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

G Wirobski,F Range,F.S Schaebs,R Palme,T Deschner,S Marshall-Pescini

doi:10.1016/j.yhbeh.2020.104901

Abstract

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.

Highlights

Animal domestication is a process comprising dramatic changes in morphology, physiology, and behavior (‘domestication syndrome’; Wilkins et al, 2014)
We found that urinary glucocorticoid metabolite (GCM) concentrations were signifi cantly higher in pack-living dogs than in raised and kept wolves
Feeding status and female reproductive phase affected this: wolves that were not fed the day before sampling had higher GCM concentrations than fed wolves and GCM concentrations were higher during diestrus than anestrus

Summary

Introduction

Animal domestication is a process comprising dramatic changes in morphology, physiology, and behavior (‘domestication syndrome’; Wilkins et al, 2014). Domesticated animals show reduced fear responses and increased inclination to approach humans, in contrast to their wildtype, non-domestic counterparts (Belyaev, 1969; Trut et al, 2009; Wilkins et al, 2014). Changes in their endocrine profiles, in particular, dampened reactivity of the hypothalamo-pituitary-adrenal (HPA) axis and heightened oxytocinergic system activity, have been suggested as important underlying mechanisms (Künzl and Sachser, 1999; Zipser et al, 2014; Kaiser et al, 2015; Buttner, 2016; Herbeck et al, 2017). OT reduces fear and anxiety in social contexts (Smith and Wang, 2014) by down-regulating parts of the HPA axis (Jurek et al, 2015; Winter and Jurek, 2019), and OT admin istration results in lowered circulating GC levels during physical and social challenges (Linnen et al, 2012; Cardoso et al, 2013)

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Conclusion