Walking African fish reveals how our ancestors evolved

 Polypterus senegalus. (Photo: Morin, Standen, Larsson)
Polypterus senegalus. (Photo: Morin, Standen, Larsson)

Cape Town – Scientific experiments on an African fish have shown what might have happened when the first fish ‘walked’ out of water, an evolutionary step that gave rise to today’s tetrapods – amphibians, reptiles, birds, and mammals.

Researchers from the McGill University used a living fish, Polypterus, to examine the developmental changes associated with the transition to conditions on land.

Polypterus is an African fish that has the ability to breath air, ‘walk’ on land, and resembles the ancient fish that evolved into tetrapods.

The research team raised juvenile Polypterus on land for a year and observed the manner in which the ‘terrestrialised’ fish looked and moved differently.

“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,” says project leader Emily Standen.

According to the study, published in Nature, the fish showed significant changes in their behaviour and anatomy.

“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,” says study collaborator Trina Du.

Hans Larsson, Canada Research Chair in Macroevolution, says that because the anatomical changes mirror the findings in the fossil record, it can be hypothesized that the behavioural changes observed also reflect what may have occurred when fossil fish first walked with their fins on land.

“This is the first example we know of that demonstrates developmental plasticity may have facilitated a large-scale evolutionary transition,” Larsson added.

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