Guppies microbiome

Growing scientific interest in the relationship between microbiome composition and host biology has revealed the variety of ways in which host-associated microbes can influence host's physiology, ecology and evolution. However, the microbial communities associated with reproductive organs, and their specific roles in reproductive processes, remain poorly understood. To address this gap, we characterized the skin and sperm microbiomes in an internally fertilizing fish. We tested whether microbial diversity and the presence of specific bacterial taxa correlate with key sperm motility traits known to influence reproductive success. We conducted this study using the guppy (Poecilia reticulata), a well-established model in ecology and evolutionary biology, whose reproductive physiology is exceptionally well characterised. In guppies, sperm velocity is a validated predictor of fertilisation success, making it a reliable proxy for male reproductive success. This makes the guppy a powerful system for exploring microbiome fertility interactions in vivo. Our analyses reveal a strong correlation between skin microbiome diversity and sperm performance. Notably, increased skin microbiome richness is associated with reduced sperm velocity and greater linearity in sperm trajectories. Additionally, we identified specific bacterial genera in both the skin and sperm microbiomes that predict inter-individual variation in sperm swimming performance. These findings suggest that while particular taxa in the sperm microbiome may directly influence sperm traits, the skin microbiome serves as a reliable proxy for broader physiological factors linked to reproductive capacity. Overall, our results highlight the multifaceted roles of microbiomes and inter-organ crosstalk in shaping reproductive biology, sexual selection, and the eco-evolutionary dynamics of gametes, underscoring the need for further research into the mechanisms mediating these interactions.