There have been fish and fossils found with leg-like fins, but now scientists have raised such animals themselves.
Three researchers raised a fish called Polypterus, also known as Bichir, to learn what exactly happened when fish first began to walk on land, and found physiological changes happened when it lived on land.
The research is published in the article, "Developmental plasticity and the origin of tetrapods," in the journal Nature. It was authored by Emily M. Standen, Trina Y. Du and Hans C. E. Larsson.
Polypterus are a fish from Africa that can already breathe air and "walk" on land. It resembles the ancient fish that evolved into early land animals. The researchers raised juvenile Polypterus on land and found these "terrestrialized" fish began to appear and act differently.
"Stressful environmental conditions can often reveal otherwise cryptic anatomical and behavioural variation, a form of developmental plasticity," said Emily Standen, who led the project, in a statement. "We wanted to use this mechanism to see what new anatomies and behaviours we could trigger in these fish and see if they match what we know of the fossil record."
The terrestrialized fish began to walk more effectively by placing their fins closer to their bodies, lifting their heads higher and carefully prevented their fins from slipping on the ground.
"Anatomically, their pectoral skeleton changed to become more elongate with stronger attachments across their chest, possibly to increase support during walking, and a reduced contact with the skull to potentially allow greater head/neck motion," said another researcher Trina Du.
These changes mirror other legged fish discovered in the past. "Because many of the anatomical changes mirror the fossil record, we can hypothesize that the behavioural changes we see also reflect what may have occurred when fossil fish first walked with their fins on land", said Hans Larsson, the third researcher. "This is the first example we know of that demonstrates developmental plasticity may have facilitated a large-scale evolutionary transition, by first accessing new anatomies and behaviours that could later be genetically fixed by natural selection".
The study was conducted by Emily Standen, formerly of McGill University and now at the University of Ottawa, as well as Hans Larsson and Trina Du at McGill University, in Montreal, Canada.
