Context-Specific Arousal During Resting in Wolves and Dogs: Effects of Domestication?

Abstract

Due to domestication, dogs differ from wolves in the way they respond to their environment, including to humans. Selection for tameness and the associated changes to the autonomic nervous system (ANS) regulation have been proposed as the primary mechanisms of domestication. To test this idea, we compared two low-arousal states in equally raised and kept wolves and dogs: resting, a state close to being asleep, and inactive wakefulness, which together take up an important part in the time budgets of wolves and dogs. We measured arousal via cardiac output in three conditions: alone, with a familiar human partner, or with pack members (i.e., conspecifics). Specifically, we compared heart rate (HR) and heart rate variability (HRV) of six wolves and seven dogs. As patterns of resting can vary adaptively, even between closely related species, we predicted that dogs would be generally more aroused than wolves, because living with humans may come with less predictable contexts than living with conspecifics; hence, dogs would need to be responsive at all times. Furthermore, we predicted that due to the effects of domestication, emotional social support by familiar people would reduce arousal more in dogs than in equally human-socialized wolves, leading to more relaxed dogs than wolves when away from the pack. Overall, we found a clear effect of the interactions between species (i.e., wolf versus dog), arousal state (i.e., resting or awake inactive) and test conditions, on both HR and HRV. Wolves and dogs were more aroused when alone (i.e., higher HR and lower HRV) than when in the presence of conspecifics or a familiar human partner. Dogs were more relaxed than wolves when at rest and close to a familiar human but this difference disappeared when awake. In conclusion, instead of the expected distinct overall differences between wolves and dogs in ANS regulation, we rather found subtle context-specific responses, suggesting that such details are important in understanding the domestication process.

Heart rate as a measure of emotional arousal in evolutionary biology

“…Domestication is also assumed to affect physiological traits. Wild animals had higher average heart rates compared to farmed individuals in Atlantic salmon, Salmo salar [77], and dogs have higher resting heart rate compared to wolves, Canis lupus : [78].…”

“…In kennelled dogs, the presentation of auditory and olfactory enrichment decreased heart rate and changed heart rate variability, indicating stress reduction [52,53], and mice, Mus musculus , that were housed in enriched conditions had a significantly lower heart rate compared to individuals housed under minimal husbandry conditions without enrichment and periods of individual housing [55]. Generally, social isolation can cause significant increases in heart rate (alpaca, Vicugna pacos : [90]; dogs: [78]; cattle: [54]; cynomolgus monkeys, Macaca fascicularis : [91]; goats: [18]; wolves [78]). However, affiliative behaviours, even if performed by heterospecifics, can have a stress-reducing effect; grooming carried out by a familiar human decreased heart rate in laboratory-kept rhesus monkeys [92], dairy cows [93] and lambs [94].…”

Non-invasive sleep EEG measurement in hand raised wolves

“…had lower HRs) in both inactive wakefulness and resting conditions, compared to dogs. However, another study found contrasting results, with dogs' HR being lower in the “alone” resting condition compared to wolves 38 . It should be noted that these discrepancies may primarily stem from the different experimental settings across studies and the small sample sizes used in the experiments (six wolves and six/seven dogs were included in both studies).…”

“…So far, most studies investigated the activity patterns of free-ranging wolves, using methods such as radiotelemetry 35 and GPS collars 36 . Other studies compared the resting behaviour of captive wolves and dogs (raised and socialized equally), measuring physiological parameters such as heart rate (HR) and heart rate variability (HRV) 37 , 38 . While Kortekaas et al 37 assumed that wild species are more alert and sensitive towards their environment than their domesticated relatives based on previous reports 39 , 40 , they found that wolves (separated from their pack) were less alert (e.g.…”