Association Between Back Scent Gland Development and Reproductive Status in Male Brown Bears (Ursus arctos)

Abstract

Cutaneous scent glands secrete chemical signals for communication, a significant portion of which is to convey information about male reproductive status. This might be particularly important to animals with intraspecific variation in male reproductive activity, such as bears. Male brown bears mark trees with their scent secreted from back apocrine and sebaceous glands during the breeding season and thus might convey information about reproductive status. Therefore, we speculated that the development of scent glands in the back reflects reproductive performance. We investigated the effects of reproductive status on the development of scent glands in the back using contraception and explored relationships between reproductive parameters (testosterone levels, testis size, and spermatogenic scores) and the size of skin glands in the backs of intact male brown bears. During the breeding season, we sampled back and rump (control) skin, sperms by urethral catheterization, and blood under anesthesia from four male bears that were vaccinated with the contraceptive gonadotropin hormone-releasing hormone (GnRH) vaccine and five others that were not (controls). The back sebaceous and apocrine glands were significantly smaller in bears vaccinated with than without GnRH vaccine, suggesting that these glands are associated with reproductive status. Testosterone levels were significantly and positively associated with the size of sebaceous glands, whereas none of the reproductive parameters were associated with the size of either sebaceous or apocrine glands. Mating opportunities increase testosterone production. The positive association between testosterone and sebaceous glands might mean that sebaceous glands in the back can secrete chemicals on demand for reproduction.