Aquatic respiration and underwater survival of two freshwater turtle species

Abstract

Uptake of dissolved O 2 and survival time of forcibly submerged, free swimming turtles ( Sternothaerus minor and Pseudemys scripta) were measured at Po 2 = 0, 154, and 738 torr. Vo 2 of turtles breathing air was also measured. Turtle body temperature in all experiments was 22 °C. In S. minor, survival time was clearly related to aquatic respiration. Aquatic Vo- of P. scripta was directly related to Po 2 but was too slight to contribute significantly to underwater survival. In progressive hypoxia experiments, the critical Po 2 of S. minor was found to be about 425 torr for aquatic respiration, as compared with about eight torr for air breathing. S. minor was thus able to survive indefinitely in O 2-equilibrated water without pulmonary ventilation. Behavioral observations suggest that buccoy pharyngeal ventilation is a respiratory response to prolonged submersion in S. minor, but not in P. scripta. Low metabolic rate, high O 2 transport capacity, and insensitivity of the CNS to extreme hypoxia enable some turtles, in contrast to all other amniotes, to make significant use of aquatic respiration.