Effects of temperature and moisture on embryonic diapause of the veiled chameleon (Chamaeleo calyptratus).

The development of lizard embryos is typically initiated at fertilization and continues until birth or hatching. In contrast, embryonic development of some chameleons is arrested at the gastrula stage, and embryos remain at this stage for months after the eggs are laid. Our research tested the hypothesis that increased temperature, moisture, or both, are associated with the resumption of development by diapausing embryos of Chamaeleo calyptratus, the veiled chameleon. After 40 days of incubation at 25 degrees C in a relatively dry substrate, eggs were subjected to: 1) no change in temperature or moisture, 2) no change in temperature but change from a dry to a wet substrate, 3) change to a warmer temperature but no change in substrate moisture, or 4) an increase in both temperature and substrate moisture. Overall, embryos initiated development after 50-60 days to 80 or more days of incubation. Neither substrate moisture nor water uptake by eggs was related to the interval when development resumed. In contrast, development was initiated about 10 days earlier for eggs in the high temperature treatment compared to eggs in the low temperature treatment. Our results suggest that neither water availability nor water uptake by eggs affect the length of diapause but that an increase in ambient temperature initiates development of diapausing embryos of C. calyptratus.