QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online August 18, 2005
Journal of Experimental Biology 208, 3321-3330 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01773

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Tattersall, G. J. Articles by Gerlach, R. M. Search for Related Content PubMed PubMed Citation Articles by Tattersall, G. J. Articles by Gerlach, R. M.

Hypoxia progressively lowers thermal gaping thresholds in bearded dragons, Pogona vitticeps

Glenn J. Tattersall^* and Rebecca M. Gerlach

Department of Biological Sciences, Brock University, St Catharines, Ontario, L2S 3A1, Canada

View larger version (16K): [in a new window]   Fig. 1. The three types of gaping categorised in this study. Type I was ascribed to situations when the mouth was visibly, but barely, open (i.e. there was no obvious sealing of the upper jaw with the lower jaw), which is readily distinguished from a normal closed mouth. Type II was ascribed to situations when the mouth was obviously open by more than a few millimetres. Type III was easily distinguished from other types as the lizard's tongue was easily visible and the throat was obviously distended due to the open mouth.

View larger version (106K): [in a new window]   Fig. 2. Infrared thermal images of lizards at different ambient temperatures showing Type II gaping (A), Type III gaping with the inside of the mouth clearly visible (B) and cloacal discharge in two different lizards (C, in hypoxia; D, in normoxia). In all cases, regional temperature differences can be observed across the body surfaces. Note the different temperature keys to the right of each image.

View larger version (24K): [in a new window]   Fig. 3. Mean times (± S.E.M.) spent gaping in lizards at three different levels of oxygen – 21% (filled circles), 10% (open circles) and 6% O2 (filled triangles) – during 15 min periods of observations of lizards that were in thermal equilibrium with different environmental temperatures (30–40°C). The broken lines represent Hill equations (see equation 1) fitted through the mean data. The vertical dotted lines represent the mean time at which lizards spent 50% of their time gaping (ET50) at each level of oxygen inspired, as calculated from each lizard. The inset graph refers to the ET50 values for male (filled circles) and female lizards (open circles) at 21, 10 and 6% O2.

View larger version (19K): [in a new window]   Fig. 4. Mean times (± S.E.M.) spent engaged in (A) Type I, (B) Type II and (C) Type III gaping at 21, 10 and 6% O2. Data for 40°C are shown for comparison, although not included in statistical analysis, since data points were not available at 6% O2. refers to a significant difference between 10 and 21% O2, and * refers to a significant difference between 6 and 21% O2 with post-hoc tests.

View larger version (19K): [in a new window]   Fig. 5. Mean surface temperatures (± S.E.M.) exposed to (A) 21, (B) 10 and (C) 6% O2 during changes in ambient temperature ranging from 30 to 40°C. Shown are surface temperatures of the head, body, nose, eye and tongue (when visible). The dotted lines represent the line of equality for surface temperature and ambient temperature.

View larger version (19K): [in a new window]   Fig. 6. Body surface temperature minus tongue temperature at 21, 10 and 6% O2 between ambient temperatures of 32–38°C. There was a significant effect of oxygen and ambient temperature on this difference (two-way repeated-measures ANOVA), suggesting that hypoxic conditions led to a higher value at lower ambient temperatures. The dotted line represents an extrapolation beyond 38°C in the 6% O2 group.

View larger version (28K): [in a new window]   Fig. 7. Various threshold parameters in bearded dragons as they pertain to the appropriateness of thermoregulation. (A) The plot of ET50 versus cumulative time spent gaping during experimental procedures demonstrates that ET50 estimates provided a good fit across all three levels of O2. (B) Cloacal discharge threshold (TCD) in normoxia versus mean cage temperature (see Materials and methods) showed no significant relationships. (C) A significant relationship between ET50 in normoxia and mean cage temperature was not apparent, although a significant intercept did occur, suggesting that the ET50 tends to occur at temperatures higher than preferred cage temperatures. (D) There was a significant relationship between ET10 (the temperature at which the lizards were gaping for 10% of the time) and mean cage temperature, although no significant intercept, suggesting an isometric relationship between the two variables.