HEULIN, B.; STEWART, J.R.*; SURGET-GROBA, Y.; BELLAUD, P.; JOUAN, F.; LANCIEN, G.; DEUNFF, J.; Station Biologique de Paimpont, France; East TN State Univ., Johnson City, USA; Univ. Rennes, France; Univ. Rennes, France; Univ. Rennes, France; Univ. Rennes, France; Univ. Rennes, France: Histology and histochemistry of the uterine glands and eggshell of the reproductively bimodal lizard, Lacerta vivipara

Thinning of the eggshell is a major innovation in the evolution of viviparity in squamate reptiles. The eggshell typically consists of several layers of organic fibers overlain by calcium carbonate. We studied oviparous and viviparous females during vitellogenesis and early gestation in a reproductively bimodal lizard to test the hypothesis that reduction in eggshell thickness is correlated with reduction in preovulatory recrudescence of the uterine glands. The eggshell of both reproductive modes consists of an inner boundary layer that stains positively for acidic mucosubstances and a thicker fibrous layer that stains for disulfide and sulfhydryl rich protein. The fibrous layer is 10 times thicker in oviparous females. During late vitellogenesis the glands of oviparous females are 60% larger than those of viviparous females. Because uterine glands of both reproductive modes stain positively for disulfide and sulfhydryl groups and the uterine epithelium is positive for acidic mucosubstances, we conclude that the uterine glands are the likely source of the fibrous proteinaceous layer and the uterine epithelium secretes the inner boundary layer. Our methods did not include study of the source of calcium carbonate which is present in oviparous but not viviparous eggshells. Our intraspecific comparison supports the hypothesis that thinning of the eggshell is coincident with the evolution of viviparity and is regulated by reduction in uterine glands.