They call it…seriously…vomit fruit. Tahitian Noni is a Polynesian shrub that smells so bad, well, you get the idea. Anyway, most species of fruit fly stay away from the plant, which gets its nasty smell from the presence of hexanoic and octanoic acids. The flies’ aversion is well-founded—if they even alight on the fetid fruit, they die. But one species of fruit fly, Drosphila sechellia, loves the pukey plant. It even lays its eggs there.
In a study just published in Public Library of Science Biology, researchers looked at the genetic differences between Sechellia and close relatives that shun the Noni. They found a very different pattern of expression of two genes responsible for olfaction, smell for us, that made the Sechellia fruit flies no longer notice the bad smell. More research will unravel the rest of the story—but it seems a good bet that once the Sechellia stopped minding the funk, they quickly developed a resistance to the acidic environment that kills other species of Drosophila. And mutations that made a few flies tolerate a smelly plant may have been the first steps toward a new species.