Measuring Stabilized Heart Rates in the Prairie Lizard, a Small Vertebrate Ectotherm

Abstract The ability to accurately measure heart rates is vital for studying the ecological and evolutionary pressures on animals because cardiovascular regulation is associated with key physiological responses to environmental change. Heart rates, especially in ectotherms, are influenced by multiple factors over both the short and long term, including environmental temperatures, handling frequency, metabolic rates and hemodynamic demands. Traditional methods for measuring heart rate in small vertebrates often involve invasive techniques or unreliable non‐invasive tools. In this study, we present a novel, non‐invasive methodology for stabilizing and measuring heart rates in a small vertebrate ectotherm, the lizard Sceloporus consobrinus. We measured heart rates at both 28 and 32°C using a Doppler ultrasound system fixed within a custom‐built restraint chamber and a commonly employed egg heart monitor (The Buddy®). Compared to the conventional egg monitor device, the Doppler system measured heart rates with greater accuracy and precision while providing greater flexibility in experimental design and organismal size. Our design provides an improved non‐invasive monitoring technique for physiological research and a standardized approach for studying cardiovascular responses in small vertebrates.