Plasma ion balance of North American freshwater turtles during prolonged submergence in normoxic water

Abstract

1. 1. Plasma ion (Na +, K +, Cl −, HCO − 3, lactate, Ca, and Mg) concentrations were measured during apneic submergence in aerated water at 10°C of 4 species of freshwater turtles: Chelydra serpentina serpentina (Chelydridae), Chrysemys picta bellii (Emydidae), Sternotherus odoratus (Kinosternidae), and Trionyx spiniferus asperus (Trionychidae). Measurements were made at intervals up to 21, 13, 100, and 100 days, respectively. In addition, final wet and dry masses were measured in Sternotherus and Trionyx and compared to control values to assess changes in body water and dry mass. 2. 2. In Chelydra and Chrysemys, which have a relatively poor aquatic O 2 uptake capacity, plasma ions changed as previously reported in animals submerged in anoxic water; [Na +] was unchanged, [K +], [Ca], and [Mg] were evaluated, and [Cl −1] and [HCO − 3] were depressed. This overall pattern is probably a regulated response and respresents a compensation for the severe acidosis exhibited by these animals. 3. 3. In Sternotherus and Trionyx, which have effective aquatic respiration and could remain submerged much longer, plasma ion concentrations, except [K +] and [lactate], fell due (largely in Sternolherus, less so in Trionyx to dilution by water uptake. Both species were slightly alkalotic after prolonged normoxic submergence, and we suggest that changes in ion concentrations can be considered as compensatory to this alkalosis. 4. 4. We conclude that these turtles fall into two distinct physiologic response types. In Chelydra and Chrysemys, normoxic submergence at 10°C is limited principally by acidosis, and observed plasma ionic changes act to counteract this effect; in Sternotherus, and to a much lesser degree, Trionyx, the limitation is largely osmoregulatory, due to a failure to exclude ambient water and to maintain ionic homeostatasis.