Captive gibbons (Hylobatidae) use different referential cues in an object-choice task: insights into lesser ape cognition and manual laterality

Abstract

BackgroundUtilization of visual referential cues by non-human primates is a subject of constant scientific interest. However, only few primate species, mostly great apes, have been studied thoroughly in that regard, rendering the understanding of phylogenetic influences on the underlying cognitive patterns difficult.MethodsWe tested six species of captive gibbons in an object-choice task (n = 11) for their ability to interpret two different pointing gestures, a combination of body orientation and gaze direction as well as glancing as referential cues. Hand preferences were tested in the object-choice task and in a bimanual tube task (n = 18).ResultsWe found positive responses to all signals except for the glancing cue at the individual as well as at the group level. The gibbons’ success rates partially exceed results reported for great apes in comparable tests and appear to be similarly influenced by prior exposure to human communicative cues. Hand preferences exhibited by the gibbons in the object-choice task as well as in a bimanual tube task suggest that crested gibbons (Nomascus sp.) are strongly lateralized at individual but not at population level for tasks involving object manipulation.DiscussionBased on the available data, it can be assumed that the cognitive foundations to utilize different visual cues essential to human communication are conserved in extant hominoids and can be traced back at least to the common ancestor of great and lesser apes. However, future studies have to further investigate how the social environment of gibbons influences their ability to exploit referential signals. Gibbons’ manual laterality patterns appear to differ in several aspects from the situation found in great apes. While not extensive enough to allow for general conclusions about the evolution of hand preferences in gibbons or apes in general, our results add to the expanding knowledge on manual lateralization in the Hylobatidae.

Ocular pigmentation in humans, great apes, and gibbons is not suggestive of communicative functions

“…So far, most information on gaze and glance cue understanding in apes derive from studies in which human experimenters signal to an ape subject in a captive setting 3 , 14 , 21 , 22 . It is important to note that responsiveness to human eye orientation by habituated animals does not equate with the usage of glance cues among conspecifics, as for instance the successful exploitation of human glances by Californian sea lions ( Zalophus californianus ) demonstrates 39 .…”

“…Despite their phylogenetic position and resulting relevance to understand the evolution of hominoid cognitive traits, gibbons are widely ignored in primate behavioral research (excluding acoustic communication), so that little is known about their socio-cognitive traits 19 , 20 . However, there currently is consensus that glancing does not carry noteworthy communicative value to them 21 , 22 . In line with this, gibbon gaze following is less sophisticated than in their large-bodied relatives.…”

Ocular pigmentation in humans, great apes, and gibbons is not suggestive of communicative functions - having an eye on the ‘cooperative eye hypothesis’

“…So far, most information on gaze and glance cue understanding in apes derive from studies in which human experimenters signal to an ape subject in a captive setting (Barth et al, 2005;Tomasello et al, 2007;Caspar et al, 2018;Sanchez-Amaro et al, 2020). It is important to note that responsiveness to human eye orientation by habituated animals does not equate with the usage of glance cues among conspecifics, as for instance the successful exploitation of human glances by Californian sea lions (Zalophus californianus) demonstrates (Arkwright et al, 2016).…”

“…Despite their phylogenetic position and resulting relevance to understand the evolution of hominoid cognitive traits, gibbons are widely ignored in primate behavioral research (excluding acoustic communication), so that little is known about their sociocognitive traits (Butler & Suddendorf, 2014;ManyPrimates et al, 2019). However, there currently is consensus that glancing does not carry noteworthy communicative value to them (Caspar et al, 2018;Sanchez-Amaro et al, 2020). In line with this, gibbon gaze following is less sophisticated than in their large-bodied relatives.…”

How do gibbons solve social dilemmas?

“…Nevertheless, despite the lack of studies on gibbons' socio-cognitive abilities in relation to other primate species 22 , researchers have made signi cant advancements on this area. For instance, it has been investigated whether gibbons recognize themselves in the mirror (see 25 for review) or whether they are able to follow others gaze to discover an unseen object [38][39][40][41][42] . In the case of gaze-following studies, researchers have found that gibbons are able to shift their gaze in response to a previous experimenter gaze shift but it remains unclear whether gibbons are taking the perspective of the experimenter into account, including her mental states.…”