Meeting Abstract

P1.40  Jan. 4  Effects of atmospheric oxygen levels on embryonic growth of the American alligator OWERKOWICZ, T.*; HICKS, J.W.; University of California, Irvine; University of California, Irvine towerkow@uci.edu

Adequate oxygen supply to the embryo is necessary for normal growth and development. Hypoxia is known to constrain embryonic growth of endothermic vertebrates, but little data are available for ectothermic vertebrates. Crocodilian ancestors are known to have endured and survived large-scale fluctuations in oxygen levels, including a significant drop (from close to 30%, down to almost 12%) at the Permo-Triassic boundary. To model the influence of such an atmospheric change on embryonic growth, we incubated embryos of the extant American alligator (Alligator mississipiensis) under different laboratory conditions: hypoxia (12-13%) , normoxia (20-21%) or hyperoxia (29-30%). All embryos were incubated at 30C and were litter-matched. There were no significant differences in the morphology of hatchlings incubated under normoxia and hyperoxia. However, hypoxic hatchlings showed a significantly smaller yolk-free body mass and a greater unutilized yolk mass. The absolute wet masses of heart and liver were significantly smaller in hypoxic hatchlings. Expressed in mass-specific terms, the wet heart mass of hypoxic hatchlings was significantly higher that of normoxic or hyperoxic hatchlings, but no such differences existed in wet liver masses between groups. In comparison to their normoxic and hyperoxic siblings, hypoxic hatchlings also showed reduced skeletal growth, in terms of skull, limb, snout-vent and total axial lengths. Interestingly, total incubation time and hatching success rate were not affected by the atmospheric oxygen levels. Altogether, this suggests that changes in oxygen levels may have had a profound influence on growth rates of ectothermic amniotes in their evolutionary history, and may explain a pattern of body-size reduction in some of the Triassic amniote taxa.