A gene that stops different species of fruit flies from interbreeding is evolving faster than other genes, according to researchers at the University of California, Davis, and the University of Cambridge in England. The findings may help scientists understand how new species evolve from existing ones.

The offspring of matings between different species are often sterile, like mules, or don't form viable animals at all. This incompatibility is important for evolution, as new species form when they are genetically cut off from their close relatives. Over 60 years ago, geneticist Theodosius Dobzhansky proposed that matings between closely related species would cause harmful or lethal genetic effects in the offspring, preventing interbreeding and driving the two species apart.

Daniel Barbash, a postgraduate researcher at UC Davis, together with postgraduate researchers Dominic Siino and Aaron Tarone at UC Davis and John Roote, a genetics researcher at Cambridge University, studied a gene called Hybrid male rescue (Hmr) in the fruit fly Drosophila melanogaster and three close relatives.

When D. melanogaster mates with these related species, which separated only two million to three million years ago, female offspring are sterile and male offspring die.

Barbash and colleagues isolated and compared the Hmr genes from the different flies and found that they were getting more different, more quickly than other genes. Almost 8 percent of the genetic code had changes that would alter the protein made by Hmr.

"This is one of the most diverse proteins we've seen in this species comparison," Barbash said.

The researchers found that the Hmr protein belongs to a family of proteins that bind to DNA and control how it is copied.

The work is published online April 7 in the Proceedings of the National Academy of Sciences of the USA.