Meeting Abstract
P1.84 Tuesday, Jan. 4 Hypoxia-Induced Alterations in Limb Bone Growth and Geometry in Alligator mississippiensis LUJAN, S.L.*; MIDDLETON, K.M.; OWERKOWICZ, T.; ELSEY, R.M.; HICKS, J.W.; California State University, San Bernardino; California State University, San Bernardino; University of California, Irvine; Rockefeller Wildlife Refuge, Grand Chenier, LA; University of California, Irvine lujans@csusb.edu
Levels of atmospheric oxygen varied over the Phanerozoic Eon, ranging between hyperoxic (30%O2) and hypoxic (12%O2) extremes relative to present-day normoxic levels (21%O2). Prior studies in vertebrates show that hypoxia reduces overall growth rates, except in fossorial species, which may be adapted to chronic hypoxia. To test the effects of environmental oxygen on growth and biomechanics of the archosaur skeleton, we incubated eggs and raised post-hatchling American alligators in either hypoxic (16% O2) or one of three hyperoxic (26%, 31%, 36% O2) environments. At intervals, animals were sacrificed, femora removed, and cross sectional geometry of the mid-diaphyses studied. Traits were standardized to femur length to allow comparisons between animals of different sizes. We found that cross sectional area and maximum and minimum moments of inertia scaled isometrically in hypoxic alligators, but with negative allometry in hyperoxic groups. Thus, in alligators raised under hypoxic conditions, the femur is significantly more robust in size and resistance to torsional loads per unit body size is greater than predicted. Our results indicate that atmospheric oxygen levels have a significant effect on growth rates in archosaurs. Because growth rates in fossil and extinct taxa are often based on comparisons with those of extant archosaurs raised in normoxia, we suggest these inferences be made with caution, prevalent atmospheric conditions be considered, and that biomechanical hypotheses based on limb bone geometry may require revision. Supported by NSF IOS-0922756.
