Oxygen isotope variability in bones of wild caught and constant temperature reared sub-adult American alligators

(1) The mean δ 18O BP (‰SMOW) for any given bone sampled from captive alligators maintained at high constant temperature was lower (indicative of higher temperatures of bone deposition) than that of the same bone from wild alligators caught in Northern Florida, but these differences were only greater than two standard deviations from the mean for the thoracic vertebrae and metatarsal bones. (2) Inter-bone variability of δ 18O BP (‰SMOW) was similar for captive alligators maintained at constant temperatures and the wild alligators, but intra-bone variability was much greater in wild alligators. (3) The order of mean δ 18O BP (‰SMOW) of bones (from highest to lowest) differed between treatment groups. However, intra-bone variability obscured the significance of those differences. Nevertheless, the thoracic vertebra had the highest mean δ 18O BP (‰SMOW), indicative of lower temperatures, and the lowest variability of bones in both groups of alligators. Conversely, the tibia was one of the warmest and more variable bones in both groups of alligators. (4) The pattern of δ 18O BP (‰SMOW) values across sites within long bones were identical between alligator treatment groups for the femur and humerus but differed between groups for the tibia and metatarsus, and differed between different long bones. The predicted intra-bone pattern for long bones of increasing δ 18O BP (‰SMOW) indicative of lower temperatures in more distal sampling sites was only obtained from the femurs. (5) Paired cortical and cancellous bone samples from the same site from all individuals in both treatment groups were available for proximal humeri and distal femurs. δ 18O BP (‰SMOW) values from cortical bone were more variable than those from cancellous bone for both bones. (6) Cortical bone had lower δ 18O BP (‰SMOW) values indicative of warmer temperatures than cancellous bone at sites sampled on the proximal humeri and distal femurs of all three animals from both treatment groups.