Physiology of common map turtles (Graptemys geographica) hibernating in the Lamoille River, Vermont

Common map turtles (Graptemys geographica) were collected from a natural underwater hibernaculum in Vermont at monthly intervals during the winter of 1997-1998. Blood was sampled by cardiac puncture and analyzed for pH, PCO2, PO2, and hematocrit; separated plasma was tested for Na+, K+, Cl-, total [Ca], total [Mg], [lactate], and osmolality (mOsm kg(-1) H2O). Control (eupneic; 1 degrees C) values for pH, PO2, PCO2, [HCO3-], and [lactate] were 7.98 +/- 0.03, 47.4 +/- 18.7, 10.1 +/- 0.7 (mm Hg), 36.1 +/-. 0.2 (mmol liter-l), and 2.1 +/- 0.1 (mmol liter(-1)), respectively. Between November 1997 and March 1998, ice covered the river and the turtles rested on the substratum, fully exposed to the water, and were apneic. Blood PO2 was maintained at less than 3 mm Hg (range 0.9 +/- 0.2 to 2.1 +/- 0.7 mm Hg), PCO2 decreased slightly, plasma [lactate] was 15 mmol liter-l, and plasma [HCO3-] decreased significantly. In March [lactate] rose to 7.5 +/- 1.5 mmol liter(-1), but there was no acidemia. Map turtles meet, most of their metabolic demand for Oz via aquatic respiration and tolerate prolonged submergence at 1 degrees C with little change in acid-base or ionic status. The adaptive significance of remaining essentially aerobic during winter is to avoid the life-threatening progressive acidosis that results from anaerobic metabolism. (C) 2000 Wiley-Liss, Inc.