Sticklebacks Have No Problem Evolving Eyes For Freshwater

By on May 9, 2016

USFWS, Public domain

We’ve reported before on the quickness with which some species of sticklebacks have been able to evolve. A new study adds yet more proof that sticklebacks are amazingly quick at adapting to changing conditions, this time with their eyes.

Scientists at the University of British Columbia in Canada, looking at differences between marine and freshwater species of the fish, have found that sticklebacks in freshwater only needed about 10,000 years to develop the eyes needed to thrive in inland waterways. That’s next to nothing in evolutionary terms.

To make the find, researchers compared each fish type’s sensitivity to different light wavelengths. The marine sticklebacks were found to be more sensitive to ultraviolet and blue light, while those living in freshwater were found to be more so to the wavelengths of light typical for their environments — greens and oranges.

Since some sticklebacks switched to living in freshwater only about 12,000 years ago, about the time the last ice age ended, scientists were able to pinpoint the remarkable pace at which the fish have been able to change their eyes. All they needed to do was alter the expression of one of their genes that handles light sensitivity.

Researchers involved in the discovery have noted just how fast the switch came in terms of evolution. What is more typical, they say, is to see changes occur over millions of years, not thousands.

Three-spine stickleback. (Credit: Wikimedia Commons User JaySo83 via Creative Commons 3.0)

Three-spine stickleback. (Credit: Wikimedia Commons User JaySo83 via Creative Commons 3.0)

But in addition to that, scientists also found that freshwater stickleback fish included in the study actually continued to adapt their vision further to best suit the lakes they were living in. Because of that find, investigators guess that sticklebacks may actually be able to change their vision gene expression much faster than 10,000 years.

The way that sticklebacks see color is important clearly for their suitability for the environments they inhabit. But University of British Columbia scientists say that the ability is also important for mate selection.

From that, they guess that changes to the way sticklebacks express their visual genes have probably influenced the creation of new species.

The fish adapted by altering the expression of their opsin genes, which encode the light-sensitive receptors on retinal rod and cone cells. The fish populations came from the Strait of Georgia and lakes along British Columbia’s Sunshine Coast.

The research was funded by the Natural Sciences and Engineering Research Council of Canada and the National Science Foundation. Full results are published in the journal Proceedings of the Royal Society B.

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