Live bearing (viviparity) has arisen many times among skinks, although many species retain the ancestral condition and lay eggs (oviparity). In two Australian species of skinks (Lerista bougainvillii and Saiphos equalis), both egg laying and live bearing occur among different populations within each species. Brood sizes vary greatly among skinks, from one to two in some species (such as Lobulia and Prasinohaema, which appear to have a fixed clutch size, as in anoles and geckos) to 53 or even 67 in others (such as the Australian Tiliqua gerrardii). Some skinks lay their eggs in communal nests, which could be an indication that suitable nest sites are in short supply. This behavior also could represent repeated use by one or more females of nest sites with a history of high hatching success.
Some viviparous skinks give birth to a single, extremely large neonate (Corucia zebrata, Tiliqua rugosa, and Typhlosaurus garie-pensis). Within viviparous skinks, the entire range of fetal nutritional types occurs. Many species ovulate large eggs containing all the nutrients necessary for development; thus, developing offspring feed on their own yolk (lecithotrophy, ovo-viviparity) before being born alive. Various degrees of placental development take place, in which nutrients are passed from mother to offspring (matrotrophy) during development. For example, Chalcides have complex placental connections between mother and progeny through which pass substantial amounts of nutrients required for development. Still other species, such as Mabuya heathi in Brazil, have an advanced placental arrangement, passing more than 99% of nutrients necessary for neonatal development from the mother through a placenta.
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