Delving into the rabbit brain to understand animal domestication

    A study reveals the role of amygdala dopamine modulation and hippocampal ciliary function in the rabbit domestication process


    The evolutionary process by which a species adapts to living with humans is known as domestication, and is associated with a series of phenotypic changes in animals derived from the so-called “domestication syndrome”. Many domestic animals share some of these characteristics, such as a reduction in brain size, the development of more stylized skulls, dispigmentation of the fur, the presence of drooping ears or changes in the reproductive cycle.

    In addition, the most distinctive and widespread characteristic of domestic animals is their docile behavior, showing less fear of humans and a reduction or elimination of flight behaviors, suggesting the important role played by the nervous system in domestication.

    Among the animals that have been domesticated more recently we find the rabbit, whose domestic version shows numerous morphological, physiological and behavioral differences compared to the wild rabbit (Oryctolagus cuniculus). Previous studies have shown the genetic differences between domestic and wild rabbits in conserved non-coding regions that were close to genes involved in the development of the nervous system. Another study based on brain imaging it also revealed differences in brain architecture between wild and domestic rabbits. But it is precisely their behavioral differences that provide an opportunity to explore the genetic underpinnings of the rapid evolution of behavior brought about during domestication.

     

    In "The origin of species”, Charles Darwin stated that “there is no animal more difficult to tame than a baby wild rabbit, and hardly any animal is more tame than a baby domestic rabbit.".

    Scientists from the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM) and the Institute for Advanced Social Studies (IESA-CSIC) have collaborated with CIBIO/InBIO (Portugal), Uppsala University (Sweden) and other research centers in Japan and the United States with the aim of studying gene expression in different brain regions in domestic and wild rabbits. To do this, they sequenced RNA in the amygdala, hypothalamus, hippocampus, and parietal/temporal cortex of domestic and wild rabbits.

    The results of the study reveal the existence of hundreds of genes that show differences in expression levels between the two types of rabbits. For example, in the amygdala, which is related to the cognitive function of emotions and aggressiveness, genes associated with dopaminergic function showed higher expression in domestic rabbits. This may be related to the fact that dopamine is a neurotransmitter that is associated with feelings of pleasure and relaxation, which could be related to the behavior observed in domestic rabbits.

    On the other hand, in the hippocampus, which is related to memory and learning, genes associated with ciliary function showed lower expression in domestic rabbits. Ciliary beating may be related to the transport of nutrients, wastes, or signaling molecules, but also to the migration or proliferation of neural stem cells. It is suggested that downregulation of ciliary genes could cause reduced neurogenesis in the hippocampus, which is consistent with the smaller size of the hippocampus and with reduced neural speed and/or compromised information processing observed in previous investigations of the architecture of the domestic rabbit brain.

     

    The figure on the left shows overlapping genes with differential expression between wild and domestic rabbits in four brain regions (A). In the figure on the right, the purple color indicates the genes with a higher expression in the wild rabbits and the green color in the domestic ones (B).

    The results of this research work reveal the important role of dopamine signaling and ciliary function in the evolution of domestication. In turn, it shows that the expression of genes in specific pathways has been profoundly altered during domestication. However, most of the genes that showed differential expression in this study were not the direct targets of selection, possibly because domestication-associated differences in expression may occur in a small subset of cells and over a short period of development. This motivates further exploration of expression changes during different phases of development.

    In relation to this work, one of its authors, Dr. José Antonio Blanco Aguiar, from IREC, reveals in the program “What animal! – Domestic. Part 2” of Radio Televisión Española (RTVE) what they never told us about domesticated rabbits and the process of their domestication. Do not miss it!

     

    The program "What animal! – Domestic. Part 2” from RTVE reveals what they never told us about domesticated animals. Our colleague José Antonio Blanco Aguiar tells us about the case of the rabbit.

    The scientific publication of this research is available at: