Machine Learning Predicts Non-Preferred and Preferred Vertebrate Hosts of Tsetse Flies (Glossina spp.) Based on Skin Volatile Emission Profiles

Tsetse fly vectors of African trypanosomosis preferentially feed on certain vertebrates largely determined by olfactory cues they emit. Previously, we established that three skin-derived ketones including 6-methyl-5-hepten-2-one, acetophenone and geranyl acetone accounted for avoidance of zebra by tsetse flies. Here, we tested the hypothesis that these three ketones serve as biomarkers for tsetse flies to distinguish between non-preferred- and preferred-vertebrate hosts. We used coupled gas chromatography/mass spectrometry to analyze and compare the skin volatile emissions of two non-preferred- (waterbuck and zebra) and four preferred- (buffalo, donkey, horse, warthog) vertebrate hosts in two wildlife parks in Kenya. We detected a total of 96 volatile organic compounds (VOCs) in the skin emissions composed mainly of aldehydes, ketones, alcohols, phenols and alkanes, which varied with the vertebrate host. Using random forest analysis, we found a weak correlation between the three skin-odor repellent ketones and non-preferred and preferred vertebrate hosts. However, we found that the three repellent ketones plus skin background odors may be more sensitive chemical signals for tsetse flies to discriminate vertebrate hosts. These results contribute to understanding tsetse fly vertebrate host preferences in their natural habitat across geographic scales.

Climate and Socio-Sexual Environment Predict Interpopulation Variation in Chemical Signaling Glands in a Widespread Lizard

Many animal species show considerable intraspecific phenotypic variation. For species with broad distributions, this variation may result from heterogeneity in the strength and agents of selection across environments and could contribute to reproductive isolation among populations. Here, we examined interpopulation variation in a morphological trait related to chemical communication, femoral pore number (FP), using 3437 individuals from 55 Pyrenean populations of the common wall lizard (Podarcis muralis). Specifically, we tested the relative roles of genetic relatedness and gene flow, and adaptation to local conditions in generating this variation, with particular interest in the influence of climate and the socio-sexual environment (i.e., the intensity of sexual selection, estimated using sexual size dimorphism [SSD] and adult sex ratio as proxy measures). We found significant interpopulation variation and sexual dimorphism in FP, as well as high genomic differentiation among populations driven by both geographic and environmental distances. Specifically, FP differences across populations were best predicted by a combination of positive allometry and the local intensity of sexual selection, as determined by SSD, or local climatic conditions. Higher FP in more male-competitive environments, or with higher temperature and vegetation complexity, is consistent with adaptation to maintaining signaling efficacy of territorial scent marks. These results suggest that adaptation to local conditions contributes to interpopulation divergence in FP and thus environmental changes can potentially impact the fine-tuning of chemical communication mediating social and sexual behavior.

Biostimulation methods based on chemical communication improve semen quality in male breeder rabbits

Biostimulation aims to optimize reproductive parameters as part of animal management practices by modulating animal sensory systems. Chemical signals, mostly known as pheromones, have a great potential in this regard. This study was conducted to determine the influence of short-term male rabbit exposure to different biological secretions, potentially pheromone-mediated, on reproductive parameters of males. Four groups of 18 males each were exposed to A) doe urine, B) 2-phenoxyethanol, C) doe vaginal swab, and D) distilled water (control), three times over a 2.5h exposure window, just before semen collection. Semen volume, sperm concentration and motility, as well as subpopulation analysis of the spermatozoa were assessed for each condition. Additionally, testosterone levels in blood samples were monitored at five time points over the 2.5 h exposure window. We found a higher percentage of motile, progressive, fast progressive and mid-progressive spermatozoa in any of the three experimental groups compared to the control group. In contrast, the semen volume and the percentage of immotile and non-progressive spermatozoa was generally higher in the control group. We then identified a higher proportion of a subpopulation of fast and progressive spermatozoa in groups A, B, and C compared to group D. Our data indicates that sperm motility increases when animals are exposed to specific biological fluids potentially containing pheromones, and that an increase in sperm volume does not correlate with an increase in spermatozoa concentration, progressiveness, and speed. Finally, no differences in testosterone levels were found among comparisons, although males of groups A and C (exposed to natural female biological fluids) showed a tendency towards higher testosterone levels. In conclusion, our results indicate that rabbit sperm quality increases upon exposure to the biological secretions proposed, thereby supporting further investigation into their molecular identity. This exploration could eventually pave the way for implementing the use of pheromones in rabbit husbandry to enhance reproductive and productive parameters in farmed rabbits.

Characterizing the metabolome and microbiome at giant panda scent marking sites during the mating season

Scent marking sites served as a primary means of chemical communication for giant pandas, enabling intraspecific communication. We integrated metabolomics and high-throughput sequencing techniques to examine the non-targeted metabolome and microbial community structure of scent marking sites and feces in the field. Integrative analysis revealed a more comprehensive array of chemical compounds compared to previous investigations, including ketones, acids, heterocycles, alcohols, and aldehydes. Notably, specific compounds such as 2-decenal, (E)-, octanal, decanal, L-α-terpineol, vanillin, and nonanal emerged as potential key players in scent signaling. Intriguingly, our study of the microbial domain identified dominant bacterial species from the Actinobacteria, Bacteroidetes, and Proteobacteria phyla, likely orchestrating metabolic processes at scent marking sites. Comparative analyses showed, for the first time, that feces do not share the same functions as scent markers, indicating distinct functional roles. This research deepens scientific understanding of chemical communication in wild pandas.

Carbonic anhydrase IV in lizard chemical signals

The evolution of chemical signals is subject to environmental constraints. A multicomponent signal may combine semiochemical molecules with supporting compounds able to enhance communication efficacy. Carbonic anhydrases (CAs) are ubiquitous enzymes catalysing the reversible hydration of carbon dioxide, a reaction involved in a variety of physiological processes as it controls the chemical environment of the different tissues or cellular compartments, thus contributing to the overall system homeostasis. CA-IV isoform has been recently identified by mass spectrometry in the femoral gland secretions (FG) of the marine iguana, where it has been hypothesized to contribute to the chemical stability of the signal, by regulating blend pH. Lizards, indeed, use FG to communicate by delivering the waxy secretion on bare substrate, where it is exposed to environmental stressors. Therefore, we expect that some molecules in the mixture may play supporting functions, enhancing the stability of the chemical environment, or even conferring homeostatic properties to the blend. CA-IV may well represent an important candidate to this hypothesized supporting/homeostatic function, and, therefore, we can expect it to be common in FG secretions of other lizard species. To evaluate this prediction and definitely validate CA identity, we analysed FG secretions of eight species of wall lizards (genus Podarcis), combining mass spectrometry, immunoblotting, immunocytochemistry, and transmission electron microscopy. We demonstrate CA-IV to actually occur in the FG of seven out of the eight considered species, providing an immunochemistry validation of mass-spectrometry identifications, and localizing the enzyme within the secretion mass. The predicted structure of the identified CA is compatible with the known enzymatic activity of CA-IV, supporting the hypothesis that CA play a signal homeostasis function and opening to new perspective about the role of proteins in vertebrate chemical communication.

