Volatile Signals During Pregnancy: A Possible Chemical Basis for Mother–Infant Recognition

Smell throughout the life course

The sense of smell is an important mediator of health and sociality at all stages of life, yet it has received limited attention in our lineage. Olfaction starts in utero and participates in the establishment of social bonds in children, and of romantic and sexual relationships after puberty. Smell further plays a key role in food assessment and danger avoidance; in modern societies, it also guides our consumer behavior. Sensory abilities typically decrease with age and can be impacted by diseases, with repercussions on health and well-being. Here, we critically review our current understanding of human olfactory communication to refute outdated notions that our sense of smell is of low importance. We provide a summary of the biology of olfaction, give a prospective overview of the importance of the sense of smell throughout the life course, and conclude with an outline of the limitations and future directions in this field.

À la carte: how mosquitoes choose their blood meals

Mosquitoes are important vectors for human diseases, transmitting pathogens that cause a range of parasitic and viral infections. Mosquito blood-feeding is heterogeneous, meaning that some human hosts are at higher risk of receiving bites than others, and this heterogeneity is multifactorial. Mosquitoes integrate specific cues to locate their hosts, and mosquito attraction differs considerably between individual human hosts. Heterogeneous mosquito biting results from variations in both host attractiveness and availability and can impact transmission of vector-borne diseases. However, the extent and drivers of this heterogeneity and its importance for pathogen transmission remain incompletely understood. Here, we review methods and recent data describing human characteristics that affect host-seeking behavior and host preferences of mosquito disease vectors, and the implications for vector-borne disease transmission.

Intrinsic and extrinsic factors affecting axillary odor variation. A comprehensive review

Humans produce odorous secretions from multiple body sites according to the microbiomic profile of each area and the types of secretory glands present. Because the axilla is an active, odor-producing region that mediates social communication via the sense of smell, this article focuses on the biological mechanisms underlying the creation of axillary odor, as well as the intrinsic and extrinsic factors likely to impact the odor and determine individual differences. The list of intrinsic factors discussed includes sex, age, ethnicity, emotions, and personality, and extrinsic factors include dietary choices, diseases, climate, and hygienic habits. In addition, we also draw attention to gaps in our understanding of each factor, including, for example, topical areas such as the effect of climate on body odor variation. Fundamental challenges and emerging research opportunities are further outlined in the discussion. Finally, we suggest guidelines and best practices based on the factors reviewed herein for preparatory protocols of sweat collection, data analysis, and interpretation.

Investigating the Use of SARS-CoV-2 (COVID-19) Odor Expression as a Non-Invasive Diagnostic Tool-Pilot Study

Since the beginning of the COVID-19 pandemic, there has been enormous interest in the development of measures that would allow for the swift detection of the disease. The rapid screening and preliminary diagnosis of SARS-CoV-2 infection allow for the instant identification of possibly infected individuals and the subsequent mitigation of the disease spread. Herein, the detection of SARS-CoV-2-infected individuals was explored using noninvasive sampling and low-preparatory-work analytical instrumentation. Hand odor samples were obtained from SARS-CoV-2-positive and -negative individuals. The volatile organic compounds (VOCs) were extracted from the collected hand odor samples using solid phase microextraction (SPME) and analyzed using gas chromatography coupled with mass spectrometry (GC-MS). Sparse partial least squares discriminant analysis (sPLS-DA) was used to develop predictive models using the suspected variant sample subsets. The developed sPLS-DA models performed moderately (75.8% (±0.4) accuracy, 81.8% sensitivity, 69.7% specificity) at distinguishing between SARS-CoV-2-positive and negative -individuals based on the VOC signatures alone. Potential markers for distinguishing between infection statuses were preliminarily acquired using this multivariate data analysis. This work highlights the potential of using odor signatures as a diagnostic tool and sets the groundwork for the optimization of other rapid screening sensors such as e-noses or detection canines.

