Red-capped mangabeys (Cercocebus torquatus) adapt their interspecific gestural communication to the recipient's behaviour.

Sensitivity to recipient's attention and responsiveness are critical markers of intentional communication. Although previous research showed that ape gestures can be intentional, few studies have yet addressed this question concerning monkeys. Here, we characterise the effect of a recipient's presence, attentional state and responsiveness on the interspecific gestural communication of captive red-capped mangabeys (Cercocebus torquatus). Previous reports showed that they produced learnt begging gestures towards a human recipient preferentially when the latter was facing them. We used here a novel setup that allows subjects to move around an experimenter and to use different modalities (visual and acoustic) to communicate. We found that when the recipient was not facing them, mangabeys moved to a position in the visual field of their recipient rather than using attention-getters. Interestingly, unlike apes, they did not elaborate their communication visually or acoustically when the experimenter did not respond favourably to their begging. However, our results may suggest that begging gestures were goal-directed, since mangabeys inhibited them when the experimenter was not available to answer immediately (i.e. give a reward). Overall, red-capped mangabeys' interspecific visual communication presented intentionality features, but their use of begging gestures was less flexible than that of great apes in similar situations.

Factors of influence and social correlates of parturition in captive Campbell's monkeys: Case study and breeding data.

How nonhuman primates deal with birth, at the moment of delivery, and during the following days, remains poorly explored because of the unpredictability of this event, particularly for forest-dwelling arboreal species. Available studies highlight intra- and interspecific variation which suggest flexibility of the timing of delivery, of behavior associated with labor contractions and parturition, and the social context and ambient noise surrounding delivery. Here, we present the findings of a two-decade survey of reproduction in a population of captive Campbell's monkeys. Analysis of 34 births (with a female-biased sex ratio) showed that deliveries occurred systematically at night and more frequently during week-ends and in fall (September-November). This suggests the existence of both circadian and infradian biological rhythms. We present the first detailed description of a birth for this species and its short-term social consequences. In line with previous findings for other monkeys and apes, labor (estimated by unusual stretching postures) and parturition were rapid, and delivery occurred in a clear social and vocal context. During the following days, the new mother became the center of attention of for young (kin and non-kin) females and rose through the hierarchy. We discuss socio-ecological factors, notably captivity conditions and the high degree of tolerance in the species' social system, and confirm the existence of both "rigidity" and "flexibility" in the primates' adaptive reproductive strategies.

Which are the features of the TUBE task that make it so efficient in detecting manual asymmetries? An investigation in two Cercopithecine species (Cercopithecus neglectus and Cercocebus torquatus).

In the last decade, the TUBE task has been repeatedly shown to be highly efficient in detecting manual asymmetries that are strong hand preferences reflecting hemispheric specialization, in non human primates. The TUBE task was thus classified as a high-level task, presumably because it involves bimanual coordination. However, this task also requires a precise action made by digit(s), which may also be a crucial feature in eliciting manual asymmetries. In the present study, we compared hand preferences for a new TUBE-unimanual task and the classic TUBE-bimanual task, both performed mostly by using the forefinger, in 12 guenons (De Brazza's monkey: Cercopithecus neglectus) and 18 mangabeys (red-capped mangabey: Cercocebus torquatus). We found a relationship between hand preferences exhibited for the two tasks, suggesting that precise use of the forefinger may induce the activation of a specialized hemisphere in both the TUBE-unimanual and the TUBE-bimanual task. However, we showed that the strength of manual laterality was higher in the TUBE-bimanual task than in the TUBE-unimanual task, indicating that bimanual coordination may enhance the expression of hand preferences. We propose that the TUBE-bimanual task is highly efficient in detecting hemispheric specialization because bimanual role differentiation would make precise digit use highly skillful. Finally, we revealed species differences in hand use, especially in females: the most arboreal species, De Brazza's monkeys, increased left-hand use from the TUBE-unimanual to the TUBE-bimanual task whereas the most terrestrial species, red-capped mangabeys, increased right-hand use.

