Over 350 million years ago, a few fish evolved the ability to leave the water and live on land. This was generally thought of as a unique, chance event. New research by scientists at the University of New South Wales have found that this wasn’t an accident—this trait actually evolved separately at least thirty times.
The researchers analyzed over one hundred extant (still living) amphibious fish, such as eels and mudskippers. Some of these fish leap out of the water to escape predation, some head out onto land in order to find food, and some have made an almost complete transition to terrestrial living. Most of the fish were at least partially marine, many of them living in tidal areas. Fish in tidal areas are more likely to evolve the ability to leave the water since they have to deal with constantly changing conditions and low water levels during low tide. The authors found that 33 separate fish families included at least one amphibious species, showing that this trait wasn’t unique to a single family. Interestingly, the researchers noted that some fish currently classified as exclusively marine actually spend most of their time out of water. This means that the estimate of this trait evolving at least 30 times might actually be an underestimation.
One particular fish family seemed to have a real affinity for life on land. The Blenniidae family includes several different species that are capable of leaving the water. Blennies have a tendency to hop around on rocks and some species have special fins that allow them to grip onto the rocks, helping them stay in one place when the waves are especially strong. Within the family, as many as seven species evolved to support an amphibious lifestyle, all separately at different points in time.
The transition from water to land was clearly not a one-time event. The trait has evolved independently many times and across ecologically diverse families of fish. The transformation to terrestrial life was no fluke, it was an adaptation by fish that evolved multiple times throughout history.
Ord, Terry J., and Georgina M. Cooke. Repeated Evolution of Amphibious Behavior in Fish and Its Implications for the Colonisation of Novel Environments. Evolution (2016).