Chemical cues of female fertility states in a non-human primate

Influence of visual information on sniffing behavior in a routinely trichromatic primate

Most catarrhine primates are considered to be strongly visually oriented, obtaining information about conspecifics and their environment from a diversity of visual cues. Other sensory modalities may provide information that is redundant and/or complimentary to visual cues. When cues from multiple sensory modalities are available, these may reinforce or suppress each other, as shown in several taxa ranging from insects to humans. Here, we tested how the presence and ambiguity of visual information affect the use of olfactory cues when exploring food and non-food items in semi-free-ranging Barbary macaques at Affenberg Salem, Germany. We presented monkeys with pipes containing food (peanuts, popcorn), non-food (stones, feces), or no items in transparent or opaque containers and assessed whether animals looked, sniffed, and/or grabbed into the pipes depending on the visibility of the contents (experiment 1). Visual information had no robust effect on sniffing probability, but monkeys were more likely to sniff before any other form of inspection if the can was opaque than if it was transparent. Both visual and olfactory information affected, whether or not monkeys attempted to retrieve the items from the pipes, whereby monkeys showed an overall decrease in the propensity to grab after sniffing. Furthermore, we manipulated the visual appearance of familiar food items (popcorn) with food colorant (experiment 2), which resulted in substantially increased olfactory inspections compared to unmanipulated popcorn. Taken together, reliance on the olfactory sense was modulated by the available visual information, emphasizing the interplay between different sensory modalities for obtaining information about the environment.

The social and defensive function of olfactory behaviors in a pair-living sexually monogamous primate

Olfactory behaviors serve a wide variety of social functions in mammals. Odor may signal information about attributes of individuals important for mating and reproduction. Olfactory behaviors, such as scent-marking, may also function as part of home range or resource defense strategies. We assessed the potential social and home range defense functions of olfactory behavior in a pair-living and sexually monogamous primate, Azara's owl monkey (Aotus azarae), in the Argentinian Chaco. This is the most extensive investigation of owl monkey olfactory behaviors in the wild. Individuals regularly performed olfactory behaviors (group mean + SD = 1.3 + 0.5 per hour). The patterns were generally comparable to those observed in studies of captive owl monkeys, except that urine washing was the most common behavior in the wild, as opposed to scent-marking and genital inspections. Most olfactory behaviors were performed by adults, and there were striking sex differences in genital inspections: almost all consisted of an adult male inspecting the paired adult female. These findings suggest that olfactory behaviors play an important role in signaling and coordinating reproduction among owl monkeys, particularly during periods of female conception and pregnancy. Additionally, our research indicates that these behaviors may also serve as a defense strategy for maintaining the core area of their home ranges. This study offers the first assessment of the role of olfactory behaviors in reproductive contexts and home range defense in pair-living, monogamous platyrrhine primates.

Combined perceptual and chemical analyses show no compelling evidence for ovulatory cycle shifts in women's axillary odour

Although men's attraction to women's body odour has been suggested to vary over the ovulatory cycle, peaking around the fertile window, we still lack methodologically robust evidence corroborating this effect. Further, the chemical underpinnings of male preference for the odour of ovulating women remain unknown. Here, we combined perceptual and chemical analyses to investigate the axillary odour of naturally cycling women over 10 days, covering the gradual change in fertility across the ovulatory cycle with a focus on fertile days. The fertile state was confirmed by urinary ovulation tests as well as salivary oestradiol and progesterone levels. Men rated the scent of unfamiliar women, resembling a first encounter. We used multivariate analyses to relate variation in both odour ratings and chemical composition to female conception probability, temporal distance to ovulation and ovarian hormone levels. Our results provide no evidence that males prefer the odour of fertile women. Furthermore, the volatile analysis indicated no link between axillary odour composition and current fertility status. Together, our results showed no convincing support for a chemical fertility cue in women's axillary odour, questioning the presence of olfactory fertility information that is recognizable during first encounters in modern humans.

