REESE, S.A.; JACKSON, D.C.; CROCKER, C.E.; ULTSCH, G.R.; Brown University, Providence; Brown University, Providence; San Francisco State University, San Francisco; University of Alabama, Tuscaloosa: Acid-base and respiratory physiology of three species of turtles (Trachemys scripta, Terrapene carolina, and Apalone spinifera) and one species of tortoise (Gopherus polyphemus) in anoxia at 20 ^oC.

Adult red-eared slider turtles (Trachemys scripta), box turtles (Terrapene carolina), softshell turtles (Apalone spinifera), and gopher tortoise (Gopherus polyphemus) with indwelling, arterial catheters were exposed to an anoxic environment at 20 &degC to investigate the evolutionary relationship of anoxia tolerance within this taxonomic group. Blood samples were taken periodically and used to measure pH, PO₂, PCO₂, [lactate], [glucose], [Na⁺], [K⁺], [Cl^–], total calcium, total magnesium, and osmolality. [HCO₃^–] was calculated and hematocrit was determined. Turtles from all four species started at similar blood pHs (7.624 in Trachemys scripta, 7.704 in Terrapene carolina, 7.633 in Gopherus polyphemus, and 7.666 in Apalone spinifera) and similar plasma [lactate] (1.3, 1.5, 0.4, and 3.3 mmol/L, respectively). The endpoint of the experiment was when the turtles had a 0.6-drop in blood pH. Red-eared slider turtles reached the endpoint in 6-8 h and had [lactate] of 22-40 mmol/L, box turtles reached the endpoint in 8-12 h and had [lactate] of 27-40 mmol/L, softshell turtles reached the endpoint in 6-10 h and had [lactate] of 26-34 mmol/L, while gopher tortoise reached the endpoint in 10-14 h and had [lactate] of 18-31 mmol/L. Following anoxic exposure, turtles were allowed to recover in normoxia for 24 h and the pH of all turtles had returned to control values, though lactate concentrations had not completely recovered. Although land turtles may never experience anoxia as would certain aquatic turtles, they appear to retain similar abilities.