Acoustic variability and social significance of calls in female Campbell's monkeys (Cercopithecus campbelli campbelli)

International audienceAlthough the vocal repertoire of nonhuman primates is strongly constrained by genetic, a growing number of studies evidence socially determined flexibility. According to Snowdon et al. [Social Influences on Vocal Development (University Press, Cambridge, 1997), pp. 234-248], calls with a higher social function (affiliative or agonistic) would be expected to show more flexibility than lesser social calls. Owren and Rendall [Evol. Anthropol., 10, 58-71 (2001)] nuanced this by defending a structure-function relationship. Calls with particular acoustic properties, which directly influence the listener's affect, would be less individually distinctive than calls involved in an affective conditioning process. These hypotheses were tested in Campbell's monkeys using telemetric recordings. This is the first detailed description of female Campbell's monkeys' vocal repertoire emphasizing a possible relationship between social function and flexibility level. The vocal repertoire displayed an "arborescent" organization (call type, subtype, and variants). The highest number of subtypes and the greatest acoustic variability, within and among individuals, were found in calls associated with the highest affiliative social value. However, calls associated with agonism were the most stereotyped, whereas less social alarm calls were intermediate. This only partially validate the hypothesis of Snowdon et al. In accordance with Owren and Rendall's hypotheses, the level of individual distinctiveness was minimum for noisy pulsed calls and maximum for calls involved in affiliative interactions

Morphologically structured vocalizations in female Diana monkeys

Research was funded by the French Ministry of Research, Institut Universitaire de France, ANR ‘Orilang’ and the European Union's Seventh Framework Programme (FP7/2007-2013)/European Research Council grant agreement n° 283871.Social complexity is often thought of as a driving force in the evolution of communication and cognition, but this is at odds with the fact that nonhuman primates generally display only very limited flexibility in vocal production. Some primates partially overcome their limited vocal flexibility by combining two or more acoustically inflexible calls into complex sequences. Equally relevant is that some primate calls consist of separable morphological elements whose combinations create different meanings. Here, we focus on the vocal system of wild female Diana monkeys, Cercopithecus diana, which produce three call units (R, L, A) either singly or merged as RA or LA call combinations. Previous work has shown that R and L convey information about external events, while A conveys information about caller identity. We tested this hypothesis experimentally, by broadcasting artificially combined utterances to eight adult females. To test the significance of the R and L ‘event’ units, we merged them with the A ‘identity’ unit of a group member. To test the significance of the ‘identity’ unit, we merged an R ‘event’ unit with an ‘identity’ unit from a group member or a neighbouring individual. Subjects responded in ways that suggested that both event and identity units were relevant, suggesting that Diana monkeys’ social calls possess morphosemantic features. We discuss this finding in relation to the coevolution of communication and social complexity in primates.PostprintPeer reviewe

Behavioural innovation and cultural transmission of communication signal in black howler monkeys

International audienceSocial traditions based on communication signals are widespread in birds, cetaceans and humans, but surprisingly rare in nonhuman primates known for having genetically-determined vocal repertoires. This study presents the first description of a singular case of behaviour associated with calling (placing a hand in front of the mouth while vocalizing: HFM) in black howler monkeys. We showed, first, that HFM was found only in a subset of the groups observed, at the same geographical location, and was age- and sex-specific. There was an audience effect on HFM, with highest rates when a neighbouring group was visible. HFM was non-randomly combined with audio-visual signals and always performed while roaring. High HFM rates triggered more vocal responses from group members and male neighbours, and HFM signalers temporally synchronized their behaviour in a predictable way. Finally, the positioning of the hand systematically modified the call's auditory structure. Altogether these results support the idea that HFM is an innovated, culturally transmitted communication signal that may play a role in inter-group competition and intra-group cohesion. This study opens new lines of research about how nonhuman primates developed strategies to overcome their constraints in acoustic plasticity very early in the primate lineag