ABSTRACT
Primate facial musculature enables a wide variety of movements during bouts of communication, but how these movements contribute to signal construction and repertoire size is unclear. The facial mobility hypothesis suggests that morphological constraints shape the evolution of facial repertoires: species with higher facial mobility will produce larger and more complex repertoires. In contrast, the socio-ecological complexity hypothesis suggests that social needs shape the evolution of facial repertoires: as social complexity increases, so does communicative repertoire size. We tested these two hypotheses by comparing chimpanzees (Pan troglodytes) and gibbons (family Hylobatidae), two distantly related apes who vary in their facial mobility and social organization. While gibbons have higher facial mobility than chimpanzees, chimpanzees live in more complex social groups than gibbons. We compared the morphology and complexity of facial repertoires for both apes using Facial Action Coding Systems designed for chimpanzees and gibbons. Our comparisons were made at the level of individual muscle movements (action units [AUs]) and the level of muscle movement combinations (AU combinations). Our results show that the chimpanzee facial signaling repertoire was larger and more complex than gibbons, consistent with the socio-ecological complexity hypothesis. On average, chimpanzees produced AU combinations consisting of more morphologically distinct AUs than gibbons. Moreover, chimpanzees also produced more morphologically distinct AU combinations than gibbons, even when focusing exclusively on AUs present in both apes. Therefore, our results suggest that socio-ecological factors were more important than anatomical ones to the evolution of facial signaling repertoires in chimpanzees and gibbons. (PsycInfo Database Record (c) 2024 APA, all rights reserved).
Subject(s)
Animal Communication , Hylobates , Animals , Hylobates/physiology , Pan troglodytes/physiology , Facial Expression , FaceABSTRACT
Lately, there has been a growing interest in studying domestic cat facial signals, but most of this research has centered on signals produced during human-cat interactions or pain. The available research on intraspecific facial signaling with domesticated cats has largely focused on non-affiliative social interactions. However, the transition to intraspecific sociality through domestication could have resulted in a greater reliance on affiliative facial signals that aid with social bonding. Our study aimed to document the various facial signals that cats produce during affiliative and non-affiliative intraspecific interactions. Given the close relationship between the physical form and social function of mammalian facial signals, we predicted that affiliative and non-affiliative facial signals would have noticeable differences in their physical morphology. We observed the behavior of 53 adult domestic shorthair cats at CatCafé Lounge in Los Angeles, CA. Using Facial Action Coding Systems designed for cats, we compared the complexity and compositionality of facial signals produced in affiliative and non-affiliative contexts. To measure complexity and compositionality, we examined the number and types of facial muscle movements (AUs) observed in each signal. We found that compositionality, rather than complexity, was significantly associated with the social function of intraspecific facial signals. Our findings indicate that domestication likely had a significant impact on the development of intraspecific facial signaling repertoires in cats.
Subject(s)
Mammals , Social Behavior , Humans , Adult , Animals , CatsABSTRACT
Researchers frequently use focal individual sampling to study primate communication. Recent studies of primate gestures have shown that opportunistic sampling offers benefits not found in focal individual sampling, such as the collection of larger sample sizes. What is not known is whether the opportunistic method is biased towards certain signal types or signalers. Our goal was to assess the validity of the opportunistic method by comparing focal individual sampling to opportunistic sampling of facial and gestural communication in a group of captive chimpanzees (Pan troglodytes). We compared: (1) the number of observed facial and gestural signals per signal type and (2) the number of observed facial and gestural signals produced by each signaler. Both methods identified facial signals, gesture signals, and gesture signalers at similar relative rates, but the opportunistic sampling method yielded a more even distribution of signalers and signal types than the focal individual sampling method. In addition, the opportunistic sampling method resulted in larger sample sizes for both facial and gestural communication. However, the opportunistic method did not allow us to calculate the signals per time for each individual, which is easily done with the focal individual method. These results suggest that the opportunistic sampling method is (1) comparable to the focal individual sampling method in multiple important measures, (2) associated with additional sampling benefits, and (3) limited in measuring some variables. Thus, we recommend that future studies use a mixed-methods approach, as focal individual and opportunistic sampling have distinct strengths that complement each other's limitations.