Oxygen concentration affects upper thermal tolerance in a terrestrial vertebrate

Area of Science:

• Physiological Ecology
• Comparative Physiology
• Herpetology

Background:

• The oxygen limitation hypothesis proposes that high temperatures reduce oxygen supply, limiting animal performance and thermal tolerance.
• Understanding thermal tolerance limits is crucial for predicting species responses to climate change.

Purpose of the Study:

• To test the oxygen limitation hypothesis in air-breathing lizards.
• To investigate the role of oxygen concentration on thermal tolerance thresholds.

Main Methods:

• Lizards were exposed to varying oxygen concentrations: hypoxic (6% O2), normoxic (21% O2), and hyperoxic (35% O2).
• Key physiological responses (gaping, panting, loss of righting response) were monitored at different temperatures.
• Effects of sex and body size on thermal tolerance were analyzed.

Main Results:

• Lizards in hypoxic air exhibited lower critical temperatures for gaping, panting, and loss of righting response compared to normoxic and hyperoxic conditions.
• A higher percentage of lizards tolerated temperatures above 44°C in hyperoxic air than in normoxic air.
• Female lizards had a higher panting threshold; larger lizards lost righting response at lower temperatures under hypoxia.

Conclusions:

• Oxygen availability significantly impacts the thermal tolerance of lizards.
• These findings provide mechanistic support for the oxygen limitation hypothesis in ectotherms.
• Environmental changes affecting oxygen levels may alter lizard thermal performance and survival.