Evolutionary jump-start

Unstable stretches of DNA have served as hot spots for rapid, dramatic skeletal mutations the helped three-spined sticklebacks adapt to new environments.

Illustration of spine growth on stickleback fish

A typical three-spined stickleback fish rarely grows beyond 4 inches long, but don’t let that fool you. This humble creature has been responsible for a host of biological insights. Most recently, a study of the evolution of sticklebacks found that unstable stretches of DNA serve as hot spots for rapid, dramatic genetic mutations.

As a result, after the Ice Age, when stickleback migrated to new lakes and streams, the fish could quickly adapt. Those in marine waters developed a hind fin with a large spine projecting down from their pelvic structure, providing better protection from predators. Some of their freshwater counterparts lost that hind fin — its absence likely reduces their need for calcium and chances of being nabbed and eaten by hungry insects.

Similar findings have been described in bacteria, but this is one of the first studies to show that the process has occurred in vertebrates to create dramatic changes in body structure.

“This study describes at a biochemical level, down to the atoms and sequences in DNA, how a particular type of mutation can arise repeatedly, which then contributes to a complex skeletal trait evolving over and over again in wild fish species,” said David Kingsley, PhD, professor of developmental biology and senior author of a study published Jan. 4 in Science.

“It’s a great example of how DNA fragility can sometimes contribute to favorable traits rather than diseases in natural populations, and it may give us important insights into the process of human evolution.”