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All animals harbor beneficial microbes. One way these microbes can benefit their animal hosts is by increasing the diversity and efficacy of communication signals available to the hosts. The fermentation hypothesis for mammalian chemical communication posits that bacteria in the scent glands of mammals generate odorous metabolites used by their hosts for communication and that variation in host chemical signals is a product of underlying variation in the bacterial communities inhabiting the scent glands. An effective test of this hypothesis would require accurate surveys of the bacterial communities in mammals’ scent glands and complementary data on the odorant profiles of scent secretions—both of which have been historically lacking. Here we use next-generation sequencing to survey deeply the bacterial communities in the scent glands of wild spotted and striped hyenas. We show that these communities are dominated by fermentative bacteria and that the structures of these communities covary with the volatile fatty acid profiles of scent secretions in both hyena species. The bacterial and volatile fatty acid profiles of secretions differ between spotted and striped hyenas, and both profiles vary with sex and reproductive state among spotted hyenas within a single social group. Our results strongly support the fermentation hypothesis for chemical communication, suggesting that symbiotic bacteria underlie species-specific odors in both spotted and striped hyenas and further underlie sex and reproductive state-specific odors among spotted hyenas. We anticipate that the fermentation hypothesis for chemical communication will prove broadly applicable among scent-marking mammals as others use the technical and analytical approaches used here.

The Japanese marten ( Martes melampus ) is a solitary mustelid species with a strict territorial space that might be maintained by scent marking. However, whether Japanese martens have scent glands that secrete chemical signals remains unknown. We aimed to clarify whether the abdominal glands in these animals secrete chemical signals and, if so, to characterize their morphological and histological features. We investigated nine Japanese martens (eight M. m. tsuensis and one M. m. melampus ) that were all roadkilled. Regardless of sex, season, and subspecies, they all had abdominal glands located at the rostral aspect of the penis or vagina, and brown secretions were evident on the skin area. Enlarged sebaceous and small apocrine glands were spread mostly throughout the abdominal glands. Obviously enlarged, specialized glands were located in the caudal and medial areas of the abdominal glands. The specialized and sebaceous gland cells were connected through a duct at the border between them. This suggested that the specialized gland cells were derived from the sebaceous type. However, eosin staining of the specialized gland cells possessing a nucleus was strongly positive for cytoplasm, whereas that of the sebaceous gland cells was weakly positive. Moreover, the specialized gland cells were weakly stained with Oil Red O, whereas the sebaceous gland cells were strongly stained. Thus, the secretory mechanism of the abdominal specialized glands may not be holocrine like sebaceous glands. In conclusion, Japanese martens had characteristic abdominal glands with developed sebaceous and specialized glands.

Background Insects have evolved various antipredator defenses, some of which produce copious chemicals when threatened, such as ants, beetles, butterflies, moths, stick insects, and true bugs. The true bugs (Hemiptera: Heteroptera) are known for their foul odor, which comprises over 45,000 species of biologically and economically important insects. One key element to the success of heteropterans is the evolution of specialized defensive glands, specifically the metathoracic scent gland in adults and the dorsal abdominal scent glands in nymphs, a hallmark synapomorphy for the clade. Within Pentatomomorpha, the scent gland peritreme exhibits remarkable morphological diversity, yet its evolutionary origins and drivers remain poorly understood due to sparse fossil evidence of these delicate structures. Results We report a series of Mesozoic fossils with well-preserved scent gland anatomy, including the earliest evidence from the Jurassic (165 million years ago), revealing an ancestral auricle-type morphology. Ancestral-state reconstruction across 40 extant and fossil taxa confirms the auricle as the plesiomorphic condition for Pentatomomorpha. Fossil evidence demonstrates phenotypic diversification by the Early Cretaceous (~ 125 Ma), with many peritreme types (auricle, spout, groove) emerging by the mid-Cretaceous. Developmental analyses of extant taxa show no pre-adult differentiation, indicating rapid peritreme formation during the final molt. Conclusions The scent gland peritreme evolved as a rapidly developing from a simple underdeveloped to auricle to five well-developed basic derived types in early Pentatomomorpha. Its subsequent diversification into specialized forms coincided with mid-Mesozoic habitat shifts and predator pressures, particularly during angiosperm proliferation. Convergent morphologies across lineages reflect shared ecological constraints and developmental plasticity.

Floral scent is considered an integral component of pollination syndromes, and its composition and timing of emission are thus expected to match the main pollinator type and time of activity. While floral scent differences among plant species with different pollination systems can be striking, studies on intraspecific variation are sparse, which limits our understanding of the role of pollinators in driving scent divergence. Here, we used dynamic headspace sampling to quantify floral scent emission and composition during the day and at night in the natural habitat of six Scandinavian populations of the fragrant orchid Gymnadenia conopsea. We tested whether diel scent emission and composition match pollinator type by comparing four populations in southern Sweden, where nocturnal pollinators are more important for plant reproductive success than are diurnal pollinators, with two populations in central Norway, where the opposite is true. To determine to what extent scent patterns quantified in the field reflected plasticity, we also measured scent emission in a common growth chamber environment. Both scent composition and emission rates differed markedly between day and night, but only the latter varied significantly among populations. The increase in scent emission rate at night was considerably stronger in the Swedish populations compared with the Norwegian populations. These patterns persisted when plants were transferred to a common environment, suggesting a genetic underpinning of the scent variation. The results are consistent with a scenario where spatial variation in relative importance of nocturnal and diurnal pollinators has resulted in selection for different scent emission rhythms. Our study highlights the importance of adding a characterization of diel variation of scent emission rates to comparative studies of floral scent, which so far have often focused on scent composition only.

