When humans tamed rabbits, we changed around 100 regions of their genome. The shifts were subtle, but they may have made domestic rabbits less fearful than wild ones.
Pet rabbits will happily sit in their owner's lap, but wild rabbits are famously timid, fleeing at the slightest hint of a human, let alone a fox or hawk. This tolerance for human company was only bred into bunnies recently: about 1400 years ago in southern France. But it was not clear how this worked at the genetic level. Did domestication make drastic changes to a few important genes, or many subtle alterations?
To find out, Leif Andersson at Uppsala University in Sweden and his colleagues compared the genomes of pet rabbits with those of their wild counterparts (Oryctolagus cuniculus) from Spain and southern France.
No genes had been turned off outright, a process that in theory might have helped reduce fear of humans. "Gene loss has not played a prominent role during rabbit domestication," says Andersson.
Instead, the team found that lots of small, pre-existing genetic variations became more common in rabbits as they were domesticated. Most of these variations involved just one letter of DNA code. All in all, about 100 regions were selected to be different in the domesticated rabbits.
Rather than affecting the genes themselves, most of the DNA tweaks were in regulatory regions of the genome, which control whether genes are switched on or off. "Wild and domestic rabbits do not differ so much in actual protein sequences, but in how gene and protein expression is regulated," says Andersson.
The genetic shifts were often associated with regions of the genome involved in the development of neurons and the brain. That makes sense, says Andersson, considering the differences in behaviour between domestic and wild rabbits.
"Selection during domestication might have focused on tameness and lack of fear," says Pat Heslop-Harrison of the University of Leicester in the UK. "As a farmer, you neither want the animal to hurt you, nor for the animal to die from stress." Keeping lookout and fleeing from potential predators uses up lots of an animal's energy, which humans would rather see turned into meat.
Because rabbits were only domesticated relatively recently, the new sequences are not all present in all domestic rabbits. As a result, Andersson says escaped domestic rabbits could revert to wild-like forms over just a few generations - assuming they survived in the wild.
Journal reference: Science, DOI: 10.1126/science.1253714
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