Brown bear skin-borne secretions display evidence of individuality and age-sex variation

Scent originates from excretions and secretions, and its chemical complexity in mammals translates into a diverse mode of signalling. Identifying how information is encoded can help to establish the mechanisms of olfactory communication and the use of odours as chemical signals. Building upon existing behavioural and histological literature, we examined the chemical profile of secretions used for scent marking by a solitary, non-territorial carnivore, the brown bear (Ursus arctos). We investigated the incidence, abundance, and uniqueness of volatile organic compounds (VOCs) from cutaneous glandular secretions of 12 wild brown bears collected during late and post-breeding season, and assessed whether age-sex class, body site, and individual identity explained profile variation. VOC profiles varied in the average number of compounds, compound incidence, and compound abundance by age-sex class and individual identity (when individuals were grouped by sex), but not by body site. Mature males differed from other age-sex classes, secreting fewer compounds on average with the least variance between individuals. Compound uniqueness varied by body site and age for both males and females and across individuals. Our results indicate that brown bear skin-borne secretions may facilitate age-sex class and individual recognition, which can contribute towards further understanding of mating systems and social behaviour.

How can the MHC mediate social odor via the microbiota community? A deep dive into mechanisms

Genes of the major histocompatibility complex (MHC) have long been linked to odor signaling and recently researchers’ attention has focused on MHC structuring of microbial communities and how this may in turn impact odor. However, understanding of the mechanisms through which the MHC could affect the microbiota to produce a chemical signal that is both reliable and strong enough to ensure unambiguous transmission of behaviorally important information remains poor. This is largely because empirical studies are rare, predictions are unclear, and the underlying immunological mechanisms governing MHC–microbiota interactions are often neglected. Here, we review the immunological processes involving MHC class II (MHC-II) that could affect the commensal community. Focusing on immunological and medical research, we provide background knowledge for nonimmunologists by describing key players within the vertebrate immune system relating to MHC-II molecules (which present extracellular-derived peptides, and thus interact with extracellular commensal microbes). We then systematically review the literature investigating MHC–odor–microbiota interactions in animals and identify areas for future research. These insights will help to design studies that are able to explore the role of MHC-II and the microbiota in the behavior of wild populations in their natural environment and consequently propel this research area forward.

Neighborhood bully: no difference in territorial response toward neighbors or strangers in marmots

Territorial animals are expected to adjust their response to intruders according to the perceived threat level. One of the factors that drives threat level is the identity of the intruder. The dear enemy phenomenon theory postulates that individuals should respond with lower intensity to neighbors, already possessing a territory, than to strangers that may fight to evict them. In social species, the hierarchical status of the intruder might also mediate this response. Such behavioral adjustments presuppose a capacity to discriminate between individuals posing different threat levels. Here, we tested the behavioral response of Alpine marmots to territorial intrusions in a wild population. We compared both dominant females’ and males’ responses to scents from neighbor and stranger dominant males (dear enemy phenomenon) and to dominant and subordinate stranger males (social status-specific response). In addition, we tested for any covariance between male scents and social status. We showed that female and male dominant marmots do not adjust the intensity of their behavioral responses to whether the intruder’s territory is bordering or not (neighbors or strangers) or to the intruder’s social status, even though dominant and subordinate males are thought to pose different threats and social status is encoded in scents. Thus, we did not find support for the dear enemy phenomenon and conclude instead that, in dominant Alpine marmots, no intruder should enter a foreign territory. Research taking a more holistic approach of the evolution and maintenance of territoriality is required to understand the flexibility of responses to intruders in group-living species.

Knowing Me, Knowing You: Anal Gland Secretion of European Badgers (Meles meles) Codes for Individuality, Sex and Social Group Membership

European badgers, Meles meles, are group-living in the UK, and demarcate their ranges with shared latrines. As carnivores, badgers possess paired anal glands, but olfactory information on the content of badger anal gland secretion (AGS) is largely uninvestigated. Here, we examined the volatile organic compounds (VOCs) of AGS samples from 57 free-living badgers using solid-phase microextraction (SPME) and gas chromatography—mass spectrometry. AGS was rich in alkanes (C7–C15, 14.3% of identified compounds), aldehydes (C5–C14, 9.7%), phenols (C6–C15, 9.5%), alcohols (C5–C10, 7.3%), aromatic hydrocarbons (C6–C13, 6.8%), ketones (C6–C13, 6.3%) and carboxylic acids (C3–C12, 5.6%) and contained a variety of esters, sulfurous and nitrogenous compounds, and ethers. The number of VOCs per profile ranged from 20 to 111 (mean = 65.4; ± 22.7 SD), but no compound was unique for any of the biological categories. After normalization of the raw data using Probabilistic Quotient Normalization, we produced a resemblance matrix by calculating the Euclidian distances between all sample pairs. PERMANOVA revealed that AGS composition differs between social groups, and concentration and complexity in terms of number of measurable VOCs varies between seasons and years. AGS VOC profiles encode individual identity, sex and vary with female reproductive state, indicating an important function in intraspecific communication. Because AGS is excreted together with fecal deposits, we conclude that chemical complexity of AGS enables particularly latrine-using species, such as badgers, to advertise more complex individual-specific information than in feces alone.

