The physiology of diving in a north-temperate and three tropical turtle species

We examined changes in blood gases, plasma ions, and acid-base status durin g prolonged submergence (6 h) of four aquatic turtle species in aerated wat er at 20 degrees C. Our objective was to determine whether the temperate sp ecies, Chrysemys picta bellii, exhibits greater tolerance to submergence ap nea than the tropical species, Pelomedusa subrufa, Elseya novaeguineae, and Emydura subglobosa. Blood was sampled from indwelling arterial catheters f or measurements of blood PO2, PCO2, pH, and hematocrit and for plasma conce ntrations of lactate, glucose, Na+, K+, Cl-, total Ca, and total Mg. The pa ttern of change was similar in all species: a combined respiratory and meta bolic acidosis associated with a marked decrease of blood PO2. The severity of the acidosis developed in the temperate species, however, was significa ntly less than that of the tropical turtles. Lactate rose significantly and HCO3- fell proportionately in all turtles; changes in other plasma ion con centrations were small but were generally in the directions consistent with compensatory exchanges with other body compartments; i.e., cations (K+, Ca , and Mg increased) and anions (Cl- decreased). The results indicate that h ypoxia tolerance is a conserved trait in turtles, even in those that do not experience enforced winter submergence, and that the temperate species may be superior in this capacity because of reduced metabolic rate.