Heart Rate Response to Threat and Diving in the Ornate Box Turtle, Terepene ornata

Behavior and heart rate response of seven ornate box turtles (Terepene ornata) to visual threat, touch, forced diving, and voluntary diving were investigated. Visual stimulus resulted in two different behavioral and two different heart rate responses. Three of seven turtles turned and walked away from the stimulus with no change in heart rate. Four turtles stopped walking and withdrew their feet and head. Heart rate was reduced 37%. Atropine had no effect on behavior but abolished bradycardia. Tactile stimulus resulted in withdrawal of feet and head and reduction of heart rate by each of the turtles. Heart rate was reduced 68%. Atropine abolished bradycardia but did not alter behavior. Reduction in heart rate was instantaneous and occurred during the first R-R interval following stimulus. Forced diving reduced the heart rate 56%. Bradycardia was abolished with atropine. Bradycardia onset was gradual, suggesting chemoreceptor involvement. Voluntary diving was not accompanied by bradycardia.