It's Not Evolution, But It Is Amazing—Researchers Teach Fish To Walk On Land

• comments
• 
• 

It's a question that comes out of the primordial soup itself: how did life that came from the sea begin to walk on land? It's a central debate for archaeologists, evolutionary physiologists and even chemists, that has long gone unanswered. But thanks to a small, whip-like fish equipped with lungs and the motivation to walk, researchers from the University of Ottowa have proven that necessity is a great means to an end.

Thanks to a well-documented and well-preserved fossil record, we know that fish first became adapted to life on land roughly 350 to 400 million years ago, when life was solely water-based. Evolving from fins to four limbs, the resulting tetrapods (animals with four legs) gave rise to amphibians, reptiles, birds and mammals. Though while the history has been set in stone, the physiological changes have yet to be understood...until now, that is.

Looking to Africa's Nile Basin, where some of the ancient tetrapods relatives still live today, researchers from the University of Ottowa sought to watch the emergence from water to land again but this time in a lab. Choosing a fish species (Polypterus senegalus) known as the Birchir fish as their primary test subjects, the team of evolutionary biologists decided that the eel-like fish could give them a better understanding of the first amphibian tetrapods.

As an ancient descendent of the first land-walking fish, Birchirs are evolutionarily adept to make the transition in their daily lives. With true lungs as well as gills, and a streamlined body that can easily be twisted for terrestrial movement, the species gives a modern view of how fish stepped out of the water and onto land. Looking to show the effects of rearing the fish on land versus primarily in water, the researchers found that the species adapted with a considerable amount of plasticity, to movement on land.

In the research paper, reported in this month's issue of the journal Nature, the researchers found that not only did the fish learn to walk better, but their bodies and muscle movement actually changed.

"The anatomy of the fish raised on land changed, and those changes reflected what we see in t he fossil record, in the transition from fish to four-legged terrestrial vertebrates" co-author and evolutionary biologist, Emily Standen says. "The main outcome was that if Polypterus were raised on land, behaviorally they walked more effectively."

Now here is the tricky part that many non-evolutionary biologists are taking as fact: the changes did not represent an evolution in the species. Rather, these changes that have nothing to do with the genetic makeup of the Birchirs, are simply adaptations that they learned to better survive in their terrestrial environment. This process of adaptations is much more of a learning process than an evolutionary change, which requires genetic modifications and many generations to take place. The researchers found that the bones and muscles of the terrestrial fishes' shoulders and fins changed to better allow the fish to leverage their bodies with their fins, however, the slight changes can simply be attributed to stretching limbs, muscle activity, and environmental factors that helps the species learn to walk. A classic case of nature versus nurture!

"This data is the first to present evidence that environmentally induced developmental plasticity may hve been present in the stem tetrapods" Standen says. "This [could have] helped facilitate their successful transition onto land."