Thermoregulatory and metabolic responses to hypoxia in the oviparous lizard, Phrynocephalus przewalskii.

The effects of hypoxia on behavioral thermoregulation, rate of heating and cooling, hysteresis of heart rate, and standard metabolic rate (SMR) were investigated in Phrynocephalus przewalskii, a small size toad headed lizard. Preferred temperature (T(b)) descended when lizards were exposed to severe hypoxia (8% O(2) and 6% O(2)) for 22 h, and lizards were able to maintain preferred T(b) after one week at 12% and 8% O(2) respectively. The period of heating increased after being treated with hypoxia (12% and 8% O(2)) for one week. Hysteresis of heart rate appeared at any given body temperature and oxygen level except at 39 °C and 40 °C at 8% O(2). SMR significantly increased after one-week acclimatization to 12% and 8% O(2) when ambient temperature (T(a)) was 25 °C, however, it did not change at 35 °C. Thus, we suggest that P. przewalskii has special thermoregulatory and metabolic mechanisms to acclimatize to the hypoxic environment.