REESE, Scott A.*; MOORE, Douglas; ULTSCH, Gordon R.; WARREN, Daniel E.; JACKSON, Donald C.; Kennesaw State University; Brown University/Rhode Island Hospital; University of Alabama; Brown University; Brown University: Mechanical characteristics of bone change little during anoxic submergence at 3 ^oC in red-eared slider turtles, Trachemys scripta.

We submerged red-eared slider turtles, Trachemys scripta, in nitrogen-equilibrated water at 3^oC to investigate mechanical changes that occur in the shell due to acid-base regulation. We analyzed shell samples for hardness and femur samples for hardness, stiffness, peak load, and energy to peak load at 0, 13, 29 and 44 d of submergence. We also measured shell [Ca⁺²], [Mg⁺²], [Na⁺], [K⁺], [CO₂], [inorganic phosphate (P_i)] and [lactate] to correlate changes in shell composition with mechanical changes. Similar to other turtles, red-eared slider turtles had a blood pH=7.09 (control=7.77) after 44d due to a lactacidosis and plasma Ca⁺² and Mg⁺² increased significantly. Shell Ca⁺² remained steady, however shell [CO₂] and [Mg⁺²] decreased over the 44d (from 486 &micro/g ww shell to 369 &micro/g ww shell and from 71.0 µ/g ww shell to 53.0 µ/g ww shell, respectively) while shell [lactate] increased (from 0.6 µ/g ww shell to 69 µ/g ww shell). These changes were not accompanied by significant changes to femur stiffness (0d=296.5±33.9 N/mm, 44d=253.1±11.5 N/mm), peak load (0d=204.5±10.4 N, 44d=197.6±7.7 N), energy to peak load (0d=380.9±37.7 Nmm, 44d=334.3±19.5 Nmm), or hardness (0d=35.0±2.6, 44d=32.0±2.3). Shell hardness decreased from 33±2.5 to 28±3.1.