Sniffing behavior of semi free-ranging Barbary macaques (Macaca sylvanus)

Olfaction is one of the evolutionarily oldest senses and plays a fundamental role in foraging and social interactions across mammals. In primates, the role of olfaction is now well recognized, but better investigated in strepsirrhine and platyrrhine primates than in catarrhines. We observed the sniffing behavior of semi-free ranging Barbary macaques, Macaca sylvanus, at Affenberg Salem, Germany, to assess how frequently macaques sniff and in which contexts, and how sniffing is affected by sex and age. Focal observations of 24 males and 24 females aged 1-25 years showed that Barbary macaques sniffed, on average, 5.24 times per hour, with more than 80% of sniffs directed at food. Irrespective of the context, younger individuals sniffed more often than older ones. Females' sniffs were more often directed at food than male sniffs, while males sniffed more often than females in a social context. Sniffs at conspecifics occurred primarily in a sexual context, with 70% of social sniffs directed at female anogenital swellings performed by males. Of the observed 176 anogenital inspections, 51 involved sniffing of the swelling. Olfactory inspections were followed by copulation significantly less often than merely visual inspections, suggesting that anogenital odors may play a role in male mating decisions, but the role of olfaction in sexual interactions warrants further investigations. In sum, results show that Barbary macaques routinely use olfaction during feeding, but also in a socio-sexual context, corroborating the relevance of the olfactory sense in the lives of catarrhine primates.

Chemical Profiles Differ between Communal Breeding Groups in a Highly Social Bird

AbstractGregarious species must distinguish group members from nongroup members. Olfaction is important for group recognition in social insects and mammals but rarely studied in birds, despite birds using olfaction in social contexts from species discrimination to kin recognition. Olfactory group recognition requires that groups have a signature odor, so we tested for preen oil and feather chemical similarity in group-living smooth-billed anis (Crotophaga ani). Physiology affects body chemistry, so we also tested for an effect of egg-laying competition, as a proxy for reproductive status, on female chemical similarity. Finally, the fermentation hypothesis for chemical recognition posits that host-associated microbes affect host odor, so we tested for covariation between chemicals and microbiota. Group members were more chemically similar across both body regions. We found no chemical differences between sexes, but females in groups with less egg-laying competition had more similar preen oil, suggesting that preen oil contains information about reproductive status. There was no overall covariation between chemicals and microbes; instead, subsets of microbes could mediate olfactory cues in birds. Preen oil and feather chemicals showed little overlap and may contain different information. This is the first demonstration of group chemical signatures in birds, a finding of particular interest given that smooth-billed anis live in nonkin breeding groups. Behavioral experiments are needed to test whether anis can distinguish group members from nongroup members using odor cues.

Characterization of the microbiome and volatile compounds in anal gland secretions from domestic cats (Felis catus) using metagenomics and metabolomics

Many mammals rely on volatile organic chemical compounds (VOCs) produced by bacteria for their communication and behavior, though little is known about the exact molecular mechanisms or bacterial species that are responsible. We used metagenomic sequencing, mass-spectrometry based metabolomics, and culturing to profile the microbial and volatile chemical constituents of anal gland secretions in twenty-three domestic cats (Felis catus), in attempts to identify organisms potentially involved in host odor production. We found that the anal gland microbiome was dominated by bacteria in the genera Corynebacterium, Bacteroides, Proteus, Lactobacillus, and Streptococcus, and showed striking variation among individual cats. Microbiome profiles also varied with host age and obesity. Metabolites such as fatty-acids, ketones, aldehydes and alcohols were detected in glandular secretions. Overall, microbiome and metabolome profiles were modestly correlated (r = 0.17), indicating that a relationship exists between the bacteria in the gland and the metabolites produced in the gland. Functional analyses revealed the presence of genes predicted to code for enzymes involved in VOC metabolism such as dehydrogenases, reductases, and decarboxylases. From metagenomic data, we generated 85 high-quality metagenome assembled genomes (MAGs). Of importance were four MAGs classified as Corynebacterium frankenforstense, Proteus mirabilis, Lactobacillus johnsonii, and Bacteroides fragilis. They represent strong candidates for further investigation of the mechanisms of volatile synthesis and scent production in the mammalian anal gland.

Characterization of the microbiome and volatile compounds in anal gland secretions from domestic cats (Felis catus) using metagenomics and metabolomics

Animals rely on volatile chemical compounds for their communication and behavior. Many of these compounds are sequestered in endocrine and exocrine glands and are synthesized by anaerobic microbes. While the volatile organic compound (VOC) or microbiome composition of glandular secretions has been investigated in several mammalian species, few have linked specific bacterial taxa to the production of volatiles or to specific microbial gene pathways. Here, we use metagenomic sequencing, mass-spectrometry based metabolomics, and culturing to profile the microbial and volatile chemical constituents of anal gland secretions in twenty-three domestic cats (Felis catus), in attempts to identify organisms potentially involved in host odor production. We found that the anal gland microbiome was dominated by bacteria in the genera Corynebacterium, Bacteroides, Proteus, Lactobacillus, and Streptococcus, and showed striking variation among individual cats. Microbiome profiles also varied with host age and obesity. Metabolites such as fatty-acids, ketones, aldehydes and alcohols were detected in glandular secretions. Overall, microbiome and metabolome profiles were modestly correlated (r=0.17), indicating that a relationship exists between the bacteria in the gland and the metabolites produced in the gland. Functional analyses revealed the presence of genes predicted to code for enzymes involved in VOC metabolism such as dehydrogenases, reductases, and decarboxylases. From metagenomic data, we generated 85 high-quality metagenome assembled genomes (MAGs). Of these, four were inferred to have high relative abundance in metagenome profiles and had close relatives that were recovered as cultured isolates. These four MAGs were classified as Corynebacterium frankenforstense, Proteus mirabilis, Lactobacillus johnsonii, and Bacteroides fragilis. They represent strong candidates for further investigation of the mechanisms of volatile synthesis and scent production in the mammalian anal gland.

