Researchers find the secret of the bunny hop: it's all in the genes
It sounds like a conundrum that Rudyard Kipling would have tackled in his Just So stories, but it turns out the reason why rabbits hop is rooted not in fables but genetics.
Researchers say that by studying an unusual breed of bunny that walks on its front paws, they have pinpointed a key gene that is necessary for animals to adopt a typical gait. For rabbits, as well as animals such as hares and kangaroos, that is the ability to hop.
“If you [were to] introduce the same mutation [seen in these unusual rabbits] in humans, you would not remove hopping but you will change our locomotion in some other way,” said Prof Leif Andersson, co-author of the research, from Uppsala University in Sweden.
Writing in the journal Plos Genetics, Andersson and colleagues reported how they made their discovery by focusing on the sauteur d’Alfort breed of domestic rabbit. Rather than hopping, these animals adopt a “handstand” pose and walk forward on their front paws. The breed is also known for having eye problems, including blindness and cataracts.
Both characteristics were known from breeding experiments to be caused by a mutation in a single gene. However, which gene contained the mutation was unknown.
To delve deeper, Andersson and colleagues bred sauteur d’Alfort rabbits with New Zealand white rabbits – a breed that hops – confirming previous theories that two copies of the mutant gene are needed for rabbits to lose their bounce.
The researchers then carried out a genetic analysis of the rabbits, revealing the inability to hop appears to be down to a mutation at a single position in a gene known as RORB. The sauteur d’Alfort rabbits were found to have two copies of this mutation. However, the mutation was not found in other wild and domestic breeds of rabbit, or in a host of other mammals including humans.
“The DNA sequences that are important for function are highly conserved across species,” said Andersson.
Crucially, said Andersson, the RORB gene gives rise to a protein that switches other genes on and off. If this gene does not function properly, he added, the production of other proteins in the spinal cord may not be properly regulated, affecting the way the spinal cord coordinates messages between the brain and muscles in the limbs.
Indeed, further work by the team found that rabbits with two copies of the RORB mutation have no detectable RORB protein in their spinal cord.
The team say their discovery ties in with previous work showing that mice which had a mutation in their RORB gene not only had eye problems but an unusual walk akin to a duck waddle.
However, Andersson said the RORB gene was not the only gene important for gait. For example, the ability for horses to amble, found in certain breeds such as the Icelandic pony, has previously been linked to a mutation in a gene known as DMRT3.
Arne Ludwig, professor of animal genetics at the Albrecht Daniel ThaerInstitute at Humboldt University and the Leibniz Institute for zoo and wildlife research in Berlin, who was not involved in the study, said gait is a complex trait.
“Several genes are involved and this study shows that RORB is one of them,” he said.
But, he added, the rearing of sauteur d’Alfort rabbits is of concern given their host of disorders. “Likely sauteur rabbits would have no chance to survive in nature,” he said.