From microbiome to sperm motility traits: An inside out perspective

Growing interest in the relationship between microbiome composition and
host biology has revealed the many ways host-associated microbes influence
physiology, ecology, and evolution. However, microbial communities
associated with reproductive organs -and their roles in reproduction
-remain poorly understood. Here, we characterized the skin-and
ejaculate-associated microbiomes in an internally fertilizing fish and
tested whether microbial diversity and specific bacterial taxa correlate
with sperm motility traits key for reproductive success. We used the guppy
(Poecilia reticulata), a well-established model in ecology and
evolutionary biology with well-characterised reproductive physiology. In
guppies, sperm velocity is a validated predictor of male reproductive
performance, making them a powerful system for exploring
microbiome-fertility interactions. Our analyses reveal a correlation
between skin microbiome diversity and sperm performance. Notably,
increased skin microbiome total richness is associated with reduced sperm
velocity, whereas no significant associations were detected for
ejaculate-associated microbiomes. We also identified bacterial taxa across
both tissues that were positively or negatively linked with sperm
performance. These findings suggest that, while the ejaculate-associated
microbiome may directly influence sperm traits, the skin microbiome could
serve as a proxy for reproductive potential by reflecting systemic
physiological and immunological states associated with fertility.