When Schumer began working with species of swordtail fish in Mexican rivers about six years ago, scientists still thought hybrids were rare among animals. (sciencenews.org)
In the Calnali River in Mexico, two pure species of swordtail fish live side by side with a third population that's a mix of the original two. (sciencemag.org)
Researchers examined the two pure swordtail species, Xiphophorus birchmanni and Xiphophorus malinche, as well as the hybrids, tagging the animals and extracting DNA to probe their mating patterns. (sciencemag.org)