A tale of two hierarchies: Hormonal and behavioral factors underlying sex differences in social dominance in cooperative breeding callitrichids

Callitrichid primates are recognized for high levels of sociality in small groups, their great behavioral flexibility, and single-female dominant hierarchies. Previous work has highlighted that dominant, breeding callitrichids engage in behavioral and hormonal reproductive suppression of related and unrelated subordinates by both producing more offspring, having higher levels of ovulatory hormones, and accessing more sociosexual opportunities. This suppression constitutes a nexus of changes in pituitary responsiveness, ovarian cyclicity, sexual behavior, affiliation, and aggression. In this review, I will highlight important features that characterize callitrichid social hierarchies across broad social contexts. Dominant females sometimes exert reproductive suppression on subordinate nonbreeding females, but this suppression varies across callitrichids based on social stability and changes in group composition, particularly related to the number, experience, and age of nonbreeding subordinates. Meanwhile, dominant males may induce suppression of reproduction in subordinate males, but these effects occur by different behavioral and endocrine mechanisms and to a much lesser extent than their female counterparts; While dominant female callitrichids usually show higher levels of aggression relative to their male counterparts, callitrichids show a general absence of intersexual dominance, likely as an effort of maintaining a cohesive breeding pair within a stable social group and social cooperation. Future efforts are needed to identify precise neuroendocrine mechanisms underlying the presence of sex differences in callitrichid behavior separate from peripheral reproductive function. This is especially important with regard to parental experience, social relationships, development and aging, with larger implications toward understanding sex differences in overall health and wellbeing.

Potential trade-off between olfactory and visual discrimination learning in common marmosets (Callithrix jacchus): Implications for the assessment of age-related cognitive decline

Olfactory dysfunction has been identified as an early biomarker for dementia risk but has rarely been assessed in nonhuman primate models of human aging. To better characterize common marmosets as such models, we assessed olfactory discrimination performance in a sample of 10 animals (5 females), aged 2.5-8.9 years old. The monkeys were proficient in the discrimination and reversal of visual stimuli but naïve to odor stimuli. For olfactory discrimination, the monkeys performed a series of six discriminations of increasing difficulty between two odor stimuli. We found no evidence for an age-related decline as both young and older individuals were able to perform the discriminations in roughly the same number of trials. In addition, the older monkeys had faster responses than the younger animals. However, we noted that when adjusted for age, the speed of acquisition of the first discrimination in the olfactory modality was inversely correlated to the speed of acquisition of their first discrimination of two visual stimuli months earlier. These results suggest that marmosets may compensate for sensory deficits in one modality with higher sensory performance in another. These data have broad implications for the assessment of age-related cognitive decline and the categorization of animals as impaired or nonimpaired.

Anogenital scent-marking signals fertility in a captive female Alaotran gentle lemur

The Lake Alaotra gentle lemur (Hapalemur alaotrensis) is one of the 25 most endangered primates in the world and shows low success rate in captive breeding programmes. It is therefore vital to further understand its reproductive biology. We studied a captive troop consisting of five individuals hosted at Jersey Zoo during breeding and non-breeding periods over 1 year. We collected behavioural data (n = 318 h) using all occurrence of some behaviours and ad libitum sampling methods, as well as faecal (n = 54) and anogenital scent (n = 35) samples of the breeding female. We measured sex hormone levels using enzyme immunoassay technique and investigated the volatile component of odour signals using solid-phase microextraction and gas chromatography-mass spectrometry. We observed sexual and aggressive behaviours occasionally during the breeding period. Our regression analysis showed that only period significantly predicted rates of female anogenital scent-marking, whereby the female performed anogenital scent-marking more frequently during the breeding rather than the non-breeding period. In contrast, female hormone levels did not significantly explain variation in rates of neither male nor female olfactory, sexual and affiliative behaviours, suggesting that individuals' behaviour alone is not an effective indicator of the ovulation window. The volatile chemical profile of anogenital odour secretions changed over the study, with four compounds distinguishing the fertile window during the breeding period. In conclusion, our findings suggest that anogenital scent-marking may signal the reproductive status of captive female gentle lemurs.

