Determinants of Embryonic Stage at Oviposition in the Lizard
Robin M. Andrews
Department of Biology, Virginia Polytechnic Institute and
State University, Blacksburg, Virginia 24061-0406
Relatively few squamate reptiles oviposit eggs with embryos at
developmental stages greater than stage 30. To investigate po-
tential proximate and ultimate bases of this phenomenon, we
experimentally induced females of the lizard Urosaurus ornatus
to retain their eggs past the normal time of oviposition (NTO).
This procedure allowed us to determine whether the length of
egg retention is fixed or facultative and to evaluate the effects
of retention on embryos, hatchlings, and females. Females were
able to retain eggs facultatively for at least 29 d past the NTO.
However, retention resulted in arrested development of em-
bryos; arrest occurred at stages 3030.5, which is only slightly