Are the number and size of scales in Liolaemus lizards driven by climate?

Abstract

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.

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

“…In our study, we found a strong positive relationship between scale size and body size in A. cristatellus (scale size scales isometrically with body size). This result is not unexpected, as the scale‐size to body‐size link has been documented (predominantly on the interspecific scale) in many lizards groups, such as Liolaemus (Tulli & Cruz, ), Sceloporus (Oufiero et al. ) and Anolis (Wegener et al.…”

“…In our study, we found a strong positive relationship between scale size and body size in A. cristatellus (scale size scales isometrically with body size). This result is not unexpected, as the scale-size to body-size link has been documented (predominantly on the interspecific scale) in many lizards groups, such as Liolaemus (Tulli & Cruz, 2018), Sceloporus (Oufiero et al 2011) andAnolis (Wegener et al 2014). Interestingly, most studies do not measure the actual size of the scale, but instead count the number of scales along a defined transect on the skin and use the inverse of these scale counts as a proxy of scale size (Kerfoot, 1970;Thorpe & Baez, 1987;Malhotra & Thorpe, 1997;Oufiero et al 2011;Wegener et al 2014).…”

“…). Indeed, scale number per unit length is often a strong predictor of scale size, as it explains approximately 95% of the interspecific variation in scale size among Liolaemus species, for instance (Tulli & Cruz, ). Based on microscopically detailed images, however, our study shows that scale number could only explain approximately 82% of the intraspecific variation in A. cristatellus , leaving 18% still unaccounted for.…”

“…; Broeckhoven et al. ; Tulli & Cruz, ), the (ontogenetic) scaling relationships of their 3D surface structure, particularly measurements of scale height, have remained largely unexplored. With modern advances in high‐resolution imaging techniques (Eggeling, ), however, the tools to rapidly collect detailed data on reptilian skin surface structures are now routinely available.…”

“…As such, knowledge of the explanatory power of body size on squamate surface diversity provides the foundation for future studies aimed at disentangling the relationships between morphological, functional and ecological diversity in skin architecture. While several previous studies have assessed how lizard scale and scale ornamentation relate to body size (Calsbeek et al 2006;Oufiero et al 2011;Wegener et al 2014;Lourdais et al 2017;Broeckhoven et al 2018;Tulli & Cruz, 2018), the (ontogenetic) scaling relationships of their 3D surface structure, particularly measurements of scale height, have remained largely unexplored. With modern advances in high-resolution imaging techniques (Eggeling, 2018), however, the tools to rapidly collect detailed data on reptilian skin surface structures are now routinely available.…”