Oxygen concentration affects upper thermal tolerance in a terrestrial vertebrate.
We tested the oxygen limitation hypothesis, which states that animals decline in performance and reach the upper limits of their thermal tolerance when the metabolic demand for oxygen at high temperatures exceeds the circulatory system's ability to supply adequate oxygen, in air-breathing lizards exposed to air with different oxygen concentrations. Lizards exposed to hypoxic air (6% O2) gaped, panted, and lost their righting response at significantly lower temperatures than lizards exposed to normoxic (21% O2) or hyperoxic (35% O2) air. A greater proportion of lizards in the hyperoxic treatment were able to withstand body temperatures above 44°C than in the normoxic treatment. We also found that female lizards had a higher panting threshold than male lizards, while sex had no effect on gaping threshold and loss of righting response. Body size affected the temperature at which lizards lost the righting response, with larger lizards losing the response at lower temperatures than smaller lizards when exposed to hypoxic conditions. These data suggest that oxygen limitation plays a mechanistic role in the thermal tolerance of lizards.
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: tkshea@calpoly.edu.
Tanner K
TK
Shea
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: pmdubois@calpoly.edu.
P Mason
PM
DuBois
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: nclaunch@calpoly.edu.
Natalie M
NM
Claunch
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: nicolettemurphey@gmail.com.
Nicolette E
NE
Murphey
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: karucker@calpoly.edu.
Kiley A
KA
Rucker
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: rabrewst@calpoly.edu.
Robert A
RA
Brewster
Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407-0401, USA. Electronic address: etaylor@calpoly.edu.
Emily N
EN
Taylor
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D049628:Body Size / Q000502:physiology; D003080:Cold Temperature; D005260:Female; D006358:Hot Temperature; D008116:Lizards / Q000502:physiology*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D012737:Sex Factors; D013696:Temperature
D010100:Oxygen
Critical thermal maximum; Gaping; Lizard; Loss of righting response; Oxygen; Panting; Sceloporus occidentalis; Thermal tolerance