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Do fungi look like macroparasites? Quantifying the patterns and mechanisms of aggregation for host-fungal parasite
Sarah A R Schrock1, Jason C Walsman2, Joseph DeMarchi1
1School of Natural Resources, University of Tennessee Institute of Agriculture, Knoxville, TN, USA.
Abstract:
Most hosts contain few parasites, whereas few hosts contain many. This pattern, known as aggregation, is well-documented in macroparasites where parasite intensity distribution among hosts affects host-parasite dynamics. Infection intensity also drives fungal disease dynamics, but we lack a basic understanding of host-fungal aggregation patterns, how they compare to macroparasites, and if they reflect biological processes. To address these gaps, we characterized aggregation of the fungal pathogen Batrachochytrium dendrobatidis (Bd) in amphibian hosts. Utilizing the slope of Taylor's Power Law, we found Bd intensity distributions were more aggregated than macroparasites, conforming closely to lognormal distributions. We observed that Bd aggregation patterns are strongly correlated with known biological processes operating in amphibian populations, such as epizoological phase-invasion, post-invasion, and enzootic-and intensity-dependent disease mortality. Using intensity-dependent mathematical models, we found evidence of evolution of host resistance based on aggregation shifts in systems persisting with Bd following disease-induced declines. Our results show that Bd aggregation is highly conserved across disparate systems and is distinct from aggregation patterns in macroparasites, and contains signatures of potential biological processes of amphibian-Bd systems. Our work lays a foundation to unite host-fungal dynamics under a common theoretical framework and inform future modeling approaches that may elucidate host-fungus interactions.
Insights
Amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) shows higher aggregation than macroparasites. This distinct aggregation pattern reflects biological processes and potential host resistance evolution in amphibian populations.
Area of Science:
- Ecology
- Parasitology
- Mycology
Background:
- Aggregation, where few hosts contain many parasites, is common in macroparasites.
- Fungal pathogen infection intensity also drives disease dynamics, but host-fungal aggregation patterns are poorly understood.
- The fungal pathogen Batrachochytrium dendrobatidis (Bd) causes significant amphibian declines.
Purpose of the Study:
- To characterize aggregation patterns of Batrachochytrium dendrobatidis (Bd) in amphibian hosts.
- To compare Bd aggregation with macroparasite aggregation.
- To investigate if Bd aggregation reflects underlying biological processes and host resistance evolution.
Main Methods:
- Utilized the slope of Taylor's Power Law to quantify aggregation.
- Analyzed Bd intensity distributions among amphibian hosts.
- Employed intensity-dependent mathematical models to assess host resistance evolution.
Main Results:
- Bd intensity distributions exhibited higher aggregation than macroparasites, closely matching lognormal distributions.
- Bd aggregation patterns correlated strongly with amphibian epizoological phases and intensity-dependent mortality.
- Mathematical models indicated host resistance evolution in systems with persistent Bd following disease-induced declines.
Conclusions:
- Bd aggregation is highly conserved, distinct from macroparasites, and indicative of biological processes in amphibian-Bd systems.
- The study provides a foundation for unifying host-fungal dynamics under a common theoretical framework.
- Findings can inform future modeling to elucidate host-fungus interactions and amphibian disease dynamics.
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