BLACKBURN, D.G.*; WEABER, K.K.; STEWART, J.R.; THOMPSON, M.B.: Do pregnant lizards reabsorb or abort inviable eggs? Morphological evidence from an Australian skink, Pseudemoia pagenstecheri.

Among lizards and snakes, pregnant females commonly are believed to be able to reabsorb inviable embryos and infertile eggs from their oviducts. Such reabsorption would allow females to recycle nutrients, while freeing the uterus for further reproduction. However, no definitive evidence for egg resorption has ever been published. Moreover, careful study of one viviparous species in which resorption has been claimed (the European skink Chalcides chalcides) has revealed that dead eggs and embryos simply pass down the oviducts, rather than being reabsorbed (Blackburn et al., 1998). We brought pregnant female lizards, Pseudemoia pagenstecheri, into captivity, causing embryonic development to cease. Uterine oviducts were harvested at measured time periods and examined histologically. Females contained abnormal and degenerating eggs that had died in various stages of development, well before being harvested. Dead embryos had undergone cytolysis, dissolution, and aseptic necrosis. The oviducts showed no evidence of digestion of yolk and embryonic material, nor of uptake by the uterine epithelium. Instead, yolk material was passing caudally down the oviduct. Our observations indicate that P. pagenstecheri females retain dead eggs and embryos for several weeks or longer, and do not reabsorb them during that period. This lizard is the second placentotrophic skink in which resorption has been suspected, but in which abortive eggs are retained or expelled by the oviduct. Future studies on reptiles should not assume that inviable eggs are reabsorbed by the oviduct in the absence of definitive morphological evidence.