Olfactory Inspection of Female Reproductive States in Chimpanzees

In mammalian species, olfactory cues are important for within and between species communication. These cues can be part of multimodal signals indicating, for example, female fertility potentially perceived by male conspecifics. However, a large gap exists in our understanding of multimodal signaling in non-human catarrhines. Chimpanzees (Pan troglodytes) live in fission-fusion societies, mate promiscuously and express high levels of male-male competition. Females show a striking visual signal, an exaggerated sexual swelling, known to be a proxy of ovulation, while the maximum swelling is not matching the exact time of ovulation. The question remains if males use additional olfactory cues when being able to approach females closely. This would allow males to pinpoint the exact timing of ovulation and could be one reason why high-ranking males sire offspring more successfully than other males. Here, we present the first systematic test of such multimodal signaling by investigating male sniffing behavior directed to females in relation to their fertility in a group of 13 captive chimpanzees. Our results show that male sniffing behavior significantly increased with female swelling size, with female age as well as when fewer male competitors were present. Hence, odors might be part of a multimodal fertility cue, supporting the idea that males monitor both visual and olfactory cues to gain comprehensive information on female fertility.

Towards an understanding of multimodal traits of female reproduction in chimpanzees

Although primates have long been regarded as microsmatic, recent studies indicate that olfaction is an important sensory mode of primate communication, e.g., in the context of reproduction. However, large gaps remain in our understanding of primate olfactory traits, especially in the great apes. Female chimpanzees (Pan troglodytes) possess an exaggerated sexual swelling, which is an imprecise signal of fertility that is thought to serve to confuse paternity. However, some high-ranking males that copulate most frequently on the days when females are most fertile seem to have more precise information on the timing of ovulation, which suggests the existence of an olfactory fertility trait. In order to examine, and provide evidence for, fertility-related chemical information in female chimpanzees, we used gas chromatography-mass spectrometry to analyze the chemical composition of female body odor collected across the menstrual cycle during various stages of sexual swelling (97 samples of six females). The chemical composition was significantly affected by swelling stage, and eight substances were detected that were strongly related to the latter. The existence of an additional, olfactory, fertility trait may help males to fine-tune their sexual behavior or allow females to strengthen concealment of the exact timing of ovulation, and needs to be further investigated in follow-up studies. The results of our study provide much-needed evidence for the existence of an olfactory cue related to reproduction in chimpanzees, and form a basis for future studies on the interplay between visual and olfactory information on female fertility.

Chemical cues of identity and reproductive status in Japanese macaques

Olfactory communication plays an important role in the regulation of socio-sexual interactions in mammals. There is growing evidence that both human and nonhuman primates rely on odors to inform their mating decisions. Nevertheless, studies of primate chemical ecology remain scarce due to the difficulty of obtaining and analyzing samples. We analyzed 67 urine samples from five captive female Japanese macaques (Macaca fuscata) and 30 vaginal swabs from three of these females using gas chromatography-mass spectrometry and examined the relationship between odor (compounds identified, richness, intensity, and diversity) and female identity as well as cycle phase. We found a total of 36 urine compounds of which we identified 31, and 68 vaginal compounds of which we identified 37. Our results suggest that urine and vaginal odor varied more between individuals than within cycle phases. However, we found that within a female cycle, urine samples from similar phases may cluster more than samples from different phases. Our results suggest that female odor may encode information about identity (vaginal and urine odor) and reproductive status (urine odor). The question of how conspecifics use female urine and vaginal odor remains open and could be tested using bioassays. Our results and their interpretation are constrained by our limited sample size and our study design. Nonetheless, our study provides insight into the potential signaling role of female odor in sexual communication in Japanese macaques and contributes to our understanding of how odors may influence mating strategies in primates.

