Analysis of the microstructure of Xenodontinae snake scales associated with different habitat occupation strategies.
The morphology of many organisms seems to be related to the environment they live in. Nonetheless, many snakes are so similar in their morphological patterns that it becomes quite difficult to distinguish any adaptive divergence that may exist. Many authors suggest that the microornamentations on the scales of reptiles have important functional value. Here, we examined variations on the micromorphology of the exposed oberhautchen surface of dorsal, lateral, and ventral scales from the mid-body region of Xenodontinae snakes: Sibynomorphus mikani (terricolous), Imantodes cenchoa (arboreal), Helicops modestus (aquatic) and Atractus pantostictus (fossorial). They were metallized and analyzed through scanning electron microscopy. All species displayed similar microstructures, such as small pits and spinules, which are often directed to the scale caudal region. On the other hand, there were some singular differences in scale shape and in the microstructural pattern of each species. S. mikani and I. cenchoa have larger spinules arranged in a row which overlap the following layers on the scale surface. Species with large serrate borders are expected to have more frictional resistance from the caudal-cranial direction. This can favor life in environments which require more friction, facilitating locomotion. In H. modestus, the spinules are smaller and farther away from the posterior rows, which should help reduce water resistance during swimming. The shallower small pits found in this species can retain impermeable substances, as in aquatic Colubridae snakes. The spinules adhering to the caudal scales of A. pantostictus seem to form a more regular surface, which probably aid their fossorial locomotion, reducing scale-ground friction. Our data appear to support the importance of functional microstructure, contributing to the idea of snake species adaptation to their preferential microhabitats.
Comparative Morphology of the Skin of Natrix tessellata (Family: Colubridae) and Cerastes vipera (Family: Viperidae)
We studied beneficial difference of the skin of two snakes. Two snakes were chosen from two different habitats and two families: Colubridae (Natrix tessellata) and Viperidae (Cerastes vipera). The investigations were performed by light and electron microscopy. Histologically, the skin of the studied species show pronounced modifications that correlated with functional demands. The scales in Natrix tessellata overlapped slightly, while in Cerastes vipera they were highly overlapped. SEM shows that scales of Natrix tessellata had bidentate tips while the scales of Cerastes vipera were keeled. Histochemically, in both studied species, melanocytes and collagenous fibres were distributed throughout the dermis. Polysaccharides were highly concentrated in the epidermis and dermis of both species while proteins were highly concentrated only in the epidermis. Transmission electron microscopy (TEM) showed that the skin of both snakes consisted of keratins located in the epidermis. Some lipids and mucus were incorporated into the outer scale surfaces such that lipids were part of the fully keratinised hard layer of the snakes' skins. Lipids are probably responsible for limiting water loss and ion movements across the skin. Melanosomes from epidermal melanocytes were present only in Cerastes vipera. In aggregate, these results indicate that snakeskin may provide an ecological indicator whereby epidermal and integumentary specializations may be ecologically correlated.
Fibrous Proteins of Snake Scale
HISTOLOGICAL1 and electron microscope2 investigations of snake scale indicate that there are three morphologically distinct keratinized layers on the outer scale surface (Fig. 1). Rudall3 showed that two different X-ray diffraction patterns can be obtained in the large ventral scales. Because keratinized layers arise from the same germinative cell population it seems that the cells of snake epidermis alternately produce at least two structural proteins. This report confirms previous observations on the nature of these fibrous proteins in the dorsal scales of a different species and adds new information on their orientation.