Gut Microbes Drive New Species Evolution

Although it may seem like we're just one species, we're actually made up of thousands. Humans, and other animals, harbor microbes inside of them. Now, scientists have discovered that our microbial companions may play a crucial and important role in evolution; they can contribute to the origin of new species by reducing the viability of hybrids produced between males and females of different species.

Together, microbes form a microbiome, which is unique to each species of plant and animal. This, in particular, has been known for some time. But more and more evidence indicates that these microbiomes have a major impact on their hosts, affecting everything from brain development to digestion.

In fact, these microbial communities are so important that a new theory arose when it came to evolution. The hologenomic theory of evolution has long been debated among scientists. This particular idea proposes that the object of Darwin's natural selection is not just the individual organism, but also its microbial community.

In order to study whether the hologenomic theory of evolution was actually vialbe, the researchers used three species of the jewel wasp Nasonia. These tiny, match-head sized insects parasitize blowflies and other pest flies. This, in particular, makes the jewel wasp useful for biological control.

With a microbiome of 96 different groups of microorganisms, these wasps possess a unique community of creatures inside them. Two of the species of these wasps only diverged about 400,000 years ago; unsurprisingly, their microbiomes were also similar. The third species, though, had a much greater difference in its microbiome since it diverged about a million years ago.

So what did the researchers find? The mortality of hybrid offspring from the closely related species was relatively low-only about 8 percent. In contrast, the mortality of the offspring between the species that diverged longer ago was more around 90 percent. The reasons for this mortality seemed to be related to the microbiomes of the offspring.

"The microbiomes of viable hybrids looked extremely similar to those of their parents, but the microbiomes of those that did not survive looked chaotic and totally different," said Robert Brucker, one of the researchers, in a news release.

The findings seem to move the controversy of hologenomic evolution from merely an idea to an observed phenomenon. The fact that these microbiomes play such a huge part in a species reveals how they can help drive evolution, which could allow researchers to better understand the process of how species change over time.

The findings are published in the journal Science.