Heart Rate Response to Anthropogenic Disturbance in the Red‐eared Slider

Abstract

When confronted with a disturbance, most mammals experience a fight or flight response, causing heart rate to increase. Submerged crocodilians, on the other hand, undergo a fright bradycardia, or a reduction in heart rate, which may help conserve oxygen while under water. It is not clear how the red‐eared slider (Trachemys scripta) responds to disturbances in the wild or in a laboratory setting. We hypothesized that turtles would experience an increase in heart rate in response to anthropogenic disturbances, suggesting a fight or flight response. To test this hypothesis, we measured heart rate in eight red‐eared sliders exposed to different disturbances. EKG leads were placed through the plastron above and below the heart and EKG data were collected by a self‐contained EKG data logger glued to the turtle's carapace. The logger was minimally invasive and did not interfere with the turtle's natural movements and activities. We first exposed the turtles to the sudden presence or absence of light when no investigator was present. In a separate experiment, we presented the turtles with a noise disturbance with an investigator present. The behavior of each turtle during these disturbance periods was analyzed using synchronized video recordings. We compared the change in heart rate of turtles that were engaged in similar behavior before, during, and after each disturbance. No significant change in heart rate was observed in response to the light disturbance. In response to the noise disturbance, none of the turtles demonstrated a reduction in heart rate. Post‐noise disturbance heart rate increased significantly compared to pre‐noise disturbance heart rate (p=0.02). The average heart rate before the noise disturbance ranged from 7.31 to 15.72 beats per minute (bpm), while the average heart rate after each noise disturbance ranged from 12.49 to 19.39 bpm. There was an overall average increase of 49.13% in heart rate after the noise disturbance. Although having a fright bradycardia would be advantageous for oxygen conservation, turtles have an extraordinary tolerance for anoxia and lactate accumulation. Therefore, it is reasonable that turtles would experience an increase in heart rate due to a fight or flight response, rather than a drop in heart rate caused by a fright bradycardia.