Endocrine changes related to dog domestication: Comparing urinary cortisol and oxytocin in hand-raised, pack-living dogs and wolves

Dogs are exceptionally well adapted to life close to humans, and alterations in their endocrine system during the domestication process may be an underlying mechanism. In particular, it has been suggested that low circulating cortisol concentrations in conjunction with simultaneously high oxytocin concentrations may have resulted in dogs' increased docility (‘selection for tameness’ hypothesis) and heightened propensity to interact and form relationships with humans (‘hypersociability’ hypothesis) compared to wolves. To investigate this, we analyzed cortisol and oxytocin metabolite concentrations from urine samples of hand-raised, pack-living domestic dogs and their non-domestic relatives, grey wolves. Based on the hypotheses outlined above, we predicted lower cortisol but higher oxytocin concentrations in dogs than wolves. In contrast to our prediction, we found higher cortisol concentrations in dogs than wolves. However, oxytocin concentrations were higher in dogs compared to wolves although the effect was relatively small. Indeed, male dogs had the highest oxytocin concentrations while female dogs' oxytocin concentrations were comparable to wolves'. Feeding status, reproductive phase, and conspecific social interactions also significantly affected cortisol and oxytocin concentrations. Furthermore, we compared two methods of correcting for variable water content of urine samples. We discuss our results in light of physiological and behavioral changes during domestication and highlight the importance of accounting for confounding variables in future studies

Life experience rather than domestication accounts for dogs’ increased oxytocin release during social contact with humans

Dogs’ increased human-directed sociability compared to wolves may be the result of increased oxytocin system activity and decreased stress responses, but comparative studies accounting for life experience are lacking. We compared hand-raised, pack-living wolves’ and dogs’ behavior and hormone concentrations after interacting with a closely bonded and a familiar human. Both preferred the bonded partner, but dogs showed less variability in human-directed sociability than wolves. Physical contact was not associated with oxytocin but correlated positively with glucocorticoids in the pack-living animals when the human was not bonded. To clarify the role of life experience, we tested pet dogs and found that oxytocin concentrations correlated positively with physical contact with their owners, while glucocorticoids remained unaffected. Results show that, given similar experiences, wolf-dog differences in human-directed sociability and associated hormones are subtle and indicate that factors related to life as a pet dog rather than domestication account for oxytocin release during human–dog interactions

Analytical validation of an Enzyme Immunoassay for the measurement of urinary oxytocin in dogs and wolves

Assessing changes in oxytocin (OT) levels in response to a variety of social stimuli has become of major interest in the field of behavioral endocrinology. OT is involved in the regulation of various aspects of social behavior such as tolerance, and the formation and maintenance of social bonds but also the regulation of stress. All of these aspects have been identified as potential targets of selection during the domestication process. Therefore, comparing the role of the oxytocinergic system in various aspects of dog and wolf social behavior, might help to understand whether this system was involved in the domestication process. Studies assessing OT levels in dogs and wolves have used invasively collected plasma and serum samples and non-invasively collected urine samples. However, when using an assay system on a new species a careful and complete validation of the method is of crucial importance, and to date no proper validation, to assess urinary OT levels in dogs and wolves, has been reported. We therefore conducted an analytical validation of an Enzyme Immunoassay (EIA) for the measurement of OT in urine of dogs and wolves, using a commercially available EIA. Stability tests revealed that OT levels degrade over time when stored at 4 °C, but are little affected by repeated thawing. In addition, our results indicate that the variance in OT levels is slightly lower when phosphoric acid is added following collection to prevent OT degradation. Long term storage tests revealed that urinary OT levels are least variable when stored as extracts in ethanol at −20 °C, rather than as unextracted urine samples. Validation results were acceptable with regard to parallelism, but values for accuracy and extraction efficiency were not meeting the standard criteria usually applied to steroid EIAs, especially when assessed for the lower range of the assay. The results of this study highlight the importance of an analytical assay validation, since even if validation parameters are not optimal, if published, they allow readers to estimate the relevance of studies using the validated method

Consistency and efficacy of two methods of intranasal oxytocin application in dogs

Over the last few years, oxytocin (OT) administration to investigate the role of the oxytocinergic system in the social behavior of dogs has become of more and more interest. To date, the most common OT administration method for dogs is the intranasal spray commonly used for humans. Due to the different nasal conformation of dogs and the unpleasantness of the procedure, most dogs need to be restrained to allow administration. This has 2 main drawbacks—it may hinder reliable administration, which might lead to tremendous variance in the uptake of OT across individuals and it is likely to be stressful for the dogs. Alternatively, a vaporizer mask can be used to administer aerolized OT and dogs can be trained to voluntarily enter the mask, which might enable a more reliable administration without having to restrain the dogs. The aim of this study was to compare the efficacy of these 2 methods to identify a reliable non-invasive method for exogenous OT administration, thereby assisting future research on the role of OT in canines. We administered OT to pet dogs using either an intranasal spray bottle or a vaporizer mask and assessed urinary OT concentrations as a measure of OT uptake. We found that only when administered using a vaporizer mask, OT significantly increased in all subjects, while using a spray bottle led to considerable variance in OT uptake and an inconsistent increase in urinary OT concentrations across individuals. These results suggest that using a vaporizer mask should be preferred over using an intranasal spray bottle for OT administration in dogs. If not available, experimenters should at least monitor OT uptake after administration using spray bottles, to evaluate the success of the method