The structural design of the bat wing web and its possible role in gas exchange

Abstract

The structure of the skin in the epauletted fruit bat (Epomophorus wahlbergi) wing and body trunk was studied with a view to understanding possible adaptations for gas metabolism and thermoregulation. In addition, gas exchange measurements were performed using a respirometer designed for the purpose. The body skin had an epidermis, a dermis with hair follicles and sweat glands and a fat-laden hypodermis. In contrast, the wing web skin was made up of a thin bilayered epidermis separated by a connective tissue core with collagen and elastic fibres and was devoid of hair follicles and sweat glands. The wings spanned 18–24 cm each, with about 753 cm² of surface exposed to air. The body skin epidermis was thick (61 ± 3 µm, SEM), the stratum corneum alone taking a third of it (21 ± 3 µm). In contrast, the wing web skin epidermis was thinner at 9.8 ± 0.7 µm, with a stratum corneum measuring 4.1 ± 0.3 µm (41%). The wing capillaries in the wing web skin ran in the middle of the connective tissue core, with a resultant surface-capillary diffusion distance of 26.8 ± 3.2 µm. The rate of oxygen consumption (V̇O₂) of the wings alone and of the whole animal measured under light anaesthesia at ambient temperatures of 24 ºC and 33 ºC, averaged 6% and 10% of the total, respectively. Rate of carbon dioxide production had similar values. The membrane diffusing capacity for the wing web was estimated to be 0.019 ml O₂ min⁻¹ mmHg⁻¹. We conclude that in Epomophorus wahlbergi, the wing web has structural modifications that permit a substantial contribution to the total gas exchange.