi associated with a parasitic plant (Cuscuta cuspidata) and its most frequent host plant (Ambrosia psilostachya) in a tallgrass prairie habitat in Oklahoma. For each plant sample we cultured fungal endophytes from surface-sterilized above-ground tissues. From the cultured fungi we extracted DNA to identify fungi, and extracted double-stranded RNA (dsRNA) to detect mycoviruses. Mycoviruses were further characterized using reverse transcription-PCR and sequence analyses. We found at least 25 fungal taxa associated with the two plants, and 10 % of these fungi contained readily detectable viruses. Several mycovirus types were shared among fungal taxa, indicating that mycoviruses may be less specialized than originally thought. Although the virus community was not as diverse as the fungal endophyte community (16 taxa), species accumulation rates of mycoviruses (inferred from rescaled rarefaction curves) may be higher than those of their associated fungal hosts. Thus, mycoviruses represent a further layer of undocumented biodiversity in ecological communities.