In mammals, especially rodents, social behaviours, such as parenting, territoriality or mate attraction, are largely based on olfactory communication through chemosignals. These behaviours are mediated by species-specific chemosignals, including small organic molecules and proteins that are secreted in the urine or in various fluids from exocrine glands. Chemosignal detection is mainly ensured by olfactory neurons in two specific sensory organs, the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). This study aimed to characterise the olfactory communication in the fossorial ecotype of the water voles, Arvicola terrestris. We first measured the olfactory investigation of urine and lateral scent gland secretions from conspecifics. Our results showed that water voles can discriminate the sex of conspecifics based on the smell of urine, and that urinary male odour is attractive for female voles. Then, we demonstrated the ability of the VNO and MOE to detect volatile organic compounds (VOCs) found in water vole secretions using live-cell calcium imaging in dissociated cells. Finally, we evaluated the attractiveness of two mixtures of VOCs from urine or lateral scent glands in the field during a cyclical outbreak of vole populations.

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.

Floral scents and fruit aromas are crucial volatile organic compounds (VOCs) in plants. They are used in defense mechanisms, along with mechanisms to attract pollinators and seed dispersers. In addition, they are economically important for the quality of crops, as well as quality in the perfume, cosmetics, food, drink, and pharmaceutical industries. Floral scents and fruit aromas share many volatile organic compounds in flowers and fruits. Volatile compounds are classified as terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives. Many genes and transcription factors regulating the synthesis of volatiles have been discovered. In this review, we summarize recent progress in volatile function, composition, biosynthetic pathway, and metabolism regulation. We also discuss unresolved issues and research perspectives, providing insight into improvements and applications of plant VOCs.

Puberty is a key stage in mammalian ontogeny, involving endocrinological, physiological and behavioural changes, moderated by intrinsic and extrinsic factors. Thus, not all individuals within one population achieve sexual maturity simultaneously. Here, using the European badger (Meles meles) as a model, we describe male testosterone and female oestrone profiles (using Enzyme-immunoassays) from first capture (3 months, post-weaning) until 28 months (attaining sexual maturity and final body size), along with metrics of somatic growth, scent gland development and maturation of external reproductive organs as well as intra-specific competition. In both sexes, endocrinological puberty commenced at ca. 11 months. Thereafter, cub hormone levels followed adult seasonal hormone patterns but at lower levels, with the majority of cubs reaching sexual maturity during their second mating season (22-28 months). Interestingly, there was evidence for two endocrinological phenotypes among male cubs (less evident in females), with early developers reaching sexual maturity at 11 months (first mating season) and late developers reaching sexual maturity at 22-26 months (second mating season). Early developers also attained a greater proportion of their ultimate adult size by 11 months, exhibiting faster growth rates than late developers (despite having similar adult size). Male cubs born into larger social groups tended to follow the late developer phenotype. Our results support the hypothesis that a minimum body size is required to reach sexual maturity, which may be achieved at different ages, even within a single population, where early maturity can confer individual fitness advantages and enhance population growth rate.

The microbiome of mammalian scent glands is thought to contribute to the production of odorant compounds involved in sensory communication. Yet, the extent to which glandular microbiomes contain bacteria relevant to odor production and vary by host species, scent marking behavior, or gland morphology remains poorly understood, particularly in wild animals. We sampled microbes collected from skin swabs of suprapubic and sternal scent glands in wild Peruvian saddleback tamarins ( Leontocebus weddelli ; n = 19) and emperor tamarins ( Tamarinus imperator ; n = 20) to better understand glandular microbial communities. We aimed to: (1) profile glandular microbiomes of both species, focusing on odor‐related taxa and metabolic pathways, and (2) determine whether suprapubic glands, more often in contact with the external environment, had higher diversity and distinct composition of odor‐related taxa and pathways compared to sternal glands. We generated metagenomic reads using short‐read DNA shotgun sequencing from glandular swabs. We identified 18 odor‐associated microbial taxa in both tamarin species, mainly Staphylococcus and Corynebacterium , and 26 pathways, including pyruvate fermentation and amino acid metabolism. Suprapubic glands had lower Shannon alpha diversity relative to sternal glands, especially in L. weddelli . The glands of L. weddelli also differed in taxonomic composition, with odor‐related taxa more abundant in suprapubic glands. Our results provide evidence for the involvement of scent gland microbiomes in host communication biology. Glandular specializations differed not only between closely related tamarin species but also between gland types within the same individuals, suggesting a nuanced pattern of host–microbe coevolution that may shape interactions important for olfactory communication.

Although several mammals impregnate their fur with environmental odors, a phenomenon termed scent anointing or rubbing, the functional relevance of this behavior often is unclear. One theory is that scent anointing could be a form of scent matching with environmental odors to signal competitiveness and home range occupation. In this study we presented giant pandas with a range of odors to determine whether scent matching could provide a functional explanation for scent anointing in this species. We found that only a musk-based perfume elicited significantly more scent-anointing and scent-marking behavior than control. Males were also significantly more likely to scent-anoint and scent-mark than females. A preference for anointing, but not scent marking, when presented with peppermint (an insecticide) also was revealed. Our results suggest that giant pandas differentially scent-anoint with foreign odors to signal home range occupation, and possibly to repel ectoparasites. We also highlight how chemical signaling of resource-holding potential is likely to play an important role in determining competitive interactions between adult male giant pandas.