First published online December 16, 2008
Journal of Experimental Biology 212, 137-144 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.023531
Decreased precision contributes to the hypoxic thermoregulatory response in lizards
Viviana Cadena* and
Glenn J. Tattersall
Department of Biological Sciences, Brock University, St Catharines, ON,
Canada, L2S 3A1
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Fig. 1. Representative trace of body temperature (Tb) and
selected ambient temperature (Ta) of two different lizards
(P. vitticeps) allowed to thermoregulate inside an electronic
temperature-choice shuttle box. Traces are plotted for the 4.5 h acclimation
period and the subsequent 7.5 h of exposure to (A) 21% O2 and (B)
5% O2. Arrow denotes the onset of hypoxia at 12:00 h. Arrowhead
represents the moment at which 5% oxygen was reached (12:30 h).
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Fig. 2. Values for the different parameters of precision of thermoregulation with
exposures to different levels of oxygen. Upper and lower escape ambient
temperatures (UETa and LETa, respectively), high and low
limits of the Tb range (HTbL and
LTbL) and preferred Tb are plotted as
the mean of the 7.5 h median values of 12 lizards (P. vitticeps)
±s.e.m. (for visual clarity) instead of s.d. Values for s.d. are
reported in Table 1. Animals
were tested for 7.5 h in an electronic shuttle box at each of the experimental
conditions. *Significant effect compared with normoxic values with
the Holm–Sidak post-hoc test (P<0.05).
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Fig. 3. Coefficients of variation of upper and lower (A) ambient (UETa
and LETa, respectively) and (B) body (UETb and
LETb, respectively) escape temperatures of bearded dragons during
exposure to different oxygen concentrations. Values are means of 12 lizards
during a 7.5 h period. *Significant differences relative to 21%
oxygen, with the Holm–Sidak post-hoc test
(P<0.05).
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Fig. 4. Number of shuttles at different oxygen concentrations. Plotted values are
mean values of 12 lizards ±s.d. during a 7.5 h period inside an
electronically controlled temperature-choice shuttle box.
*Significant difference vs 21% oxygen conditions. For
comparison, the filled circles show the average number of times a lizard
shuttled during the 7.5 h in the absence of a thermal stimulus (constant
34.5°C at 21% O2) (Cadena
and Tattersall, 2009 ). The open square denotes the average number
of shuttles (error bars not shown; see text for details) in the extreme
temperatures shuttle box trials at 21% and 4% O2 (offset slightly
for clarity).
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Fig. 5. Effect of methodology on Tb of lizards when exposed to
hypoxia. The `preferred' Tb of nine bearded dragons was
determined at 4% and 21% oxygen in an extreme temperatures shuttle box, a
thermal gradient and an electronically operated temperature shuttle box
(ramping shuttle box). Values are means of nine lizards' median
Tb values ±s.d.*Significant difference
between the extreme temperature trials and the other trials.
 Significant effect of 4% O2 on
Tb within a trial.
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Fig. 6. Influence of methodology on the normoxic (black lines) and hypoxic (grey
lines) thermoregulatory responses of bearded dragons. A, B and C show the
average change in Tb over the 7.5h of measurements
(starting at 0h) in the ramping shuttle box, extreme shuttle box and thermal
gradient trials, respectively. D, E and F show the corresponding average
frequency histograms (expressed as per cent of observations) for lizards in
the ramping shuttle box, extreme shuttle box and thermal gradient trials,
respectively.
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© The Company of Biologists Ltd 2009
