Meeting Abstract

12.1  Monday, Jan. 4  Exhaustive terrestrial and aquatic exercise does not affect periosteal deposition, structural properties or mineral content in limb bones of the American alligator TSAI, H.P.*; OWERKOWICZ, T.; SANCHEZ, L.; FELBINGER, K.; ANDRADE, F.; BLANK, J.M.; EME, J.; GWALTHNEY, J.; HICKS, J.W.; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine hptsai@uci.edu

Effects of exercise on skeletal growth and remodelling have been studied in a variety of mammals and birds, but exercise effects on bone microstructure in reptiles have received scant attention. We investigated the effects of long-term exercise on a motorized treadmill or in a flume on limb bones of the American alligator (Alligator mississippiensis). This allowed us to separate biomechanic and metabolic effects of exercise on bone – whereas terrestrial exercise increases both limb bone loading and metabolic rate, aquatic exercise increases only the latter. Juvenile female alligators were run or swum to exhaustion every other day for 17 months, and received fluorescent dye injections to determine bone deposition rates. We found no significant differences in whole bone morphology and cortical bone deposition rates in the alligator humeral or femoral midshaft, regardless of exercise regimen. Similarly, we found no effects of either exercise regimen on trabecular bone tissue density, number or thickness in the distal femur. In addition, bone mineral content was similar across exercise groups. Altogether, this suggests that long-term exercise has no discernible effect on bone microstructure in alligators. These results stand in contrast to studies on endothermic vertebrates. The disparity could be due to metabolic differences between ectothermic and endothermic vertebrates. An alternative explanation is that alligator limb bones are subjected to insufficient strain levels or load cycles during exercise bouts, which may account for lack of bone tissue response to exercise in alligators. Funded by the NSF IOB 04445680 to JWH.