Anaerobic metabolism in freely diving painted turtles (Chrysemys picta)

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Abstract
The degree to which painted turtles (Chrysemys picta) rely on anaerobic metabolism during unrestrained, voluntary dives was estimated by measuring the total body lactate content of turtles in the lab and in outdoor pools in summer and in winter. Experiments with forcibly submerged animals were carried out for comparative purposes. Summer turtles diving voluntarily in an aquarium at 25°C during a 5‐day experiment did not accumulate lactate (x̄ = 20 mg%). When turtles in water at 25°C were threatened and prodded but not restrained or forcibly immersed, their total body lactate content increased fourfold in 60 min. Animals forcibly submerged for 2 days at 25°C exhibited total body lactate levels up to 300 mg%. Summer turtles diving undisturbed in outdoor pools had lactate levels which were low (x̄ = 10 mg%) and which were correlated with water temperature, but not with time of day, intensity of activity in the hour prior to sampling, or the time interval since the last breath. Winter turtles forcibly submerged in an aquarium at 5°C did not exhibit a total body lactate level of 300 mg% until 2 weeks had elapsed. Winter animals diving undisturbed in an outdoor tank had lactate levels (up to 558 mg%) unrelated to time of day, water temperature (x̄ = 3.7°C), or ice thickness, but highly correlated with the duration of their hibernation (up to 67 days). These results are consistent with the hypothesis that painted turtles in nature rely on anaerobiosis when forced by a predator to remain submerged and during hibernation but not during routine diving at moderate temperatures.