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

Abstract

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.

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

“…Therefore, secretory activity and reproductive status seem to be the cause of the structural changes in mitochondria of apocrine gland cells. Because apocrine secretion is activated during the breeding season in the back skin of brown bears (Tomiyasu, Kondoh, et al, 2018), reproductive status and altered apocrine secretion might also regulate the structural changes in mitochondria of apocrine gland cells.…”

“…Six healthy, sexually‐mature male bears (ID numbers, I, V, VI, VIII, XIII and XIV; age, 15–26 years) living on Sahoro Bear Mountain, Hokkaido, Japan (43°N, 142°E) were sampled during the breeding (June) and non‐breeding (October) seasons (Tsubota, Kanagawa, Takahashi, Yasue, & Fukunaga, 1985). Bears I, V, VI, and VIII were included in a previous study (Tomiyasu, Kondoh, et al, 2018). During the daytime, the bears can roam freely in an open, fenced mountainous area of 150,000 m 2 , where the vegetation is similar to that of wild‐bear habitats, then they are separated in a single location at night.…”

“…The frequency of this behavior increases among male brown bears during the breeding season (Lamb et al, 2017). We previously found that apocrine and sebaceous glands are enlarged, and that oily secretions increase in the back skin of male brown bears during the breeding season, compared with the non‐breeding season (Tomiyasu, Yanagawa et al, 2018; Tomiyasu, Kondoh, et al, 2018). Therefore, secretions in the back skin of brown bears play important roles in communicative behavior.…”

“…In apocrine gland cells, apocrine secretion and exocytosis are main secretory manners (Kurosumi, Shibasaki, & Ito, 1984). We previously determined that apocrine secretions are highly activated in the back skin of male brown bears during the breeding, compared with the non‐breeding season (Tomiyasu, Kondoh, et al, 2018). However, the mechanism through which apocrine gland cells produce the components of apocrine secretions during the breeding season remains obscure, but understanding seasonal changes in apocrine gland cells at the organelle level should address this issue.…”

“…(Tsubota, Kanagawa, Takahashi, Yasue, & Fukunaga, 1985). Bears I, V, VI, and VIII were included in a previous study (Tomiyasu, Kondoh, et al, 2018). During the daytime, the bears can roam freely in an open, fenced mountainous area of 150,000 m 2 , where the vegetation is similar to that of wild-bear habitats, then they are separated in a single location at night.…”