Evidence of steroid hormone activity in the chorioallantoic membrane of a Turtle (Pseudemys nelsoni)
13
Citation
58
Reference
10
Related Paper
Citation Trend
Keywords:
Oviparity
Amniote
Steroid hormone
Chorioallantoic membrane
Sex steroid
Chordate
An understanding of the evolutionary morphology of extraembryonic membranes in reptiles requires information about oviparous as well as viviparous species. We are studying histology and ultrastructure of the extraembryonic membranes of snakes to clarify the evolutionary history of reptilian fetal membranes, including determination of basal (ancestral) ophidian and squamate patterns. Microscopic anatomy of the membranes of oviparous corn snakes (Elaphe guttata) was examined using light and electron microscopy. At mid-development the inner surface of the eggshell is lined by two extraembryonic membranes, the chorioallantois and the omphalallantoic membrane. The chorioallantois consists of a bilayered cuboidal epithelium that overlies the allantoic blood vessels. During development, allantoic capillaries become more abundant, and the chorionic epithelium thins, decreasing the diffusion distance for respiratory gas exchange. The abembryonic pole of the egg is delimited by a bilaminar omphalopleure and isolated yolk mass, the latter of which is lined on its inner face by the allantois. The isolated yolk mass regresses developmentally, and patches of yolk droplets become isolated and surrounded by allantoic blood vessels. By late development, the abembryonic hemisphere has been fully vascularized by allantoic vessels, forming a "secondary chorioallantois." With regard to its extraembryonic membranes, Elaphe gutatta is similar to viviparous snakes. However, this species exhibits features that have not previously been reported among squamates, perhaps reflecting its oviparous reproductive habits. Morphological evidence for the uptake of eggshell material by epithelia of the chorion and omphalopleure suggests that the potential for absorption by extraembryonic membranes predates the origin of viviparity.
Oviparity
Chorioallantoic membrane
Allantois
Yolk
Histology
Cite
Citations (44)
A recent study used 61 extant animal genomes to reconstruct the chromosomes of the hypothetical amniote ancestor. Comparison of this karyotype to the 17 chordate linkage groups previously inferred in the ancestral chordate indicated that two whole genome duplications probably occurred in the lineage preceding the ancestral vertebrate.
Chordate
Amniote
Lineage (genetic)
Ancestor
Human genetics
Synteny
Cite
Citations (74)
Oviparity
Amniote
Yolk
Female Reproductive Tract
Cite
Citations (20)
Somites are transitory metameric structures at the basis of the axial organization of vertebrate musculoskeletal system. During evolution, somites appear in the chordate phylum and compartmentalize mainly into the dermomyotome, the myotome, and the sclerotome in vertebrates. In this review, we summarized the existing literature about somite compartmentalization in Xenopus and compared it with other anamniote and amniote vertebrates. We also present and discuss a model that describes the evolutionary history of somite compartmentalization from ancestral chordates to amniote vertebrates. We propose that the ancestral organization of chordate somite, subdivided into a lateral compartment of multipotent somitic cells (MSCs) and a medial primitive myotome, evolves through two major transitions. From ancestral chordates to vertebrates, the cell potency of MSCs may have evolved and gave rise to all new vertebrate compartments, i.e., the dermomyome, its hypaxial region, and the sclerotome. From anamniote to amniote vertebrates, the lateral MSC territory may expand to the whole somite at the expense of primitive myotome and may probably facilitate sclerotome formation. We propose that successive modifications of the cell potency of some type of embryonic progenitors could be one of major processes of the vertebrate evolution.
Amniote
Chordate
Myotome
Compartmentalization (fire protection)
Compartment (ship)
Notochord
Cite
Citations (8)
ABSTRACT Oviparous amniotes exchange respiratory gases across a specialized vascular membrane, the chorioallantois. Although many investigations into the physiology of amniote eggs, particularly those of the chicken, have been carried out, there is no comparative information about the chorioallantoic membrane. Given the differences in size and phylogeny, it might be expected that significant morphological differences exist in this gas-exchange organ.
Chorioallantoic membrane
Amniote
Oviparity
Cite
Citations (14)
Oviparity
Amniote
Yolk
Female Reproductive Tract
Gonopod
Cite
Citations (26)
Oviparity
Amniote
Yolk
Female Reproductive Tract
Gonopod
Cite
Citations (25)
Oviparity
Amniote
Chorioallantoic membrane
Yolk
Deuterostome
Cite
Citations (33)
We critically examine a recent explanation for the absence of viviparity in birds that depends heavily on a model that was developed to account for viviparity in squamate reptiles. We propose that the elevated body temperature of birds precludes extended egg retention, presumably an early stage in the evolution of viviparity from an oviparous ancestor, probably through constraints on the rate of oxygen transfer to developing embryos. We demonstrate that if the effects of endothermy are included in the model developed to account for the evolution of viviparity in reptiles, then qualitative and quantitative differences in embryonic developmental rates are predicted between reptiles and birds as a result of eggs being retained within the uterine environment. Our modification of the model thus offers an explanation for the total absence of viviparity in birds. We propose that the evolutionary sequence for mammalian viviparity from an endothermic oviparous ancestor was through the progressive production of smaller eggs, with proportionally shorter embryonic developmental times, which would allow for relatively longer periods of egg retention before oxygen-supply constraints would be reached. The critical characteristic allowing extensive egg size reduction in the mammals was lactation, which allowed the feeding of tiny altricial neonates. The absence of lactation, or some analogous method of feeding very small young, has constrained birds from following the evolutionary pathway to viviparity that we propose for mammals.
Oviparity
Amniote
Hatchling
Altricial
Cite
Citations (8)