Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel‐based stereo‐profilometry

Abstract

The skin surface structure of squamate reptiles varies greatly among species, likely because it plays a key role in a range of tasks, such as camouflage, locomotion, self‐cleaning, mitigation of water loss and protection from physical damage. Although we have foundational knowledge about squamate skin morphology, we still know remarkably little about how intraspecific variation in skin surface structure translates to functional variation. This gap in our understanding can be in part traced back to: (i) our lack of knowledge on how body size determines skin surface structure; and (ii) the lack of means to perform high‐throughput and detailed analysis of the three‐dimensional (3D) anatomy of reptilian skin surfaces in a non‐destructive manner. To fill this gap, we explored the possibilities of a new imaging technique, termed gel‐based stereo‐profilometry, to visualize and quantify the 3D topography of reptilian skin surface structure. Using this novel approach, we investigated intra‐specific and intra‐individual variation in the skin surface morphology of a focal lizard species, Anolis cristatellus. We assessed how various characteristics of surface topography (roughness, skew and kurtosis) and scale morphology (area, height, width and shape) scale with body size across different body regions. Based on an ontogenetic series of A. cristatellus males, we show that skin roughness increases with body size. Skin patches on the ventral body region of lizards were rougher than on the dorsum, but this was a consequence of ventral scales being larger than dorsal scales. Dorsal surface skew and kurtosis varied with body size, but surfaces on the ventral skin showed no such relationship. Scale size scaled isometrically with body size, and while ventral scales differed in shape from dorsal scales, scale shape did not change with ontogeny. Overall, this study demonstrates that gel‐based stereo‐profilometry is a promising method to rapidly assess the 3D surface structure of reptilian skin at the microscopic level. Additionally, our findings of the explanatory power of body size on skin surface diversity provide a foundation for future studies to disentangle the relationships among morphological, functional and ecological diversity in squamate reptile skin surfaces.

Quantifying surface topography of biological systems from 3D scans

“…For example, Baeckens et al. (2019) showed that the skewness and kurtosis of the dorsal scales of Anolis cristatellus lizards scaled with body size; intriguingly, no such trend was observed for the ventral scales. Scientists of various disciplines are encouraged to use QuSTo to study functional variation in the skin surface topography of different species for both fundamental and applied research (e.g.…”

“…Surface topography can be quantified by means of the surface roughness of a 2D profile taken along a cross‐section (e.g. Baeckens et al., 2019; Lauder et al., 2016; Wainwright et al., 2017, 2019). Among the different surface roughness parameters used in science and engineering, the arithmetic mean roughness or average roughness and root mean square roughness ( R q ) are commonly used to describe the degree of vertical relief in a 2D profile; in general, a greater surface roughness value indicates more prominent structures (Figure 3a).…”

Convergent evolution of skin surface microarchitecture and increased skin hydrophobicity in semi-aquatic anole lizards

“…Liquid-preserved specimens are widely used for the study of skin surface ornamentation in squamates because the keratinized oberhautchen layer of the skin surface preserves well (Harvey, 1993;Irish et al, 1988;Martinez et al, 2021;Matveyeva and Ananjeva, 1995;Peterson, 1984;Riedel et al, 2015;Ruibal, 1968). Previous work has found no significant effect of preservation on anole skin surface structure (Baeckens et al, 2019). In order to eliminate any potential effect of ontogenetic or intersexual variation in skin surface anatomy and to increase statistical power, only male adult lizards were included in this study.…”

The denticle surface of thresher shark tails: Three‐dimensional structure and comparison to other pelagic species

“…Once the images are processed, a 3D-image of the surface is reconstructed to create a topographical representation of that surface. This surface profilometry approach has been validated in our previous research with known standards and used in the past to image other shark species, several bony fish species, cetacean skin, and other materials with known surface structure (Ankhelyi et al, 2018;Baeckens, Wainwright, Weaver, Irschick, & Losos, 2019;Wainwright et al, 2017Wainwright et al, , 2019.…”