Ultrastructure of eggshell and embryological development of Salvator merianae (Squamata: Teiidae)

Abstract

The objective of this study was to characterize the external morphology of Salvator meriane embryos in different stages of embryonic development and establish a relationship with the ultrastructure of the shell from oviductal transit to hatching. A total of 120 embryos were analyzed to describe their external morphology, and 78 eggs were used for the analysis of the shell. For embryonic development, the series was established according to the total length of the body. We established 40 embryonic stages from the primitive streak. In the early stages, the external morphological features are the C-shaped body, the maxillary, and mandibular fusion processes with the frontal process and the fusion of the forelimb with the digital plate. In the middle stages, the eyelid appears, and there are claws on the toes, cornification of fingers, and the onset of pigmentation. The last stage of embryonic development is characterized by the beginning of the formation of the scales, appear the toenails, and finalize the entire pigmentation. Regarding the relationship that exists with the ultrastructure of the egg during development, it was possible to observe a marked change in the composition of the shell and well-marked compaction during embryonic development, which may be related to the transport of calcium during embryonic ossification. Our results allowed us to show the complete sequence of embryonic development, determining the laying stage for this species. It was possible to establish a relationship with the ultrastructure of the eggshell from the oviductal transit to the moment of hatching.

The diverse terminology of reptile eggshell microstructure and its effect on phylogenetic comparative analyses

“…Additionally, even in squamate eggs with no shell units, variation has been recorded in all layers of the eggshell, but has rarely been the subject of classifications analogous to those of shell units in other reptile eggs. This includes the outer ornamentation of the CL, which can include grooves and cracks, calcite granules, or rosettes, etc., the size and shape of which appear to be unique to specific clades (Arrieta et al, 2021; Osborne & Thompson, 2005; Packard & DeMarco, 1991; Packard et al, 1982; Packard, Packard, & Boardman, 1982; Packard et al, 1991; Schleich & Kästle, 1988); bundles of protein fibers in the membrana testacea, often arranged in highly specific and complex patterns (Legendre, Rubilar‐Rogers, Musser, et al, 2020; Osborne & Thompson, 2005; Packard et al, 1982; Schleich & Kästle, 1988); and mineralized nodules in the membrana testacea, highly variable in shape and size but almost never reported in formal descriptions (Schleich & Kästle, 1988). Such structures, as well as their location on or within the shell, have been categorized and discussed in the context of calcification patterns and shell porosity (D'Alba et al, 2021; Kohring, 1995; Schleich & Kästle, 1988), although such classifications remain to be tested in a phylogenetic context.…”

“…Such structures, as well as their location on or within the shell, have been categorized and discussed in the context of calcification patterns and shell porosity (D'Alba et al, 2021; Kohring, 1995; Schleich & Kästle, 1988), although such classifications remain to be tested in a phylogenetic context. Many species also present pore‐like structures, the structure and function of which has never been assessed due to their “simple” aspect compared with the well‐defined pores of hard‐shelled eggs (Arrieta et al, 2021; Osborne & Thompson, 2005; Packard & DeMarco, 1991; Schleich & Kästle, 1988). The CL in some species has also been reported to be completely absent, or made of hydroxyapatite instead of calcite (Schleich & Kästle, 1988).…”

“…The specialized oviduct of birds and crocodilians, each region of which produces a different part of the eggshell sequentially during ontogeny, has been proposed as a synapomorphy of archosaurs (Palmer & Guillette, 1992). Similarly, the development of proteinaceous eggshell layers has been described in a few turtle and squamate species (Arrieta et al, 2021;Hoffman, 1970), sometimes in relation with the structure and function of the uterine shell glands that produce them (Aitken & Solomon, 1976;Corso et al, 2000;Guillette et al, 1989;Palmer & Guillette, 1988;Palmer et al, 1993;.…”