Comparative ecomorphology of the sandstone night lizard (Xantusia gracilis) and the granite night lizard (Xantusia henshawi)

Abstract

Abstract It is hypothesized that shape differences between the closely related sandstone night lizard (Xantusia gracilis) and the granite night lizard (X. henshawi) may be correlated with structual differences in their respective microhabitats. Multivariate and univariate analyses of 22 morphometric characters taken from the head, body, and limbs of both saxicolus specialists recovered statistically significant differences between them with X. gracilis having a wider head, longer snout, larger eyes, wider sternum, higher and wider pelvis, thinner limbs, longer forearms and thighs, and longer hind limbs. Many of these same proportional differences have been reported among very closely related saxicolus species in other lizard families (i.e. Eublepharidae, Gekkonidae, Phrynosomatidae) that also live on different rocky substrates. This supports the inference that morphometric differences between X. gracilis and X. henshawi are ecomorphological adaptations for navigating the substantially different substrates of their respective microhabitats. Xantusia gracilis is restricted to a loose, heterogeneous, sandstone microhabitat composed of large boulders, small rocks, and cliff faces where cracks, crevices, holes, and exfoliations are used as retreats versus the compact, more homogeneous, granite boulder microhabitat of X. henshawi where narrow spaces beneath exfoliations and cap-rocks are the preferred retreats.