Comparative Morphology of the Skin of the Water Deer (Hydropotes inermis) and Muntjacs (Muntiacus spp.), Cervidae, Artiodactyla

Abstract The fur and skin glands were compared in phylogenetically related species with partially overlapping ranges—the water deer (Hydropotes inermis) and muntjacs (Muntiacus muntjak, M. reevesi, M. vaginalis, and M. vuquangensis)—using light and electron microscopy. The species differed in fur coloration and heterogeneity and in the development of specific skin glands, reflecting adaptations to their respective habitats: the water deer favors riparian habitats, whereas muntjacs inhabit savannas and forests. The water deer has a variegated fur, whereas coloration in muntjacs is more uniform, although markings are present. In both groups, fur coloration provides habitat-specific camouflage. The water deer also has a highly heterogeneous fur, with pronounced variation in hair dimensions, particularly on the back, flanks, and thighs, and distinctive nodular guard hairs. These features protect the skin as the animal moves through thickets of thorny shrubs and sharp-leaved grasses along rivers and around swamps. Neither group has abundant underfur, as these deer inhabit the temperate monsoon and tropical zones and do not require a dense insulating coat. Nevertheless, the well-developed medulla of the guard hairs enhances thermal insulation against seasonal and diurnal fluctuations in temperature and humidity. The medullary architecture of water deer hairs resembles that of moose, musk deer, roe deer, and Manchurian wapiti, whereas the muntjac medulla is simpler and resembles that of sika deer, suggesting a basal phylogenetic position for muntjacs and sika deer. Quantitative characteristics of the cuticular pattern indicate that the water deer is similar to members of the subfamily Alceinae. In muntjacs, as in the European roe deer and Siberian musk deer, these characteristics differ from those in the main group of species in the genus Cervus, consistent with the taxonomy of the infraorder Pecora. Both groups possess a broad complement of specific skin glands typical of cervids. The water deer also has inguinal glands, a unique condition among cervids, whereas muntjacs have frontal and mental glands. Neither group has tarsal or metatarsal glands. These differences may reflect habitat-specific scent-marking behavior: water deer mark herbaceous and shrub vegetation and possibly bedding sites, whereas muntjacs leave marks on trunks, branches, and the crowns of trees and shrubs.