Biology subjects

Mitchell, C. E.

Publications and source records attributed to Mitchell, C. E..

3 recordsLinked to original sources

bioRxiv2021

Higher-order interactions among coinfecting parasites and a microbial mutualist impact disease progression

Interactions among parasites and other microbes within hosts can impact disease progression, yet study of such interactions has been mostly limited to pairwise combinations of microbes. Given the diversity of microbes within hosts, higher-order interactions among more than two microbial species may also impact disease. To test this hypothesis, we performed inoculation experiments that investigated interactions among two fungal parasites, Rhizoctonia solani and Colletotrichum cereale, and a systemic fungal endophyte, Epichloe coenophiala, within a grass host. Both pairwise and higher-order interactions impacted disease progression. While the endophyte did not directly influence R. solani growth or C. cereale symptom development, the endophyte modified the interaction between the two parasites. The magnitude of the facilitative effect of C. cereale on the growth of R. solani tended to be greater when the endophyte was present. Moreover, this interaction modification strongly affected leaf mortality. For plants lacking the endophyte, parasite co-inoculation did not increase leaf mortality compared to single-parasite inoculations. In contrast, for endophyte-infected plants, parasite co-inoculation increased leaf mortality compared to inoculation with R. solani or C. cereale alone by 1.9 or 4.9 times, respectively. Together, these results show that disease progression can be strongly impacted by higher-order interactions among microbial symbionts.

ecology↗

bioRxiv2020

Parasites as niche modifiers for the microbiome: A field test with multiple parasites

Parasites can affect and be affected by the hosts microbiome, with consequences for host susceptibility, parasite transmission, and host and parasite fitness. Yet, there are two aspects of the relationship between parasite infection and the host microbiome that remain little understood: the nature of the relationship under field conditions, and how the relationship varies among parasite species. To overcome these limitations, we assayed the within-leaf fungal community in a grass population to investigate how diversity and composition of the fungal microbiome are associated with natural infection by fungal parasites with different feeding strategies. We hypothesized that parasites that more strongly modify niches available within a host will thereby alter the microbial taxa that can colonize the community and be associated with greater changes in microbiome diversity and composition. A parasite that creates necrotic tissue to extract resources (necrotrophs) may act as a particularly strong niche modifier whereas one that does not (biotrophs) may not. Barcoded amplicon sequencing of the fungal ITS region revealed that the microbiome of leaf segments that were 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 that were symptomatic of other parasite feeding strategies. This supports the hypothesis that within-host niches link infection by parasites to the hosts microbiome. Together, these results highlight the importance of parasite traits in determining parasite impacts on the hosts microbiome.

ecology↗

bioRxiv2019

Host community assembly modifies the relationship between host and parasite richness

Host and parasite richness are generally positively correlated, but the stability of this relationship during community assembly remains untested. The composition of host communities can alter parasite transmission, and the relationship between host and parasite richness is sensitive to parasite transmission. Thus, changes in composition during host community assembly could strengthen or weaken the relationship between host and parasite richness. Host community assembly, in turn, can be driven by many processes, including resource enrichment. To test the hypothesis that host community assembly can alter the relationship between host and parasite richness, we experimentally crossed host diversity and resource supply to hosts, then allowed communities to assemble. As previously shown, initial host diversity and resource supply determined the trajectory of host community assembly, altering post-assembly host species richness, richness-independent host phylogenetic diversity, and colonization by exotic host species. Throughout community assembly, host richness predicted parasite richness. As predicted, this effect was moderated by exotic abundance: communities dominated by exotic species exhibited a stronger positive relationship between post-assembly host and parasite richness. Ultimately, these results suggest that, by modulating parasite transmission, community assembly can modify the relationship between host and parasite richness, providing a novel mechanism to explain contingencies in this relationship.

ecology↗