Primates are traditionally considered to be microsmatic, with decreased reliance on olfactory senses in comparison to other sensory modalities such as vision. This is particularly the case for Old World monkeys and apes (catarrhines). However, various lines of evidence suggest that chemical communication may be important in these species, including the presence of a sternal scent-gland in the mandrill. We investigated the volatile components of mandrill odor using gas chromatography–mass spectrometry. We identified a total of 97 volatile components in 88 swabs of the sternal gland secretion and 95 samples of sternal gland hair saturated with scent-gland secretion collected from 27 males and 18 females. We compared odor profiles with features of the signaler using principle components and discriminant function analyses and found that volatile profiles convey both variable (age, dominance rank in males) and fixed (sex, possibly individual identity) information about the signaler. The combination of an odor profile that signals sex, age, and rank with increased motivation to scent-mark and increased production of secretion in high-ranking males leads to a potent signal of the presence of a dominant, adult male with high testosterone levels. This may be particularly relevant in the dense Central African rain forest which mandrills inhabit. By contrast, we were unable to differentiate between either female cycle stage or female rank based on odor profiles, which accords with behavioral studies suggesting that odor signals are not as important in female mandrills as they are in males. The similarity of our findings to those for other mammals and in primates that are more distantly related to humans suggests a broader role for odor in primate communication than is currently recognized.

The major histocompatibility complex (MHC) is an extraordinarily diverse cluster of genes that play a key role in the immune system. MHC gene products are also found in various body secretions, leading to the suggestion that MHC genotypes are linked to unique individual odourtypes that animals use to assess the suitability of other individuals as potential mates or social partners. We investigated the relationship between chemical odour profiles and genotype in a large, naturally reproducing population of mandrills, using gas chromatography-mass spectrometry and MHC genotyping. Odour profiles were not linked to the possession of particular MHC supertypes. Sex influenced some measures of odour diversity and dominance rank influenced some measures of odour diversity in males, but not in females. Odour similarity was strongly related to similarity at the MHC, and, in some cases, to pedigree relatedness. Our results suggest that odour provides both a cue of individual genetic quality and information against which the receiver can compare its own genotype to assess genetic similarity. These findings provide a potential mechanism underlying mate choice for genetic diversity and MHC similarity as well as kin selection.

Fifty years after the term ‘pheromone’ was coined by Peter Karlson and Martin Lüsher, the search for these semiochemicals is still an elusive goal of chemical ecology and communication studies. Con...

Mandrills are one of the few Old World primates to show scent-marking. We combined ethological and chemical approaches to improve our understanding of this behavior in 3 zoo-managed groups. We observed the olfactory behavior performed by adults and adolescents (N = 39) for 775h. We investigated the volatile components of sternal scent-marks using gas chromatography-mass spectrometry and compared volatile profiles with traits of the signaler. Males marked more than females and within each sex the frequency of scent-marking was related to age and dominance status, but alpha males scent-marked most frequently and particularly in specific areas at the enclosure boundaries. We identified a total of 77 volatile components of sternal gland secretion, including compounds functioning as male sex pheromones in other mammals, in scent-marks spontaneously released on filter paper by 27 male and 18 female mandrills. We confirmed our previous findings that chemical profiles contain information including sex, male age and rank, and we also found that odor may encode information about group membership in mandrills. Our results support the hypotheses that scent-marking signals the status of the dominant male as well as playing territorial functions but also suggest that it is part of sociosexual communication.

Positive reinforcement training (PRT) is an established tool to facilitate animal husbandry, care and research in modern zoos, with potential positive implications for captive animal welfare. The study explored the role of an isolation PRT training programme on the well-being of ring-tailed lemurs (Lemur catta). Eleven subjects were observed during an isolation training protocol to induce the animals to enter an area (training area) calmly and retrieve rewards separated from group members. Duration of individual and social behaviours were collected over two different periods: the baseline period, before the beginning of the isolation training protocol and the training period, in which the collection of the data started at the end of the isolation training sessions. Additionally, behavioural data within the isolation training sessions (latency to enter the training area and retrieve the reward, display of stress-related behaviours) were recorded. Outside the training sessions, lemurs were out of sight significantly more in the baseline (Mean ± SD: 15.46 ± 5.20) than in the training (Mean ± SD: 4.36 ± 2.89) period. Social behaviour was performed significantly more in the training (Mean ± SD: 31.80 ± 12.34) than in the baseline (Mean ± SD: 12.52 ± 5.14) period; particularly, lemurs were in social contact significantly more in the training (Mean ± SD: 14.09 ± 6.00) than in the baseline period (Mean ± SD: 4.58 ± 2.73). Agonistic behaviours were performed significantly more in the baseline (Mean ± SD: 0.23 ± 0.15) than in the training (Mean ± SD: 0.07 ± 0.07) period. Within the training sessions, all the individuals entered the training area, were isolated from conspecifics, and retrieved the reward in 6 out of 9 sessions. Our findings show that, during the PRT period, lemurs displayed their natural behaviour in their everyday social life with significant increase of their affiliative behaviours and decrease of aggressive behaviours with benefits for their welfare status. Thus, lemurs were able to cope with the use of PRT to isolate each individual from its social group − a situation which, without training, might be very stressful. In conclusion, PRT may play a crucial role for the captive management of ring-tailed lemurs in captive facilities, including zoos