COS 252-2 - Once a reservoir, always a reservoir? Seasonality affects the pathogen maintenance potential of amphibian hosts

Thursday, August 18, 2022

1:45 PM – 2:00 PM EDT

Location: 515C

Presenting Author(s)

MW

Mark Q. Wilber

University of Tennessee, Institute of Agriculture, United States

Coauthor(s)

MO

Michel E. Ohmer

University of Mississippi, United States
KA

Karie A. Altman

St. Bonaventure University, United States
LB

Laura Brannelly

University of Melbourne, Australia
VS

Veronica Saenz

University of Pittsburgh, United States
EL

Emily LeSage

Vanderbilt University, United States
BL

Brandon LaBumbard

University of Massachusetts, United States
NM

Nina McDonnell

University of Massachusetts, United States
AM

Aura Y. Muniz Torres

University of Massachusetts Boston
Boston, Massachusetts, United States
CN

Caitlin Nordheim

University of Pittsburgh, United States
FP

Ferdinand Pfab, n/a

Postdoctoral Scholar
University of California, Santa Barbara, United States
CR

Corinne Richards-Zawacki

University of Pittsburgh, United States
LR

Louise A. Rollins-Smith

Vanderbilt University., Tennessee, United States
JV

Jamie Voyles

University of Nevada, Reno, United States
DW

Daniel Wetzel

University of Pittsburgh, United States
DW

Douglas Woodhams

University of Massachusetts Boston, Massachusetts, United States
CB

Cherie J. Briggs

University of California, Santa Barbara, United States

Background/Question/Methods

Host species that can independently maintain a pathogen in a host community and contribute to infection in other species are important targets for disease management. However, the potential of host species to maintain a pathogen is not fixed over time, and an important challenge is understanding how within- and across-season variability in host maintenance potential affects pathogen persistence over longer time scales relevant for disease management (e.g., years). Here, we sought to understand the causes and consequences of seasonal infection dynamics in leopard frogs (Rana sphenocephala and R. pipiens) infected with the fungal pathogen Batrachochytrium dendrobatidis (Bd). We addressed three questions broadly applicable to seasonal host-parasite systems. First, to what degree are observed seasonal patterns in infection driven by temperature-dependent infection processes compared to seasonal host demographic processes? Second, how does seasonal variation in maintenance potential affect long-term pathogen persistence in multihost communities? Third, does high deterministic maintenance potential relate to the long-term stochastic persistence of pathogens in host populations with seasonal infection dynamics?

Results/Conclusions

To answer these questions, we used field data collected over three years on >1400 amphibians across four geographic locations, laboratory and mesocosm experiments, and a novel mathematical model. We found that the mechanisms that drive seasonal prevalence were different than those driving seasonal infection intensity. Seasonal variation in Bd prevalence was driven primarily by changes in host contact rates associated with breeding migrations to and from aquatic habitat. In contrast, seasonal changes in infection intensity were driven by temperature-induced changes in Bd growth rate. Using our model, we found that the maintenance potential of leopard frogs varied significantly throughout the year and that seasonal troughs in infection prevalence made it unlikely that leopard frogs were responsible for long-term Bd persistence in these seasonal amphibian communities, highlighting the importance of alternative pathogen reservoirs for Bd persistence. Our results have broad implications for management in seasonal host-pathogen systems, showing that seasonal changes in host and pathogen vital rates, rather than the depletion of susceptible hosts, can lead to troughs in pathogen prevalence and stochastic pathogen extirpation.