Researchers Observe Striking Differences Between Brains of Wild, Domesticated Rabbits

The most characteristic feature of domestic animals is their tame behavior.

Rabbits DNA
This illustration, by Fabian Sinzinger, highlights the striking phenotypic differences between domestic and wild rabbits including changes in the size of the amygdala and the medial prefrontal cortex. After examining brain scans of domesticated rabbits, an international team of scientists has determined that domestication has had a profound effect on the morphology in particular regions of the brain.

Using high-resolution magnetic resonance imaging (MRI), the team—led by Texas A&M College of Veterinary Medicine & Biomedical Sciences (CVM) professor Leif Andersson—has found that domesticated rabbits’ amygdala and medial prefrontal cortex, those regions of the brain involved in fear processing, have been particularly effected. The study has been published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS)

In contrast to domestic rabbits, wild rabbits have a very strong flight response because they are hunted by eagles, hawks, foxes and humans and, therefore, must be very alert and reactive to survive in the wild.

“In fact, Charles Darwin wrote in ‘On the Origin of Species’ that ‘no animal is more difficult to tame than the young of the wild rabbit; scarcely any animal is tamer than the young of the tame rabbit,’” Andersson said. “There is no doubt that this type of differences in behavior between wild and domestic animals to a large extent are genetically determined.”

In the study, scientists raised eight domesticated and eight wild rabbits under very similar conditions to minimize changes due to environmental effects. The brain MRI data were interpreted with sophisticated image analysis in which the scientist carrying out the analysis was unaware of the status animals—that is, wild or domestic.

“We observed three profound differences between the brains of wild and domestic rabbits,” said Irene Brusini, first author and doctoral student at KTH Royal Institute of Technology in Stockholm. “Firstly, wild rabbits have a larger brain-to-body size ratio than domestic rabbits. Secondly, domestic rabbits have a reduced amygdala and an enlarged medial prefrontal cortex. Thirdly, we noticed a generalized reduction in white matter structure in domestic rabbits.”

“These differences in brain morphology make perfect sense in relation to the fact that domestic rabbits are less fearful and have an attenuated flight response compared with wild rabbits,” said Mats Fredrikson, a professor at Uppsala University and Karolinska Institute, both in Sweden, and one of the senior authors on the paper.

The results show that an area involved in sensing fear, the amygdala, is smaller in size, while an area controlling the response to fear, the medial prefrontal cortex, is larger in domestic rabbits.

“The reduced amount of white matter suggests that domestic rabbits have a compromised information processing, possibly explaining why they are more slow reacting and phlegmatic than their wild counterparts,” Fredrikson said.

This study follows a previous study in which the team reported that genetic differences between wild and domestic rabbits are particularly common in the vicinity of genes expressed during brain development, according to Miguel Carneiro, from the University of Porto’s CIBIO-InBIO, in Portugal, who is one of the leading authors on the paper.

No previous study on animal domestication has explored changes in brain morphology between wild and domestic animals in such depth as Andersson’s team has done in this study, said Andersson.

“When we initiated the study, the concern was that any changes may be too subtle to be noticeable with MRI, but that was clearly not the case as we noticed distinct changes,” he said. “This study is not only important for our understanding of animal domestication but also for the basic understanding how variation in brain morphology can impact a complex behavior like fear response.”


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