A tiny fish is helping to answer a big question about evolution. The threespine stickleback (Gasterosteus aculeatus) has long been abundant in the sea. But after glaciers melted 10,000 years ago, many wound up in new freshwater lakes and streams. In these unfamiliar environments, the fish lost their bony plates and spines and developed novel behaviors and physiology. A new study reveals that many of these relatively rapid changes were due not to mutations in specific genes, as some biologists had long assumed, but rather to changes in the activity of these genes. The finding should help focus more attention on the role of gene regulation in evolution, not just of fish but of all organisms, including humans.
For decades, evolutionary biologists have been fascinated by the repeated evolution of freshwater traits in marine sticklebacks. In these fish, evolution has duplicated itself thousands of times as marine ancestors moved into fresh water in many parts of the Northern Hemisphere, including Alaska, California, Europe, and Japan. All of these fish have undergone similar changes in their kidneys, body shape, eye size, and number of bony plates on their bodies. David Kingsley, an evolutionary biologist at Stanford University in Palo Alto, California, took advantage of this parallel evolution to look at how the genome causes these changes.