Testing the Population-Level Effects of Stress-Induced Susceptibility in the Ranavirus-Wood Frog System

Area of Science:

• Ecology
• Environmental Science
• Disease Ecology

Background:

• Chronic stressors (physical, chemical, biotic) increase individual animal susceptibility to infections.
• This increased susceptibility is often assumed to lead to more likely and severe disease epidemics at the population level.

Purpose of the Study:

• To investigate whether individual-level stress-induced susceptibility to ranavirus scales up to population-level epidemic outcomes.
• To test the impact of environmental stressors (salinity and temperature) on ranavirus epidemic dynamics in larval wood frogs.

Main Methods:

• Ranavirus epidemics were initiated in mesocosm populations of larval wood frogs (Lithobates sylvaticus).
• Populations were exposed to a factorial combination of low and high salinity with ambient or elevated temperatures.
• Epidemic likelihood, severity, and progression rate were monitored.

Main Results:

• Contrary to expectations, ranavirus epidemics were not more likely or severe under stressful conditions (low/high salinity, elevated temperature).
• Elevated temperatures significantly increased the speed of epidemic progression.
• Individual susceptibility to stressors did not directly translate to population-level epidemic severity.

Conclusions:

• The scaling of individual-level stressor impacts to population-level disease outcomes is not always straightforward.
• Environmental stressors may influence disease dynamics in complex ways that do not simply amplify epidemic risk.
• Further research is needed to understand the mechanisms behind the decoupling of individual susceptibility and population-level epidemic severity.