Interplay between antipredator behavior, parasitism, and gut microbiome in wild stickleback populations

Background The role of predation stress in driving behavioral and microbial-host interaction changes is recognized, but the impact of microbial composition in aquatic organisms and its relationship with stress-related behavior remains poorly understood. This study explored the relationship between antipredator behavior, parasitism, and the gut microbiome in wild stickleback fish populations from two different lakes: Galtaból, clear and spring-fed versus Þristikla, turbid and glacial-fed. We aimed to identify potential links between these factors by analyzing behavioral responses to simulated predation, comparing microbiomes between populations with or without parasite infection, and examining potential correlations between behavior and microbiome composition. Results Behavioral analysis revealed differences between populations, with each exhibiting unique baseline behaviors i.e., higher activity in Galtaból fish and higher angular velocity in Þristikla fish, and varied responses to the presence of predator i.e., increased boldness in Galtaból fish and higher activity in Þristikla fish. The response to the predator attack was similar between fish from both populations. Parasitism influenced behavior, with parasitized fish displaying increased boldness. Microbiome analysis showed that a small proportion of its variation was explained by population, likely reflecting differences in lake environments. Only the marine genus Pseudoalteromonas abundance differed between populations. Parasitism in Galtaból fish population was linked to decreased alpha diversity in the microbiome, with an increase in specific microbial taxa, including potential pathogens, and a decrease in commensal microbes. Conclusions Our findings suggest that behavior and microbiome correlations may primarily reflect environmental adaptations and parasite status rather than direct gut-brain interactions. However, some tentative evidence suggests a potential innate connection between swimming activity, stress levels, and specific microbes. The study highlights the complexity of the gut-brain axis in wild populations and suggests future research directions, including experimental manipulations to uncover causal relationships between microbiome composition and behavior.