Meet the African walking fish, Polypterus, who is helping scientists unravel a 400 million year-old evolutionary trick. McGill University scientists are fishing out how fish–ancestors of today’s amphibians, reptiles, birds and mammals–first started walking on dry land.
Walking is no small evolutionary step: it requires the ability to breathe oxygen and the physical anatomy to supports walking. Able to breathe air, Polypterus was halfway there. One could say that Polypterus is a fish of many colors, known to go walking on shoreline jaunts by shuffling around on its fins…but this isn’t quite walking. Scientists were curious whether a change in the fish’s environment would cause a change in behavior or anatomy or both.
Walking to the bottom of the fishy secret, scientists took two groups of identical Polypterus fish and raised one group on land and the other in water. Once grow up, scientists wanted to observe which fish group was walking better and ask why.
Scientists noted that the land-raised fish were walking better and faster than the water-raised fish. So what was the land-raised fish’s fishy secret? It turns out that the land-raised fish were walking better and faster because they had changed their anatomy–the land-raised fish had developed a longer chest skeleton with longer muscles that made for a longer, faster walking stride. Evolution at work?
The results of the walking fish study are reported in the prestigious journal Nature, who has also created a podcast of the walking fish experiment. In a press release, Emily Staden explains that the stressful environment is what caused the change:
Stressful environmental conditions can often reveal otherwise cryptic anatomical and behavioural variation, a form of developmental plasticity[…] 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.
Hans Larsson, Chair of Macroevolution at McGill, applauded the walking fish experiment and explains the significance of the study,
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.
For other curious evolutionary tid-bits, see a walking neuroscience experiment, the monkey selfie.