The Scent Enriched Primate

Zoos worldwide play an important role in both in situ and ex situ conservation via efforts such as providing breeding programmes and reintroductions into the wild. Zoo populations are crucial as a buffer against extinction. However, a mismatch between the wild and zoo environments can lead to psychological as well as physiological health issues, such as stress, boredom, diabetes, and obesity. These problems, in turn, can impact the reproductive success of individuals. Consequently, some primate species have reduced breeding success when housed in zoos compared to their wild counterparts. To prevent the onset of behavioural, physiological, and cognitive negative effects and to continually improve the welfare of their animals, zoos widely implement different types of environmental enrichment. There are many forms enrichment can take, such as feeding, puzzles and training, but sensory enrichments, including implementing the use of scents, are currently understudied. Scent enrichments are less utilized despite multiple research studies showing that they may have positive effects on welfare for zoo-housed animal species, including non-human primates. Despite being traditionally considered to be microsmatic, various lines of evidence suggest that olfaction plays a larger role in primates than previously thought. This review therefore focuses on scent-based enrichment and the specifics of captive primates.

Conspecific scent marks may influence underground site selection by a fossorial reptile

Abstract

Conspecific cues often provide social information on habitat quality that is considered when deciding to settle at a specific site. The type of sensory cues useful for this will depend on the environment. For amphisbaenians, reptiles adapted to an underground life with highly reduced sight, chemoreception is especially useful to recognize conspecifics. Here, we first analyzed the lipophilic compounds from precloacal gland secretions of the amphisbaenian Blanus cinereus, showing that there were sex- and size-related variations in the proportions of the three major compounds. Then, we tested in the laboratory whether there was an underground site selection based on conspecific chemical cues (substrate scent marks) in two different contexts. In loose substrates, both male and female amphisbaenians tended to choose first the scent-marked substrates more often when the individual that produced the scent, independently of its sex, was relatively larger than the focal individual. In contrast, inside semi-permanent galleries, males, but not females, chose the scent-marked gallery more often when the scent donor, independently of its sex, was relatively smaller. These results suggest that the proportions of compounds in scent marks may allow amphisbaenians to estimate the body size of the producer and that this information affects their site selection decisions. However, the different substrate-dependent responses suggest a different meaning and usefulness of scent marks depending on the context.

Significance statement

The presence of your conspecific in a site may indicate that this is a “quality” site to live in. If you are blind and live underground, smell is one of the best options for detecting conspecifics and assessing how good are your surroundings. Here, we test whether a blind amphisbaenian reptile that spends its life buried in sandy substrates uses conspecific chemical stimuli to choose where to settle. We found that this decision is influenced by the microhabitat type, sex, and the size difference between the individual that sniffs and the producer of the scent. Amphisbaenians seem to detect and assess conspecific traits based on the differences in compounds in their odors. Therefore, using conspecific scent to assess habitat quality may help fossorial animals to live underground.

Assessing the effect of compounds from plantar foot sweat, nesting material, and urine on social behavior in male mice, Mus musculus

Home cage aggression causes poor welfare in male laboratory mice and reduces data quality. One of the few proven strategies to reduce aggression involves preserving used nesting material at cage change. Volatile organic compounds from the nesting material and several body fluids not only correlate with less home cage aggression, but with more affiliative allo-grooming behavior. To date, these compounds have not been tested for a direct influence on male mouse social behavior. This study aimed to determine if 4 previously identified volatile compounds impact home cage interactions. A factorial design was used with cages equally split between C57BL/6N and SJL male mice (N = 40). Treatments were randomly assigned across cages and administered by spraying one compound solution on each cage's nesting material. Treatments were refreshed after day 3 and during cage change on day 7. Home cage social behavior was observed throughout the study week and immediately after cage change. Several hours after cage change, feces were collected from individual mice to measure corticosterone metabolites as an index of social stress. Wound severity was also assessed after euthanasia. Measures were analyzed with mixed models. Compound treatments did not impact most study measures. For behavior, SJL mice performed more aggression and submission, and C57BL/6N mice performed more allo-grooming. Wound severity was highest in the posterior region of both strains, and the middle back region of C57BL/6N mice. Posterior wounding also increased with more observed aggression. Corticosterone metabolites were higher in C57BL/6N mice and in mice treated with 3,4-dimethyl-1,2-cyclopentanedione with more wounding. These data confirm previous strain patterns in social behavior and further validates wound assessment as a measure of escalated aggression. The lack of observed treatment effects could be due to limitations in the compound administration procedure and/or the previous correlation study, which is further discussed.

A pachyderm perfume: odour encodes identity and group membership in African elephants

Group-living animals that live in complex social systems require effective modes of communication to maintain social cohesion, and several acoustic, olfactory and visual signaling systems have been described. Individuals need to discriminate between in- and out-group odour to both avoid inbreeding and to identify recipients for reciprocal behaviour. The presence of a unique group odour, identified in several social mammals, is a proposed mechanism whereby conspecifics can distinguish group from non-group members. African elephants (Loxodonta africana) live in stable, socially complex, multi-female, fission-fusion groups, characterized by female philopatry, male dispersal and linear dominance hierarchies. Elephant social behaviour suggests that individuals use odour to monitor the sex, reproductive status, location, health, identity and social status of conspecifics. To date, it is not clear what fixed or variable information is contained in African elephant secretions, and whether odour encodes kinship or group membership information. Here we use SPME GC-MS generated semiochemical profiles for temporal, buccal and genital secretions for 113 wild African elephants and test their relationship with measures of genetic relatedness. Our results reveal the existence of individual identity odour profiles in African elephants as well as a signature for age encoded in temporal gland and buccal secretions. Olfactory signatures for genetic relatedness were found in labial secretions of adult sisters. While group odour was not correlated with group genetic relatedness, our analysis identified "group membership" as a significant factor explaining chemical differences between social groups. Saturated and short-chain fatty acids (SCFAs), derived from key volatile compounds from bacterial fermentation, were identified in temporal, buccal and genital secretions suggesting that group odour in African elephants may be the result of bacterial elements of the gut microbiome. The frequent affiliative behavior of African elephants is posited as a likely mechanism for bacterial transmission. Our findings favour flexible group-specific bacterial odours, which have already been proposed for other social mammals and present a useful form of olfactory communication that promotes bond group cohesion among non-relatives in fission-fusion mammals.

