Contraceptive effect of a gonadotropin-releasing hormone vaccine on captive male brown bears (Ursus arctos)

Fertility control has traditionally been applied in zoos to control captive populations, and reversible contraception is important. However, contraceptive methods for male bears have not been reported. We aimed to establish a reversible contraceptive for male brown bears by investigating the effects of a gonadotropin-releasing hormone (GnRH) vaccine (Improvac®) that was developed for the immune castration of pigs. We vaccinated six bears with two sequential doses of 400 (n = 2) or 600 μg Improvac® (n = 4) with a 1-month interval during the pre-breeding season (February to April). We compared the reproductive parameters (testosterone levels and semen parameters) of the six vaccinated and four non-vaccinated (control) bears once during the breeding season (May or June). To investigate whether the reproductive performance could be restored in the following year of contraception, we also compared the reproductive parameters once during the breeding season in two bears between the year with GnRH vaccination and the following year without vaccination. Vaccination treatments suppressed reproductive parameters in 5 bears, although vaccination with 400 μg of Improvac® was not effective in one bear. Testosterone levels and the rate of progressive sperm motility were significantly lower, and total sperm count and testis size tended to be lower in vaccinated bears, compared with the controls. Blood biochemical findings and direct observations after Improvac® vaccination did not reveal side effects. Moreover, testosterone levels and spermatogenic scores of two bears were restored in the following year. We confirmed that the Improvac® vaccine elicited a reversible contraceptive effect in male brown bears.

A review of sebum in mammals in relation to skin diseases, skin function, and the skin microbiome

Diseases vary among and within species but the causes of this variation can be unclear. Immune responses are an important driver of disease variation, but mechanisms on how the body resists pathogen establishment before activation of immune responses are understudied. Skin surfaces of mammals are the first line of defense against abiotic stressors and pathogens, and skin attributes such as pH, microbiomes, and lipids influence disease outcomes. Sebaceous glands produce sebum composed of multiple types of lipids with species-specific compositions. Sebum affects skin barrier function by contributing to minimizing water loss, supporting thermoregulation, protecting against pathogens, and preventing UV-induced damage. Sebum also affects skin microbiome composition both via its antimicrobial properties, and by providing potential nutrient sources. Intra- and interspecific variation in sebum composition influences skin disease outcomes in humans and domestic mammal species but is not well-characterized in wildlife. We synthesized knowledge on sebum function in mammals in relation to skin diseases and the skin microbiome. We found that sebum composition was described for only 29 live, wild mammalian species. Sebum is important in dermatophilosis, various forms of dermatitis, demodicosis, and potentially white-nose syndrome. Sebum composition likely affects disease susceptibility, as lipid components can have antimicrobial functions against specific pathogens. It is unclear why sebum composition is species-specific, but both phylogeny and environmental effects may drive differences. Our review illustrates the role of mammal sebum function and influence on skin microbes in the context of skin diseases, providing a baseline for future studies to elucidate mechanisms of disease resistance beyond immune responses.

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.

Sex-, age-, and time-specific visual communication in brown bears

Intraspecific communication in mammals is well-documented but generally restricted to chemical and acoustic signaling. However, other overlooked channels, such as visual signaling, may be used to communicate among conspecifics. Here, by using experimental manipulations together with camera traps on 13 brown bear (Ursus arctos) rubbing trees in the Cantabrian Mountains (northwestern Spain), we document detailed temporal patterns and behavioral aspects of a recently discovered novel communication channel for this species, visual signaling through the trunk debarking of focal trees. Video footage showed that visual marking is a sex-, age-, and time-specific means of communication in brown bears, being performed exclusively by adult males during the mating season (mainly April–June in the study area). Trunk debarking was always associated with chemical marking and was never an isolated behavior, suggesting that visual and chemical signals might be complementary. Visual and chemical marks may provide different information; for example, visual marks could be an indicator of individual size and, thus, the dominance status of adult males looking for mating opportunities. This is the first time that evidence is provided showing that visual signaling in a large carnivore is exclusive to a specific class of individuals (adult males) and linked to reproductive needs only. Bear visual signaling not only represents an advance in our comprehension of animal communication but may also serve to easily locate the mating areas of mammals, which are crucial for large carnivore species, such as the brown bear, that frequently need specific and urgent plans for conservation and management.

