Resting metabolic rates increase with elevation in a mountain-dwelling lizard.

Area of Science:

• Ecology
• Physiology
• Evolutionary Biology

Background:

• Organisms in high-elevation environments face thermal challenges, impacting ectotherm activity and energy expenditure.
• Resting metabolic rate (RMR) is a crucial indicator of an animal's energy requirements and fitness.
• Mesquite lizards (Sceloporus grammicus) at La Malinche Volcano occupy a wide elevational gradient, including areas above the tree line.

Purpose of the Study:

• To investigate the resting metabolic rate (RMR) of Mesquite lizards across different elevations.
• To determine how temperature and body mass influence RMR in this species.
• To understand the physiological adaptations of high-elevation populations to thermal stress.

Main Methods:

• RMR was measured in Mesquite lizards from three distinct elevations (2,600 m, 3,200 m, and 4,100 m).
• Measurements were conducted at four ecologically relevant temperatures (15°C, 25°C, 30°C, and 35°C).
• RMR was analyzed in relation to elevation, temperature, and body mass.

Main Results:

• RMR increased with both temperature and body mass in Mesquite lizards.
• Lizards from the highest elevation (4,100 m) exhibited significantly higher mass-specific RMR across all tested temperatures.
• Despite higher metabolic costs, high-elevation lizards were characterized by smaller body size.

Conclusions:

• Higher mass-specific RMR in high-elevation populations suggests an adaptation to increased metabolic costs in colder environments.
• Smaller body size in these populations may further contribute to thermoregulation and survival.
• These combined traits likely enable Mesquite lizards to thrive under the extreme thermal conditions found at high altitudes.