Multiscale Mineralization in the Leopard Gecko Eggshell

Abstract

Reptilian (non-avian) eggshell biomineralization is markedly different from avian eggshells. Despite discontinuous/variable mineralization, the reptilian eggshell (like in birds) is responsible for protective and developmental functions of the egg as part of a highly successful reproduction strategy. Using multiscale imaging and characterization methods including X-ray and electron microscopy/tomography, a 3D overview of eggshell ultrastructure in the gekkotan Eublepharis macularius – the common leopard gecko is provided. Eggshell mineral is shown to be sensitive to aqueous preparations, where cryogenic methods are essential for accurate mineral and organic preservation. Interwoven with the mineral are underlying organic fibers involved in the formation of complex hierarchical order in the eggshell, including nucleation and growth of mineral. The calcitic mineral phase of the eggshell takes on three microstructural motifs at the shell surface: nodular scutes (≈40 µm), intermittent blunt or star-shaped mineral rosettes (≈1 mm), and smaller mineral corollas (≈10 µm). Individual scutes have two hierarchical mineral structures – mineral nanospheres (≈500 nm) and mineral nanodomains (≈40 nm). Diverse and variable biomineralization features of reptilian eggshells likely reflect the importance of differences in ecology and physiology on egg formation, survival, and eggshell mechanics, and are likely related to hydration sensitivity, structural organic-inorganic interactions, and mineral polymorphism.