Chemical Characterization of the Marking Fluid of Breeding and Non-Breeding Male Cheetahs

Simple Summary

The study aimed at chemically characterizing the marking fluid of both breeding and non-breeding male cheetahs (Acinonyx jubatus). Specifically, it focused on identifying potential differences in pheromones related to sexual behavior/attraction in this species. Furthermore, it aimed at providing more information as a basis for future studies, such as the investigation of specific semiochemicals in the reproductive behavior of cheetahs. The results of this study support the hypothesis of differences in the relative concentration of volatile organic chemicals between male cheetahs; however, they highlight the importance of diet and age on the presence of volatile organic chemicals in the marking fluid.

Abstract

Scent is known to play an important role in the reproduction of cheetahs and other felids. In fact, the presence/odor of a male cheetah has been noted to trigger the estrous cycle in females. The objective of this study was to analyze the marking fluid (MF) of male cheetahs from different breeding groups to determine the composition of volatile organic compounds (VOCs) present, with the aim of identifying potential pheromones relating to sexual behavior/attraction in this species. Four breeding (B; age: 8.9 ± 1.3 years old) and four non-breeding (NB; age: 5.5 ± 0.8 years old) males were selected for this study. Samples were collected into a glass beaker, transferred immediately into a 20 mL glass screw-cap vial with a polytetrafluoroethylene (PTFE) coated silicone septum, and stored until analyzed by headspace solid-phase microextraction (HS-SPME) using gas chromatography–mass spectrometry. A contingency test with Fisher’s exact test, using the frequency (FREQ) procedure of SAS 9.4, was conducted to determine the difference between the number of VOCs identified per breeding group; furthermore, differences in relative concentration (RC) of the identified VOCs between breeding groups were analyzed using ANOVA for repeated measures with the GLIMMIX procedure. From the 13 MF samples analyzed, 53 VOCs were identified, and 12 were identified in all the samples. Five of these (dimethyl disulfide, benzaldehyde, acetophenone, phenol, and indole) are known to be involved in attraction/sexual behavior in mammals. Between the two groups, the RC of indole was significantly higher in the NB group, whereas the RC of dodecanoic acid was significantly higher in the B group. Although not significant, the RC of benzaldehyde was higher in the B versus the NB group. The results of this study do support the hypothesis of differences in VOCs’ between B and NB male cheetahs. However, the overlapping of age and breeding status and the diet differences could not be controlled. Still, the evidence of changes in MF composition in male cheetahs necessitates further studies on possible strategies to improve reproduction in captivity.

Protein profiles from used nesting material, saliva, and urine correspond with social behavior in group housed male mice, Mus musculus

Current understanding of how odors impact intra-sex social behavior is based on those that increase intermale aggression. Yet, odors are often promoted to reduce fighting among male laboratory mice. It has been shown that a cage of male mice contains many proteins used for identification purposes. However, it is unknown if these proteins relate to social behavior or if they are uniformly produced across strains. This study aimed to compare proteomes from used nesting material and three sources (sweat, saliva, and urine) from three strains and compare levels of known protein odors with rates of social behavior. Used nesting material samples from each cage were analyzed using LC-MS/MS. Sweat, saliva, and urine samples from each cage's dominant and subordinate mouse were also analyzed. Proteomes were assessed using principal component analyses and compared to behavior by calculating correlation coefficients between PC scores and behavior proportions. Twenty-one proteins from nesting material either correlated with affiliative behavior or negatively correlated with aggression. Notably, proteins from the major urinary protein family, odorant binding protein family, and secretoglobin family displayed at least one of these patterns, making them candidates for future work. These findings provide preliminary information about how proteins can influence male mouse behavior. SIGNIFICANCE: Research on how olfactory signals influence same sex social behavior is primarily limited to those that promote intermale aggression. However, exploring how olfaction modulates a more diverse behavioral repertoire will improve our foundational understanding of this sensory modality. In this proteome analysis we identified a short list of protein signals that correspond to lower rates of aggression and higher rates of socio-positive behavior. While this study is only correlational, it sets a foundation for future work that can identify protein signals that directly influence social behavior and potentially identify new murine pheromones.

Understanding the Role of Semiochemicals on the Reproductive Behaviour of Cheetahs (Acinonyx jubatus)-A Review

Simple Summary

This review aims to provide an in-depth overview of the reproductive physiology and behaviour of cheetahs (Acinonyx jubatus). Specifically, it focuses on the role that pheromones (a class of semiochemicals) play by directly affecting the reproductive (e.g., precopulatory and copulatory) behaviour. Furthermore, it aims to critically analyze current research and provide new insights on study areas needing further investigation. It is clear, for instance, that further research is necessary to investigate the role of semiochemicals in the reproductive behaviour of cheetahs in order to rectify the current behavioural difficulties experienced when breeding younger females. This, in turn, would aid in improving captive breeding and the prevention of asymmetric reproductive aging.

Abstract

The cheetah species (Acinonyx jubatus) is currently listed as vulnerable according to the International Union for Conservation of Nature (IUCN). Captive breeding has long since been used as a method of conservation of the species, with the aim to produce a healthy, strong population of cheetahs with an increased genetic variety when compared to their wild counterparts. This would then increase the likelihood of survivability once released into protected areas. Unfortunately, breeding females have been reported to be difficult due to the age of these animals. Older females are less fertile, have more difficult parturition, and are susceptible to asymmetric reproductive aging whereas younger females tend to show a significantly lower frequency of mating behaviour than that of older females, which negatively affects breeding introductions, and therefore mating. Nonetheless, the experience from breeding methods used in some breeding centres in South Africa and the Netherlands, which also rely on the role that semiochemicals play in breeding, proves that cheetahs can be bred successfully in captivity. This review aims to give the reader an in-depth overview of cheetahs’ reproductive physiology and behaviour, focusing on the role that pheromones play in this species. Furthermore, it aims to provide new insight into the use of semiochemicals to improve conservation strategies through captive breeding.

The Chemical Ecology of Elephants: 21st Century Additions to Our Understanding and Future Outlooks

Chemical signals are the oldest and most ubiquitous means of mediating intra- and interspecific interactions. The three extant species of elephants, the Asian elephant and the two African species, savanna and forest share sociobiological patterns in which chemical signals play a vital role. Elephants emit secretions and excretions and display behaviors that reveal the importance of odors in their interactions. In this review, we begin with a brief introduction of research in elephant chemical ecology leading up to the 21st century, and then we summarize the body of work that has built upon it and occurred in the last c. 20 years. The 21st century has expanded our understanding on elephant chemical ecology, revealing their use of odors to detect potential threats and make dietary choices. Furthermore, complementary in situ and ex situ studies have allowed the careful observations of captive elephants to be extended to fieldwork involving their wild counterparts. While important advances have been made in the 21st century, further work should investigate the roles of chemical signaling in elephants and how these signals interact with other sensory modalities. All three elephant species are threatened with extinction, and we suggest that chemical ecology can be applied for targeted conservation efforts.

