Thermal responses to feeding in a secretive and specialized predator (Gila monster, Heloderma suspectum)

Abstract

We investigate how a unique dietary specialist, the Gila monster (Heloderma suspectum), uses behavioral thermoregulation to elevate body temperature (Tb) after feeding. Lizards in a laboratory thermal gradient were fed rodent meals of three different sizes (5, 10, or 20% of body mass), or sham fed (meal of 0% body mass), and Tbs were recorded for three days before feeding and seven days after feeding. Gila monsters selected a mean Tb of 25.2°C while fasting (set-point range 23.6–27.1), and increased Tbs after feeding. The magnitude and duration of post-prandial Tb increases are positively related to meal size, and Gila monsters selected mean Tbs up to 3.0°C higher and maintain elevated Tbs for 3–6 days after feeding. Selection of Tb does not appear to differ between day and night time periods, and because the lizards are both diurnal and nocturnal (at different times of year), photoperiod may not be an important influence on Tb selection.