Biology subjects

Grunberg, R. L.

Publications and source records attributed to Grunberg, R. L..

4 recordsLinked to original sources

bioRxiv2023

Order of arrival and nutrient supply alter outcomes of coinfection with two fungal pathogens

A pathogen arriving on a host typically encounters a diverse community of microbes that can shape priority effects, other within-host interactions, and infection outcomes. In plants, environmental nutrients can drive tradeoffs between host growth and defense and can mediate interactions between coinfecting pathogens. Nutrients may thus alter the outcome of pathogen priority effects for the host, but this possibility has received little experimental investigation. To disentangle the relationship between nutrient availability and coinfection dynamics, we factorially manipulated nutrient availability and order of arrival of two foliar fungal pathogens (Rhizoctonia solani and Colletotrichum cereale) on the host grass tall fescue (Festuca arundinacea) and tracked disease outcomes. Overall, C. cereale infection facilitated infection by R. solani, increasing its infection rate regardless of their order of inoculation. Additionally, simultaneous and C. cereale-first inoculations decreased plant growth and - in plants that did not receive nutrient addition - increased leaf nitrogen concentrations compared to uninoculated plants. Nutrient addition did not influence infection rates, severity of infection, or plant biomass. These findings highlight the importance of understanding the intricate associations between the order of pathogen arrival, host nutrient availability, and host defense to better predict infection outcomes.

ecology↗

bioRxiv2022

Disease decreases variation in host community structure in an old-field grassland

Disease may modulate variation in host community structure by modifying the interplay of deterministic and stochastic processes. For instance, deterministic processes like ecological selection can benefit species less impacted by disease. When disease consistently selects for certain host species, this can reduce variation in host community composition. On the other hand, when host communities are less impacted by disease and selection is weaker, stochastic processes (e.g., drift, dispersal) may play a bigger role in host community structure, which can increase variation in structure among communities. While effects of disease on host community structure have been quantified in field experiments, few have addressed the role of disease in modulating variation in structure among host communities. To address this, we conducted a field experiment spanning three years, using a tractable system: foliar fungal pathogens in an old-field grassland community dominated by the grass Lolium arundinaceum, tall fescue. We reduced foliar fungal disease burden in replicate host communities (experimental plots in intact vegetation) in three fungicide regimens that varied in the duration of fungicide exposure and included a fungicide-free control. We measured host diversity, biomass, and variation in community structure among replicate communities. Disease reduction generally decreased plant richness and increased aboveground biomass relative to communities experiencing ambient levels of disease. Despite changes in structure of the plant communities over the experiments three years, the effects of disease reduction on plant richness and biomass were consistent across years. However, disease reduction did not reduce variation in host community structure, providing little evidence for ecological selection by competition or other deterministic processes. Instead, disease reduction tended to amplify variation in host community structure among replicate communities (i.e., within fungicide treatment groups), suggesting that disease diminished the degree to which host communities were structured by stochastic processes. These results of experimental disease reduction both highlight the potential importance of stochastic processes in plant communities and reveal the potential for disease to regulate variation in host community structure.

ecology↗

bioRxiv2022

Elemental content of a host-parasite relationship in the threespine stickleback

Parasite infections are ubiquitous and their effects on hosts may play a role in ecosystem processes. Ecological stoichiometry provides a framework to study linkages between consumers and ecosystem process, but the stoichiometric traits of host-parasite associations are rarely quantified. Specifically, whether parasites elemental ratios closely resemble those of their host or if infection is related to host stoichiometry remains less known. To answer such questions, we measured the elemental content (%C, %N, and %P) and ratios (C:N, C:P, and N:P) of parasitized and unparasitized Gasterosteus aculeatus (three-spined stickleback) and their cestode parasite, Schistocephalus solidus. Host and parasite elemental content were distinct from each other, and parasites were generally higher in %C and lower in %N and %P. Parasite infections were related to some elemental ratios, specifically C:N, with more intense parasite infections corresponding to hosts with lower C:N ratio. Parasite stoichiometry was independent of their host and there was no relationship between host and parasite stoichiometry. Instead, parasite body mass and parasite density were important drivers of parasite stoichiometry where larger parasites had lower %C, %N, and %P. Overall, these potential effects of parasite infections on host stoichiometry along with parasites distinct elemental compositions suggest parasites may further contribute to how hosts store and cycle nutrients.

ecology↗

bioRxiv2021

Host exposure to symbionts and ecological drift generate divergence in parasite community assembly

The initial colonization of a host by symbionts, ranging from parasites to mutualists, can generate priority effects that alter within-host interactions and the trajectory of parasite community assembly. At the same time, variation in parasite communities among hosts can also stem from stochastic processes. Community ecology theory posits that multiple processes (e.g. dispersal, selection and drift) interact to generate variation in community structure, but these processes are rarely considered simultaneously during community assembly. To test the role of these processes in a parasite community, we experimentally simulated dispersal of three symbionts by factorially inoculating individual plants of tall fescue with two foliar fungal parasites, Colletotrichum cereale and Rhizoctonia solani, and a hypothesized mutualist endophyte, Epichloe coenophiala. We then tracked parasite infections longitudinally in the field. After the initial inoculations, hosts were exposed to a common pool of parasites in the field, which we expected to cause parasite communities to converge towards a similar community state. To test for convergence, we analyzed individual hosts parasite community trajectories in multivariate space. In contrast to our expectation, there was no signal of convergence. Instead, parasite community trajectories generally diverged over time between treatment groups and the magnitude of divergence depended on the symbiont species inoculated. Parasite communities of hosts that were inoculated with only the mutualist, Epichloe, showed significant trends of divergence relative to all other symbiont inoculation treatments. In contrast, hosts inoculated with only Rhizoctonia did not exhibit clear trends of divergence when compared to other parasite inoculations. Further, co-inoculation with both parasite species resulted in faster rates of divergence and greater temporal change in parasite communities relative to hosts inoculated with only the parasite Colletotrichum. As predicted by existing theory, parasite communities showed evidence of drift during the beginning of the experiment, which contributed to among-host divergence in parasite community structure. Overall, these data provide evidence that initial dispersal of symbionts produced persistent changes in parasite community structure via ecological selection, that drift was important during the early stages of parasite community assembly, and together, dispersal, selection and drift resulted in parasite community divergence. Open Research statementThe data and code that support the findings of this study are available through Zenodo at https://doi.org/10.5281/zenodo.5714452

ecology↗