Infectious stress: interspecific synchronization of cortisol levels on the example of dogs and their owners

Man is a social being. No matter how much a single individual tries to be separate or detached, other people will influence him in one way or another, they themselves may not want to. This phenomenon is called intraspecific bidirectional psycho-emotional reaction. An important word in this long definition is “intraspecific”. This means that a similar reaction can be observed not only in a group of people, but also in flocks of birds, in the pride of lions or even in a herd of sheep. Organisms that have been in close contact for a long time, one way or another will influence each other, including in aspects of the psycho-emotional state. Today we’ll talk with you about the study, the results of which, according to the authors, became the first material evidence of an interspecific bidirectional psycho-emotional reaction. How exactly does this phenomenon manifest itself, who became experimental in the study, and how do scientists support their findings? This we learn from the report of the research group. Go.

Study basis

If you ask what characteristics a person stands out from other creatures, many will first call intelligence, and this will be true. Others will add sociality and emotionality, but these epithets apply not only to people. Any creatures living in groups are social. As for emotions, a person can and has a wider range of emotions and methods of expressing them than some meerkat, but emotions are not its unique feature.

The psycho-emotional state of an individual is very dough connected with his environment, in particular with the society that surrounds him. Scientists call this contagious emotions, among which the most powerful “infection” is stress. For example, it was found that students whose teacher was writing constant stress had an increased level ofcortisol * .

Cortisol * is a biologically active glucocorticoid hormone that takes part in the body's response to stressful situations.

A similar picture can be observed even in prairie voles (Microtus ochrogaster), which demonstrate a correlation of stress levels with a partner who was previously exposed to a stressor * .

Stressor * - any factor that causes stress.

But these are examples of intraspecific stress correlation. Interspecific also exists, although not as much studied. In order to fix this, scientists proposed to study stress levels in domestic dogs and their owners. As we discussed the previous Friday , man and dog have coexisted for thousands of years. Both of them are social beings, therefore it is expected that a psycho-emotional relationship takes place in this kind of relationship.

Scientists argue that between a person and his four-legged friend, interspecific long-term synchronization of the stress hormone (cortisol) can occur, the level of which can be checked with the help of hair. They decided to discard blood and saliva, as these materials give results that describe the recent period, and hair allows you to evaluate the long-term hormonal background. Hair grows, no matter how trite it may sound, and cortisol leaves its imprint in them, having studied which you can get a retrospective calendar of the concentrations of this hormone. A similar analysis was previously conducted with the participation of mothers and their children, whose cortisol level was synchronized according to the results.

As for dogs, an important feature in the communication of a person with his pet is training and setting up a hierarchy. If the dog is not trained, she can play pranks (for example, water your favorite flowers not the way you would like, or bark and throw at people passing by). In order to achieve discipline, the dog must understand that its owner is the leader, that is, the dominant individual in the pack. The process of training and discipline of dogs leads not only to an emotional connection between it and a person, but also bi-directionally affects the behavior of each dyad * .

Dyad * - a symbiosis in which there is a hierarchical dependence. A dyad is also a combination of two interconnected objects, that is, a pair.

Studies on cortisol levels in dogs and humans also depend on the personality characteristics of the host, and even the combination of dog / host gender in the dyad.


Study participants: Border Collie (left) and Sheltie (right).

In this work, scientists decided to study in more detail the issue of interspecific psycho-emotional synchronization using the example of a man-dog diode. For this, 58 people and their pets (i.e. 58 dyads) were invited as subjects. Scientists watched the physical activity of each dog through a special collar that transmits them with information about the dog’s body condition. The level of cortisol in dogs and hosts was measured in the summer and winter months in order to analyze its changes between the intake of biomaterials (hair). Two types of dogs took part in the study: Sheltie (33 individuals: 18 females and 15 males) and Border Collie (25 individuals: 13 females and 12 males), among which were both ordinary pets and regular participants in various competitions. All dog owners were women. The average age of the caudate subjects was 4.7 ± 0, 4 years for ordinary pets and 4.7 ± 0.7 for competitors. The average age of the dog owners was 46.3 ± 1.7 years.

