Robert Brucker and Seth Bordenstein, biologists at Vanderbilt University in Nashville, Tennessee, have found that the gut bacteria of two recently diverged wasp species act as a living barrier that stops their evolutionary paths from reuniting. The wasps have subtly different collections of gut microbes, and when they cross-breed, the hybrids develop a distorted microbiome that causes their untimely deaths.
“This is the most convincing evidence that the microbiome evolves with hosts over long time periods and might affect the speciation process,” says Bordenstein. The results are published in Science.
Jürgen Gadau, an evolutionary biologist at Arizona State University in Tempe, says that the microbiome is just one of many factors that drive the origin of species. “The important point is that microbes can change very rapidly,” he says — so they could very quickly enforce the separation of nascent species.