Vocal expression of emotional valence in Przewalski’s horses (Equus przewalskii)

Abstract

Vocal expression of emotions has been suggested to be conserved throughout evolution. However, since vocal indicators of emotions have never been compared between closely related species using similar methods, it remains unclear whether this is the case. Here, we investigated vocal indicators of emotional valence (negative versus positive) in Przewalski’s horses, in order to find out if expression of valence is similar between species and notably among Equidae through a comparison with previous results obtained in domestic horse whinnies. We observed Przewalski’s horses in naturally occurring contexts characterised by positive or negative valence. As emotional arousal (bodily activation) can act as a confounding factor in the search for indicators of valence, we controlled for its effect on vocal parameters using a behavioural indicator (movement). We found that positive and negative situations were associated with specific types of calls. Additionally, the acoustic structure of calls differed according to the valence. There were some similarities but also striking differences in expression of valence between Przewalski’s and domestic horses, suggesting that vocal expression of emotional valence, unlike emotional arousal, could be species specific rather than conserved throughout evolution.

Encoding of Emotional Valence in Wild Boar (Sus scrofa) Calls

“…The parks’ policies did not allow us to manipulate the animals. Therefore, recording of individual animals was performed opportunistically during presumed positive and negative expressions of emotions in naturally occurring situations [ 12 , 19 , 26 ].…”

“…There is now good evidence that this is the case for vocal expression of emotional arousal, suggesting that some vocal indicators of arousal could be shared across species [ 7 , 18 ]. However, whether this also applies to vocal indicators of valence remains unknown, since these indicators have been investigated in only a few species, and rarely in closely related species (but see [ 19 ]). So far, it seems that across several species, calls associated with positive emotions tend to be shorter, with a lower and less variable fundamental frequency (F0), compared to those associated with negative emotions [ 7 , 20 ].…”

“…The main genetic difference between the two species is that wild boars have 36 chromosomes, while domestic pigs have 38 [ 25 ]. A comparison of vocal indicators of emotion between these two species could shed light on the impact of domestication on emotion expression, and highlight the potential of vocal indicators of valence to be applied across species [ 19 ].…”

Communication is key: Mother-offspring signaling can affect behavioral responses and offspring survival in feral horses (Equus caballus)

“…On the other hand, nickers seemed to elicit different outcomes depending on initiator type: while they were more likely to result in no change to the animals' distance or current activity when used by mares to initiate communication, they were more likely to result in suckling and/or decreases in the mare-foal distance when used by foals ( Fig 5). The use of nickers by mares and foals in lieu of the signals they more commonly use (snorts and whinnies, respectively) may be indicative of situational "urgency" or the level of mare and foal arousal [55][56][57][58]. For example, the use of nickers vs. snorts by mares may indicate increased arousal: if snorts are not effective, mares may use the louder nicker to ensure contact is made with their foals.…”

Emotion Communication Through Voice Modulation: Insights on Biological and Evolutionary Underpinnings of Language

“…A different approach, which includes dimensional emotion models, argues that emotional states can be classified based on their valence (positive or negative) and their arousal level (i.e., activation or responsiveness levels, typically classified as low/high or calm/excited) (Mendl, Burman, & Paul, 2010;Mendl, Paul, & Chittka, 2011;Russell, 1980). Crucially, unlike discrete emotions and emotional valence, different levels of arousal can be directly linked to the physiological state of the signaler, enabling quantitative mapping of physiological, Emotion Communication Through Voice Modulation behavioral and acoustic data (Briefer, Tettamanti, & Mcelligott, 2015a;Briefer et al, 2015b;Maigrot et al, 2017). This is particularly suitable for precise quantitative comparisons within and across species, aimed at exploring biologically universal aspects of emotional expression.…”