Through the eyes of a wolf: Using non-invasive methods to quantify and classify the facial signalling of wolves (Canis lupus) and domestic dogs (Canis lupus familiaris)

Abstract

The morphologies of wild animals typically evolved via natural selection as a result of environmental pressures leading to specific adaptations to cope with life-history challenges, such as foraging, mating and communication. However, many animals, in particular mammals, have been domesticated by humans. As a result of domestication a range of divergent morphological traits are frequently seen in domesticated mammals that separate them from their wild, ancestral counterparts. Many of these diverged traits pertain to cranium morphologies, such as different head shapes and sizes, shorter muzzles, and different ear shapes and positions. To date, there is little research into the potential implications that these diverged morphological traits of domesticated mammals may pose for their behaviour.

A model example of diverged cranium morphologies is seen in the domestic dog (Canis lupus familiaris), the selectively bred descendant of wolves (Canis lupus). It is thought that the head and facial feature morphologies of wolves aid the production of facial expressions for communicative purposes. Previous researchers have also speculated on the ability of wolves to convey affective states as well as social status via their facial expressions. Affective states are forms of motivation such as emotions, moods, attitudes, desires, preferences, intentions and dislikes. However, to date there has been no quantitative analyses of these suggested links between facial expressions, affective states and social status in wolves.

The relative shape and position of the eyes, ears, forehead, muzzle, nose and lips (the main conveyers of facial expressiveness) are the same for all wolves, throughout the world. However, selective breeding has resulted in the main conveyers of facial expressiveness of dogs greatly diverging from those of their wolf ancestors, although, it is still thought that dogs use facial expressions to convey affective states. However, to date there has been little quantitative analyses of the links between domestic dog facial expressions and affective states. This thesis aims to quantify the affective facial expressions of wolves and domestic dogs, and to determine if the various head and facial morphologies found across different dog breeds limits their abilities to successfully produce affective facial expressions like their wolf ancestors.

The facial expressions of captive, human-habituated wolves (n = 10) and kennelled rescue dogs (n = 64) were video recorded during social interactions and reactions to ‘emotive’ stimuli. To quantify the facial expressions of wolves and dogs, the video footage was decoded using the Dog Facial Action Coding System (DogFACS). The affective states of focal canids were also quantified and classified from the video footage using independent observers. The quantified facial expressions were then mapped against the reliable classifications of affective states using hierarchical cluster analyses and linear discriminant analyses. Two separate confusion matrices for wolves and dogs were generated from the linear discriminant analyses, which revealed the level of precision (agreement) between the actual and predicted affective facial expressions of wolves and dogs.

The research presented in this thesis provides the first quantification of facial expressions in wolves and relates them to reliable classifications of affective states across a range of social contexts. This research also provides the first quantitative, preliminary evidence for wolf facial expressions conveying social status, which has never been shown to exist in any other non-human animal. The affective facial expressions of wolves are shown to be similar to those seen in primates and are discussed in the framework of the social intelligence hypothesis. For the first time, this thesis also shows that the varying head and facial feature morphologies of dogs (in particular non-wolf-like morphologies) limit their ability to produce the same range of affective facial expressions as their wolf ancestors. However, this research reveals that dogs have evolved a compensatory way to convey their affective states, via the use of vocalisations.