Abstract
In order to understand the cutaneous water loss in the desert-adapted and venomous lizard Heloderma suspectum, the microscopic structure and lipid composition of epidermal molts have been examined using microscopic, spectroscopic and chemical analysis techniques. The molt is formed by a variably thick, superficial beta-layer, an extensive mesos-region and few alpha-cells in its lowermost layers. The beta-layer contains most corneous beta proteins while the mesos-region is much richer in lipids. The proteins in the mesos-region are more unstructured than those located in the beta-layer. Most interestingly, among other lipids, high contents of cholesteryl-β-glucoside and cholesteryl sulfate were detected, molecules absent or present in traces in other species of squamates. These cholesterol derivatives may be involved in the stabilization and compaction of the mesos-region, but present a limited permeability to water movements. The modest resistance to cutaneous water-loss of this species is compensated by adopting other physiological strategies to limit thermal damage and water transpiration as previous eco-physiological studies have indicated. The increase of steroid derivatives may also be implicated in the heat shock response, influencing the relative behavior in this desert-adapted lizard.
Highlights
The complex epidermis of snakes and lizards comprises different corneous layers that play specific roles for the integrity of the integument, contributing to the adaptation of these reptiles to their specific environment[1,2,3,4,5,6]
This venomous lizard presents peculiar physiological and morphological adaptations in the dry conditions of the Sonoran Desert of the American S outhwest[14,15,16,17]. These studies have indicated that the Gila monster shows total Evaporative Water Loss (EWL) higher to that of lizards adapted to non-arid environments, and instead utilizes other physiological and behavioral mechanisms for being active in arid conditions despite the loss of water[14, 16]
The morphology of the skin shows some adaptations to the arid environment and previous microscopic analysis of the epidermis in this species has shown the presence of a thick mesos-region that comprises over 50 thin mesos-cells in some regions of the scales and in the hinge region, representing the thickest mesos-layer ever recorded in the epidermis of reptiles[18]
Summary
The complex epidermis of snakes and lizards comprises different corneous layers that play specific roles for the integrity of the integument, contributing to the adaptation of these reptiles to their specific environment[1,2,3,4,5,6]. Studies on the permeability of the epidermis in snakes with different ecological adaptations living at different environmental temperature and humidity were performed They have shown that lipids present in mesos- and alpha-layers have a crystalline packing. The morphology of the skin shows some adaptations to the arid environment and previous microscopic analysis of the epidermis in this species has shown the presence of a thick mesos-region that comprises over 50 thin mesos-cells in some regions of the scales and in the hinge region, representing the thickest mesos-layer ever recorded in the epidermis of reptiles[18] The presence of such a thick mesos-region, unique among squamates, may indicate that lipids of different types are abundant in the epidermis of this species, probably in relation to water conservation. The present study is part of a large-scale survey on the structure and composition of the epidermal molts of snakes and lizards and it can have implications on the control of water permeability through the epidermis of reptiles adapted to different ecological lifestyles
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