Meeting Abstract
39.4 Tuesday, Jan. 5 Atmospheric hypoxia increases bone robusticity in the American alligator OWERKOWICZ, T.*; ANDRADE, F.C.; ELSEY, R.M.; HICKS, J.W.; Uni. California, Irvine; Fullerton College, CA; Rockefeller Wildlife Refuge, Grand Chenier, LA; Uni. California, Irvine towerkow@uci.edu
Extinct animals’ body masses and growth rates have been inferred from the cross-sectional area and primary bone microstructure of their limb bones. These relationships are based on skeletons of extant vertebrates growing in an atmosphere containing 21% oxygen. In the past, however, atmospheric O2 levels rose as high as 30% and fell as low as 12%, and O2 supply to bone is known to affect its growth and mineralization. We tested the effect of atmospheric O2 on skeletal growth in the American alligator. We incubated eggs and subsequently grew alligator hatchlings under chronic hypoxia (12% O2), normoxia (21% O2) and hyperoxia (30% O2). Animals received monthly injections of fluorescent dyes to determine bone deposition rates. After three months, animals were sacrificed and their femora either sectioned at mid-diaphysis, or ashed. We found femora of hypoxic alligators to have significantly greater cross-sectional area (+15%), second moment of area (+20%) and polar moment of inertia (+23%) than those of either normoxic or hyperoxic hatchlings. Mineral content was also significantly higher (+6%) in femora of hypoxic animals. This suggests that exposure to chronic hypoxia, but not hyperoxia, resulted in increased resistance to compressive, bending and torsional stresses on the skeleton. Furthermore, the relationship between body mass growth and periosteal deposition rate was different between treatment groups, with hypoxic animals accruing more bone per unit body mass. We suggest that prevalent atmospheric O2 level need be considered when reconstructing size and growth curves of extinct vertebrates. Supported by NSF grants IOB 04445680 and IOS 0922756 to JWH.
