| Evaporative
Thresholds in Hypoxia |
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Most
animals, including reptiles, lower body temperature
(Tb) under hypoxic conditions. Numerous physiological
and behavioural traits significant to the regulation
of Tb are altered by hypoxia in ways that suggest an
orchestrated adjustment of Tb at a new and lower regulated
level. We examined this matter in bearded dragons, Pogona
vitticeps, a species of reptile that naturally
exhibits open mouth gaping at high temperatures, presumably
in order to promote evaporation and thus prevent or
avoid further increases in Tb. The threshold for the
onset of gaping (assessed as the temperature at which
lizards spent 50% of their time gaping) was reduced
from 36.9°C in normoxia to 35.5°C at 10% and
34.3°C at 6% O2. The overall magnitude or degree
of gaping, measured qualitatively, was more pronounced
at lower temperatures in hypoxia. Females consistently
had lower gaping threshold temperatures than males did,
and this difference was retained throughout exposure
to hypoxia. In addition to gaping, evaporative water
loss from the cloaca may also play a significant role
in temperature regulation, since the ambient temperature
at which cloacal discharge occurred was also reduced
significantly in hypoxia. The results reported herein
strongly support the view that hypoxia reduces temperature
set-point in lizards, and that such changes are coordinated
by specific behavioural thermoeffectors that modulate
evaporative water loss and thus facilitate a high potential
for controlling or modifying Tb. |
Publications
Tattersall, G. J. and Gerlach, R. M. Hypoxia progressively
lowers thermal gaping thresholds in bearded dragons, Pogona
vitticeps. Journal
of Experimental Biology 208:3321-3330.
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