Musth and sexual selection in elephants: a review of signalling properties and potential fitness consequences

Sexual selection mediated by multimodal signals is common among polygynous species, including seasonally breeding mammals. Indirect benefit models provide plausible explanations for how and why mate selection can occur in the absence of direct benefits. Musth — an asynchronous reproductive state in male elephants — facilitates both inter- and intrasexual selection via indirect benefits, and it is further communicated through a multimodal signal. In this review, we synthesise existing evidence that supports the hypothesis that musth is a multimodal signal subject to sexual selection and that male elephants increase their direct fitness by propagating this signal while females accrue indirect benefits. Musth is characterised by a suite of physiological and behavioural changes, serving to facilitate copulation between the sexes, and via multisensory modalities musth conveys honest information about the condition of a male. Female elephants mate preferentially with musth males, increasing their own fitness in the absence of direct benefits. In addition, musth resolves dynamic dominance hierarchies among male elephants and often eliminates the need for costly physical combat. Future work in this field should investigate potential postcopulatory selection mechanisms in elephants, including sperm competition and cryptic female choice. These topics join other fundamental questions related to sexual selection, signalling, and indirect benefits that are still unanswered in elephants.

What is that smell? Hummingbirds avoid foraging on resources with defensive insect compounds

Abstract

Hummingbirds utilize visual cues to locate flowers, but little is known about the role olfaction plays in nectar foraging despite observations that hummingbirds avoid resources occupied by certain insects. We investigated the behavioral responses of both wild and captive hummingbirds to olfactory cues of hymenopteran floral visitors, including native wood ants (Formica francoeuri), invasive Argentine ants (Linepithema humile), and European honeybees (Apis mellifera). We demonstrate for the first time that hummingbirds use olfaction to make foraging decisions when presented with insect-derived chemical cues under field and aviary conditions. Both wild and captive hummingbirds avoided foraging on feeders with defensive chemicals of F. francoeuri and aggregation pheromones of L. humile, but showed no response to honeybee cuticular hydrocarbons. Our experiments demonstrate the importance of olfaction in shaping hummingbird foraging decisions.

Significance statement

Recent reviews reveal that avian olfaction is not just limited to vultures and a few taxa. We demonstrate that a very charismatic group, hummingbirds, avoid defensive and aggregatory chemical cues from insects present at nectar resources. Olfactory cues can provide critical information about the presence and potential threat of insect floral visitors. This study raises new questions about the underrated importance of olfaction in avian foraging and specifically, hummingbird foraging.

Assessing urinary odours across the oestrous cycle in a mouse model using portable and benchtop gas chromatography-mass spectrometry

For female mammals, communicating the timing of ovulation is essential for reproduction. Olfactory communication via volatile organic compounds (VOCs) can play a key role. We investigated urinary VOCs across the oestrous cycle using laboratory mice. We assessed the oestrous stage through daily vaginal cytology and analysed urinary VOCs using headspace gas chromatography-mass spectrometry (GC-MS), testing a portable GC-MS against a benchtop system. We detected 65 VOCs from 40 samples stored in VOC traps and analysed on a benchtop GC-MS, and 15 VOCs from 90 samples extracted by solid-phase microextraction (SPME) and analysed on a portable GC-MS. Only three compounds were found in common between the two techniques. Urine collected from the fertile stages of the oestrous cycle had increased quantities of a few notable VOCs compared with urine from non-fertile stages. These VOCs may be indicators of fertility. However, we did not find significant differences in chemical composition among oestrous stages. It is possible that changes in VOC abundance were too small to be detected by our analytical methods. Overall, the use of VOC traps combined with benchtop GC-MS was the more successful of the two methods, yet portable GC-MS systems may still have utility for some in situ applications.

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.

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.

Appeasing Pheromones for the Management of Stress and Aggression during Conservation of Wild Canids: Could the Solution Be Right under Our Nose?

Simple Summary

Many canid species are declining globally. It is important to conserve these species that often serve as important predators within ecosystems. Continued human expansion and the resulting habitat fragmentation necessitate conservation interventions, such as translocation, artificial pack formation, and captive breeding programs. However, chronic stress often occurs during these actions, and can result in aggression, and the physiological suppression of immunity and reproduction. Limited options are currently available for stress and aggression management in wild canids. Pheromones provide a promising natural alternative for stress management; an appeasing pheromone has been identified for multiple domestic species and may reduce stress and aggression behaviours. Many pheromones are species-specific, and the appeasing pheromone has been found to have slight compositional changes across species. In this review, the benefits of a dog appeasing pheromone and the need to investigate species-specific derivatives to produce more pronounced and beneficial behavioural and physiological modulation in target species as a conservation tool are examined.

Abstract

Thirty-six species of canid exist globally, two are classified as critically endangered, three as endangered, and five as near threatened. Human expansion and the coinciding habitat fragmentation necessitate conservation interventions to mitigate concurrent population deterioration. The current conservation management of wild canids includes animal translocation and artificial pack formation. These actions often cause chronic stress, leading to increased aggression and the suppression of the immune and reproductive systems. Castration and pharmaceutical treatments are currently used to reduce stress and aggression in domestic and captive canids. The undesirable side effects make such treatments inadvisable during conservation management of wild canids. Pheromones are naturally occurring chemical messages that modulate behaviour between conspecifics; as such, they offer a natural alternative for behaviour modification. Animals are able to distinguish between pheromones of closely related species through small compositional differences but are more likely to have greater responses to pheromones from individuals of the same species. Appeasing pheromones have been found to reduce stress- and aggression-related behaviours in domestic species, including dogs. Preliminary evidence suggests that dog appeasing pheromones (DAP) may be effective in wild canids. However, the identification and testing of species-specific derivatives could produce more pronounced and beneficial behavioural and physiological changes in target species. In turn, this could provide a valuable tool to improve the conservation management of many endangered wild canids.