Exploring the interrelationship between the skin microbiome and skin volatiles: A pilot study

Unravelling the interplay between a human’s microbiome and physiology is a relevant task for understanding the principles underlying human health and disease. With regard to human chemical communication, it is of interest to elucidate the role of the microbiome in shaping or generating volatiles emitted from the human body. In this study, we characterized the microbiome and volatile organic compounds (VOCs) sampled from the neck and axilla of ten participants (five male, five female) on two sampling days, by applying different methodological approaches. Volatiles emitted from the respective skin site were collected for 20 min using textile sampling material and analyzed on two analytical columns with varying polarity of the stationary phase. Microbiome samples were analyzed by a culture approach coupled with MALDI-TOF-MS analysis and a 16S ribosomal RNA gene (16S RNA) sequencing approach. Statistical and advanced data analysis methods revealed that classification of body sites was possible by using VOC and microbiome data sets. Higher classification accuracy was achieved by combination of both data pools. Cutibacterium, Staphylococcus, Micrococcus, Streptococcus, Lawsonella, Anaerococcus, and Corynebacterium species were found to contribute to classification of the body sites by the microbiome. Alkanes, esters, ethers, ketones, aldehydes and cyclic structures were used by the classifier when VOC data were considered. The interdisciplinary methodological platform developed here will enable further investigations of skin microbiome and skin VOCs alterations in physiological and pathological conditions.

Volatilomics as an Emerging Strategy to Determine Potential Biomarkers of Female Infertility: A Pilot Study

Due to its high prevalence, infertility has become a prominent public health issue, posing a significant challenge to modern reproductive medicine. Some clinical conditions that lead to female infertility include polycystic ovary syndrome (PCOS), endometriosis, and premature ovarian failure (POF). Follicular fluid (FF) is the biological matrix that has the most contact with the oocyte and can, therefore, be used as a predictor of its quality. Volatilomics has emerged as a non-invasive, straightforward, affordable, and simple method for characterizing various diseases and determining the effectiveness of their current therapies. In order to find potential biomarkers of infertility, this study set out to determine the volatomic pattern of the follicular fluid from patients with PCOS, endometriosis, and POF. The chromatographic data integration was performed through solid-phase microextraction (SPME), followed by gas chromatography–mass spectrometry (GC-MS). The findings pointed to specific metabolite patterns as potential biomarkers for the studied diseases. These open the door for further research into the relevant metabolomic pathways to enhance infertility knowledge and diagnostic tools. An extended investigation may, however, produce a new mechanistic understanding of the pathophysiology of the diseases.

A literature survey of all volatiles from healthy human breath and bodily fluids: the human volatilome

This paper comprises an updated version of the 2014 review which reported 1846 volatile organic compounds (VOCs) identified from healthy humans. In total over 900 additional VOCs have been reported since the 2014 review and the VOCs from semen have been added. The numbers of VOCs found in breath and the other bodily fluids are: blood 379, breath 1488, faeces 443, milk 290, saliva 549, semen 196, skin 623 and urine 444. Compounds were assigned CAS registry numbers and named according to a common convention where possible. The compounds have been included in a single table with the source reference(s) for each VOC, an update on our 2014 paper. VOCs have also been grouped into tables according to their chemical class or functionality to permit easy comparison. Careful use of the database is needed, as a number of the identified VOCs only have level 2-putative assignment, and only a small fraction of the reported VOCs have been validated by standards. Some clear differences are observed, for instance, a lack of esters in urine with a high number in faeces and breath. However, the lack of compounds from matrices such a semen and milk compared to breath for example could be due to the techniques used or reflect the intensity of effort e.g. there are few publications on VOCs from milk and semen compared to a large number for breath. The large number of volatiles reported from skin is partly due to the methodologies used, e.g. by collecting skin sebum (with dissolved VOCs and semi VOCs) onto glass beads or cotton pads and then heating to a high temperature to desorb VOCs. All compounds have been included as reported (unless there was a clear discrepancy between name and chemical structure), but there may be some mistaken assignations arising from the original publications, particularly for isomers. It is the authors' intention that this work will not only be a useful database of VOCs listed in the literature but will stimulate further study of VOCs from healthy individuals; for example more work is required to confirm the identification of these VOCs adhering to the principles outlined in the metabolomics standards initiative. Establishing a list of volatiles emanating from healthy individuals and increased understanding of VOC metabolic pathways is an important step for differentiating between diseases using VOCs.

