The research on the evolution of the fish that gave rise to the tetrapods gradually adapting to life on land are generally carried out by examining fossils such as the Tiktaalik roseae, a species dating back to the Devonian period, about 375 million years ago. Instead, a study published in the journal “Nature” was conducted by three scientists from McGill University in Montreal, Canada, studying modern fishhes, the gray bichir, also known as the Senegal bichir or Cuvier’s bichir (scientific name Polypterus senegalus) (photo ©Zhyla), studying their behavior on land.
The bichirs are fishes that belong to the genus Polypterus and live in lakes and rivers, in shallow waters and muddy or sandy bottoms. In addition to having gills, they have primitives lungs that allow them to survive out of the water, breathing the oxygen in the air. The bichirs are the last remaining of an ancient family of fishes and have retained some characteristics that makes them interesting to better understand the transition between water and land.
Some features of the gray bichir makes it reminiscent of the Tiktaalik. The bichirs use their front fins to lift the head and the front part of their trunk from the ground. Subsequently, they push the rear part of their trunk to move forward. It’s possible that the Tiktaalik moved in a similar manner.
The gray bichir generally spends little time on land, preferring water, in which it moves much more smoothly. The biologists at McGill wondered what would have happened if they had forced the bichir to grow on land. Eight bichirs were grown in a terrarium for eight months, with a mister that kept their skin moist.
The result was that eight months on land caused significant changes in the bichirs. Over the months they learned to walk in a more efficient way, planting fins in the ground for less time with shorter steps. Initially they flapped their fins sideways but over time they started placing them under their body. The result was that they slipped less.
In part, the bichirs have probably learned how to walk better because they were forced to always live on land but that also caused changes in their bodies. Comparing the bones of these bichirs with those of other individuals that grew normally in water the differences in bone development were significant.
In particular, in the shoulders region some of the connections between the bones have become less tight. Thanks to this type of development, the bichirs on land could better thanks to the fact that their fins could swing more. At the same time, the bones corresponding to modern clavicles have become bigger and stronger. This allowed the bichirs to lift their bodies higher.
This ability to develop in different ways in different conditions is known as plasticity. It could be a fundamental factor in evolution, allowing organisms that find themselves in a different environment to adapt to it. At that point, subsequent mutations and natural selection determine its later evolution.
Emily Standen, who led the research, wants to go ahead keeping the bichirs in a terrarium for even longer periods. The ideal would be to continue the research for several generations of fishs to assess their changes. It would still be a short period in evolutionary terms but it could already show clearly the changes that led ancient fishes to become land or at least amphibian tetrapods.
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