Visual laterality responses to different emotive stimuli by red-capped mangabeys, Cercocebus torquatus torquatus.

Hemispheric asymmetry in emotional perception has been put forward by different theories as the right hemisphere theory or the valence theory. But no consensus was found about the role played by both hemispheres. So, in order to test the different theories, we investigated preferential use of one eye in red-capped mangabeys, at the individual as well as at the group level. In this study we investigated the influence of the emotional value of stimuli on the direction and strength of visual preference of 14 red-capped mangabeys. Temporal stability of the bias of use of a given eye was evaluated by comparing our current results to those obtained 2.5 months previously. Two experimental devices, a tube and a box, tested five different stimuli: four food types varying in palatability and a neutral stimulus. The subjects' food preferences were evaluated before testing the laterality. The mangabeys used their left eyes predominantly at the group level for the tube task. The majority of the subjects showed a visual preference at the individual level for the box task, but this bias was not present at the group level. As the palatability of the stimuli increased, the number of lateralized subjects and the number of subjects using preferentially their left eye increased. Similarly, the strength of laterality was related to food preference. Strength of laterality was significantly higher for subjects using their left eye than for subjects using their right eye. Preferential use of a given eye was stable over short periods 2.5 months later. Our data agree with reports on visual laterality for other species. Our results support the valence theory of a hemispheric sharing of control of emotions in relation to their emotional value.

Social laterality and 'transversality' in two species of mangabeys: influence of rank and implication for hemispheric specialization.

Individuals in social groups monitor many relationships by adapting their activities to the sex, age, social status, behaviour as well as the position of conspecifics. Here, we investigated the influence of the relative positions of the members of two groups of mangabeys on social visual laterality (right/left) and 'transversality' (frontal/rear) in two contexts: (1) 'one-to-one' interactions and (2) a 'one-to-many' context allowing potential observation of all group members. We discuss our data in relation to (1) the influence of rank and (2) theories explaining lateralization of cerebral hemispheres. First, in 'one-to-one' situations, members of both groups were approached more frequently from their left than from their right, and red-capped mangabeys approached a group member more frequently from their right than from their left. In 'one-to-many' situations, red-capped mangabeys kept more group members in their right than their left frontal visual field. Conversely, the social 'transversality' bias was the same in both contexts: the frontal field was favoured. Second, approach side and relative positions differed according to social rank. Mangabeys that were approached more frequently from their left ranked relatively high. The higher an individual ranked, the more it left other group members behind it; on the contrary dominated mangabeys generally remained below other group members. Thus, social structures, as well as relationships within a group, appear to be good candidates to explain social laterality and 'transversality'.

Manual laterality in Campbell's Monkeys (Cercopithecus c. campbelli) in spontaneous and experimental actions.

Behavioural asymmetries, once thought to be exclusively human, appear to be widespread in vertebrates. A population-level bias should stem from natural selection and reflect a cerebral dominance, while individual preferences might be linked to individual characteristics. Manual laterality has been extensively investigated in non-human primates. However, despite a strong data base, no general patterns have emerged, resulting in a few explanatory theories and little consensus. This study was interested in manual laterality in 12 Campbell's monkeys (Cercopithecus c. campbelli). Several theories were examined, using both direct behavioural observations during feeding behaviour and six controlled experimental conditions, in which we varied task demands to investigate the effect of two factors. We systematically varied the individual posture (sat, tripedal, bipedal, clung) and the complexity of the task (box with or without a lid to open). Concerning the direction of preference, we found individual and action-specific preferences for experimental actions, which match previous reports. No population bias emerged and each subject appeared to react differently to the factors, hereby contradicting the theories. However, concerning the strength of preference, all individuals tended to be affected in similar ways. Spontaneous actions were less lateralized than experimental ones, and the simplest task and spontaneous category tended to show the weakest laterality. The relative complexity and novelty of these actions may account for these results.