Linking pathogen-microbiome-host interactions to explain amphibian population dynamics.

Area of Science:

• Ecology and Evolutionary Biology
• Microbiology
• Conservation Biology

Background:

• Symbiotic interactions significantly influence host evolution, affecting genetic variation and population dynamics.
• Infectious diseases exert strong selective pressures, where beneficial symbionts can enhance host defense and fitness.
• Understanding multipartite interactions is crucial for predicting evolutionary trajectories in wild populations.

Purpose of the Study:

• To investigate evolutionary pressures on an amphibian species driven by a fungal pathogen and an antifungal bacterium.
• To assess the impact of these symbionts on host genetic variation, population size, and fitness.
• To explore the indirect effects of environmental conditions on symbiont abundance and host-symbiont interactions.

Main Methods:

• Generation of genome-wide data for the amphibian host species.
• Demographic modeling to infer changes in effective population size.
• Structural equation modeling to analyze host genetic associations with infection status, symbiont abundance, and microbiome diversity.

Main Results:

• Evidence of decreased effective population size, likely due to pathogen infections.
• Lower nucleotide diversity in infected frogs, with potential heterozygote advantage linked to beneficial symbiont recruitment.
• Environmental conditions indirectly affect symbiont abundance via host traits and microbiome diversity.
• Offsetting host heterozygosity-fitness correlations suggest complex ecological and evolutionary dynamics.

Conclusions:

• Evolutionary pressures arise from both pathogenic and beneficial symbionts, shaping host genetics.
• Multipartite symbiotic relationships and their dynamic interactions are key drivers of ecological and evolutionary processes in wild populations.
• The study approach provides a framework for modeling population dynamics and can inform conservation strategies like bioaugmentation for imperiled amphibians.