The effect of oxytocin on yawning by dogs (Canis familiaris) exposed to human yawns

Abstract

Previous studies have found that human yawning is contagious to dogs, but the results are still controversial. It is also debated whether contagious yawning is a sign of empathy, and the physiological mechanisms behind this phenomenon are also unknown. Our goal was to further investigate if human yawning is contagious to dogs, and how it is affected by intranasally administered oxytocin. We also tested if contagious yawning was related to dogsʼ empathetic skills measured via an owner-completed questionnaire. Dogs (N = 33) were presented with human yawns (yawning condition – YC) or mouth openings (gaping condition – GC) on two test occasions after intranasal administration of 12 IU oxytocin or placebo. Contagious yawning (defined as a significant increase in the number of yawns in YC as compared to GC) was not found in either of the treatment groups and the number of yawns was not related to the owner-reported emotion contagion of the dogs. However, oxytocin pre-treatment significantly decreased the number of yawns in dogs (in general, but more particularly during the phase when human yawns and gaping were presented). Furthermore, there was a positive relation between signs of stress and anxiety (mouth licking) and the number of yawns (in general, but more particularly during the post phase when human yawns and gaping were not any more presented). We conclude that dogs’ yawning observed in this situation may largely be due to situational stress. Thus the difference between the oxytocin and the placebo group is possibly caused by the decreased social stress and not by oxytocin’s hypothesised effect on empathy.