How Stickleback Fish Evolve and Adapt So Quickly: Scientists Explore DNA Changes

Sticklebacks are some of the fastest fish in the world--at least in terms of evolution. They've moved from the ocean into tens of thousands of freshwater streams and lakes, each time changing their skeleton to adapt to their new environment. Now, scientists have taken a closer look at these fish to get a better understanding of evolution and adaptation.

The two-inch long, threespine stickleback is anadromous. This means that it lives in oceans, but can swim up freshwater streams to breed. Yet some sticklebacks have managed to colonize lakes and streams, adapting quickly to their environment; they developed more teeth and stronger jaws, presumably to crack open larger and stronger prey found in freshwater.

In order to better understand the genetics behind these fish, the researchers sequenced the genomes of sticklebacks from 21 populations in 2012. While all sticklebacks seemed to have the same genes, rapid change in regulatory DNA allowed them to alter the expression of their genes.

"This study suggests that the gene, called Bmp6, plays a key role in regeneration of vertebrate organs," said Craig Miller, one of the researchers, in a news release. "Understanding tooth regeneration could lead to a way to replace teeth in humans, for example. It's also clear that there is some biological connection between tooth number and cleft palate, because the same regions of the genome control both. Understanding which genes control the number of teeth is important for understanding what causes malformations, such as cleft palate."

What's interesting is that while the gene, Bmp6, seems to be identical in all sticklebacks, regulatory pieces of DNA next to the gene are different in marine versus freshwater fish. This suggests that altered regulation is responsible for the extra teeth.

"We found that freshwater-derived sticklebacks keep making teeth constantly and never seem to slow down, whereas the ancestral form stops making more teeth," said Miller. "While biologists have known for a long time that sharks and some fish continually replace their teeth, almost nothing was known until now about the genetic basis of evolved changes in teeth patterning."

The findings reveal a little more about how these fish adapt to different environments. It seems as if this gene plays a large role in this particular kind of adaptation and may show researchers a bit more about adaptations in other species.

The findings are published in the journal Proceedings of the National Academy of Sciences.