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.
Coupling Effect of Morphology and Mechanical Properties Contributes to the Tribological Behaviors of Snake Scales
It is known that the tribological behaviors of snake skins are contributed by the synergistic action of multiple factors, such as surface morphology and mechanical properties, which has inspired fabrication of scale-like surface textures in recent years. However, the coupling effect and mechanism remain to be elucidated. In this work, the morphology and mechanical properties of the scales from different body sections (leading body half, middle trunk and tailing body half) and positions (dorsal, lateral and ventral) of Boa constrictor and Eryx tataricus were characterized and compared to investigate the corresponding effects on the tribological behaviors and to probe the possible coupling mechanism. The morphological characterizations of scanning electron microscopy and atomic force microscopy revealed significant differences between the two species that the scales from Boa constrictor are rougher in general. The mechanical properties measured by nanoindentation corroboratively demonstrated substantial differences in elastic modulus and hardness. Interestingly, the ventral scales with lower surface roughness, together with relatively larger elastic modulus and hardness, manifest higher friction coefficients. A “double-crossed” hypothesis was proposed to explain the observed coupling effect of morphology and mechanical properties on friction, which may afford valuable insights for the design of bionic surface with desirable tribological performance.
Morphological characterization of Eustrongylides sp. larvae (Nematoda, Dioctophymatoidea) parasite of Rhinella marina (Amphibia: Bufonidae) from Eastern Amazonia.
Absctract Eustrongylides spp. nematodes have birds as final hosts and uses other vertebrates as intermediate/paratenic host (fish, amphibians and reptiles) and have zoonotic potential. In amphibians, the larvae may be located in the subcutaneous tissues, liver and mesentery, between the muscle fibres, especially in the lower limbs. Rhinella marina, which is widely observed in Brazil, has exhibited complex diversity in its helminth fauna, reflecting the unique habitat of the Amazon biome. For the first time, this study describes the morphological aspects of third-stage larvae of Eustrongylides sp. in Rhinella marina from Santa Cruz do Ararí, Marajó Archipelago, Eastern Amazonia, using light and scanning electron microscopy.