Squamate metabolic rates decrease in winter beyond the effect of temperature

Area of Science:

• Zoology
• Physiology
• Ecology

Background:

• Reptilian brumation is less understood than mammalian hibernation.
• Evidence for metabolic regulation beyond temperature in brumating reptiles is scarce.
• Squamate physiology is often perceived as solely temperature-dependent.

Purpose of the Study:

• To investigate seasonal and environmental influences on squamate standard metabolic rates (SMR).
• To determine if reptiles actively regulate metabolism during brumation.
• To compare metabolic rates across different biomes, seasons, and times of day.

Main Methods:

• Measured SMR (oxygen uptake) in 156 individuals from 59 Israeli squamate species.
• Utilized continuous gas exchange measurements in a metabolic chamber.
• Employed phylogenetic mixed models to analyze factors influencing SMR.

Main Results:

• SMR decreased significantly between summer and winter (47% at 20°C, 70% at 12°C).
• Metabolic rates showed seasonal, diel, and geographic variations, independent of temperature alone.
• Body size scaling exponent for SMR differed between summer (0.84) and brumation (0.71).

Conclusions:

• Squamate metabolism is actively regulated by seasonal, diel, and geographic factors, not just temperature.
• Brumation involves intrinsic metabolic suppression beyond passive temperature effects.
• Findings challenge the view of reptiles as purely ectothermic regulators.