History and function of scale microornamentation in lacertid lizards

Abstract

Differences in surface structure (ober-hautchen) of body scales of lacertid lizards involve cell size, shape and surface profile, presence or absence of fine pitting, form of cell margins, and the occurrence of longitudinal ridges and pustular projections. Phylogenetic information indicates that the primitive pattern involved narrow strap-shaped cells, with low posteriorly overlapping edges and relatively smooth surfaces. Deviations from this condition produce a more sculptured surface and have developed many times, although subsequent overt reversals are uncommon. Like variations in scale shape, different patterns of dorsal body microornamentation appear to confer different and conflicting performance advantages. The primitive pattern may reduce friction during locomotion and also enhances dirt shedding, especially in ground-dwelling forms from moist habitats. However, this smooth microornamentation generates shine that may compromise cryptic coloration, especially when scales are large. Many derived features show correlation with such large scales and appear to suppress shine. They occur most frequently in forms from dry habitats or forms that climb in vegetation away from the ground, situations where dirt adhesion is less of a problem. Microornamentation differences involving other parts of the body and other squamate groups tend to corroborate this functional interpretation. Microornamentation features can develop on lineages in different orders and appear to act additively in reducing shine. In some cases different combinations may be optimal solutions in particular environments, but lineage effects, such as limited reversibility and different developmental proclivities, may also be important in their genesis. The fine pits often found on cell surfaces are unconnected with shine reduction, as they are smaller than the wavelengths of most visible light.

Lizard scales in an adaptive radiation: variation in scale number follows climatic and structural habitat diversity inAnolislizards

“…light may reflect differently from keeled and rugose scales than it does from a smooth and flat scale; Arnold, 2002). We found that relative Table 1).…”

Scale microornamentation of uropeltid snakes

“…Mapping features onto a phylogeny and reconstructing states for internal branches indicated that lineage effects were probably important because reversals in microornamentation appeared to be extremely limited, but also that many of the derived patterns had evolved many times independently, and that (p. 154) "there seem to be limits on the variations that can be produced. "Examples of intraorganismal diversity and relatively sharp transition zones in morphologies suggest that there is a strong selective regime operating on at least some aspects of scale microornamentation (e.g., Gans and Baic, 1977;Arnold, 2002a). Given that shine control and dirt shedding plus friction reduction appear to entail opposing structural solutions, yet are of "substantial importance" (Arnold, 2002a:163), it is of interest to consider microornamentation in predominantly fossorial squamates in which shine control can be expected to be of little or no concern, and dirt shedding to be of great importance.…”

“…There have been several studies of microornamentation in various groups of squamates (see Arnold, 2002a, and literature cited therein). An early concern of this research was whether taxonomic variations in microornamentation were associated with systematics or ecology; that is, whether taxonomic patterns are determined more by phylogenetic history or by functional requirements.…”

“…Recently, Arnold (2002a) applied a thorough, explicit approach to the understanding of microornamentation in lacertid lizards by attempting to explain variations in morphology through an integrated historical (phylogenetic) and functional analysis. For lacertids, a broad correlation between microornamentation and general habitat was found.…”

“…It is often composed of cell-like divisions that may bear complex three-dimensional features. The overall arrangement of these cells and their surface features are termed microornamentation (Ruibal, 1968;Arnold, 2002a), and these features are readily studied with scanning electron microscopy.There have been several studies of microornamentation in various groups of squamates (see Arnold, 2002a, and literature cited therein). An early concern of this research was whether taxonomic variations in microornamentation were associated with systematics or ecology; that is, whether taxonomic patterns are determined more by phylogenetic history or by functional requirements.…”