As part of a new study, researchers from McGill University in Canada investigated the changes that occured in a number of Senegal bichir fish (Polypterus senegalus) that were trained to live in a terrestrial environment over an extended period of time. The Senegal bichir is a species of long-bodied, freshwater fish that have been known to use their large pectoral fins to walk along river banks, and also occasionally on land. Nicknamed the 'dinosaur eel’, these fish have functional lungs as well as gills, and can breathe air.
"There’s anecdotal evidence that they move on land from ephemeral pond to ephemeral pond [when they dry up],” lead researcher and evolutionary biomechanics researcher, Emily Standen, told Arielle Duhaime-Ross at the Verge, "but they don’t do it voluntarily."
With this in mind, the researchers decided to study the difference between these fish when they are raised in an aquatic environment or a terrestrial environment. They raised 11 juvenile Senegal bichirs in a terrestrial environment with a mere 3 millimetres of water on the floor to prevent them from drying out, and a control group of 38 Senegal bichir were raised in their usual aquatic environment. High-speed video footage was recorded so the team could analyse their movements at the end of an eight-month period.
What they found was that growing up in a terrestrial environment really can change how a fish moves around. "Fish raised on land walk with a more effective gait," Standen said. "They plant their legs closer to the body’s midline, they lift their heads higher, and they slip less during that walking cycle.”
The team published the results in the journal Nature.
According to Duhaime-Ross at the Verge, the terrestrial fish were more consistent in they way they walked around, and their bones actually started to change their shape to give their heads and fins more flexibility. "It’s an important change, because if you think of a terrestrial lifestyle, you actually need a neck on land because you’re stuck on this plane, and you need to have more head motion that’s independent from the body,” says Standen.
While these birchir aren’t related to the ancient fish species that was the first to walk on the land more than 400 million years ago - eventually giving rise to creatures like us - their physical similarities are enough to give the researchers a good model with which to make some educated guesses about what prompted arguably the most important evolutionary transition on Earth. "It seems quite clear that environmentally induced changes may have facilitated their transition to land,” Standen told the Verge. "Selective pressures then acted on these changes, and they became fixed in the genome over very long periods of time.”
The team now hopes to breed their Senegal bichir fish over several generations to see what changes might occur over an extended period.