Morphological, Histological, and Immunohistochemical Characteristics of Caudal Glands in Sika Deer

ABSTRACT Sika deer ( Cervus nippon ) exhibit a “tail‐flagging” behavior when threatened. While this behavior has been hypothesized to be linked to chemical signaling, structural details responsible for odorant production in the tail remain obscure. Caudal skin glands in sika deer may be adapted to facilitate the dissemination of volatile chemical signals during tail‐flagging behavior. Therefore, we aimed to determine how scent components are produced and secreted in the tails of sika deer. We scrutinized the gross anatomy and analyzed glandular structures in skin samples from 10 postnatal and three fetal sika deer using computed tomography (CT), histology, and immunohistochemical staining. Visual assessment and CT imaging revealed that the tails consisted mainly of enlarged glandular tissues that were histologically classified as sebaceous, apocrine, or modified. The histological characteristics of modified glands were distinct from those of sebaceous and apocrine glands in terms of nuclear positioning, cell height, and the presence of disrupted cells. The modified glands extended from the deep to the superficial layers. Some apocrine and modified gland cells formed apical projections in the superficial layer, whereas other modified gland cells in the deep layer appeared disrupted. These findings indicated that modified gland cell secretions vary according to skin depth. Immunohistochemical staining to detect α‐smooth muscle actin revealed that myoepithelial cells surrounded the apocrine and modified gland cells, suggesting that the contraction of myoepithelial cells may push out the secretions in these glands. Histological staining revealed apocrine glands in the deeper layers of fetal tails, indicating that these glands are the source of the caudal modified glands. In conclusion, sika deer had caudal modified glands, derived from apocrine glands, and these results provide the morphological basis of functional specialization for facilitating the dissemination of volatile chemical signals.