Research results

To analyze the human effect on the dog, a generalized linear model was used taking into account the sex, breed and lifestyle of the pets.


Image No. 1

As can be seen in the graph above, the host cortisol level really strongly affects the same indicator in dogs both in winter (N = 55, χ ² = 13.796, P <0.001, β = 0.027), and in summer (N = 57, χ ² = 23.697, P <0.001, β = 0.235). Simply put, with an increase in human cortisol, the same thing happened in dogs.

In the summer months, the most striking relationships were between the HCC (hair cortisol concentration) and the dog’s lifestyle (χ ² = 6.268, P = 0.012, 2A ) and between the HCC and the dog’s gender (χ ²= 5.200, P = 0.023, 2B ).


Image # 2: The relationship of HCC and lifestyle ( 2A ); relationship between HCC and dog gender ( 2B ).

All dogs, regardless of gender and lifestyle, had an impact on human HCC, but females and dogs participating in competitions had the strongest effect.

In winter, the breed played an important role (χ ² = 6.451, P = 0.011): in Sheltie HCC was significantly higher than in Border Collie (12.905 ± 1.417 versus 12.069 ± 1.203).


Image 3: The relationship between HCC and the time of year when the biomaterials were taken for analysis.

In addition to the factors described above, there are others (whether the owner of the dog works, the age of the dog, whether she lived with other pets, etc.). However, these factors had practically no effect on the results, so the researchers did not pay attention to them.

But physical activity can actually affect the level of cortisol in the body, because scientists decided to check the ratio of long-term levels of cortisol and dog activity. The monitoring of the condition of tetrapods was carried out by means of a special collar for 1 week, from which scientists allocated 3 workers and 1 day off for analysis.

The amount of time spent by dogs in a state of moderate and high physical activity correlated with dogs' HCC. No significant correlations were found with either summer HCC (N = 44, r = -0.213, P = 0.165) or winter HCC (N = 43, r = -0.239, P = 0.122).

The most curious factor for scientists to influence the level of cortisol remained the character, that is, the personality characteristics of the dog and its owner. Participants in the study completed 2 questionnaires each: DPQ (Dog Personality Questionnaire - a questionnaire regarding the nature of the dog) and The Big Five Inventory (questionnaire regarding the personal qualities of a person).

As it turned out, the nature of the host greatly affects the level of pet cortisol. So an increased level of neuroticism in humans had a negative effect on the dog’s HCC (summer: χ ²= 7.951, P = 0.005, β = −0.364; winter: χ ² = 4.919, P = 0.027, β = −0.026).

Finally, scientists checked how the season itself affects the level of cortisol, because the samples were intentionally taken in the summer and winter. It turned out that in the winter, the level of stress hormone is much higher than in the summer.


Image No. 4

Analysis of the relationship between season and lifestyle showed that domestic dogs have a higher level of cortisol in winter, and dogs participating in competitions in summer ( 4A ). If we talk about the gender difference, then the females showed a higher HCC both in winter and in summer ( 4B ).

For a more detailed acquaintance with the nuances of the study, I recommend that you look into the report of scientists .

Epilogue

The relationship of the psycho-emotional states of two or more individuals of the same species, living together for a long time, has been and remains undeniable. As for interspecific synchronization of cortisol, there are no particularly surprising discoveries. This work was not aimed at discoveries; it was necessary to confirm the previously stated theory that a person and a dog, as representatives of social species, have a strong influence on each other.

Scientists from Linkoping University (Sweden), who conducted this study, believe that dogs are a projection of the emotional state of their owners. That is, a person has a great influence on a dog in terms of long-term synchronization of cortisol levels. In addition, they argue that previously no such studies have been conducted.

Does the result of this labor surprise us, was it a surprise to us? More likely no than yes. However, we once again received scientific support for the phrase "we are responsible for those we tamed."



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