Compounds from plantar foot sweat, nesting material, and urine show strain patterns associated with agonistic and affiliative behaviors in group housed male mice, Mus musculus

Excessive home cage aggression often results in severe injury and subsequent premature euthanasia of male laboratory mice. Aggression can be reduced by transferring used nesting material during cage cleaning, which is thought to contain aggression appeasing odors from the plantar sweat glands. However, neither the composition of plantar sweat nor the deposits on used nesting material have been evaluated. The aims of this study were to (1) identify and quantify volatile compounds deposited in the nest site and (2) determine if nest and sweat compounds correlate with social behavior. Home cage aggression and affiliative behavior were evaluated in 3 strains: SJL, C57BL/6N, and A/J. Individual social rank was assessed via the tube test, because ranking may influence compound levels. Sweat and urine from the dominant and subordinate mouse in each cage, plus cage level nest samples were analyzed for volatile compound content using gas chromatography-mass spectrometry. Behavior data and odors from the nest, sweat, and urine were statistically analyzed with separate principal component analyses (PCA). Significant components, from each sample analysis, and strain were run in mixed models to test if odors were associated with behavior. Aggressive and affiliative behaviors were primarily impacted by strain. However, compound PCs were also impacted by strain, showing that strain accounts for any relationship between odors and behavior. C57BL/6N cages displayed the most allo-grooming behavior and had high scores on sweat PC1. SJL cages displayed the most aggression, with high scores on urine PC2 and low scores on nest PC1. These data show that certain compounds in nesting material, urine, and sweat display strain specific patterns which match strain specific behavior patterns. These results provide preliminary information about the connection between home cage compounds and behavior. Salient compounds will be candidates for future controlled studies to determine their direct effect on mouse social behavior.

Urates of colubroid snakes are different from those of boids and pythonids

Uricotelic species, such as squamate reptiles, birds and insects, effectively eliminate nitrogen as uric acid in a solid form commonly called urates. Observations made over a decade suggested that the voided urates produced by colubroids (modern snake species) exhibit remarkable differences from those of boids and pythons (ancient snake species). Here, we compare the urates generated by eight captive snake species fed the same diet. Although all fresh urates were wet at the time of excretion, those produced by modern snakes dried to a powdery solid, whereas those of ancient species dried to a rock-hard mass that was tightly adherent to surfaces. Powder X-ray diffraction and infrared spectroscopy analyses performed on voided urates produced by five modern and three ancient snakes confirmed their underlying chemical and structural differences. Urates excreted by ancient snakes were amorphous uric acid, whereas urates from modern snakes consisted primarily of ammonium acid urate, with some uric acid dihydrate. These compositional differences indicate that snakes have more than one mechanism to manage nitrogenous waste. Why different species use different nitrogen-handling pathways is not yet known, but the answer might be related to key differences in metabolism, physiology or, in the case of ancient snakes, the potential use of urates in social communication.

Volatile scent chemicals in the urine of the red fox, Vulpes vulpes

The red fox is a highly adaptable mammal that has established itself world-wide in many different environments. Contributing to its success is a social structure based on chemical signalling between individuals. Urine scent marking behaviour has long been known in foxes, but there has not been a recent study of the chemical composition of fox urine. We have used solid-phase microextraction and gas chromatography-mass spectrometry to analyze the urinary volatiles in 15 free-ranging wild foxes (2 female) living in farmlands and bush in Victoria, Australia. Foxes here are routinely culled as feral pests, and the urine was collected by bladder puncture soon after death. Compounds were identified from their mass spectra and Kovats retention indices. There were 53 possible endogenous scent compounds, 10 plant-derived compounds and 5 anthropogenic xenobiotics. Among the plant chemicals were several aromatic apocarotenoids previously found in greater abundance in the fox tail gland. They reflect the dietary consumption of carotenoids, essential for optimal health. One third of all the endogenous volatiles were sulfur compounds, a highly odiferous group which included thiols, methylsulfides and polysulfides. Five of the sulfur compounds (3-isopentenyl thiol, 1- and 2-phenylethyl methyl sulfide, octanethiol and benzyl methyl sulfide) have only been found in foxes, and four others (isopentyl methyl sulfide, 3-isopentenyl methyl sulfide, and 1- and 2-phenylethane thiol) only in some canid, mink and skunk species. This indicates that they are not normal mammalian metabolites and have evolved to serve a specific role. This role is for defence in musteloids and most likely for chemical communication in canids. The total production of sulfur compounds varied greatly between foxes (median 1.2, range 0.4–32.3 μg ‘acetophenone equivalents’/mg creatinine) as did the relative abundance of different chemical types. The urinary scent chemistry may represent a highly evolved system of semiochemicals for communication between foxes.

Investment in chemical signalling glands facilitates the evolution of sociality in lizards

The evolution of sociality and traits that correlate with, or predict, sociality, have been the focus of considerable recent study. In order to reduce the social conflict that ultimately comes with group living, and foster social tolerance, individuals need reliable information about group members and potential rivals. Chemical signals are one such source of information and are widely used in many animal taxa, including lizards. Here, we take a phylogenetic comparative approach to test the hypothesis that social grouping correlates with investment in chemical signalling. We used the presence of epidermal glands as a proxy of chemical investment and considered social grouping as the occurrence of social groups containing both adults and juveniles. Based on a dataset of 911 lizard species, our models strongly supported correlated evolution between social grouping and chemical signalling glands. The rate of transition towards social grouping from a background of ‘epidermal glands present’ was an order of a magnitude higher than from a background of ‘no epidermal glands’. Our results highlight the potential importance of chemical signalling during the evolution of sociality and the need for more focused studies on the role of chemical communication in facilitating information transfer about individual and group identity, and ameliorating social conflict.

Symbiotic bacteria mediate volatile chemical signal synthesis in a large solitary mammal species

Mammalian chemosignals—or scent marks—are characterized by astounding chemical diversity, reflecting both complex biochemical pathways that produce them and rich information exchange with conspecifics. The microbiome of scent glands was thought to play prominent role in the chemical signal synthesis, with diverse microbiota metabolizing glandular products to produce odorants that may be used as chemosignals. Here, we use gas chromatography–mass spectrometry and metagenomic shotgun sequencing to explore this phenomenon in the anogenital gland secretions (AGS) of the giant panda (Ailuropoda melanoleuca). We find that this gland contains a diverse community of fermentative bacteria with enzymes that support metabolic pathways (e.g., lipid degradation) for the productions of volatile odorants specialized for chemical communication. We found quantitative and qualitative differences in the microbiota between AGS and digestive tract, a finding which was mirrored by differences among chemical compounds that could be used for olfactory communication. Volatile chemical compounds were more diverse and abundant in AGS than fecal samples, and our evidence suggests that metabolic pathways have been specialized for the synthesis of chemosignals for communication. The panda’s microbiome is rich with genes coding for enzymes that participate in the fermentation pathways producing chemical compounds commonly deployed in mammalian chemosignals. These findings illuminate the poorly understood phenomena involved in the role of symbiotic bacteria in the production of chemosignals.

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.

