CUTANEOUS WATER LOSS AND THE EPIDERMAL SHEDDING CYCLE IN THE TOKAY (GEKKO GECKO) (LACERTILIA, REPTILIA) A. H. ZUCKER* and P. F. A. MADERSON Department of Biology, Brooklyn College, Brooklyn, New York 11210 USA (Receirrtl 20 June 1979) Abstract-l. The relationship between cutaneous water loss (CWL) and the squamate shedding cycle has not been investigated previously. 2. We measured CWL in the tokay by compartmentalized chamber and capsule techniques through- out the shedding cycle and related the values to changes in epidermal morphology. 3. CWL is high during shedding, decreases thereafter, and reaches lowest levels during the resting stage and the early renewal phase. CWL increases thereafter until the shed occurs. 4. Analysis of this pattern shows that it supports the thesis that the alpha layer of the tokay epidermis is the main permeability barrier INTRODUCTION Like all amniotes. extant lepidosaurs (the tuatara, lizards, and snakes) have a cornified or keratinized epidermal body surface, and it is generally assumed that this covering is an adaptation reducing the cuta- neous component of evaporative water loss (EWL), a prerequisite for successful terrestrial life. Lepidosaurs are unique, however, in that their scaled integument contains an epidermis wherein two fundamentally dif- ferent types of fibrous protein alternate vertically over the entire body surface. In all other amniotes, the epidermal cells over any one portion of the body syn- thesize either the alpha form (characterized by hair) or the feather form (characterized by feather); the entire body covering may be homogeneous with re- spect to one type, as in mammals, or there may be regional variation (Baden & Maderson, 1970). The vertical alternation of epidermal cells synthesizing the two distinct types of fibrous protein in lepidosaurs is the basis for the characteristic periodic “skin-shed- ding”, and the cytological basis of this phenomenon has been extensively studied at the gross, light, and electron-microscopic levels (see references in Chiu & Maderson, 1975; and Maderson et al., 1972). No definitive explanation has yet been proposed for the anatomy of the lepidosaurian epidermis, but the fact that its structure changes regularly in association with periodic shedding raises the question as to the poss- ible effect of this phenomenon on its physiological properties. No terrestrial vertebrate is known to have an in- tegument completely impermeable to water, so that cutaneous water loss (CWL) is always a factor to be considered when an animal is exposed to a desiccat- ing environment. Snakes and lizards are found in * Present address: Department of Physiology and Bio- physics, University of Tennessee Center for the Health Sciences. 894 Union Avenue,. Memphis, Tennessee 38163, U.S.A. various habitats, and several studies have reported rates of CWL in a variety of species (Chew & Dam- mann, 1961; Crawford & Kampe, 1971; Dmi’el, 1972; Krakauer, 1970); but none of these reports considered the structure of the epidermis with respect to the shedding cycle. While other authors (Claussen, 1967; Cohen, 1975; Dunson & Robinson, 1976; Gans rt crl., 1968; Minnich, 1970) made certain comments in this context, there has not yet appeared a specific study attempting to relate epidermal changes throughout the shedding cycle to rates of CWL. It has been sug- gested (Maderson et al., 1978; Zucker, 1980) that the complex epidermal structure of squamates might be explained by assuming that the outer beta layer (con- taining feather-type keratin) has primarily a mechani- cal function, serving partly to maintain scale shape and partly to preserve the underlying alpha layer from abrasion; the alpha layer (containing alpha-type keratin) appears to be the main barrier to percu- taneous water loss. In this present paper, estimations of CWL by two different techniques have been corre- lated with changes in epidermal histology. The results of these studies show that there is cyclic variation in CWL, and this variation can be correlated with changes in the alpha layer. MATERIALS AND METHODS Tokays zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO (Gekko gecko) from Thailand were obtained from a local dealer. They were housed in individual zyxwvutsrqponm wire mesh cages at 30°C and kept on a 12:12 hr light:dark cycle. Crickets, mealworms, and mouse pups were provided ad libitum, animals were sprayed daily with water, and shed- ding frequencies were noted. Unrestrained tokays ingest their outer epidermal generation (shed material) as they remove it. The entire shedding process usually takes less than an hour, and is synchronized over the entire body. All animals were followed through at least one complete cycle before being use d in an experiment. The apparatus and methods used to measure CWL have been described elsewhere (Zucker, 1980), and are only briefly summarized below. 381