Seasonal and reproductive variation in chemical constituents of scent signals in wild giant pandas

Seasonally reproducing animals show many behavioral and physiological changes during the mating period, including increased signaling for intrasexual competition and mate attraction. We collected 102 anogenital gland secretions (AGS) from marking trees in Foping Nature Reserve, and used gas chromatography mass spectrometry analyze these chemical composition. Of these marks, all but one were from males, confirmed with DNA analysis. We found that several chemical constituents, especially volatile compounds, is present only during the mating season and that the relative abundance of many compounds changed as a function of breeding season, whereas nonvolatile compounds were lower in the mating season. This seasonal variation in chemical composition of AGS most likely plays an important role in governing giant panda reproduction, including mate location, attraction, and male-male competition. The chemical properties of many of these putative chemosignals-such as volatility and longevity-are suggestive of these roles, and undoubtedly contribute to successful reproduction for this species with a characteristically sophisticated chemical communication system. We also found a number of important differences between the chemical constituents of AGS from wild pandas and those found in previous studies with captive pandas, suggesting that inappropriate chemosignal composition may contribute to poor reproductive success in captive breeding programs.

Spurs, sexual dimorphism and reproductive maturity in Tasmanian echidnas (Tachyglossus aculeatus setosus)

We present data from an 18-year study of a wild population of Tasmanian echidnas, which show that the presence of spurs in an adult are a reliable indicator of sex, and that there is a slight but significant sexual dimorphism in size, with a male to female mass ratio of 1.1. Minimum age at first breeding in the wild for Tasmanian echidnas was 5 years, as has been found on Kangaroo Island, compared with 3 years in captive echidnas. It is often assumed that although the echidna is distributed throughout Australia, New Guinea and off-shore islands that all aspects of its basic biology are the same in all populations, but comparisons of our results with data from other populations suggest that there may be differences in size and sexual dimorphism.

Female Chemical Signalling Underlying Reproduction in Mammals

Chemical communication plays many key roles in mammalian reproduction, although attention has focused particularly on male scent signalling. Here, we review evidence that female chemical signals also play important roles in sexual attraction, in mediating reproductive competition and cooperation between females, and in maternal care, all central to female reproductive success. Female odours function not only to advertise sexual receptivity and location, they can also have important physiological priming effects on male development and sperm production. However, the extent to which female scents are used to assess the quality of females as potential mates has received little attention. Female investment in scent signalling is strongly influenced by the social structure and breeding system of the species. Although investment is typically male-biased, high competition between females can lead to a reversed pattern of female- biased investment. As among males, scent marking and counter-marking are often used to advertise territory defence and high social rank. Female odours have been implicated in the reproductive suppression of young or subordinate females across a range of social systems, with females of lower competitive ability potentially benefiting by delaying reproduction until conditions are more favourable. Further, the ability to recognise individuals, group members and kin through scent underpins group cohesion and cooperation in many social species, as well as playing an important role in mother-offspring recognition. However, despite the diversity of female scent signals, chemical communication in female mammals remains relatively understudied and poorly understood. We highlight several key areas of future research that are worthy of further investigation.

Energy Homeostasis in Monotremes

In 1803, the French anatomist Étienne Geoffroy Saint-Hilaire decided that the newly described echidna and platypus should be placed in a separate order, the monotremes, intermediate between reptiles and mammals. The first physiological observations showed monotremes had low body temperatures and metabolic rates, and the consensus was that they were at a stage of physiological development intermediate between "higher mammals" and "lower vertebrates." Subsequent studies demonstrated that platypuses and echidnas are capable of close thermoregulation in the cold although less so under hot conditions. Because the short-beaked echidna Tachyglossus aculeatus, may show very large daily variations in body temperature, as well as seasonal hibernation, it has been suggested that it may provide a useful model of protoendotherm physiology. Such analysis is complicated by the very significant differences in thermal relations between echidnas from different climates. In all areas female echidnas regulate Tb within 1°C during egg incubation. The lactation period is considered to be the most energetically expensive time for most female mammals but lactating echidnas showed no measurable difference in field metabolic rate from non-lactating females, while the lactation period is more than 200 days for Kangaroo Island echidnas but only 150 days in Tasmania. In areas with mild winters echidnas show reduced activity and shallow torpor in autumn and early winter, but in areas with cold winters echidnas enter true hibernation with Tb falling as low as 4.5°C. Monotremes do not possess brown adipose tissue and maximum rates of rewarming from hibernation in echidnas were only half those of marmots of the same mass. Although echidnas show very large seasonal variations in fat stores associated with hibernation there is no relationship between plasma leptin and adiposity. Leptin levels are lowest during post-reproductive fattening, supporting suggestions that in evolutionary terms the anorectic effects of leptin preceded the adiposity signal. BMR of platypuses is twice that of echidnas although maximum metabolism is similar. High levels of thyroid hormones in platypuses may be driving metabolism limited by low body temperature. Monotremes show a mosaic of plesiomorphic and derived features but can still inform our understanding of the evolution of endothermy.