Accessory chemosignaling mechanisms in primates

Bank vole alarm pheromone chemistry and effects in the field

Chemical communication plays an important role in mammalian life history decisions. Animals send and receive information based on body odour secretions. Odour cues provide important social information on identity, kinship, sex, group membership or genetic quality. Recent findings show, that rodents alarm their conspecifics with danger-dependent body odours after encountering a predator. In this study, we aim to identify the chemistry of alarm pheromones (AP) in the bank vole, a common boreal rodent. Furthermore, the vole foraging efficiency under perceived fear was measured in a set of field experiments in large outdoor enclosures. During the analysis of bank vole odour by gas chromatography–mass spectrometry, we identified that 1-octanol, 2-octanone, and one unknown compound as the most likely candidates to function as alarm signals. These compounds were independent of the vole’s sex. In a field experiment, voles were foraging less, i.e. they were more afraid in the AP odour foraging trays during the first day, as the odour was fresh, than in the second day. This verified the short lasting effect of volatile APs. Our results clarified the chemistry of alarming body odour compounds in mammals, and enhanced our understanding of the ecological role of AP and chemical communication in mammals.

On the trail of primate scent signals: A field analysis of callitrichid scent-gland secretions by portable gas chromatography-mass spectrometry

Chemosignals are mediators of social interactions in mammals, providing con- and hetero-specifics with information on fixed (e.g., species, sex, group, and individual identity) and variable (e.g., social, reproductive, and health status) features of the signaler. Yet, methodological difficulties of recording and quantifying odor signals, especially in field conditions, have hampered studies of natural systems. We present the first use of the Torion® portable gas chromatography-mass spectrometry (GC-MS) instrument for in situ chemical analysis of primate scents. We collected and analyzed swab samples from the scent glands and skin from 13 groups (57 individuals) of two sympatric species of wild emperor tamarins, Saguinus imperator, and Weddell's saddleback tamarins, Leontocebus weddelli (Callitrichidae). In total, 11 compounds of interest (i.e., probably derived from the animals) could be detected in the samples, with 31 of 215 samples containing at least one compound of interest. The composition of these 31 samples varied systematically with species, group, sex, and breeding status. Moreover, we tentatively identified seven of the compounds of interest as methyl hexanoate, benzaldehyde, ethyl hexanoate, acetophenone, a branched C15 alkane, 4-methoxybenzaldehyde, and hexadecan-1-ol. As the field of primate semiochemistry continues to grow, we believe that portable GC-MS instruments have the potential to help make progress in the study of primate chemosignaling in field conditions, despite limitations that we encountered. We further provide recommendations for future use of the Torion® portable GC-MS for in situ analyses.

Contextual complexity of chemical signals in callitrichids

In nearly four decades our research and that of others on chemical signaling in callitrichid primates suggest a high degree of contextual complexity in both the use of signals and the response to these signals. We describe our research including observational field studies, behavioral bioassays ("playbacks"), functional imaging, and conditioning studies. Scent marking in both captivity and the wild is used for more than just territorial marking. Social contextual effects are seen in responses by subordinate females responding with ovulatory inhibition only to chemical signals from familiar dominant reproductive females. Males detect ovulation through changes in scent marks. Males responded behaviorally and hormonally to chemical signals of novel ovulating females as a function of their reproductive status (fathers, males paired with a female but not fathers, and single males). Multiple brain areas are activated in males by female chemical signals of ovulation including areas relating to memory, evaluation, and motivation. Furthermore, males can be conditioned to respond sexually to a nonsexual odor demonstrating that learning plays an important role in response to chemical signals. Male androgen and estrone levels changed significantly in response to infant chemical signals as a function of whether the males were fathers or not, whether the odors were from their own versus other infants, as well as the infant's stage of development. Chemical signals in callitrichids are providing a rich source of understanding the context and function of the chemical sensory system and its stimulation of neural, behavioral, and hormonal actions in the recipients.

Nasopalatine ducts and flehmen behavior in the mandrill: reevaluating olfactory communication in Old World primates

Compared to other modes of communication, chemical signaling between conspecifics generally has been overlooked in Old World primates, despite the presence in this group of secretory glands and scent-marking behavior, as well as the confirmed production and perception of olfactory signals. In other mammalian species, flehmen is a behavior thought to transport primarily nonvolatile, aqueous-soluble odorants via specialized ducts to the vomeronasal organ (VNO). By contrast, Old World primates are traditionally thought to lack a functional VNO, relying instead on the main olfactory system to process volatile odorants from their environment. Here, in the mandrill (Mandrillus sphinx), we document unusual morphological and behavioral traits that typically are associated with the uptake of conspecific chemical cues for processing by an accessory olfactory system. Notably, we confirmed that both sexes possess open nasopalatine ducts and, in response to the presentation of conspecific odorants, we found that both sexes showed stereotyped behavior consistent with the flehmen response. If, as in other species, flehmen in the mandrill serves to mediate social or reproductive information, we expected its occurrence to vary with characteristics of either the signaler or receiver. Flehmen, particularly in a given male, occurred most often in response to odorants derived from male, as opposed to female, conspecifics. Moreover, odorants derived during the breeding season elicited more flehmen responses than did odorants collected during the birthing season. Lastly, odorants from reproductively cycling females also elicited more responses than did odorants from contracepted females. Although confirming a link between the nasopalatine ducts, flehmen behavior, and olfactory processing in mandrills would require further study, our observations provide new information to suggest anatomical variability within Old World primates, calling further attention to the underappreciated role of chemical communication in this lineage.

Does nonnutritive tree gouging in a rainforest-dwelling lemur convey resource ownership as does loud calling in a dry forest-dwelling lemur?

Nonhuman primates may defend crucial resources using acoustic or chemical signals. When essential resources are limited, ownership display for a resource may be enhanced. Defending resources may depend on population density and habitat characteristics. Using the Milne Edwards' sportive lemurs (Lepilemur edwardsi) and weasel sportive lemurs (L. mustelinus) as models, we tested whether two cryptic nocturnal lemur species differing in population density and habitat show differences in their vocal and chemical communication for signaling ownership of resources. L. edwardsi inhabits a western dry deciduous forest in a high-density population, whereas L. mustelinus is found in an eastern rainforest in low density. We followed ten L. edwardsi (six males and four females) and nine L. mustelinus (four males and five females) for 215 hr during the early evening (06:00-10:00 p.m.) and the early morning (02:00-05:00 a.m.) and recorded their behavior using focal animal sampling. We found that both species differed in their vocal and chemical communication. L. edwardsi was highly vocal and displayed loud calling in the mornings and evenings while feeding or in the vicinity of resting places. In contrast, L. mustelinus never vocalized during observations, but displayed tree-gouging behavior that was never observed in L. edwardsi. Tree gouging occurred more often during early evening sessions than early morning sessions. Subjects gouged trees after leaving their sleeping hole and before moving around. We suggest that, in weasel sportive lemurs, non-nutritive tree gouging is used as a scent-marking behavior in order to display ownership of sleeping sites. Altogether, our findings provide first empirical evidence on the evolution of different communication systems in two cryptic nocturnal primate species contrasting in habitat quality and population density. Further investigations are needed to provide more insight into the underlying mechanisms.