USING LIVING FISH TO STUDY ANCIENT EVOLUTIONARY CHANGES: How plasticity works in evolution race
Ambitious experimental and morphological studies of a modern fish show how developmental flexibility may have helped early ‘fishapods’ to make the transition from finned aquatic animals to tetrapods that walk on land.
The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was coupled with the origin of terrestrial locomotion and the evolution of supporting limbs. Polypterus is a ray-finned fish (actinopterygians) and is pretty similar to elpistostegid fishes, which are stem tetrapods. Polypterus therefore serves as an extant analogue of stem tetrapods, allowing us to examine how developmental plasticity affects the ‘terrestrialization’ of fish. How else would you find out what behavioral and physiological changes might have taken place when fish first made the move from sea to land over 400 million years ago? putting a fish walking on land.
To find out exactly what might have happened when aquatic animals first moved to land, Researchers took 111 juvenile Polypterus senegalus a fish species that goes by the common name Senegal bichir, or “dinosaur eel" — and raised them for eight months in a terrestrial environment. This environment consisted of mesh flooring covered in pebbles and just 3 millimeters of water — a precaution that, combined with water misters, prevented the fish from drying out. The researchers also formed a control group using 38 fish growing up in their usual aquatic environment.
Dinosaur eels also have gills, but they breathe at the surface regularly to increase their oxygen supply. They also occasionally use their fins to walk on land. Results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods.
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