Abstract
BackgroundVentilatory parameters have been investigated in several species of Testudines, but few species have had their ventilatory pattern fully characterized by presenting all variables necessary to understand changes in breathing pattern seen under varying environmental conditions.MethodsWe measured ventilation and gas exchange at 25 °C in the semi-aquatic turtle Trachemys scripta and the terrestrial tortoise Chelonoidis carbonarius under normoxia, hypoxia, and hypercarbia and furthermore compiled respiratory data of testudine species from the literature to analyze the relative changes in each variable.ResultsDuring normoxia both species studied showed an episodic breathing pattern with two to three breaths per episode, but the non-ventilatory periods (TNVP) were three to four times longer in T. scripta than in C. carbonarius. Hypoxia and hypercarbia significantly increased ventilation in both species and decreased TNVP and oxygen consumption in T. scripta but not in C. carbonarius.DiscussionContrary to expectations, the breathing pattern in C. carbonarius did show considerable non-ventilatory periods with more than one breath per breathing episode, and the breathing pattern in T. scripta was found to diverge significantly from predictions based on mechanical analyses of the respiratory system. A quantitative analysis of the literature showed that relative changes in the ventilatory patterns of chelonians in response to hypoxia and hyperbarbia were qualitatively similar among species, although there were variations in the magnitude of change.
Highlights
The order Testudines differs from the other groups of reptiles by the presence of a rigid shell, impeding lung ventilation through movement of the ribs (Lyson et al, 2014)
Once the hypoxic exposure ended, all variables returned to pre-hypoxic values within 1 hour, with the exception of breathing frequency (fR) in C. carbonarius, which was significantly greater when compared to the pre-hypoxic value
The relationships between duration of expiration (TEXP), duration of inspiration (TINSP) and total duration of one ventilatory cycle (TTOT) (i.e., TEXP/TTOT, and TINSP/TEXP respectively) were not significantly affected by either hypoxia nor hypercarbia, just as expiratory flow rate (VT/TEXP), but the latter did show a tendency to increase in both species with increasing levels of hypoxia and hypercarbia (Fig. 5)
Summary
The order Testudines differs from the other groups of reptiles by the presence of a rigid shell, impeding lung ventilation through movement of the ribs (Lyson et al, 2014). We measured ventilation and gas exchange at 25 ◦C in the semi-aquatic turtle Trachemys scripta and the terrestrial tortoise Chelonoidis carbonarius under normoxia, hypoxia, and hypercarbia and compiled respiratory data of testudine species from the literature to analyze the relative changes in each variable. During normoxia both species studied showed an episodic breathing pattern with two to three breaths per episode, but the non-ventilatory periods (TNVP) were three to four times longer in T. scripta than in C. carbonarius. Hypoxia and hypercarbia significantly increased ventilation in both species and decreased TNVP and oxygen consumption in T. scripta but not in C. carbonarius. A quantitative analysis of the literature showed that relative changes in the ventilatory patterns of chelonians in response to hypoxia and hyperbarbia were qualitatively similar among species, there were variations in the magnitude of change
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