Sexual Dimorphism in Crowned Lemur Scent-Marking

Simple Summary

Primates are typically thought to use hearing and vision more than the sense of smell. However, lemurs show a complex olfactory repertoire which includes conspicuous scent-marking behaviours (i.e., a form of olfactory communication displayed by animals that deposit their odour in specific places to transmit a message to other animals). We studied two pairs of crowned lemurs at Colchester and Twycross zoos (UK) by combining behavioural observations and chemical analyses of odour secretions released via scent-marking. Male lemurs scent-marked most frequently, showing three types of behaviours: ano-genital marking for applying their scent onto females; head marking for placing their secretions on or near the mark left by another individual; and wrist marking to deposit their mark in specific meaningful areas of the enclosure. Female lemurs displayed only ano-genital marking, primarily on feeding devices. We detected a total of 38 volatile compounds in male ano-genital scent-marks and 26 in female ano-genital odour secretions, including many compounds that have been identified in odour profiles of other primates. In conclusion, we found sexual dimorphism in crowned lemur scent-marking. In males, head and wrist marking behaviours would play defensive territorial functions, while ano-genital marking may be related to socio-sexual communication; female ano-genital marking could be involved in resource defense. This study contributes to improving our understanding of lemur communication.

Abstract

Primates are traditionally considered to have a poor sense of smell. However, olfaction is important for non-human primates as demonstrated by conspicuous scent-marking behaviours in lemurs. We studied two pairs (n = 4) of crowned lemurs (Eulemur coronatus) housed at Colchester and Twycross zoos (UK) by combining behavioural observations and chemical analyses of scent-marks and glandular swabs. We recorded observations of olfactory behaviours for 201 h using instantaneous scan sampling. We investigated the volatile compounds of ano-genital odour secretions (n = 16) using solid-phase microextraction and gas chromatography-mass spectrometry. Males scent-marked most frequently, displaying ano-genital marking for allomarking, head marking for countermarking and wrist marking in specific areas of the enclosure. Females displayed ano-genital marking, predominantly on feeding devices. We detected a total of 38 volatile components in all male ano-genital scent-marks and 26 in all female samples of ano-genital odour secretions, including a series of esters, aldehydes, ketones, alcohols, terpenes, volatile fatty acids and hydrocarbons that have been identified in odour profiles of other primates. In conclusion, we found sexual dimorphism in crowned lemur scent-marking. Male head and wrist marking behaviours might play defensive territorial functions, while ano-genital marking would be related to socio-sexual communication as chemical mate-guarding. Female ano-genital marking might be involved in resource defense.

Olfactory signals and fertility in olive baboons

Female primates signal impending ovulation with a suite of sexual signals. Studies of these signals have focussed on visual, and to a lesser extent, acoustic signals, neglecting olfactory signals. We aimed to investigate the information content of female olfactory signals in captive olive baboons (Papio anubis) and relate these to the female fertile period. We studied eight adult females living in four groups at the CNRS Station de Primatologie, Rousset-sur-Arc, France. We used vaginal cytology to detect ovulation. We investigated the volatile component of odour signals using solid-phase microextraction and gas chromatography-mass spectrometry. We found a total of 74 volatile compounds, of which we tentatively identified 25, including several ketones, alcohols, aldehydes, terpenes, volatile fatty acids and hydrocarbons that have been identified in odour profiles of other primates. Our results show that vaginal odour intensity differs with sexual cycle stage suggesting that odour might play a role in signalling female baboon fertility. We found differences in vaginal odour between females living in all-female and in mixed sex groups but we could not distinguish the effects of group composition, female age and identity. This study of olfactory signalling improves our understanding of how female primates advertise their sexual receptivity.

Scent Marks Signal Species, Sex, and Reproductive Status in Tamarins (Saguinus spp., Neotropical Primates)

Olfactory communication is an important mediator of social interactions in mammals, thought to provide information about an individual’s identity and current social, reproductive, and health status. In comparison with other taxa such as carnivores and rodents, few studies have examined primate olfactory communication. Tamarins (Callitrichidae) conspicuously deposit odorous secretions, produced by specialized scent glands, in their environment. In this study, we combined behavioral and chemical data on captive cotton-top tamarins, Saguinus oedipus, and bearded emperor tamarins, S. imperator subgrisescens, to examine the role of olfactory communication in the advertisement of species, sex, and reproductive status. We observed no difference in scent-marking behavior between species; however, females marked more frequently than males, and reproductive individuals more than non-reproductive ones. In addition, tamarins predominantly used their anogenital gland when scent-marking, followed by the suprapubic gland. We collected swabs of naturally deposited tamarin anogenital scent marks, and analyzed these samples using headspace gas chromatography-mass spectrometry. Despite a limited sample size, we established differences in tamarin anogenital mark chemical composition between species, sex and reproductive status, and identified 41 compounds. The compounds identified, many of which have been reported in previous work on mammalian semiochemistry, form targets for future bioassay studies to identify semiochemicals. Our non-invasive method for collecting deposited scent marks makes it a promising method for the study of olfactory communication in scent-marking animal species, applicable to field settings and for the study of elusive animals.

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.