Allometric scaling of skin weight and thickness to body weight in relation to taxonomic orders and habitats in mammals.

Skin is the largest organ in a mammal body, and it exhibits most significant range of adaptations to different habitats. It is a complex, biological composite structure, consisting of epidermis, dermis and subcutaneous tissues and is used for the therapeutic application of medical devices to improve healthcare. Extensive studies have been performed on the roles of the skin; however, little is known on its physiological characteristics in relation to body size among different species. The purpose of this study was therefore to evaluate the allometric scaling of skin weight (SW) and thickness (ST) to body weight (BW) in relation to genetics and habitats. Also analysed the relationship of BW to thicknesses of epidermis, dermis and subcutaneous tissues. This study used 249 adult animals of both sexes, belonging to 144 species, clustered in 18 taxonomic orders and five types of habitats. The animals were obtained from various sources in Japan. SW and BW were weighed, and ST was measured using a calliper followed by data analysis. Results showed that SW and ST were related to BW [log SW = 0.969 × logBW - 0636, adjust. R : 0.975]. The BW increased with increasing skin dermal thickness (y = 0.3916x + 1.5253, adjust. R : 0.6921), slightly with epidermal thickness (y = 0.2495x + 0.3984, adjust. R : 0.3402), but not all with the thickness of subcutaneous tissues (y = 0.1454x + 2.2437, adjust. R : 0.0752). The ratio of SW to BW (SW/BW) distributed over a large range from 0.06 to 0.64 values and varied among animal taxonomic orders and their dwelling habitats. Close relationship of BW to SW/BW was observed in species weighing ≥200 g but not in species weighing <200 g. In conclusion, SW and ST in mammals are determined by BW. The SW/BW varies based on BW, taxonomic orders and habitat and is large in small mammals weighing ≥200 g to provide a mechanism used for survival strategy.