The development of cephalic armor in the tokay gecko (Squamata: Gekkonidae: Gekko gecko)

Abstract

Armored skin resulting from the presence of bony dermal structures, osteoderms, isan exceptional phenotype in gekkotans (geckos and flap-footed lizards) only knownto occur in three genera:Geckolepis,Gekko, andTarentola. The Tokay gecko (GekkogeckoLINNAEUS 1758) is among the best-studied geckos due to its large size andwide range of occurrence, and although cranial dermal bone development has previ-ously been investigated, details of osteoderm development along a size gradientremain less well-known. Likewise, a comparative survey of additional species withinthe broaderGekkoclade to determine the uniqueness of this trait has not yet beencompleted. Here, we studied a large sample of gekkotans (38 spp.), including 18 speci-mens ofG. gecko, using X-rays and high-resolution computed tomography for visual-izing and quantifying the dermal armorin situ. Results from this survey confirm thepresence of osteoderms in a second species within this genus,Gekko reevesiiGRAY1831, which exhibits discordance in timing and pattern of osteoderm developmentwhen compared with its sister taxon,G. gecko. We discuss the developmentalsequence of osteoderms in these two species and explore in detail the formation andfunctionality of these enigmatic dermal ossifications. Finally, we conducted a compar-ative analysis of endolymphatic sacs in a wide array of gekkotans to explore previousideas regarding the role of osteoderms as calcium reservoirs. We found thatG. geckoand other gecko species with osteoderms have highly enlarged endolymphatic sacsrelative to their body size, when compared to species without osteoderms, whichimplies that these membranous structures might fulfill a major role of calcium storageeven in species with osteoderms. Show more