The allantoplacenta of Mabuya mabouya (Sauria, Scincidae)

Abstract

Analysis of placentation in the final stages of development in Mabuya mabouya shows that the placenta is formed by the apposition of the chorioallantois to the uterine mucosa implicating the entire embryonic chamber, because the allantoic vesicle invades all the exocoelom. The chorioallantoic placenta presents the features proper of a type IV allantoplacenta. However, in the mesometrial area peripheral to the placentome, we found that the paraplacentome is an additional zone specialized for histotrophic transfer, and is separated from the rest of the embryonic chamber by a chorionic invagination formed of polymorphic cells. The chorionic areolae are components of the embryonic hemisphere; they are in apposition to an endometrium with columnar epithelial cells and several glands that secrete toward the cavity of the areolae. They are observed only in the preparturition stage, probably operating in maternal-fetal transfer of nutrients during the last embryonic growth stage. The mesometrial hemisphere possesses specializations related to histotrophic nutrition (placentome, paraplacentome, and chorionic areolae), while in the abembryonic hemisphere there is an allantoplacenta of mixed function, with capacity for histotrophic nutrition and for gas exchange. The absorptive plaques are small rounded areas constituted by chorionic cells similar to the paraplacentomal chorionic cells, in intimate apposition with a secretory uterine epithelium. Separating the absorptive plaques are respiratory segments histologically similar to the type I allantoplacenta. The additional histotrophic areas found for this species demonstrate the great specialization of this allantoplacenta, and support the highest degree of matrotrophy among reptiles reached in the Neotropical Mabuya.

The evolution of viviparity: molecular and genomic data from squamate reptiles advance understanding of live birth in amniotes

“…The highly placentotrophic Eumecia sp., Mabuya sp., and Trachylepis sp. also appear to transport nutrients across yolk-sac placentae (Flemming & Branch 2001, Jerez & Ramirez-Pinilla 2001, Blackburn & Flemming 2009). In contrast, the genera Eulamprus, Thamnophis, and Virginia are not placentotrophic, which suggests that uterine epithelial hypertrophy in the yolk-sac placenta is not always associated with organic nutrient transport , Thompson et al 2001a.…”

Evolution of placental specializations in viviparous African and South American lizards

“…These lizards ovulate tiny (1 mm diameter) eggs and provide virtually all of the nutrients for development by placental means (Blackburn and Vitt,'92). The chorioallantoic placenta (allantoplacenta) is correspondingly specialized, and exhibits specializations for uterine secretion and fetal absorption (Blackburn, '98;Jerez and Ramírez-Pinilla, 2001; Blackburn and Vitt, 2002). In some respects, these lizards have converged evolutionarily on a reproductive pattern generally thought to be confined to eutherian mammals (Blackburn et al,'84;Blackburn,'92).…”

Biología reproductiva y placentotrofía en lagartijas del género Mabuya

“…Las lagartijas de la población de Yacopí colectadas para estos dos trabajos nos dieron la oportunidad de afinar el trabajo de grado de la por entonces Bióloga Adriana Jerez y comenzar una nueva línea de trabajo con otra estudiante de pregrado, utilizando esta vez tejidos especialmente fijados para trabajo histológico (Jerez & Ramírez-Pinilla, 2001Gómez & Ramírez-Pinilla, 2004). …”

“…La placenta madura de Mabuya tiene especializaciones morfológicas complejas exclusivas de este clado: 1) un placentoma altamente elaborado con una fuerte interdigitación de los tejidos maternos y fetales, en donde se destaca un arreglo sincitial del epitelio uterino frente a un epitelio coriónico biestratificado especializado; 2) una zona que rodea al placentoma, denominada paraplacentoma, delimitada por un pliegue coriónico; 3) areolas coriónicas que reciben materiales nutritivos del epitelio uterino a partir especialmente de glándulas endometriales, 4) placas de absorción o áreas redondeadas y pequeñas formadas por células coriónicas hipertrofiadas en aposición a células epiteliales columnares secretoras del endometrio; 5) segmentos respiratorios, o áreas de atenuación de los epitelios del corion y endometriales de manera que los capilares sanguíneos uterinos y del corioalantoides quedan en una muy cercana proximidad (Figura 4 a, b, c). Las cuatro primeras especializaciones de la alantoplacenta estarían relacionadas con el intercambio de materiales nutritivos por procesos como la histotrofía, la quinta especialización con el intercambio de gases entre el embrión y el útero materno (Jerez & Ramírez-Pinilla, 2001; Ramírez-Pinilla, 2010). Cabe resaltar que ninguna placenta de mamíferos euterios reúne simultáneamente toda esta serie de especializaciones morfológicas como las que se encuentran en Mabuya.…”