Weird 'walking' fish holds evolutionary clues

"Fish that had the plasticity to allow them to move out onto land benefited by removing themselves from a very competitive environment," said Emily Standen.
By Brooks Hays   |   Aug. 28, 2014 at 11:29 AM
A dragon fish perfects his craw. (CC/Nature/screen-grab)
OTTAWA, Aug. 28 (UPI) -- Some 400 million years ago, the first fish species gave up water and took to the land. These four-limbed pioneers were called stem tetrapods and their preference for fresh air and dry land enabled the rise of amphibians, reptiles, birds and mammals.

Knowing that this sea-to-land transition happened is one thing, but knowing how exactly it happened is a whole different question -- a question that's befuddled scientists for some time now.

But a new study of an air-breathing, land-walking species of fish suggests that ancient transition might not have been as difficult or complicated as previously thought. The two-lunged Polypterus senegalus, more commonly called bichir or dragon fish, is a small but aggressive fish from Africa that can crawl from pond to pond, traversing parched stretches of land.

To test the bichir's land-living capabilities, researchers subjected young fish to a wholly land-based existence for eight months -- allowing them to mature out of the water. What they found, was that bichir raised on land developed in ways distinct form their water-based brethren. When raised on land, the skeletons and musculature of the dragon fish specimens developed in ways that allowed them to hold their heads up higher, keep their fins tucked in closer to their body, and facilitated a faster, more efficient walking technique.

The study into the bichir's penchant for life on the land was published in the journal Nature this week. Lead author Emily Standen, an evolutionary and comparative biomechanist at the University of Ottawa in Canada, said the bichir's genetic similarity to ancient transitioning fish "raises the possibility that plasticity may have also existed in stem tetrapods to facilitate their transition to land."

"Fish that had the plasticity to allow them to move out onto land benefited by removing themselves from a very competitive environment into a new habitat of plants and insects supplying shelter and food resources, free of major predation or competition," Standen told LiveScience. Standen said that over time, plastic traits that prove advantageous can become permanent.

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