They perform a veritable dance of joy – and at the same time dogs apparently also cry tears of happiness: When they meet their owner happily again, the production of their tears increases sharply, a study shows: The effect is due to the release of the “cuddling hormone” oxytocin from the experiments. The researchers were also able to demonstrate a psychological effect of the wet dog look: it evokes positive feelings towards the animal in humans. The scientists say that the emotional tear production probably fulfills a function in the context of the special relationship between humans and dogs.
An amazing relationship that transcends species boundaries: In the course of the long history of domestication, the wolf eventually became man's best friend. A basis for this is the understanding of the behavior of the other person. This has to do with the fact that both humans and dogs are social creatures by nature. Interestingly, their ability to bond goes beyond species boundaries: Dog owners love their four-legged friends and vice versa, corresponding emotions are involved in the animal. This is even reflected on the hormonal level: Studies have already shown that close human-dog relationships are characterized by the release of oxytocin, known as the “cuddling hormone”, in both partners.
On the trail of emotional dog tears
Some people will certainly get tears in their eyes when they see their beloved four-legged friend again, because it is well known that joy or strong positive emotions can be associated with tears. The scientists around Takefumi Kikusui from the Japanese Azabu University have therefore now asked themselves to what extent similar reactions could also occur in dogs. Observations of his own dog provided the concrete impetus for the study: when she was nursing her puppies, Kikusui noticed that her gaze seemed to change: her eyes seemed unusually moist. Although no drops rolled down like in humans, the animal apparently got watery eyes as part of the probably emotionally shaped behavior. In the end, he and his colleagues specifically investigated whether this effect also occurs in connection with emotional animal-human interactions.
First, the researchers recorded the normal tear volume of test dogs in their home environment in the presence of the owner. They then compared these values with the tear volume, which they determined as part of the joy of reunion: within the first five minutes after the owner had returned to the animal after an absence of up to seven hours. The comparisons showed a significant increase in the flow of tears when the joy of seeing each other again, the scientists report. If, on the other hand, the dogs only greeted known people, there was not the increased flow of tears as with the owner, as further comparative tests showed.
Wet dog look with effect
According to the researchers, it was suggested that the hormone oxytocin plays a role in the phenomenon. To investigate the effect, the researchers dripped oxytocin-containing solutions into the eyes of their test animals. The control consisted of eye drops containing a similar but ineffective substance. Subsequent tear production studies then confirmed that the oxytocin did indeed significantly increase tear production. But is this just a random effect, or does the emotionally increased tear production actually serve a purpose?
In humans, it is known that the emotional signal of crying can in turn trigger emotions in observers. In order to investigate whether this effect also occurs in the case of dogs, the researchers presented test persons with photos of dogs. Some of them had a normal look – the scientists had caused tears in the eyes of others. Questioning the subjects' feelings when looking at these pictures revealed that the dog photos with artificial tears had a particularly emotionalizing effect – they tended to make the viewers feel like they wanted to take care of the animal. "So it seems possible that dogs that show teary eyes during interaction with the owner are more cared for by the owner," says Kikusui. These results thus suggest that dog tear production helps strengthen the bond between humans and their dogs.
In the case studied so far, the dogs appear to cry "tears of joy" when interacting with humans—these are situations we would describe as "happy." So now there are more questions: Do dogs get teary-eyed even in sad situations? And do they also cry during emotional experiences with other dogs? Kikusui and his colleagues now want to examine these potentially more far-reaching meanings of animal tears in detail.
Source: Cell Press, Article: Current Biology, doi: 10.1016/j.cub.2022.07.031