Lungfish Gives Hints on Human Ancestry
Media Release
4 October 2011
Three Australian fish – including the iconic lungfish – have given insights into the giant genetic leap that set the scene for the evolution of humans.
A team of Australian scientists led by Professor Peter Currie, of the Australian Regenerative Medicine Institute at Monash University, and Dr Nicolas Cole, of the University of Sydney, has discovered how the evolution of muscles controlling the pelvic, or hind, fins of some fish cleared the way for the evolution of back legs in higher animals.
This innovation gave rise to the tetrapods – four-‐legged creatures, and our distant ancestors – that made the first small steps on land some 400 million years ago.
The scientists reported their results in the latest edition of PLoS Biology.
Scientists have long known that ancient lungfish species are the ancestors of the tetrapods. These fish could survive on land, breathing air and using their pelvic fins to propel themselves. Australia is home to three species of the few remaining lungfish – two marine species and one inhabiting Queensland’s Mary River basin.
There have been big gaps in the knowledge, however. Most of the conclusions have been drawn from fossil skeletons, but the muscles critical to locomotion cannot be preserved in the fossil record.
The Australian scientists used fish living today to trace the evolution of pelvic fin muscles to find out how the load bearing hind limbs of the tetrapods evolved.
They compared embryos of the descendants of species representing key turning points in vertebrate evolution to see if there were differences in pelvic fin muscle formation.
They studied “primitive” cartilaginous fish – Australia’s bamboo shark and its cousin, the elephant “shark”, and three bony fishes – the Australian lungfish, the zebrafish and the American paddlefish. The bony fish are more “advanced”, and of them, the lungfish is the closest living relative of the tetrapods’ most recent common ancestor with fish.
“We examined the way the different fish species generated the muscles of their pelvic fins, which are the evolutionary forerunners of the hind limbs,” said Professor Currie, a developmental biologist.
The scientists genetically engineered fish to trace the migration of precursor muscle cells in early developmental stages as the animal’s body took shape. These cells in the engineered fish emitted red or green light.
The team found that the bony fish had a different mechanism of pelvic fin muscle formation from that of the cartilaginous fish, a mechanism that was a stepping stone to the evolution of tetrapod physiology.
“Humans are just modified fish,” said Professor Currie. “The genome of fish is not vastly different from our own.
“We have shown that the mechanism of pelvic muscle formation in bony fish is transitional between that in sharks and in our tetrapod ancestors,” he said.
Click here to download a copy of this media release (pdf)
Information: Professor Peter Currie
Ph: +61 3 9902 9602
Email: peter.currie@monash.edu
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