Male brain processing of the body odor of ovulating women compared to that of pregnant women

Female chemical signals underlie the advertising of sexual receptivity and fertility. Whether the body odor of a pregnant woman also has a signaling function with respect to male behavior is yet to be conclusively established. This study examines how the body odors of ovulating and pregnant women differentially affect the behavior of heterosexual men. Body odor samples were collected from 5 pregnant women and 5 matched controls during ovulation. In a double-blind functional magnetic resonance imaging design, 18 heterosexual men were exposed to female body odors during ovulation (OV) and pregnancy (PRG) while being required to indicate the attractiveness of concurrently presented female portrait images. The participants were also required to indicate whether they assumed a depicted woman was pregnant. While neither OV nor PRG altered the perceived attractiveness of a presented face, the men tended to identify the women as pregnant while exposed to a PRG body odor. On the neural level, OV activated a network of the frontotemporal and limbic regions, while PRG activated the superior medial frontal gyrus. The results suggest that the detection of sexual availability activates the male brain regions associated with face processing and reward/motivation, whereas sensing pregnancy activates a region responsible for empathy and prosocial behavior. Thus, the female body odor during pregnancy likely helps foster circumstances conducive to the future care of offspring while the body odor advertising sexual availability promotes mating behavior. The brains of heterosexual men may be capable of unconsciously discriminating between these two types of olfactory stimuli.

What smells? Developing in-field methods to characterize the chemical composition of wild mammalian scent cues

Olfactory cues play an important role in mammalian biology, but have been challenging to assess in the field. Current methods pose problematic issues with sample storage and transportation, limiting our ability to connect chemical variation in scents with relevant ecological and behavioral contexts. Real-time, in-field analysis via portable gas chromatography-mass spectrometry (GC-MS) has the potential to overcome these issues, but with trade-offs of reduced sensitivity and compound mass range. We field-tested the ability of portable GC-MS to support two representative applications of chemical ecology research with a wild arboreal primate, common marmoset monkeys (Callithrix jacchus). We developed methods to (a) evaluate the chemical composition of marmoset scent marks deposited at feeding sites and (b) characterize the scent profiles of exudates eaten by marmosets. We successfully collected marmoset scent marks across several canopy heights, with the portable GC-MS detecting known components of marmoset glandular secretions and differentiating these from in-field controls. Likewise, variation in the chemical profile of scent marks demonstrated a significant correlation with marmoset feeding behavior, indicating these scents' biological relevance. The portable GC-MS also delineated species-specific olfactory signatures of exudates fed on by marmosets. Despite the trade-offs, portable GC-MS represents a viable option for characterizing olfactory compounds used by wild mammals, yielding biologically relevant data. While the decision to adopt portable GC-MS will likely depend on site- and project-specific needs, our ability to conduct two example applications under relatively challenging field conditions bodes well for the versatility of in-field GC-MS.

Design, delivery and perception of condition-dependent chemical signals in strepsirrhine primates: implications for human olfactory communication

The study of human chemical communication benefits from comparative perspectives that relate humans, conceptually and empirically, to other primates. All major primate groups rely on intraspecific chemosignals, but strepsirrhines present the greatest diversity and specialization, providing a rich framework for examining design, delivery and perception. Strepsirrhines actively scent mark, possess a functional vomeronasal organ, investigate scents via olfactory and gustatory means, and are exquisitely sensitive to chemically encoded messages. Variation in delivery, scent mixing and multimodality alters signal detection, longevity and intended audience. Based on an integrative, 19-species review, the main scent source used (excretory versus glandular) differentiates nocturnal from diurnal or cathemeral species, reflecting differing socioecological demands and evolutionary trajectories. Condition-dependent signals reflect immutable (species, sex, identity, genetic diversity, immunity and kinship) and transient (health, social status, reproductive state and breeding history) traits, consistent with socio-reproductive functions. Sex reversals in glandular elaboration, marking rates or chemical richness in female-dominant species implicate sexual selection of olfactory ornaments in both sexes. Whereas some compounds may be endogenously produced and modified (e.g. via hormones), microbial analyses of different odorants support the fermentation hypothesis of bacterial contribution. The intimate contexts of information transfer and varied functions provide important parallels applicable to olfactory communication in humans. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Sampling, identification and sensory evaluation of odors of a newborn baby's head and amniotic fluid

