The relationship between body temperature, heart rate, breathing rate, and rate of oxygen consumption, in the tegu lizard (Tupinambis merianae) at various levels of activity

Abstract

The present study determined whether EEG and/or EMG recordings could be used to reliably define activity states in the Brazilian black and white tegu lizard (Tupinambis merianae) and then examined the interactive effects of temperature and activity states on strategies for matching O2 supply and demand. In a first series of experiments, the rate of oxygen consumption (VO2), breathing frequency (fR), heart rate (fH), and EEG and EMG (neck muscle) activity were measured in different sleep/wake states (sleeping, awake but quiet, alert, or moving). In general, metabolic and cardio-respiratory changes were better indictors of the transition from sleep to wake than were changes in the EEG and EMG. In a second series of experiments, the interactive effects of temperature (17, 27 and 37 °C) and activity states on fR, tidal volume (VT), the fraction of oxygen extracted from the lung per breath (FIO2-FEO2), fH, and the cardiac O2 pulse were quantified to determine the relative roles of each of these variables in accommodating changes in VO2. The increases in oxygen supply to meet temperature- and activity-induced increases in oxygen demand were produced almost exclusively by increases in fH and fR. Regression analysis showed that the effects of temperature and activity state on the relationships between fH, fR and VO2 was to extend a common relationship along a single curve, rather than separate relationships for each metabolic state. For these lizards, the predictive powers of fR and fH were maximized when the effects of changes in temperature, digestive state and activity were pooled. However, the best r(2) values obtained were 0.63 and 0.74 using fR and fH as predictors of metabolic rate, respectively.

Winter metabolic depression does not change arterial baroreflex control of heart rate in the tegu lizard (Salvator merianae)

“…Collectively, these results indicate a certain degree of metabolic depression, which is supported by observations in reptiles, including tegu lizards, of a linear correlation between f H and metabolic rate under steady-state conditions (Butler et al, 2002;Piercy et al, 2015). Therefore, gas exchange and f H are seasonally adjusted to match the differing steady-state metabolic demands (Andrade et al, 2004;Clark et al, 2005;Piercy et al, 2015). In fact, hibernation in S. merianae is characterized by an active metabolic reduction during the winter season (Abe, 1983(Abe, , 1995Andrade and Abe, 1999;Lopes and Abe, 1999;de Souza et al, 2004;Sanders et al, 2015), which, in southeastern Brazil, is synchronized with the driest phase of the year.…”

“…Interestingly, it was recently reported that tegus implanted with a telemetry ECG device and kept under semi-natural conditions anticipate the winter season through a gradual monthly decrease in f H at constant body temperatures (Sanders et al, 2015). Collectively, these results indicate a certain degree of metabolic depression, which is supported by observations in reptiles, including tegu lizards, of a linear correlation between f H and metabolic rate under steady-state conditions (Butler et al, 2002;Piercy et al, 2015). Therefore, gas exchange and f H are seasonally adjusted to match the differing steady-state metabolic demands (Andrade et al, 2004;Clark et al, 2005;Piercy et al, 2015).…”

“…It is interesting to note that baroreflex sensitivity is enhanced at a high temperature (30°C) in C. latirostris (Hagensen et al, 2010), and also in the toad Rhinella schneideri (Zena et al, 2015), but the ability to respond mainly to hypotension is preserved regardless of temperature in both species. Temperature is known to directly influence metabolic rate and the cardiovascular adjustments to the new metabolic demands seem to be a proportional response (Piercy et al, 2015). In contrast, there are situations when metabolic rate can be downregulated independent of temperature in ectotherms; for example, when they are seasonally exposed to adverse environmental conditions and enter the physiological/behavioural state of hibernation or aestivation (Abe, 1995;Glass et al, 1997;Bícego-Nahas et al, 2001;Andrade et al, 2004;Milsom et al, 2008;Navas and Carvalho, 2010).…”

Daily and annual cycles in thermoregulatory behaviour and cardio-respiratory physiology of black and white tegu lizards

“…Monthly nighttime minimum levels of oxygen consumption were calculated from the formula derived by Piercy et al (2015) from the relationship between heart rate and metabolic rate for this species of tegu lizard under quiescent conditions. The equation used was: log 10 (O 2 consumption) = −1.47 + 0.67 (log 10 (heart rate)).…”

“…Here, we record continuously behaviour and T b along with heart and breathing rates as physiological surrogates for metabolism (Zaar et al 2004;Butler et al 2000Butler et al , 2002Clark et al 2004Clark et al , 2006Green et al 2008;Piercy et al 2015), in a group of black and white tegus, T. merianae, housed outdoors under semi-natural conditions. We hypothesized that metabolic suppression (as indicated by changes in heart rate and breathing frequency) would not be evident until the tegus remained in the burrows for extended periods but that metabolism would then progressively fall and be sustained throughout the dormant period.…”