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.
Are the number and size of scales in Liolaemus lizards driven by climate?
Ectothermic vertebrates are sensitive to thermal fluctuations in the environments where they occur. To buffer these fluctuations, ectotherms use different strategies, including the integument, which is a barrier that minimizes temperature exchange between the inner body and the surrounding air. In lizards, this barrier is constituted by keratinized scales of variable size, shape and texture, and its main function is protection, water loss avoidance and thermoregulation. The size of scales in lizards has been proposed to vary in relation to climatic gradients; however, it has also been observed that in some groups of Iguanian lizards it could be related to phylogeny. Thus, here, we studied the area and number of scales (dorsal and ventral) of 60 species of Liolaemus lizards distributed in a broad latitudinal and altitudinal gradient to determine the nature of the variation of the scales with climate, and found that the number and size of scales are related to climatic variables, such as temperature and geographical variables as altitude. The evolutionary process that best explained how these morphological variables evolved was the Ornstein-Uhlenbeck model. The number of scales seemed to be related to common ancestry, whereas dorsal and ventral scale areas seemed to vary as a consequence of ecological traits. In fact, the ventral area is less exposed to climate conditions such as ultraviolet radiation or wind and is, thus, under less pressure to change in response to alterations in external conditions. It is possible that scale ornamentation, such as keels and granulosity, may bring some more information in this regard.
Ecomorphology, Locomotion, and Microhabitat Structure: Patterns in a Tropical Mainland Anolis Community
According to the habitat—matrix model, arboreal microhabitat specialists are adapted behaviorally and morphologically for locomotion in different subsets of the vegetation, each characterized by its three—dimensional structure, and these adaptations help explain morphological patterns among coexisting species. I tested this model's predictions for Anolis lizards near Monteverde, Costa Rica. Anolis humilis, A. tropidolepis, and A. woodi were active at different heights in the shaded forest understory, and A. insignis inhabited the canopy. Gap specialists, A. altae and A. intermedius, resembled one another in microhabitat use but were largely separated by elevation. Adult males of forest—understory and gap species were active higher above ground than adult females, which averaged higher than juveniles. In their different structural environments, species, sexes, and age classes differed in proportional use of locomotor modes: running, jumping, and crawling. During field observations of forest—understory and gap species, frequency of crawling was highest for anoles that used slender, widely spaced supports, though much variation in crawling frequency was unexplained. Frequency of jumping increased as mean support size and average distance between supports decreased; the latter variable, expressed relative to body length, accounted for most of the variation in jump frequency. With enclosure experiments, I assessed proximate effects of microhabitat features on locomotor behavior and removed these effects to test for interspecific differences in intrinsic locomotor tendencies. Jump frequency of A. altae consistently increased with decreasing distance between supports, whereas the effects of support diameter were more complex, and varied with spacing of supports. Support diameter exerted both a surface—area effect (a lower tendency to jump from larger supports compared with smaller ones) and, where supports were widely spaced, a target—size effect (a higher tendency to jump to larger supports compared with smaller ones). Compared in the same array of supports, A. tropidolepis, A. altae, and A. intermedius, although similar in body size, differed in frequency of jumping. Thus, differences in locomotor behavior among species reflected not only proximate influences of vegetation structure but also intrinsic tendencies. Morphological traits were strongly associated with locomotor behavior and microhabitat specialty. Differences in limb proportions of primarily running anoles (A. altae and A. intermedius), crawling anoles (A. insignis), and anoles that jumped frequently (A. humilis, A. tropidolepis, and A. woodi) accorded with predictions from biomechanics. Body size was also functionally related to locomotion and was correlated with microhabitat structure. Thus, ability to exploit various structural environments may depend not only on body shape but also size. Nonrandom patterns of interspecific differences in morphology suggested limiting similarity without revealing the underlying ecological process(es). The mechanistic basis for these patterns,however, appears to lie, at least in part, in the functional relationships between morphology and habitat structure.