For baby odor analyses, noninvasive, stress-free sample collection is important. Using a simple method, we succeeded in obtaining fresh odors from the head of five newborn babies. These odors were chemically analyzed by two-dimensional gas chromatography coupled with mass spectrometry (GC × GC-MS), and compared with each other or with the odor of amniotic fluid from the baby's mother. We identified 31 chemical components of the volatile odors from neonate heads and 21 from amniotic fluid. Although 15 of these components were common to both sources, there was an apparent difference in the GC × GC patterns between the head and amniotic fluid odors, so the neonate head odor might be individually distinct immediately after birth. Therefore, we made artificial mixtures of the major odor components of the neonate head and maternal amniotic fluid, and used psychological tests to examine whether or not these odors could be distinguished from each other. Our data show that the artificial odor of a neonate head could be distinguished from that of amniotic fluid, and that the odors of artificial head odor mixtures could be correctly discriminated for neonates within an hour after birth and at 2 or 3 days of age.

Preparation for fatherhood: A role for olfactory communication during human pregnancy?

There is evidence across a range of bi-parental species that physiological changes may occur in partnered males prior to the birth of an infant. It has been hypothesised that these hormonal changes might facilitate care-giving behaviours, which could augment infant survival. The mechanism that induces these changes has not been identified, but evidence from several species suggests that odour may play a role. The current study investigated this in humans by recording testosterone and psychological measures related to infant interest and care in men (n = 91) both before and after exposure to odours from either pregnant women or non-pregnant control women. We found no evidence for an effect of odour cues of pregnancy on psychological measures including self-reported sociosexual orientation and social dominance scores, ratings of infant or adult faces, or testosterone levels. However, we found that brief exposure to post-partum odours significantly increased the reward value of infant faces. Our study is the first to show that the odour of peri-partum women may lead to upregulation of men's interest in infants.

Implementing solid phase microextraction (SPME) as a tool to detect volatile compounds produced by giant pandas in the environment

Chemical cues are thought to play an important role in mate identification in the solitary giant panda (Ailuropoda melanoleuca). The goal of this study was to detect and identify volatile compounds present in the enclosure air of captive giant pandas. We hypothesized that a subset of compounds produced from breeding animals would be detected in environmental samples because highly volatile chemicals are likely to facilitate mate detection. Samples were collected from the enclosures of 8 giant pandas (n = 4 male, n = 4 female) during the Mar-June breeding season and the Aug-Jan non-breeding period from 2012-2015. Volatile compounds were captured by securing a solid phase micro extraction fiber approximately 3 meters above the ground within a panda enclosure for 6-12 hours. Compounds adsorbed onto the SPME fibers were analyzed by gas chromatography mass spectrometry. Thirty-three compounds were detected in at least 10% of all samples within individual and season and across all subjects within each season. Aromatic compounds made up 27.3% of the enclosure volatile profile, while 21.2% was made of cyclic aliphatic compounds and 51.5% of the enclosure profile was comprised of acyclic aliphatic compounds. Three compounds were likely to be present in male enclosures regardless of season, while Undecane, 4-methyl had a significant (p<0.05) predicted probability of being present in female enclosures. 3,3'-(1,1-Ethanediyl)bis(1H-indole) had a significant (p<0.05) probability of occurrence in male enclosures during the breeding season. Given the prevalence of these compounds, we suspect that these chemicals are important in giant panda communication. This novel sampling technique can detect volatile compounds produced by captive species and also may be a useful tool for detecting pheromones in free-ranging individuals.

