New Data Sheds Light on the Evolution of Terrestrial Life
by Tom Edathikunnel
The breach of aquatic life to terrestrial forms is arguably one of the most interesting and puzzling evolutionary breakthroughs. This pioneering biology marks a distinct transition in the evolution of life on Earth, marking a wider variety of required anatomy and adaptations for fitness. The first organisms to cross this threshold were photosynthetic plants in the Ordovician period 450 million years ago followed by the first vertebrates in the Paleozoic Era.
These early tetrapod pioneers were undoubtedly amphibian in nature, requiring a close proximity to water for a majority of biological functions. However the mechanics of this development have been unclear. In a new experiment lead by Emily Standen of the University of Ottawa Canada, her team took juvenile bichir (Polypterus senegalus), a small freshwater fish native to the Nile River of tropical Africa, and raised them on land.
Bichirs, a species of ray-finned fishes (left), posses paired lungs connected to their esophagus. This rudimentary vascular system, along with their gills, allows these unique fish to live both on land and in water.
After eight months of terrestrially life, the bichir demonstrated a more sophisticated style of walking than did their aquatically raised counterparts. They displayed adaptations on a skeletal level, having musculature suited better for a walking lifestyle.
The results of this interesting experiment demonstrate the plasticity of evolutionary development, which allows organisms to alter their anatomy and behavior to respond to environmental changes. Emilty Standen and her team suggest that this process could have provided early tetrapods the ability to live on land. Selective pressures gave rise to the propensity of rudimentary lungs from gills, limbs from fins, and other anatomical necessities for terrestrial life.
Thus environmental conditions remain the driving force for selection, forcing dramatic and creative solutions for survival. This process works subtly, requiring millions of years and beyond. The bichir are just one example of the life branching to new territories and gaining new abilities to adapt and excel.
Source: “How Fish Can Learn to Walk,” Noah Baker, nature.2014.15778