It can even lead to the emergence of new animal species.

Reproduction may seem like an intimate moment that only involves two individuals. But nothing is less true. A whole community of micro-organisms lives in, on and around egg and sperm cells. And they turn out to have a much bigger finger on our health and fertility than we thought.

Microbes
Most of the research done focuses on microorganisms in the mouth, skin and intestines. But the microbes that live around our reproductive organs can also leave their mark, the researchers say. It means that the success of reproduction depends on who else is present. That can be both benign and malignant bacteria, fungi or viruses. These microbes can, for example, affect the quality of sperm, fertilization, embryo implantation and other aspects of reproduction. “This can affect sex, reproduction and the evolution of species in so many ways,” says researcher Melissah Rowe. “It can even lead to the emergence of new animal species. And yet it has hardly been investigated until now. ”

A sperm of a bird “hung” with bacteria. Image: NIOO

What we do know is that there are examples of microbes that affect sexual health and fertility in the animal kingdom. These effects appear to have important consequences for reproduction and behavior. A few examples. Men with large amounts of certain bacteria in their sperm sample appear to be infertile more often. In addition, bedbug females boost their defenses prior to mating. Males often pierce the abdomen of a female and a subsequent infection can be fatal. Finally, male wild ducks with more colorful beaks produce seed that is better able to kill unwanted bacteria. And that can influence the choice of a female for a (safe) partner. “I think such a thing can be an important evolutionary force,” says Rowe. Natural selection: with bacteria and other micro-organisms such as the “jury” or the “executioner”.

Plants
The same applies to the propagation of plants. “Because bacteria also live on a pollen grain,” says Rowe. The findings show that the microorganisms can influence the reproduction of humans, animals and plants.

Because the research field is still very new and unexplored, many questions are still unanswered. Are the (un) favorable effects for example due to some species, or is it the composition of the entire microbial community? Does it evolve differently in females than in males? Does it matter for the success in releasing endangered bred animals? The researchers hope to unravel these mysteries in follow-up research.