Walking fish tell us how our ancestors walked out of water


A modern species of "walking" fish is providing clues to how some fish hundreds of million years ago hoisted themselves from the water to take the first evolutionary steps toward all land animals alive today, researchers say.

To look back in time, scientists examined today's bichir, an African fish possessing both gills and primitive lungs that can use its stubby fins to pull itself forward over dry surfaces from one body of water to another.

In a study, Canadian researchers raised two collections of juvenile bichir, or Polypterus senegalus, one in their normal underwater habitat and another group essentially on dry land with just a fraction of an inch of water to keep them moist.

The scientists wanted to see if where they were raised created any anatomical differences between the two groups and in the way they made their way across dry land.

They were surprised by just how much difference was seen between the two groups.

The "dry land" fish could lift their heads up higher, hold their stiff fins more closely to their bodies, and could take faster steps than their brethren raised underwater, they found.

"I'm very surprised the fish survived so well on land," says Emily Standin, who conducted the study at McGill University in Montreal and is now an evolutionary biomechanist at the University of Ottawa.

"One can imagine there was a pretty good [evolutionary] drive for those fish that could to get out of that environment and make use of opportunities on land," she says.

The land-raised bichir also displayed changes in their musculature and skeletons that likely made possible the changes in behavior, the researchers say.

The findings suggests that the species is a lot more plastic, or malleable, during its development that previously was known, they say, making them capable of showing significant differences depending on the environment in which they were raised.

That malleability may have allowed changes of such a great advantage that they evolved as permanent changes in the ancient animals that led to land animals today, they suggest.

"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 says.

While the alterations noted in the bichir were subtle, the researchers say, they correlate with what has been observed in the fossil record of fish-to-land-animal evolution.

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