Host population dynamics in the face of an evolving pathogen

Area of Science:

• Ecology and Evolutionary Biology
• Disease Ecology
• Host-Pathogen Dynamics

Background:

• Host-pathogen interactions involve complex eco-evolutionary dynamics where ecological and evolutionary processes are intertwined.
• The house finch (Haemorhous mexicanus) and Mycoplasma gallisepticum provide a model system to study these dynamics, with evidence suggesting an evolutionary arms race driven by changes in pathogen virulence and host immunity.

Purpose of the Study:

• To investigate the population-level effects of the eco-evolutionary arms race between house finches and Mycoplasma gallisepticum in the northeastern United States.
• To determine if observed changes in host population density and disease prevalence are linked to pathogen virulence evolution.

Main Methods:

• Utilized long-term data from two citizen science projects observing house finches at bird feeders.
• Analyzed changes in house finch population density and disease prevalence over time.
• Examined the relationship between local host density and local disease prevalence.

Main Results:

• The emergence of Mycoplasma gallisepticum initially halved house finch densities, followed by stabilization or slow decline.
• Disease prevalence sharply decreased post-emergence and remained low with fluctuations.
• The relationship between local finch density and disease prevalence reversed over time, contrary to initial observations.

Conclusions:

• Observed population-level patterns suggest that host genetic changes alone are insufficient to explain the stability of house finch populations against a rapidly evolving bacterium.
• Acquired immunity in house finches is proposed as a critical factor in managing the interaction with Mycoplasma gallisepticum and maintaining population stability.