Parasites, niche modification and the host microbiome: A field survey of multiple parasites

Parasites can affect and be affected by the host's microbiome, with
consequences for host susceptibility, parasite transmission, and host and
parasite fitness. Yet, two aspects of the relationship between parasite
infection and host microbiota remain little understood: the nature of the
relationship under field conditions, and how the relationship varies among
parasites. To overcome these limitations, we performed a field survey of
the within-leaf fungal community in a tall fescue population. We
investigated how diversity and composition of the fungal microbiome
associate with natural infection by fungal parasites with different
feeding strategies. A parasite's feeding strategy affects both
parasite requirements of the host environment and parasite impacts on the
host environment. We hypothesized that parasites that more strongly modify
niches available within a host will be associated with greater changes in
microbiome diversity and composition. Parasites with a feeding strategy
that creates necrotic tissue to extract resources (necrotrophs) may not
only have different niche requirements, but also act as particularly
strong niche modifiers. Barcoded amplicon sequencing of the fungal ITS
region revealed that leaf segments symptomatic of necrotrophs had lower
fungal diversity and distinct composition compared to segments that were
asymptomatic or symptomatic of other parasites. There were no clear
differences in fungal diversity or composition between leaf segments that
were asymptomatic and segments symptomatic of other parasite feeding
strategies. Our results motivate future experimental work to test how the
relationship between the microbiome and parasite infection is impacted by
parasite feeding strategy and highlight the potential importance of
parasite traits.