Effects of Hypoxia on Growth and Biomechanics in Limb Bones of Alligator mississippiensis

Abstract

Microanatomy and cross sectional geometry of limb bones are often used to infer life history and locomotor ability of fossil vertebrates based on study of their extant relatives; often the extreme variations in atmospheric oxygen that occurred over geologic time (oxygen levels 30% or more during the Permian, 15% in the Triassic) are not considered. As hypoxia is known to inhibit growth in vertebrates, while hyperoxia may be permissive, such comparisons between extinct and modern taxa merit investigation. As members of Archosauria, a clade with a long evolutionary history, alligators are excellent models to test for effects of environmental oxygen on skeletal growth and biomechanics. We incubated eggs and reared hatchlings in hypoxic (16% O2) and hyperoxic (26%, 31%, 36% O2) conditions. After sacrifice, femora were used in whole‐bone morphometric measurements and preparation of transverse mid‐diaphyseal ground sections. For comparison, traits were standardized to femur length. Cross sectional area, second moment of area, and polar moment of inertia scaled with isometry in alligators reared in chronic hypoxia, but with negative allometry in hyperoxic groups. The stouter femora of hypoxic animals exhibited greater resistance to compression, bending and torsion than predicted. Caution in evaluation of paleohistological data and consideration of oxygen availability is suggested.Supported by NSF IOS‐0922756.