Alligator Egg Development At Prehistoric Oxygen Levels

"Alligator eggs are an ideal self-contained unit for studying theeffects of oxygen on development -- they have a limited food source inthe yolk and they are incubated in their nesting material at a constanttemperature of 89°F and 100 percent relative humidity," said John Vanden Brooks,a graduate student in the Department of Geology and Geophysics at YaleUniversity. He noted that large-scale changes in atmospheric partialoxygen pressure would have had wide-ranging effects on vertebrateevolution and development throughout geologic time.

Understanding the environment's effect on vertebrate evolutionand development is essential to the study of ecology, paleontology andevolutionary theory. Oxygen is the most important component in theatmosphere for all vertebrate animals, and while the rise in oxygenlevel during the Precambrian era has been widely studied, littleattention has previously been paid to continued fluctuations throughoutthe Phanerozoic.

His mentor, Robert A. Berner, the Alan M. Bateman Professor of Geology and Geophysicsat Yale, characterized the range of atmospheric oxygen levels overmultimillion year times scales, and established an upper value of about31 percent oxygen, and a sharp decline near the Permo-Triassic boundaryto about 12 percent. Earth's current atmosphere is about 21 percentoxygen.

"Each clutch contains 30 -- 50 eggs that are laid together, soeasy comparison can be made between sibling eggs raised under differentpartial pressures of oxygen," said Vanden Brooks. Studying fivedifferent partial oxygen pressures across this broad range, he found anoptimum at 27 percent oxygen. He found that both high and low oxygenlevels altered growth patterns and affected the timing and extent ofbone development, its chemical composition, and mortality of thedeveloping eggs.

While it is well known that oxygen balance is important inhuman premature infant development, this work provides an importantstep in understanding the complex interaction between vertebratedevelopment and oxygen levels.

The talk, "Phanerozoic Oxygen Levels and their Effect on ModernVertebrate Development" will be presented at the meeting August 8 -- 11that is co-sponsored by the Geological Society of America and theGeological Association of Canada. Eggs were made available by RuthElsey of the Rockefeller Wildlife Refuge in Louisiana. The study wasfunded by the Geological Society of America, the PaleontologicalSociety, the American Museum of Natural History, the AmericanPhilosophical Society, the National Science Foundation, Yale Institutefor Biospheric Studies, and the Ecology and Systematics of Animals onthe Verge of Extinction Fund.