Aerobic Pushups: Cutaneous Ventilation in Overwintering Smooth Softshell Turtles, Apalone mutica

Abstract

We observed the behavior of overwintering Smooth Softshell Turtles, Apalone mutica, in an outdoor simulated pond with remote cameras. Submerged overwintering turtles partially buried themselves in a sand/mud substrate where they periodically raised and lowered the posterior portion of their body into the water column in a “push-up” fashion. Push-ups occurred with variable frequency and were similar in appearance and amplitude within and among individual turtles. Push-up frequency was positively correlated with water temperature and was paused more often at lower water temperatures. We also observed push-up behavior of A. mutica under simulated winter conditions in laboratory aquaria. Turtles maintained in water with 95–100% dissolved oxygen content executed pushups less frequently than turtles in water with lower oxygen content. Our observations of push-up behavior in A. mutica in an outdoor enclosure and laboratory are consistent with a respiratory ventilation function. Softshell turtles, known to be highly intolerant of anoxia, ostensibly sustain aerobic metabolism by creating currents that replenish the oxygen-depleted boundary layer between the turtle's thin vascularized skin and oxygenated water.