Histological, chemical and behavioural evidence of pedal communication in brown bears OPEN (original) (raw)

Most mammals rely upon scent for intraspecific communication. As most bear species have large home ranges and are non-territorial, scent deposit while walking could be an effective way to communicate with conspecifics. Here, we investigate the existence of pedal glands in brown bears and their role in chemical communication from a histological, biochemical and behavioural perspective. We found eccrine glands in footpads, and prominent apocrine and sebaceous glands in the interdigital, metacarpal and metatarsal skin sections. Pedal scent contained 26 compounds including carboxylic acids, important constituents of mammalian secretions. Six of these compounds were exclusive for males. Finally, we describe a specific marking gait recorded in the field, mostly performed by males. Our study supports the existence of chemical communication through pedal marking in brown bears and suggests sex-coding potential of pedal scent. Chemical signaling is a widespread mode of communication amongst the vast majority of organisms, both terrestrial and aquatic 1. Among mammals, odours play a key role in communication, with chemical signaling used to inform about identity, sex, territorial borders, social status, reproductive state or group membership 2, 3. Apart from the prevalent chemical features of urine and faeces, mammal skin secretions offer a great potential for chemical communication, with many species showing specialized scent glands that are the main source of secretions in scent marking 4-7. Well known is the use of scent marking at communal latrines by badgers (Meles meles) and other mustelid species, which have anal glands used for specific squat-marking 8. Marking with subcaudal, chin, foot and ventral glands, and through scratching and rolling has also been recorded 7, 8. The understanding of the mechanisms behind the detection of scents and how the scent stimuli is reconstructed into scent maps used by animals in their environment has greatly advanced, but the world of odours and the way they are perceived still require a great deal more research and experimentation 9. The skin of mammals typically presents three types of glandular structures: holocrine sebaceous glands, apocrine sweat and eccrine sweat glands 4, 10. Sebaceous glands are evenly distributed over the body. They coat hair with sebum as it grows and are usually anatomically near an apocrine gland 11. Apocrine sweat glands, opening to follicles, are primarily observed in hairy skin 12 , while eccrine sweat glands secreting directly to skin surface via pores tend to be confined to specific regions, such as carnivores' footpads 5 or friction surfaces of hands, feet and tails of prosimians, monkeys and apes 11. These basic types of glands may associate in more complex structures (e.g. sacs) often located in specific areas of the skin. Finally, the presence of mammalian scent glands is often linked to typical behavioural patterns of scent marking 4-6, 13. Therefore an in-depth examination of the existence of scent glands is the first step to disentangle chemical communication. Most areas containing sebaceous and sweat glands can be involved in scent production and synthesize different odoriferous molecules 14. The secretions of these glands can be ultimately affected by bacterial fermentation,