Maternal areola pH: A chemical basis for mother-infant recognition

BACKGROUND

The human female's areolar region is the point of arrival of a natural progression from birth to breastfeeding continuum, supported by numerous functional features.

AIMS

The aim of this study was to look more closely into the areola' skin chemical signals that are uniquely important for mother-infant chemoemission, chemoreception, and breastfeeding continuum.

STUDY DESIGN

A dermatological study of the areolae and corresponding breast quadrants was undertaken on 71 healthy, at-term women. Areolar and corresponding breast quadrant pH were assessed pre-partum and 1 and 2 days post-partum using a corneometer (Soft Plus 5.5; Callegari S.P.A., Parma, Italy).

RESULTS

Pre-partum, the pH of the areola was significantly higher than the pH of the breast quadrant (4.25 ± 0.26 vs. 4.06 ± 0.44, p < 0.015). Post-partum, the pH of the areola was significantly higher that the pH of the breast quadrant both on day one (4.28 ± 0.31 vs 4.01 ± 0.25, p < 0.001) and on day two (4.39 ± 0.19 vs 4.01 ± 0.16, p < 0.001), respectively. In addition, pre-labor pH of the areola increased on day one post-partum and significantly on day two postpartum (4.25 ± 0.26 vs 4.39 ± 0.19, p 0.004). Moreover, the pH of the areola increased significantly from day one to day two post-partum (4.28 ± 0.31 v s 4.39 ± 0.19, p < 0.041).

CONCLUSIONS

Our findings show, for the first time, that the areola has a higher pH than the surrounding breast skin, and this increases from day one to day two postpartum. We believe that the pH changes of the areolar region may act as a unique chemical signal to guide the infant directly to the nipple.

Pregnancy is detected via odour in a wild cooperative breeder

Among mammals, scent has long been known to encode oestrus; however, in many species, detecting pregnancy may also be important in terms of both competition and mate-choice. Here, we show, through odour presentation experiments, that pregnancy is discernible via scent by both sexes in the cooperatively breeding banded mongoose, Mungos mungo Males spent more time investigating and were more likely to scent mark the odours of non-pregnant females, compared to pregnant females. Females showed increased levels of scent marking when odours were of the same reproductive state as themselves. These results present the first direct demonstration that pregnancy is detectable via scent in wild cooperative breeders. Detecting pregnancy may be particularly important in cooperative breeders as, in addition to the competition between males for receptive mates, there is also intense competition between females for access to alloparental care. Consequently, dominant females benefit from targeting reproductive suppression towards subordinates that represent direct threats, such as pregnant females.

Understanding the Inguinal Sinus in Sheep (Ovis aries)-Morphology, Secretion, and Expression of Progesterone, Estrogens, and Prolactin Receptors

Post-parturient behavior of mammalian females is essential for early parent–offspring contact. After delivery, lambs need to ingest colostrum for obtaining the related immunological protection, and early interactions between the mother and the lamb are crucial. Despite visual and auditory cues, olfactory cues are decisive in lamb orientation to the mammary gland. In sheep, the inguinal sinus is located bilaterally near the mammary gland as a skin pouch (IGS) that presents a gland that secretes a strong-smelling wax. Sheep IGS gland functions have many aspects under evaluation. The objective of the present study was to evaluate sheep IGS gland functional aspects and mRNA transcription and the protein expression of several hormone receptors, such as progesterone receptor (PGR), estrogen receptor 1 (ESR1), and 2 (ESR2) and prolactin receptor (PRLR) present. In addition, another aim was to achieve information about IGS ultrastructure and chemical compounds produced in this gland. All hormone receptors evaluated show expression in IGS during the estrous cycle (follicular/luteal phases), pregnancy, and the post-partum period. IGS secretion is rich in triterpenoids that totally differ from the surrounding skin. They might be essential substances for the development of an olfactory preference of newborns to their mothers.

