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house dogs (Canis lupus familiaris) are the oldest and most popular pets; modern dog breeds were tamed into human society over 10,000 years ago! But the process of domestication needs to be clarified. Less aggressive than wolves, closer to humans, dogs are also able to communicate with them. What are the biological mechanisms underlying this fundamental difference? A new study sheds light on the genetic differences involved.
Today, there are more than 400 breeds of domestic dogs. The dogs are believed to be bred because of their human closeness, physical traits, behavior and more generally their ability to form social relationships. However, the genetic basis of these abilities is not well understood and a team from the Department of Veterinary Science at Azabu University, Japan, has investigated the matter.
” It is certain that these behavioral adaptations, including obedience and the ability to socialize with humans, are important factors that have enabled the integration of the dog into human society. “, The researchers write in Scientific reports. They found that two mutations in a specific gene – which are involved in the production of cortisol – may have played a role in the domestication of dogs, allowing them to develop social cognitive skills to interact and communicate with people.
Social abilities related to the endocrine system
The behavior of animals, especially social behavior, is modulated and influenced by the actions of various hormones in the brain. For example, glucocorticoids (cortisone and cortisol) are hormones that are positively associated with anxiety and social avoidance. Therefore, they may have played a role in the domestication process, like oxytocin. The latter is a hormone that is widely involved in the association between a female and her offspring in mammals. Studies have shown that oxytocin can also mediate species relationships; it is what allows dogs to respond to human social signals, such as pointing.
Genomic research has identified a list of genes that have undergone positive selection during domestication; the functions of these genes are very different (digestion, reproduction, neurological processes, etc.). ” Some of these choices may have affected the endocrine system, prompting domestic dogs to acquire their unique behaviors during the domestication process. , The researchers note. They therefore further investigated the role of cortisols and oxytocins in this process.
Miho Nagasawa and his colleagues started by studying the social and cognitive interactions between 624 domestic dogs by exposing them to two tasks. In the first, the dog had to decide which of the two bowls contained food hidden under it, based on signals such as staring, pointing and knocking, provided by the experimenter. This assignment was designed to test the dog’s understanding of gesture and human communication.
In the second task, the dog was given a problem-solving test, which involved trying to open a container to gain access to food. During the task, the frequency and duration of the dog’s gaze on the test leaders were measured, to assess social attachment to humans. The dogs were separated into two groups based on their breed: the Old Breed group, which consists of breeds considered genetically closer to wolves, such as the Akita and Siberian Husky; and the general group, which includes all other races.
An association derived from genetic mutations
It emerged from this experiment that during the problem-solving task, older purebred dogs showed longer latency before looking at the test leaders; moreover, they looked at humans less frequently than other races – suggesting that they were generally less attached to them. The researchers, on the other hand, report no significant difference related to race during the first task, neither in the number of correct answers nor in their ability to understand human gestures and signals.
” We assumed that cortisol regulation of social tolerance and non-terrifying response to humans may have been the main turning point in canine domestication. “, The researchers explain. However, a decrease in cortisol alone may not explain dogs’ ability to understand human communication signals and form social bonds; the team therefore suspected that oxytocin was also involved in the domestication process.
They then examined, in each of the two groups, the genetic polymorphisms of oxytocin, the oxytocin receptor, the melanocortin 2 receptor (MC2R), and a gene associated with Williams-Beuren syndrome, as candidate genes for canine taming. In humans, Williams-Beuren syndrome is a congenital disorder characterized, among other developmental difficulties, by hypersocial behavior; they feel a strong need to love and be loved. However, unlike wolves, domesticated dogs have specific genetic insertions at the level of chromosome 6, in the critical region of this syndrome – which explains their extreme sociability.
Data analysis shows that two mutations in the MC2R gene, involved in cortisol production, are both associated with correct interpretation of movements in the first task and with looking more often at test leaders in the task solution of problems. This gene could therefore have played a role in the domestication of dogs, perhaps by promoting lower levels of stress in the company of humans.
However, further research will be needed to substantiate this finding. The team believes that the social cognitive skills of domestic dogs cannot be fully explained by the genes identified here alone, but must be controlled by other genes whose effects are to be determined.