Absolute Quantitative Volatile Measurement from Fresh Tea Leaves and the Derived Teas Revealed Contributions of Postharvest Synthesis of Endogenous Volatiles for the Aroma Quality of Made Teas

Characteristic aroma is a well-appreciated feature contributing to tea quality. Although extensive studies have been made to investigate aroma biosynthesis and gene expressions during tea making processes, it remains unclear whether the endogenous volatile biosynthesis during postharvest tea processing contributes to the aroma quality of made tea. To critically evaluate this question, we used the same batch of fresh tea leaves and produced three different types of tea with different degrees of fermentation (green tea, oolong tea, and black tea). Total volatiles were extracted by solvent-assisted-flavor evaporation, then quantified by gas chromatography-flame ionization detector combined with response factor correction for quantitative measurement. Compared with fresh tea leaves, the volatile profiles of the made teas were dramatically altered, with significant loss for the majority of endogenous volatiles and simultaneous gain for non-endogenous volatiles. By calculation of odor-activity values, the potential volatiles contributing to the aroma characteristics of each tea type were identified. Our data suggest that postharvest synthesis of endogenous volatiles did not contribute to the aroma quality of made tea.

Behavioural discrimination of male mental gland secretions of the gopher tortoise (Gopherus polyphemus) by both sexes

Chemical communication is important for mate choice, especially at long distances in fragmented populations. The gopher tortoise is a social species that is threatened in the southeast U.S. due to habitat fragmentation and decline. One consequence of habitat loss is reduced mating opportunities, yet chemical signalling in gopher tortoises is relatively under-studied. Here, we investigated chemoreception of tortoise discrimination of chin secretions, or mental gland (MG) secretions. To assess conspecific recognition of male MG secretions, we conducted two paired-choice experiments: one with a neutral odorant control (NC; distilled water) and one with a pungent odorant control (PC; acetone) vs. male MG secretions. Behaviours were defined a priori, and their durations were quantified relative to treatments. Each sex spent significantly more time with MG secretions vs. acetone control during the PC study (p= 0.001). Each sex also sniffed MG swabs more frequently in both studies (PC study: p=0.0003; NC study: p=0.001). A principal components analysis of behavioural durations from the PC study identified one component with a significant treatment effect performed to MG secretions (p=0.0003), including the behaviours sniffing, head bobbing, biting, and eating near a swab. Our study provides the first chemical-behavioural bioassay of MG secretions from male gopher tortoises, suggesting MG secretions may be a source of pheromones.

A novel epidermal gland type in lizards (α-gland): structural organization, histochemistry, protein profile and phylogenetic origins

Chemical signalling is an essential component of the communication system of lizards, and epidermal glands are responsible for producing semiochemicals that regulate many behavioural interactions. Two types of epidermal glands have been previously described for lizards: follicular and generation glands. Generation glands are characterized by the aggregation of novel glandular cell types in the epithelium and the lack of a lumen or external pore. Despite the fact that several subtypes of generation glands have been recognized over the years, the morphology, taxonomic distribution, function and evolutionary origins of generation glands remain nearly unexplored in Neotropical clades. Here, we describe a novel escutcheon-type generation gland (‘α-gland’) for lizards of the South American family Tropiduridae, characterize its structural and ultrastructural organization, and study the homology of the constituent parts in a phylogenetic framework. The α-glands emerged in the ancestor of Eurolophosaurus, Plica, Strobilurus, Tropidurus and Uracentron, and are found in at least 39 species with diverse ecological habits. We preliminarily analysed the protein profile of α-glands and discovered differential expression of protein components between sexes. Our investigations change the general view about epidermal gland homology, leading us to argue that generation and follicular glands are possibly more closely related functionally and evolutionarily than previously thought.

Chemical characterization of the lipids in femoral gland secretions of wild male tegu lizards, Salvator merianae (Squamata, Teiidae) in comparison with captive-bred males

Although chemical interactions play an essential role in lizard social behavior, the chemical composition of the femoral gland secretions that many lizards use for communication is known for only a few species, mainly European Lacertids. The tegu lizard, Salvator merianae, is the only species of the Teiidae family for which there is available information on lipids in femoral secretions, but only for captive bred males from Argentina. Here, based on mass spectra obtained by GC-MS, we found 69 lipophilic compounds in femoral gland secretions of wild males S. merianae from Brazil, including cholesterol and high amounts of saturated fatty acids (mainly hexadecanoic and octadecanoic). We found contrasting differences between wild and captive-bred males, which lack cholesterol but present high amount of 9,12-octadecadienoic acid. These within-species differences between wild and captive lizards strongly suggest the important influence of different diets on the chemical composition of the femoral gland secretion and suggest caution when interpreting results from captive animals, even in the same species.

The chemistry and histology of sexually dimorphic mental glands in the freshwater turtle, Mauremys leprosa

Despite evidence from anatomy, behavior and genomics indicating that the sense of smell in turtles is important, our understanding of chemical communication in this group is still rudimentary. Our aim was to describe the microanatomy of mental glands (MGs) in a freshwater turtle, Mauremys leprosa (Geoemydidae), and to assess the chemical composition of their secretions with respect to variation among individuals and between sexes. MGs are paired sac-like organs on the gular region of the neck and are dimorphic in this species with males having fully functional holocrine glands while those of females appear non-secretory and vestigial. In adult males, the glandular epithelium of the inner portion of the gland provides exocytotic products as well as cellular debris into the lumen of the gland. The contents of the lumen can be secreted through the narrow duct portion of the gland ending in an orifice on the surface of the skin. Females have invaginated structures similar in general outline to male glands, but lack a glandular epithelium. Using gas chromatography coupled to mass spectrometry, we identified a total of 61 compounds in mental gland secretions, the most numerous being carboxylic acids, carbohydrates, alkanes, steroids and alcohols. The number of compounds per individual varied widely (mean (median) ± SD = 14.54 (13) ± 8.44; min = 3; max = 40), but only cholesterol was found in all samples. We found that the relative abundances of only six chemicals were different between the sexes, although males tended to have larger amounts of particular compounds. Although the lipid fraction of mental gland secretions is rich in chemical compounds, most occur in both sexes suggesting that they are metabolic byproducts with no role in chemical signaling. However, the relative amounts of some compounds tended to be higher in males, with significantly larger amounts of two carboxylic acids and one steroid, suggesting their putative involvement in chemical communication.

