All multicellular organisms host microbial communities in and on their bodies, and these microbiomes can have major influences on host biology. Most research has focussed on the oral, skin, and gut microbiomes, whereas relatively little is known about the reproductive microbiome. Here, we review empirical evidence to show that reproductive microbiomes can have significant effects on the reproductive function and performance of males and females. We then discuss the likely repercussions of these effects for evolutionary processes related to sexual selection and sexual conflict, as well as mating systems and reproductive isolation. We argue that knowledge of the reproductive microbiome is fundamental to our understanding of the evolutionary ecology of reproductive strategies and sexual dynamics of host organisms.
The Microbiome Revolution and the Reproductive MicrobiomeAnimals and plants live and evolve in a world dominated by microbes, and host a diversity of microbial communities in and on their bodies. A recent explosion in research on host-associated microbial communities (i.e., microbiota and/or microbiomes, see Glossary) is revolutionising biology. While earlier research typically considered microorganisms from a pathological perspective, it is now widely accepted that the relationship between host and microbes spans a continuum, from detrimental to beneficial. Through their influence on host health, physiology, development, and behaviour [1,2], microbiomes can be seen as an integral part of the host phenotype, and potentially also the host genome (e.g., the hologenome concept [3], but see [4]). While considerable attention has been paid to the role of oral, skin, and gut microbiomes in host ecology, evolution, and fitness, less is known about the reproductive microbiome (Box 1). This is surprising given longstanding knowledge of microbes in male and female reproductive systems (e.g., [5]), most notably in the context of sexually transmitted infections (STIs) [6], and more recent DNA-sequencing studies demonstrating the presence of dynamic microbial communities in reproductive tissues [7], especially the vagina [8,9]. Thus, the reproductive microbiome represents an outstanding challenge in the study of host-associated microbial communities.