Embryonic responses to variation in oviductal oxygen in the lizard Sceloporus undulatus from New Jersey and South Carolina, USA

Authors

Scott L. Parker, Virginia Polytechnic Institute and State University, Blacksburg, VA
Robin M. Andrews, Virginia Polytechnic Institute and State University, Blacksburg, VA
Tom Mathies, National Wildlife Research Center

Document Type

Article

Date of this Version

April 2004

Comments

Published by Biological Journal of the Linnean Society, 2004, 83, 289–299. © 2004 The Linnean Society of London. Permission to use.

Abstract

Viviparity in reptiles is hypothesized to evolve in cold climates at high latitudes and high elevations through selection for progressively longer periods of egg retention. Oxygen consumption of embryos increases during development and therefore longer periods of egg retention should be associated with maternal or embryonic features that enhance embryonic oxygen availability. We tested the hypotheses that embryos of the oviparous lizard Sceloporus undulatus from a high-latitude population in New Jersey are oviposited at more advanced developmental stages and have a higher growth rate at low oxygen partial pressures (pO₂) than embryos from a low-latitude population in South Carolina. These hypotheses were rejected; embryos from the two populations did not differ in embryonic stage at oviposition, survival, rate of differentiation or growth in mass when incubated under simulated in utero conditions at low oxygen concentrations. We also estimated the effective pO₂ experienced by lizard embryos in utero. At an effective a pO₂ of 8.6 kPa (9% O₂), development of S. undulatus embryos is arrested at Dufaure and Hubert stage 30 and at a dry mass of 0.8 mg. Physiological and morphological features of gravid females, embryos, or both, that facilitate oxygen uptake for developing embryos appear to be a critical early step during the evolution of reptilian viviparity.