Effects of temperature on embryonic development of the veiled chameleon, Chamaeleo calyptratus.

Temperature dependence of development of the chameleon, Chamaeleo calyptratus, was assessed from observations on eggs incubated at 25, 28 and 30 degrees C. Overall, differentiation, growth in mass, and growth of the yolk sac and chorioallantois were the slowest at 25 degrees C but did not differ between 28 and 30 degrees C. The relative area of the yolk sac (YS), chorioallantoic membrane (CAM), and their precursor, the area opaca vasculosa (AV) was used to characterize developmental phases. During Phase 1, only the AV was present; development was characterized by differentiation with little increase in the size of the embryo. During Phase 2, the vascularized YS and CAM grew from about 10 to 100% coverage of the surface of the shell during a period of about two weeks. Differentiation and growth of the embryo were accordingly rapid. During Phase 3, the YS and CAM were fixed in size and the remainder of development was relatively slow. Characterization of embryonic development with respect to the relative area of the AV-YS-CAM highlighted the functional linkage between development and the systems that provide nutrients to embryos.