Departamento de Biología Comparada, Laboratorio de Biología Tisular y Reproductora, Facultad de Ciencias, Universidad Nacional Autónoma de México, México City, Mexico.
J Morphol. 2023 Mar;284(3):e21563. doi: 10.1002/jmor.21563.
Viviparity is the reproductive pattern in which females gestate eggs within their reproductive tract to complete their development and give birth to live offspring. Within extant sauropsids, only the Squamata (e.g., snakes, lizards, and amphisbaenians) evolved viviparity, representing 20% of the existing species. The genus Plestiodon is represented by 43 species and is one of the most widely distributed genera of the Scincidae in Mexico. The goal of this research has been to determine the placental morphology and ontogeny during gestation in the lizard Plestiodon brevirostris. Specimens were dissected to obtain the embryonic chambers and the embryos were categorized to carry out the correlation between the development stage and the placenta development. The embryonic chambers were processed using the conventional histological technique for light microscopy. The identified embryonic stages were 4, 29, 34, 36, and 39. A thin eggshell surrounds the egg in early developmental stages; however, this structure is already absent in the embryonic hemisphere during the developmental stage 29. The results revealed that P. brevirostris is a lecithotrophic species, but a close maternal-fetal relationship is established by tissue apposition. Ontogenically, the placental types that form in the embryonic hemisphere are the chorioplacenta, choriovitelline placenta, and chorioallantoic placenta; whereas the omphaloplacenta is formed in the abembryonic hemisphere. The structure of the chorioallantoic placenta in P. brevirostris suggests that it may play a role during gas exchange between the mother and the embryo, due to the characteristics of the epithelia that comprise it. The structure of embryonic and maternal epithelia of the omphaloplacenta suggests a role in the absorption of the eggshell during gestation and possibly in the transport or diffusion of some nutrients. In general, it is evident that ontogeny and placental characteristics of P. brevirostris match those of other species of viviparous lecithotrophic scincids.
胎生是一种繁殖方式，其中雌性在生殖道内孕育卵子，完成其发育并产下活体后代。在现存的蜥形类动物中，只有有鳞目（例如蛇、蜥蜴和蚓蜥）进化出了胎生，占现存物种的 20%。平胸龟属由 43 个物种组成，是墨西哥分布最广的石龙子科之一。本研究的目的是确定蜥蜴平胸龟在妊娠期的胎盘形态和发生。通过解剖获得胚胎室，并对胚胎进行分类，以确定胚胎发育阶段与胎盘发育的相关性。使用常规的组织学技术对胚胎室进行处理，以进行光学显微镜检查。确定的胚胎阶段为 4、29、34、36 和 39。在早期发育阶段，一个薄蛋壳环绕着卵子；然而，在发育阶段 29，这个结构在胚胎半球中已经不存在。结果表明，平胸龟是一种卵黄营养型物种，但通过组织贴附建立了密切的母婴关系。在发生学上，在胚胎半球形成的胎盘类型为绒毛胎盘、绒毛卵黄胎盘和绒毛尿囊胎盘；而卵黄胎盘则在胚胎半球形成。平胸龟的绒毛尿囊胎盘的结构表明，由于其组成的上皮细胞的特征，它可能在母体和胚胎之间的气体交换中发挥作用。卵黄胎盘的胚胎和母体上皮结构表明，它在怀孕期间可能具有吸收蛋壳的作用，并且可能在某些营养物质的运输或扩散中发挥作用。总的来说，平胸龟的发生和胎盘特征与其他卵黄营养型胎生石龙子科物种的特征相匹配。
