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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 with macroparasites and if they reflect biological processes. To begin addressing 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 many 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 (i.e. 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 contains signatures of potential biological processes of amphibian-Bd systems. Our work can inform future modelling approaches and be extended to other fungal pathogens to elucidate host-fungal interactions and unite host-fungal dynamics under a common theoretical framework.
Insights
Fungal pathogen Batrachochytrium dendrobatidis (Bd) aggregation in amphibians is more intense than many macroparasites. Bd aggregation patterns reflect biological processes and suggest host resistance evolution, offering insights into host-pathogen dynamics.
Area of Science:
- Ecology
- Pathogen Dynamics
- Amphibian Biology
Background:
- Parasite distribution often follows an aggregation pattern, where few hosts harbor many parasites.
- This aggregation is well-studied in macroparasites but poorly understood for fungal pathogens like Batrachochytrium dendrobatidis (Bd).
- Understanding host-fungal aggregation is crucial for disease dynamics and host-parasite interactions.
Purpose of the Study:
- To characterize aggregation patterns of the fungal pathogen Batrachochytrium dendrobatidis (Bd) in amphibian hosts.
- To compare Bd aggregation with macroparasite aggregation patterns.
- To investigate if Bd aggregation reflects underlying biological processes and host evolution.
Main Methods:
- Utilized Taylor's Power Law to quantify Bd intensity distribution slopes.
- Analyzed aggregation patterns in relation to amphibian population epizoological phases (invasion, post-invasion, enzootic).
- Employed intensity-dependent mathematical models to assess host resistance evolution.
Main Results:
- Bd intensity distributions exhibited higher aggregation than many macroparasites, closely matching lognormal distributions.
- Bd aggregation patterns significantly correlated with epizoological phase and intensity-dependent disease mortality.
- Evidence suggests evolution of host resistance, indicated by aggregation shifts in persistent Bd systems.
Conclusions:
- Bd aggregation is highly conserved across diverse amphibian systems.
- Bd aggregation patterns contain signatures of key biological processes in amphibian-Bd interactions.
- Findings can inform future modeling of host-fungal dynamics and potentially other fungal pathogens.