Analysis of Odorants in Marking Fluid of Siberian Tiger (Panthera tigris altaica) Using Simultaneous Sensory and Chemical Analysis with Headspace Solid-Phase Microextraction and Multidimensional Gas Chromatography-Mass Spectrometry-Olfactometry

Scent-marking is the most effective method of communication in the presence or absence of a signaler. These complex mixtures result in a multifaceted interaction triggered by the sense of smell. The objective was to identify volatile organic compound (VOC) composition and odors emitted by total marking fluid (MF) associated with Siberian tigers (Panthera tigris altaica). Siberian tiger, an endangered species, was chosen because its MF had never been analyzed. Solid phase microextraction (SPME) for headspace volatile collection combined with multidimensional gas chromatography-mass spectrometry-olfactometry for simultaneous chemical and sensory analyses were used. Thirty-two VOCs emitted from MF were identified. 2-acetyl-1-pyrroline, the sole previously identified compound responsible for the "characteristic" odor of P. tigris MF, was identified along with two additional compounds confirmed with standards (urea, furfural) and four tentatively identified compounds (3-methylbutanamine, (R)-3-methylcyclopentanone, propanedioic acid, and 3-hydroxybutanal) as being responsible for the characteristic aroma of Siberian tiger MF. Simultaneous chemical and sensory analyses improved characterization of scent-markings and identified compounds not previously reported in MF of other tiger species. This research will assist animal ecologists, behaviorists, and zookeepers in understanding how scents from specific MF compounds impact tiger and wildlife communication and improve management practices related to animal behavior. Simultaneous chemical and sensory analyses is applicable to unlocking scent-marking information for other species.

Sternal Gland Scent-Marking Signals Sex, Age, Rank, and Group Identity in Captive Mandrills

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.

Two-day-old newborn infants recognise their mother by her axillary odour

AIM

The aim of this study was to verify the influence of mother to child skin-to-skin contact and the ability of 2-day-old infants to recognise their own mother's axillary odour.

METHODS

We tested the responses of 19 vaginally delivered, breastfeeding newborns to their mothers' axillary odours using a paired-choice test. The eight males and 11 females were exposed to their own mother's axillary odour and the odour of another unfamiliar new mother taking part in the study, and their responses to each woman were taped for 60 sec. We did this by assessing how long their heads were orientated towards pads carrying the scents of their mothers and the unfamiliar women.

RESULTS

The average time that the infants' heads were orientated towards the olfactory stimulus of their own mothers was 20.53 sec, which was significantly longer than the 11.13 sec recorded for the unfamiliar women (p < 0.05). In addition, this orientation increased significantly with the newborn infants' age in hours (Spearman's Rho = 0.58, p < 0.01) and their recognition time significantly decreased (Spearman's Rho = -0.52, p < 0.05).

CONCLUSION

Two-day-old breastfeeding newborn infants who experienced skin-to-skin contact with their mothers were able to recognise their axillary odour.

Baby on board: olfactory cues indicate pregnancy and fetal sex in a non-human primate

Olfactory cues play an integral, albeit underappreciated, role in mediating vertebrate social and reproductive behaviour. These cues fluctuate with the signaller's hormonal condition, coincident with and informative about relevant aspects of its reproductive state, such as pubertal onset, change in season and, in females, timing of ovulation. Although pregnancy dramatically alters a female's endocrine profiles, which can be further influenced by fetal sex, the relationship between gestation and olfactory cues is poorly understood. We therefore examined the effects of pregnancy and fetal sex on volatile genital secretions in the ring-tailed lemur (Lemur catta), a strepsirrhine primate possessing complex olfactory mechanisms of reproductive signalling. While pregnant, dams altered and dampened their expression of volatile chemicals, with compound richness being particularly reduced in dams bearing sons. These changes were comparable in magnitude with other, published chemical differences among lemurs that are salient to conspecifics. Such olfactory 'signatures' of pregnancy may help guide social interactions, potentially promoting mother-infant recognition, reducing intragroup conflict or counteracting behavioural mechanisms of paternity confusion; cues that also advertise fetal sex may additionally facilitate differential sex allocation.

