Gut microbes keep species apart:
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.