Scale microornamentation of uropeltid snakes

Abstract

Microornamentation was examined on the exposed oberhautchen surface of dorsal, lateral, and ventral scales from the midbody region of 20 species of the fossorial snake family Uropeltidae and seven species of fossorial scolecophidian and anilioid outgroups. No substantial variation was observed in microornamentation from the different areas around the midbody circumference within species. All oberhautchen cells were flat and exhibited no major surface features other than occasional posterior margin denticulations, small pores/pits, and narrow, low ridges. This is largely consistent with the hypothesis that friction reduction and dirt shedding are the main selective pressures on microornamentation, given that reducing shine is not of key importance in fossorial animals. Variations among taxa were observed in the shape and size of oberhautchen cells, in the presence of pores/pits, in the presence and size of denticulations on posterior cell margins, and in the level or imbricate nature of cell borders. Six microornamentation characters were formulated, scored, and plotted onto a selected phylogeny. Character evolution and phylogenetic signal were explored, accepting the incomplete understanding of intraspecific variation and of uropeltid interrelationships. There is evidence that all but one of these characters evolved homoplastically, probably by multiple independent origin. There is no clear evidence for character state reversal, but greater phylogenetic resolution is required to test this further. Phylogenetic signal appears to exist in some instances, including possible microornamentation synapomorphies for Uropeltidae and Melanophidium. These derived character states are found elsewhere within Squamata. A microornamentation of narrow, finely, and regularly spaced ridges is associated with scale iridescence. These ridges, and possibly pores/pits, are also associated with scales that are less wettable, and that therefore might be expected to be better at shedding dirt in moist conditions. Testable hypotheses are presented that might explain minor variations in the form of ridges and pits among uropeltids.

Analysis of the microstructure of Xenodontinae snake scales associated with different habitat occupation strategies

“…Even when the microstructural form is similar, the distribution and organization pattern differ, which gives a characteristic microstructure to each snake (Arroyo and Cerdas, 1985). Gower (2003) does not discard the idea that variation in scale microstructure corresponds to different environmental conditions to which the organisms were exposed during the acquisition of these microornamentations. The study of microstructural variation thus must take into account the effects of selective pressures brought about by the peculiarities of each environment.…”

“…Analyzing scale microstructure in snakes of the Uropeltidae family, Gower (2003) proposed that a "smoother" and more regular microornamentation may confer advantages to underground living, possibly by reducing the adhesive force of moist soils on these snakes' scales.…”

“…Additionaly or alternatively, in species that have long denticulations overlapping the posterior borders of each spinule row, greater frictional resistance of scales from the posterior to the anterior direction is to be expected (Gower, 2003). These features should have significant importance in terricolous and arboreal snakes, since they require greater attrition for locomotion, in contrast to, e.g., aquatic snakes, in which excessive attrition hampers locomotion.…”

“…Several recent studies have suggested a functional significance for microornamentation (Manderson, 1966;Porter, 1967;Steward and Daniel, 1973;Gans and Baic, 1977;Smith et al, 1982;Renous, et al,1985;Gower, 2003) or have simply described microanatomy (Arroyo and Cerdas, 1985;Chiasson and Lowe, 1989;Velloso et al, 2005). Microstructures have also been used as tools in taxonomy (Hogue and Santos 1953;Dowling et al, 1972;Stewart and Daniel, 1975) and in ontogenetic and/or evolutionary studies of squamates (Peterson, 1985;Harvery 1993;Harvery and Gutberlet Jr, 1995).…”

Epidermis architecture and material properties of the skin of four snake species

“…From previous studies [10,[22][23][24][25][26][27][28][29], it is known that between different snake species the scale surface microstructure can vary significantly even between representatives of the same family. That is why these microstructures have been used for taxonomic purposes, but with a limited success.…”