Two species of stickleback fish, both alike in dignity
In fair Japan, where we lay our scene 

One was able to move to freshwater habitats, while the other couldn’t. New research out in Science implicates “jumping” genes as the cause.

These jumping genes, called transposable elements, discovered by Science Hero Barbara McClintock, make up half of our genome and up to 90% of corn’s, and they can copy and paste themselves willy-nilly into the genetic code. Randomly hopping through the genome is often harmful because it can disrupt otherwise functional genes, but this stickleback study gives us an example of the opposite occurring. 

When researchers compared the three-spined stickleback — which can survive in freshwater and marine environments — to another that can only live in marine waters, they found that one gene made all the difference. That gene, called Fads2, controls the metabolism of omega-3 fatty acids, which are abundant in marine environments but scarce in freshwater. 

Fads2, the researchers found, rode the coattails of a transposable element that jumped around the three-spined stickleback’s genome. This increased the number of copies of the useful gene and allowed the fish to make the most of the few omega-3 fatty acids in freshwater.