Research published Tuesday in Trends in Ecology & Evolution suggests that a couple’s ability to have kids may depend on what microorganisms are present. The reproductive tracts of males and females contain whole communities of microbes, which can have considerable impact on fertility and reproduction.

“We’ve all heard about the skin or gut microbiome and how these can affect our lives,” says first author Melissah Rowe of the Netherlands Institute of Ecology. “Well, guess what, there’s more! We have a reproductive microbiome as well.”

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However, it’s important to note that this is not just about sexually transmittable diseases. “Microbes appear to influence fertility, reproduction, and the evolution of animal species in so many ways. And yet, almost nobody is studying this, especially in non-human animals,” Rowe explains. Examples include sperm quality, mate choice, sexual health, success at producing offspring, the balance between female and male mating interests, general health, and even the origin of new species.

Here are a handful of examples of ways in which bacteria affect reproduction across species:

  • Men with large amounts of certain bacteria in their semen are more likely to be infertile.
  • Female bedbugs ramp up their immunological defenses ahead of mating, as males will pierce their abdomen with their genitalia during mating. The resulting infections from bacteria transmitted via the genitalia can be fatal.
  • In mallard ducks, males with a more colorful bill produce semen that is better able to kill bacteria, thereby possibly influencing the females’ sexual preference of ‘safe’ males.

“I think that reproductive microbiomes may be an important, yet relatively overlooked, evolutionary force,” Rowe says. It’s natural selection, but with bacteria and other microbes as the ‘jury’ and sometimes the ‘executioner.’

sperm

As this research field is new and unexplored, many questions are still waiting to be answered. For example, are the positive or negative effects of the microbiome caused by specific species or is it the composition of the whole microbial community that is important? Do these reproductive microbiomes evolve differently in females compared to males? And can knowledge of these microbial communities improve our success at breeding endangered species and reintroducing them back into the wild?

As Rowe says, “Let’s find out.”

Image: This sperm cell carries a whole community of bacteria. What will their impact be? Image courtesy of Melissah Rowe.