Volatile fatty acid and aldehyde abundances evolve with behavior and habitat temperature in Sceloporus lizards

Animal signals evolve by striking a balance between the need to convey information through particular habitats and the limitations of what types of signals can most easily be produced and perceived. Here, we present new results from field measures of undisturbed behavior and biochemical analyses of scent marks from 12 species of Sceloporus lizards to explore whether evolutionary changes in chemical composition are better predicted by measures of species behavior, particularly those associated with visual displays, chemoreception, and locomotion, or by measures of habitat climate (precipitation and temperature). We found that more active lizard species used fewer compounds in their volatile scent marks, perhaps conveying less specific information about individual and species identity. Scent marks from more active lizard species also had higher proportions of saturated fatty acids, and the evolution of these compounds has been tracking the phylogeny closely as we would expect for a metabolic byproduct. In contrast, the proportions of unsaturated fatty acids were better explained by evolutionary shifts in habitat temperature (and not precipitation), with species in warmer climates using almost no volatile unsaturated fatty acids. The proportion of aldehydes was explained by both behavior and environment, decreasing with behavioral activity and increasing with habitat temperature. Our results highlight the evolutionary flexibility of complex chemical signals, with different chemical compounds responding to different elements of the selective landscape over evolutionary time.

Structural Identification, Synthesis and Biological Activity of Two Volatile Cyclic Dipeptides in a Terrestrial Vertebrate

Single substances within complex vertebrate chemical signals could be physiologically or behaviourally active. However, the vast diversity in chemical structure, physical properties and molecular size of semiochemicals makes identifying pheromonally active compounds no easy task. Here, we identified two volatile cyclic dipeptides, cyclo(L-Leu-L-Pro) and cyclo(L-Pro-L-Pro), from the complex mixture of a chemical signal in terrestrial vertebrates (lizard genus Sceloporus), synthesised one of them and investigated their biological activity in male intra-specific communication. In a series of behavioural trials, lizards performed more chemosensory behaviour (tongue flicks, lip smacks and substrate lickings) when presented with the synthesised cyclo(L-Pro-L-Pro) chemical blend, compared to the controls, the cyclo(L-Leu-L-Pro) blend, or a combined blend with both cyclic dipeptides. The results suggest a potential semiochemical role of cyclo(L-Pro-L-Pro) and a modulating effect of cyclo(L-Leu-L-Pro) that may depend on the relative concentration of both compounds in the chemical signal. In addition, our results stress how minor compounds in complex mixtures can produce a meaningful behavioural response, how small differences in structural design are crucial for biological activity, and highlight the need for more studies to determine the complete functional landscape of biologically relevant compounds.

Simultaneous choice bioassays accompanied by physiological changes identify civetone and decanoic acid as pheromone candidates for giant pandas

Chemicals present in urine are thought to play an important role in mate identification in the solitary giant panda (Ailuropoda melanoleuca). During the breeding season, females will deposit chemical signals to advertise sexual receptivity to potential mates. The goal of this study was to determine if specific volatile compounds found in female urine could be considered as pheromones that elicit behavioral and physiological responses in males. Experimental simultaneous choice trials were conducted with captive male giant pandas (n = 3) housed at Memphis Zoo, San Diego Zoo, and Zoo Atlanta. Octanoic acid, 1H-pyrrole-2-carboxaldehyde, decanoic acid, and civetone were selected as stimuli because previous studies reported their elevation in urine during the breeding season. Male interest was determined by a behavioral preference toward these volatile compounds diluted in synthetic urine compared with nontreated synthetic urine. Male urine samples were collected 1 week prior, during, and 1 week after the experimental period to assess changes in urinary semiochemical composition and urinary androgen concentrations. No significant differences in investigation response (p = .395) or flehmen response (p = .600) were found when stimuli were compared; however, decanoic acid and civetone elicited a behavioral preference over the control (response ratio > 0.5). The relative abundance of 16 compounds identified in male urine was significantly elevated (p < .05) above baseline values after the males were exposed to the stimuli. Androgen levels were significantly elevated (p < .05) in one male after exposure to 1H-pyrrole-2-carboxaldehyde, decanoic acid, and civetone. These data suggested that civetone and decanoic acid in female urine may motivate sexual responses in males.

Proteome characterization of used nesting material and potential protein sources from group housed male mice, Mus musculus

Laboratory mice (Mus musculus) communicate a variety of social messages through olfactory cues and it is often speculated that these cues are preserved in nesting material. Based on these speculations, a growing number of husbandry recommendations support preserving used nests at cage cleaning to maintain familiar odors in the new cage. However, the content of used nesting material has never been chemically analyzed. Here we present the first comprehensive proteome profile of used nesting material. Nests from cages of group housed male mice contain a variety of proteins that primarily originate from saliva, plantar sweat, and urine sources. Most notably, a large proportion of proteins found in used nesting material belong to major urinary protein (“MUP”) and odorant binding protein (“OBP”) families. Both protein families send messages about individual identity and bind volatile compounds that further contribute to identity cues. Overall, this data supports current recommendations to preserve used nesting material at cage cleaning to maintain odor familiarity.

Differential responses by urban brown rats (Rattus norvegicus) toward male or female-produced scents in sheltered and high-risk presentations

Wild rats (Rattus norvegicus) are among the most ubiquitous and consequential organisms in the urban environment. However, collecting data from city rats is difficult, and there has been little research to determine the influence, or valence, of rat scents on urban conspecifics. Using a mark-release-monitor protocol, we previously learned rats can be attracted to remote-sensing points when baited with mixed-bedding from male and female laboratory rats. It was thus essential that we disambiguate which scents were eliciting attraction (+ valence), inspection, a conditioned response whereby attraction may be followed by avoidance (–valence), or null-response (0 valence). We used radio-frequency identification tagging and scent-baited antennas to assess extended (>40 days) responses to either male or female scents against two risk presentations (near-shelter and exposed to predators). In response to male scents, rats (n = 8) visited both treatments (shelter, exposed) more than controls (0.2 visits/day treatment vs. 0.1/day; P < 0.05) indicating scents accounted for response more so than risk. Dwell-times, however, did not differ (1.2 s/visit treatment vs. 0.9 s/visit; P > 0.5). These outcomes are consistent with inspection (–valence). In response to female scents, rats (n = 7) increased visitation (5.02 visits/day vs. 0.1/day controls; P < 0.05), while dwell-times also increased 6.8 s/visit vs. 0.2 s/visit in both risk-settings. The latter is consistent with persistent attraction (+valence), but was also influenced by shelter, as runway visits (1.1 visits/day) were a magnitude more common than predator-exposed (0.1 visits/day). Further understanding and exploiting the mobility of city rats is necessary for improvements in basic and applied research, including city pathogen-surveillance and urban wildlife management.