Associations between plasma testosterone levels and season, nutritional status, age, and body size in free-ranging male Asian black bears (Ursus thibetanus) in central Honshu, Japan

Testosterone is an important regulator of male reproduction in terms of spermatogenesis and physiological changes in the accessory reproductive organs. Despite the important role of the testosterone level in male reproduction, testosterone levels vary among male bears even during the breeding season, and the causative underlying factors remain unknown. We postulated that testosterone levels are higher during the breeding season than during other seasons in free-ranging male bears, and that testosterone levels increase with advancing age, larger body size, and better nutritional status. We assessed potential factors (season, time of sampling, body condition index, head circumference, and age) associated with the testosterone level in 80 blood samples collected from free-ranging Asian black bears (Ursus thibetanus) captured in barrel traps in the Ashio-Nikko Mountains and Okutama Mountains in central Honshu Island, Japan. The plasma testosterone level was higher during the breeding season (May-July) than during the non-breeding season (August-November). The body condition index was significantly and positively associated with the plasma testosterone level. None of the other factors were significantly associated with the plasma testosterone level. Therefore, the body condition index may be essential for maintaining high plasma testosterone levels. These findings imply that testosterone secretion might be activated in free-ranging males during the breeding season, and animals with good nutritional status may be able to maintain high plasma testosterone levels. This study uncovered an association between nutritional conditions and reproductive activity in male bears.

Rubbing behavior of European brown bears: factors affecting rub tree selectivity and density

Scent-mediated communication is considered the principal communication channel in many mammal species. Compared with visual and vocal communication, odors persist for a longer time, enabling individuals to interact without being in the same place at the same time. The brown bear (Ursus arctos), like other mammals, carries out chemical communication, for example, by means of scents deposited on marking (or rub) trees. In this study, we assessed rub tree selectivity of the brown bear in the predominantly deciduous forests of the Cantabrian Mountains (NW Spain). We first compared the characteristics of 101 brown bear rub trees with 263 control trees. We then analyzed the potential factors affecting the density of rub trees along 35 survey routes along footpaths. We hypothesized that: (1) bears would select particular trees, or tree species, with characteristics that make them more conspicuous; and (2) that bears would select trees located in areas with the highest presence of conspecifics, depending on the population density or the position of the trees within the species' range. We used linear models and generalized additive models to test these hypotheses. Our results showed that brown bears generally selected more conspicuous trees with a preference for birches (Betula spp.). This choice may facilitate the marking and/or detection of chemical signals and, therefore, the effectiveness of intraspecific communication. Conversely, the abundance of rub trees along footpaths did not seem to depend on the density of bear observations or their relative position within the population center or its border. Our results suggest that Cantabrian brown bears select trees based on their individual characteristics and their location, with no influence of characteristics of the bear population itself. Our findings can be used to locate target trees that could help in population monitoring.

Brown bear communication hubs: patterns and correlates of tree rubbing and pedal marking at a long-term marking site

Chemical communication is important for many species of mammals. Male brown bears, Ursus arctos, mark trees with a secretion from glands located on their back. The recent discovery of pedal glands and pedal-marking at a site used for tree-rubbing led us to hypothesize that both types of marking form part of a more complex communication system. We describe the patterns of chemical communication used by different age and sex classes, including differences in the roles of these classes as information providers or receivers over four years at a long-term marking site. Using video recordings from a camera trap, we registered a total of 285 bear-visits and 419 behavioral events associated with chemical communication. Bears visited the site more frequently during the mating season, during which communication behaviors were more frequent. A typical visit by male bears consisted of sniffing the depressions where animals pedal mark, performing pedal-marking, sniffing the tree, and, finally, rubbing against the trunk of the tree. Adult males performed most pedal- and tree-marking (95% and 66% of the cases, respectively). Males pedal-marked and tree-rubbed in 81% and 48% of their visits and sniffed the pedal marks and the tree in 23% and 59% of visits, respectively. Adult females never pedal marked, and juveniles did so at very low frequencies. Females rubbed against the tree in just 9% of their visits; they sniffed the tree and the pedal marks in 51% and 21% of their visits, respectively. All sex and age classes performed pedal- and tree-sniffing. There were significant associations between behaviors indicating that different behaviors tended to occur during the same visit and were more likely if another individual had recently visited. These associations leading to repeated marking of the site can promote the establishment of long-term marking sites. Marking sites defined by trees and the trails leading to them seem to act as communication hubs that brown bears use to share and obtain important information at population level.

