Do all geckos hatch in the same way? Histological and 3D studies of egg tooth morphogenesis in the geckos Eublepharis macularius Blyth 1854 and Lepidodactylus lugubris Duméril & Bibron 1836

Abstract

The egg tooth of squamates evolved to facilitate hatching from mineralized eggshells. Squamate reptiles can assist their hatching with a single unpaired egg tooth (unidentates) or double egg teeth (geckos and dibamids). Egg tooth ontogeny in two gekkotan species, the leopard gecko Eublepharis macularius and the mourning gecko Lepidodactylus lugubris, was compared using microtomography, scanning electron microscopy, and light microscopy. Investigated species are characterized by different hardnesses of their eggshells. Leopard geckos eggs have a relatively soft and flexible parchment (leathery) shell, while eggshells of mourning geckos are hard and rigid. Embryos of both species, like other Gekkota, have double egg teeth, but the morphology of these structures differs between the investigated species. These differences in shape, localization, and spatial orientation were present from the earliest stages of embryonic development. In mourning gecko, anlagen of differentiating egg teeth change their position on the palate during embryonic development. Initially they are separated by condensed mesenchyme, but later in development, their enamel organs are connected. In leopard geckos, the localization of egg tooth germs does not change, but their spatial orientation does. Egg teeth of this species shift from inward to outward orientation. This is likely related to differences in structure and mechanical properties of eggshells in the studied species. In investigated species, two hatching mechanisms are possible during emergence of young individuals. We speculate that mourning geckos break the eggshell through puncturing action with egg teeth, similar to the pipping phase of chick and turtles embryos. Egg teeth of leopard geckos cut egg membranes similarly to most squamates. Our results also revealed differences in egg tooth implantation between Gekkota and Unidentata: gekkotan egg teeth are subthecodont (in shallow sockets), while those in unidentates are acrodont (attached to the top of the alveolar ridge).

Embryonic development of the skull in a parthenogenetic lizard, the mourning gecko (Lepidodactylus lugubris)

“…Such mode of development was described for gekkonids by Kluge (1967) who illustrated it based on Lepidodactylus lugubris. However, our data show that the premaxilla starts ossifying from two separate centres, as indicated by both alizarin-stained whole-mount specimens (Figure 6a) and histological thin sections (Figure 6b, see also Figure 5a in Hermyt et al, 2020). What is the reason for these differences?…”

“…The squamosal is now much larger and more visible (Figure 4). The egg teeth first appear during this stage, although they are poorly visible in whole‐mount specimens (detailed description of the development of the egg teeth was presented by Hermyt et al, 2020). Later during this stage, the maxilla and vomer start ossifying.…”

Does the pancreas of gekkotans differentiate similarly? Developmental structural and 3D studies of the mourning gecko (Lepidodactylus lugubris) and the leopard gecko (Eublepharis macularius)

“…The research was carried out during the years 2021-2023. The literature review and our other developmental studies indicated that E. macularius is a widely used model organism in laboratory and experimental studies (Agarwal et al, 2022;Hermyt et al, 2020;Vickaryous & Gilbert, 2019). Still, the mourning gecko (L. lugubris) stands out as an ideal model for studying developmental questions (Griffing et al, 2019;Hermyt et al, 2020;Skawiński et al, 2023).…”

“…The embryos of E. macularius represented five stages: 30, 32, 34, 38, and 42. The eggs of L. lugubris are glued by females to the different vertical surfaces of the terrarium. The eggs were left and incubated in the terrarium to avoid damage to the eggshells at approximately 23-30°C (Hermyt et al, 2020). Embryos of this species were isolated every fortnight.…”