The intensity of male-male competition may affect chemical scent constituents in the dark ventral patch of male Iberian red deer

During the mating season, Iberian red deer males (Cervus elaphus hispanicus) present a large visible dark ventral area in their abdomen. This characteristic dark-haired area is formed by the impregnation of the hair with sprayed urine and gland secretions and contains volatile compounds that can be used in intraspecific communication. Here, we used gas chromatography-mass spectrometry (GC-MS) to describe the lipophilic chemicals from the dark ventral patch of males from different populations with different levels of intrasexual competition. Amongst all the compounds found, m-cresol, benzoic acid, cholesterol and 4-hydroxy-benzenopropanoic acid were the most abundant. The proportions of these compounds varied with age as well as with the level of intra-sexual competition, independently of age. In particular, red deer males experiencing higher intra-sexual competition had lower proportions of aromatic compounds (especially m-cresol) but higher proportions of carboxylic acids on their dark bellies. Males in a high male-male competition situation, invest in volatile compounds that can reveal their age, dominance status and condition, and that, in addition, enhance this signal. On the contrary, males from low intra-sexual competition populations have chemical profiles more characteristic of young individuals. This research shows a first glance of how secretion of volatile compounds of male deer can be modulated due to the intensity of male-male competition in the population.

Voles and weasels in the boreal Fennoscandian small mammal community: what happens if the least weasel disappears due to climate change?

Climate change, habitat loss and fragmentation are major threats for populations and a challenge for individual behavior, interactions and survival. Predator–prey interactions are modified by climate processes. In the northern latitudes, strong seasonality is changing and the main predicted feature is shortening and instability of winter. Vole populations in the boreal Fennoscandia exhibit multiannual cycles. High amplitude peak numbers of voles and dramatic population lows alternate in 3–5‐year cycles shortening from North to South. One key factor, or driver, promoting the population crash and causing extreme extended lows, is suggested to be predation by the least weasel. We review the arms race between prey voles and weasels through the multiannual density fluctuation, affected by climate change, and especially the changes in the duration and stability of snow cover. For ground‐dwelling small mammals, snow provides thermoregulation and shelter for nest sites, and helps them hide from predators. Predicted increases in the instability of winter forms a major challenge for species with coat color change between brown summer camouflage and white winter coat. One of these is the least weasel, Mustela nivalis nivalis. Increased vulnerability of wrong‐colored weasels to predation affects vole populations and may have dramatic effects on vole dynamics. It may have cascading effects on other small rodent–predator interactions and even on plant–animal interactions and forest dynamics.

Discovery and characterization of natural products that act as pheromones in fish

Covering: up to 2018 Fish use a diverse collection of molecules to communicate with conspecifics. Since Karlson and Lüscher termed these molecules 'pheromones', chemists and biologists have joined efforts to characterize their structures and functions. In particular, the understanding of insect pheromones developed at a rapid pace, set, in part, by the use of bioassay-guided fractionation and natural product chemistry. Research on vertebrate pheromones, however, has progressed more slowly. Initially, biologists characterized fish pheromones by screening commercially available compounds suspected to act as pheromones based upon their physiological function. Such biology-driven screening has proven a productive approach to studying pheromones in fish. However, the many functions of fish pheromones and diverse metabolites that fish release make predicting pheromone identity difficult and necessitate approaches led by chemistry. Indeed, the few cases in which pheromone identification was led by natural product chemistry indicated novel or otherwise unpredicted compounds act as pheromones. Here, we provide a brief review of the approaches to identifying pheromones, placing particular emphasis on the promise of using natural product chemistry together with assays of biological activity. Several case studies illustrate bioassay-guided fractionation as an approach to pheromone identification in fish and the unexpected diversity of pheromone structures discovered by natural product chemistry. With recent advances in natural product chemistry, bioassay-guided fractionation is likely to unveil an even broader collection of pheromone structures and enable research that spans across disciplines.

Sex differences in scent-marking in captive red-ruffed lemurs

Primate chemical communication remains underappreciated, as primates are considered to rely on other sensory modalities. However, various lines of evidence suggest that olfaction plays an important role in primate societies, including the conspicuous scent-marking behavior of many strepsirrhines and callitrichines. Although lemurs typically show scent-marking, little is known about this behavior in red-ruffed lemurs (Varecia variegata rubra). We combined behavioral observations and semiochemistry analyses to improve our understanding of scent-marking in two captive troops housed at Dudley and Twycross zoos (UK). We collected olfactory behavioral observations by focusing on two family troops (N = 7) for 132 hr. We investigated the volatile compounds of ano-genital scent-marks using solid-phase microextraction and gas chromatography-mass spectrometry and compared volatile chemical profiles with features of the signaller. Males scent-marked most frequently and predominantly in specific meaningful areas of the enclosure, while within females the occurrence of scent-marking was related to their age. We found behavioral sexual dimorphism, with male predominantly depositing secretions via neck and mandible glands and females via ano-genital glands. We identified a total of 32 volatile components of ano-genital gland secretion, including compounds that have already been found in other mammals as sex pheromones and cues to fitness, in ano-genital scent-marks spontaneously left on filter paper by adult females. Our findings suggest that red-ruffed lemurs might use scent-marking to convey information about sex and female age, with male neck-marking behavior playing defensive territorial functions and ano-genital marking related to socio-sexual communication.

The Extended Genotype: Microbially Mediated Olfactory Communication

Microbes are now known to influence inter- and intraspecific olfactory signaling systems. They do so by producing metabolites that function as odorants. A unique attribute of such odorants is that they arise as a product of microbial-host interactions. These interactions need not be mutualistic, and indeed can be antagonistic. We develop an integrated ecoevolutionary model to explore microbially mediated olfactory communication and a process model that illustrates the various ways that microbial products might contribute to odorants. This novel approach generates testable predictions, including that selection to incorporate microbial products should be a common feature of infochemicals that communicate identity but not those that communicate fitness or quality. Microbes extend an individual's genotype, but also enhance vulnerability to environmental change.

Single compounds elicit complex behavioural responses in wild, free-ranging rats

There is mounting evidence that single compounds can act as signals and cues for mammals and that when presented at their optimal concentration they can elicit behavioural responses that replicate those recorded for complex mixtures like gland secretions and foods. We designed a rapid bioassay to present nine compounds that we had previously identified in foods, each at seven different concentrations (63 treatments), to wild, free-ranging rats and scored each treatment for attraction and three behavioural responses. Nine treatments (taken from five compounds) statistically outperformed the current standard rat attractant, peanut butter. Attraction to treatments was highest at the two lowest concentrations (0.1 and 0.01 μg g⁻¹) and a statistically significant relationship of increasing attraction with decreasing treatment concentration was identified. Our study identified five compounds not previously associated with behavioural responses by rats that elicit equivalent or more intense behavioural responses than those obtained with peanut butter. Moreover, attraction to treatments was driven by a concentration-dependent relationship not previously reported. This is the first study to identify isopentanol, 1-hexanol, acetoin, isobutyl acetate and 2-methylbutyl acetate as possible semiochemicals/cues for rats. More broadly, our findings provide important guidance to researchers in the ongoing search for mammalian semiochemicals and cues.