D'scent of man: a comparative survey of primate chemosignaling in relation to sex

This article is part of a Special Issue (Chemosignals and Reproduction). As highly visual animals, primates, in general, and Old World species (including humans), in particular, are not immediately recognized for reliance in their daily interactions on olfactory communication. Nevertheless, views on primate olfactory acuity and the pervasiveness of their scent signaling are changing, with increased appreciation for the important role of body odors in primate social and sexual behavior. All major taxonomic groups, from lemurs to humans, are endowed with scent-producing organs, and either deposit or exude a wealth of volatile compounds, many of which are known semiochemicals. This review takes a comparative perspective to illustrate the reproductive context of primate signaling, the relevant information content of their signals, the sexually differentiated investigative responses generated, and the behavioral or physiological consequences of message transmission to both signaler and receiver. Throughout, humans are placed alongside their relatives to illustrate the evolutionary continuum in the sexual selection of primate chemosignals. This ever-growing body of evidence points to a critical role of scent in guiding the social behavior and reproductive function throughout the primate order.

Validation of bovine oestrous-specific synthetic molecules with trained scent dogs; similarities between natural and synthetic oestrous smell

Oestrous detection is crucial for successful dairy cow reproduction. Bulls identify cows in oestrus by oestrous-specific odours especially in urine and vaginal fluid. These have been used to train dogs to detect cows in heat. To improve and simplify the dog training, a spray containing synthetic oestrous molecules was developed. The objective of this study was to test the spray on similarities to the natural substance thus to assess its suitability as a training substance for heat detection dogs. Ten privately owned dogs of various breeds were trained. Dogs should be trained either to differentiate natural vaginal fluid from cows in oestrus and dioestrus (n = 5), or spray with or without synthetic oestrous molecules (n = 5). Dogs trained on natural fluid and on spray could detect the oestrous odour they had been trained on with an overall accuracy of 69.0% and 82.4%, respectively (p = 0.019). To validate the synthetic molecules, dogs trained with synthetic molecules had to detect oestrous odour in natural fluid without further training (accuracy 37.6%). Dogs trained on natural fluid detected the synthetic molecules with an accuracy of 50.0% (50% vs 37.4%, p < 0.05). Dogs can recognize natural vaginal fluid from cows in oestrus after they have been trained with synthetic oestrous molecules, but accuracy needs to be improved.

Nature's chemical signatures in human olfaction: a foodborne perspective for future biotechnology

The biocatalytic production of flavor naturals that determine chemosensory percepts of foods and beverages is an ever challenging target for academic and industrial research. Advances in chemical trace analysis and post-genomic progress at the chemistry-biology interface revealed odor qualities of nature's chemosensory entities to be defined by odorant-induced olfactory receptor activity patterns. Beyond traditional views, this review and meta-analysis now shows characteristic ratios of only about 3 to 40 genuine key odorants for each food, from a group of about 230 out of circa 10 000 food volatiles. This suggests the foodborn stimulus space has co-evolved with, and roughly match our circa 400 olfactory receptors as best natural agonists. This perspective gives insight into nature's chemical signatures of smell, provides the chemical odor codes of more than 220 food samples, and beyond addresses industrial implications for producing recombinants that fully reconstruct the natural odor signatures for use in flavors and fragrances, fully immersive interactive virtual environments, or humanoid bioelectronic noses.

Analytical methods for chemical and sensory characterization of scent-markings in large wild mammals: a review

