Do pregnant lizards resorb or abort inviable eggs and embryos? Morphological evidence from an Australian skink, Pseudemoia pagenstecheri.
Although pregnant viviparous squamates are sometimes claimed to be able to resorb inviable eggs and embryos from the uterus, definitive evidence for such resorption is not available. After placing pregnant female Pseudemoia pagenstecheri into conditions under which embryonic development is terminated, we periodically harvested the gravid oviducts and examined them histologically. Females contained abnormal and degenerating eggs and embryos that had died in various stages of development. Dead embryos had undergone extensive cytolysis, dissolution, and aseptic necrosis and vitelline masses showed signs of deterioration and passage down the oviduct. The uterine mucosa lay in direct contact with the vitelline material, with no intact shell membrane intervening between them. Yolk was sometimes displaced into the exocoelom and allantoic cavity due to rupture of the extraembryonic membranes. Histological examination revealed no evidence of the uptake of yolk by the uterine epithelium or its accumulation in the subepithelial connective tissue. In many specimens, the uterine epithelium showed minuscule, apical granules. The position, appearance, and staining properties of the granules suggests them to be secretory, a manifestation of placentotrophy. Our observations indicate that P. pagenstecheri females retain dead eggs and embryos for several weeks or longer, yet do not resorb them during that period. This lizard is the second placentotrophic skink species in which resorption has been suspected, but in which abortive eggs appear to be retained or extruded instead of being resorbed by the oviducts. Researchers should not assume that squamates can digest and resorb oviductal eggs without definitive morphological evidence.
Blackburn
Daniel G
DG
Department of Biology, Trinity College, Hartford, Connecticut 06106, USA. daniel.blackburn@trincoll.edu
Weaber
Kera K
KK
Stewart
James R
JR
Thompson
Michael B
MB
D000818:Animals; D004625:Embryo, Nonmammalian / Q000502:physiology* / Q000648:ultrastructure; D005260:Female; D016591:Histocytological Preparation Techniques; D008116:Lizards / Q000033:anatomy & histology* / Q000196:embryology*; D010063:Ovum / Q000502:physiology* / Q000648:ultrastructure; D014599:Uterus / Q000033:anatomy & histology