Seasonal ultrastructural changes in apocrine gland cells in back skin of male brown bears (Ursus arctos)

Oily secretions from the back skin are involved in the marking behavior of male brown bears (Ursus arctos), and apocrine glands in back skin are activated during the breeding season. Here, we investigated seasonal changes in the intracellular organelles of apocrine gland cells in the back skin of male brown bears using transmission electron microscopy (TEM) and osmium-maceration scanning electron microscopy (OM-SEM). The morphological features of mitochondria and intracellular granules, and secretory mechanisms obviously differed between breeding and non-breeding seasons. The TEM findings showed that contents of low-density granules were released into the glandular lumen by frequent exocytosis, and sausage-shaped mitochondria were located in the perinuclear region during the non-breeding season. In contrast, high-density granules appeared in the apical region and in projections during the breeding season, and swollen mitochondria and lysosome-like organelles separating into high-density granules were located in the perinuclear region. The OM-SEM findings revealed swollen mitochondria with only a few partially developed cristae, and small mitochondria with cristae shaped like those in swollen mitochondria in the apical regions during the breeding season. These findings indicated that the small mitochondria corresponded to the high-density granules identified by TEM. These findings suggested that mitochondria in apocrine gland cells swell, degenerate, fracture into small pieces, and are finally released by apocrine secretions during the breeding season. Small mitochondria released in this secretory manner might function as the source of chemical signals in the oily secretions of brown bears during the breeding season.

Lectin histochemical studies on the olfactory gland and two types of gland in vomeronasal organ of the brown bear

Olfaction is mediated by the vomeronasal and main olfactory systems, and the peripheral vomeronasal organ (VNO) processes species-specific chemicals that are associated with various behaviors in mammals. Sensory epithelial surfaces of the olfactory mucosa and VNO are covered by mucosal fluid that contains secretory products derived from associated glands, and glycoconjugates in the mucosal fluid are involved in odorant reception. The VNO of brown bears contains two types of glands; submucosal vomeronasal glands (VNG) and multicellular intraepithelial glands (MIG). The present study determined the labelling profiles of 21 lectins in the olfactory glands (OG), VNG and MIG of young male brown bears. The OG reacted with 12 lectins, and the VNG and MIG were positive for seven and eight lectins, respectively. Six lectins bound only to the OG, while four reacted with both or either of the VNG and MIG, but not the OG. The differences of lectin labelling pattern between the OG and glands in the VNO suggest that glycans in covering mucosal fluids differ between the olfactory mucosa and VNO. In addition, Bandeiraea simplicifolia lectin-I, Sophora japonica agglutinin and Jacalin reacted with the MIG but not the VNG, whereas Datura stramonium lectin and concanavalin A bound to the VNG, but not the MIG. These findings indicate that the properties of secretory substances differ between the two types of glands in the bear VNO, and that the various secretions from these two types of glands may function in the lumen of VNO together.

Testicular regulation of seasonal change in apocrine glands in the back skin of the brown bear (Ursus arctos)

Brown bears communicate with other individuals using marking behavior. Bipedal back rubbing has been identified as a common marking posture. Oily substances are secreted via enlarged sebaceous glands in the back skin of male bears during the breeding season. However, whether apocrine gland secretions are associated with seasonal changes remains unknown. The present study aimed to identify histological and histochemical changes in the secretory status and the glycocomposition of the apocrine glands in the back skin of male bears in response to changes in seasons and/or reproductive status. The apocrine glands of intact males during the breeding season were significantly larger and more active than those of castrated males during the breeding season and those of intact males during the non-breeding season. Lectin histochemical analyses revealed a more intense reaction to Vicia villosa agglutinin (VVA) in the cytoplasm, mainly Golgi zones of apocrine cells during the breeding season among castrated, compared with intact males. Positive staining for VVA was quite intense and weak in intact males during the non-breeding and breeding seasons, respectively. Ultrastructural analysis revealed VVA positivity in the Golgi zone, especially around secretory granules in apocrine cells. Changes in lectin binding might reflect a change in the secretory system in the apocrine cells. The present histological and histochemical findings of changes in the secretory status and glycocomposition of the apocrine glands according to the season and reproductive status suggest that these glands are important for chemical communication.