Infectious diseases can have large impacts on host populations. One mechanism by which host populations can reduce these negative effects is to rapidly evolve reduced susceptibility to an infectious agent. Knowledge of the specific characteristics of populations that allow them to mount a rapid evolutionary response to a pathogen is essential for predicting epidemics and mitigating disease risk. One pathogen that has substantial effects on its host population is the fungus, Batrachochytrium dendrobatidis (Bd), which infects amphibians around the world. Little is known about the mechanisms that allow amphibian populations to respond to Bd via rapid evolution. To understand this process, we constructed an agent-based model of an amphibian population infected with Bd to determine the relationships between host susceptibility, host evolution, and population persistence.
Results/Conclusions
Rapid host evolution for reduced susceptibility lowered both the probability of host extinction and the probability of clearing the pathogen (i.e. pathogen extinction). However, the degree to which this rapid evolution occurred varied greatly with the distribution of susceptibilities within a population. The probability of extinction was greatest for host populations with intermediate susceptibilities. Populations with high average susceptibility tended to clear the pathogen, while populations with low average susceptibilities tended to coexist with the pathogen. These findings suggest that variation in susceptibility dictates how rapidly host populations evolve in response to a pathogen and the likelihood that a host population will persist after an epidemic. Thus, loss of genetic diversity (e.g. due to anthropogenic influences) could create amphibian populations that are less likely to persist after the introduction of Bd.