In conjoining the disciplines of "ethology" and "chemistry" the field of "Ethochemistry" has been instituted. Ethochemistry is an effective tool in conservation efforts of endangered species and the understanding of behavioral patterns across all species. Chemical constituents of scent-markings have an important, yet poorly understood function in territoriality, reproduction, dominance, and impact on evolutionary biology, especially in large mammals. Particular attention has recently been focused on scent-marking analysis of great cats (Kalahari leopards (Panthera pardus), puma (Puma concolor) snow leopard (Panthera uncia), African lions (Panthera leo), cheetahs (Acinonyx jubatus), and tigers (Panthera tigris)) for the purpose of conservation. Sensory analyses of scent-markings could address knowledge gaps in ethochemistry. The objective of this review is to summarize the current state-of-the art of both the chemical and sensory analyses of scent-markings in wild mammals. Specific focus is placed on sampling and sample preparation, chemical analysis, sensory analysis, and simultaneous chemical and sensory analyses. Constituents of exocrine and endocrine secretions have been most commonly studied with chromatography-based analytical separations. Odor analysis of scent-markings provides an insight into the animal's sensory perception. A limited number of articles have been published in the area of sensory characterization of scent marks. Simultaneous chemical and sensory analyses with chromatography-olfactometry hyphenation could potentially aid conservation efforts by linking perceived odor, compounds responsible for odor, and resulting behavior.

A review of the volatiles from the healthy human body

A compendium of all the volatile organic compounds (VOCs) emanating from the human body (the volatolome) is for the first time reported. 1840 VOCs have been assigned from breath (872), saliva (359), blood (154), milk (256), skin secretions (532) urine (279), and faeces (381) in apparently healthy individuals. Compounds were assigned CAS registry numbers and named according to a common convention where possible. The compounds have been grouped into tables according to their chemical class or functionality to permit easy comparison. Some clear differences are observed, for instance, a lack of esters in urine with a high number in faeces. Careful use of the database is needed. The numbers may not be a true reflection of the actual VOCs present from each bodily excretion. The lack of a compound could be due to the techniques used or reflect the intensity of effort e.g. there are few publications on VOCs from blood compared to a large number on VOCs in breath. The large number of volatiles reported from skin is partly due to the methodologies used, e.g. collecting excretions on glass beads and then heating to desorb VOCs. All compounds have been included as reported (unless there was a clear discrepancy between name and chemical structure), but there may be some mistaken assignations arising from the original publications, particularly for isomers. It is the authors' intention that this database will not only be a useful database of VOCs listed in the literature, but will stimulate further study of VOCs from healthy individuals. Establishing a list of volatiles emanating from healthy individuals and increased understanding of VOC metabolic pathways is an important step for differentiating between diseases using VOCs.

The "secret" in secretions: methodological considerations in deciphering primate olfactory communication

Olfactory communication in primates is gaining recognition; however, studies on the production and perception of primate scent signals are still scant. In general, there are five tasks to be accomplished when deciphering the chemical signals contained in excretions and secretions: (1) obtaining the appropriate samples; (2) extracting the target organic compounds from the biological matrix; (3) separating the extracted compounds from one another (by gas chromatography, GC or liquid chromatography, LC); (4) identifying the compounds (by mass spectrometry, MS and associated procedures); and (5) revealing biologically meaningful patterns in the data. Ultimately, because some of the compounds identified in odorants may not be relevant, associated steps in understanding signal function involve verifying the perception or biological activity of putative semiochemicals via (6) behavioral bioassays or (7) receptor response studies. This review will focus on the chemical analyses and behavioral bioassays of volatile, primate scent signals. Throughout, we highlight the potential pitfalls of working with highly complex, chemical matrices and suggest ways for minimizing problems. A recurring theme in this review is that multiple approaches and instrumentation are required to characterize the full range of information contained in the complex mixtures that typify primate or, indeed, many vertebrate olfactory cues. Only by integrating studies of signal production with those verifying signal perception will we better understand the function of olfactory communication.

Chemical communication and mother-infant recognition

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. Contrary to what appears in the popular press, the race is still on to capture and define human scents. Over the last several years, it became increasingly clear that pheromone-like chemical signals probably play a role in offspring identification and mother recognition. Recently, we analyzed the volatile compounds in sweat patch samples collected from the para-axillary and nipple-areola regions of women during pregnancy and after childbirth. We hypothesized that, at the time of birth and during the first weeks of life, the distinctive olfactory pattern of the para-axillary area is probably useful to newborns for recognizing and distinguishing their own mother, whereas the characteristic pattern of the nipple-areola region is probably useful as a guide to nourishment.