Meeting Abstract

2.6  Thursday, Jan. 3  CHRONIC HYPOXIA, BUT NOT HYPEROXIA, CONSTRAINS GROWTH IN THE AMERICAN ALLIGATOR: A CASE STUDY IN EXPERIMENTAL PALEOPHYSIOLOGY OWERKOWICZ, T.*; HICKS, J.W.; ELSEY, R.M.; UC Irvine; UC Irvine; Louisiana Dept. of Wildlife and Fisheries towerkow@uci.edu

Ancestors of modern amniotes are known to have endured and survived large-scale fluctuations in oxygen levels, including a dramatic drop from 30% in the Permian down to 12% in the Triassic. Normal vertebrate development and growth requires an adequate oxygen supply. Chronic hypoxia is known to constrain growth in many amniotes but effects of chronic hyperoxia on amniote growth are poorly documented. To investigate the influence of atmospheric composition on reptilian growth and physiology, we incubated eggs and subsequently raised hatchlings of the American alligator under hypoxia (12%), normoxia (21%) or hyperoxia (30%). All groups were maintained at 30�C and were litter-matched. There were no differences in developmental rate or incubation time between treatments. Hatchlings incubated under normoxia and hyperoxia did not differ significantly in their somatic or cardiopulmonary morphology. In contrast, hypoxic hatchlings showed significantly reduced musculoskeletal growth, in terms of muscle mass and bone formation (both endochondral and dermal). As compared to their normoxic/hyperoxic siblings, hypoxic hatchlings showed an apparent mismatch in the capacity of their cardiovascular and pulmonary systems, with a 30% increase in relative wet heart mass and a 23% decrease in relative wet lung mass. This suggests that embryonic lung development under hypoxia does not compensate for reduced oxygen content of ambient air, which has implications for post-hatching respiration and breathing patterns. We suggest that the drop in atmospheric oxygen level across the Permo-Triassic boundary had a profound influence on metabolism and growth of amniotes in their evolutionary history, e.g., acting as a constraint on growth rates in some Triassic taxa. Supported by NSF IOB 04445680 to JWH.