A different kind of bunny hop? Rare gene causes some rabbits to handstand

In a far cry from the bunny hop, an unusual breed of domesticated rabbit uses it front paws to walk in a handstand position – and researchers have finally figured out why.

In a recent study, published in Plos Genetics, academics from Uppsala University in Sweden and the University of Porto in Portugal, discovered that a single gene may explain why the sauteur d'Alfort, or “Alfort jumping rabbit,” walks on their front legs instead of hopping.

According to the paper, this particular rabbit is unable to perform the characteristic jumping of other breeds and has therefore compensated for their discoordination by adopting an abnormal style of movement.

“Individuals from this strain adapt their locomotion behaviour for longer and/or faster movements by lifting the hindlimbs off the ground and move supported solely by their forelimbs, similarly to a human acrobat when walking on hands,” the authors wrote in the study.

The reason why these rabbits can’t move as efficiently as other rabbits comes down to a genetic mutation, according to the study.

“We have now characterized a recessive mutation present in a specific strain of domestic rabbits (sauteur d’Alfort) that disrupts the jumping gait,” the research stated.

That recessive mutation was found in the code of the RAR related orphan receptor B (RORB) gene, which affects the rabbits’ spinal cord and prevents them from performing a characteristic hop like other breeds.

In order to identify the gene in question, the research team bred a sauteur d’Alfort rabbit with a New Zealand white rabbit, which can successfully hop. They then conducted a genetic analysis of the 52 offspring in order to identify possible mutations in the ones that couldn’t hop in comparison to the ones that could

“The classical way to study this is to cross this [rabbit breed] line with a line that has normal gait and then study the inheritance of the traits in families,” the study’s co-author, Leif Andersson, a professor at Uppsala University, told CTVNews.ca in a telephone interview on Wednesday. “And then we use genetic markers to trace the different chromosome segments and by mapping data to very high resolution, you're able to identify a single gene that is underlying this.”

They discovered the mutation in the RORB gene was to blame and that sauteur d’Alfort rabbits have two copies of this mutation, unlike other wild rabbit breeds.

The RORB gene is expressed in many regions of the nervous system, including in the spinal cord, where it assists in the production of certain proteins.

“The spinal cord we have is full of these neurons that is connecting the brain with the musculature that drives our limbs and coordinate this perfect coordination of four legs,” Andersson explained.

With this particular mutation, however, the researchers noticed these particular neurons weren’t present in the spinal cords of the rabbits that couldn’t hop.

Without those proteins, which help to coordinate the left and right side of the body, the rabbits were unable to properly coordinate their hind legs.

“Our results show that expression of RORB is drastically reduced in the spinal cord of affected rabbits which results in a developmental defect,” the authors explained.

The researchers concluded that RORB function is “required” for rabbits, and potentially other animals, to be able to leap.

“It contributes to understanding how the spinal cord functions, which genes it depends on, which neurons are critical for how muscle contractions are coordinated during locomotion,” Andersson said. “RORB is not like a gene for hopping, it's a gene for coordinating limb mobility during locomotion. So RORB is most likely important for humans as well in our locomotion.”