Panting thresholds of lizards—II. Diel variation in the panting threshold of Amphibolurus muricatus

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

“…Variability, however, did not appear to be a problem in our study due to the paired, repeated nature of the experimental design and the fact that we assessed percentage time spent gaping to estimate the ET 50 threshold (Fig.·2). Previous studies have used the first attempt at gaping as the gaping threshold (Chong et al, 1973;Dupré et al, 1986;Heatwole et al, 1973;Parmenter and Heatwole, 1975). It is possible that assessing a simple value such as the initial gape has much more variability inherent in the estimate, particularly if the response is truly sigmoidal, as we have demonstrated.…”

“…Panting thresholds have been shown to be altered by dehydration (Parmenter and Heatwole, 1975), circadian rhythms (Chong et al, 1973) and the rate or source of heating . The direction of these changes reflects the constraints of other physiological processes on thermoregulation; to conserve water, lizards do not gape until higher temperatures, and, since daily metabolic demand decreases at night in many reptiles (Rismiller and Heldmaier, 1987), a concomitant decline in the threshold for gaping occurs as the thermoregulatory set-point (T set ) is reduced along with the reduced metabolic requirements (Rismiller and Heldmaier, 1982).…”

“…Since it has been shown that lizards have different gaping thresholds between night and day (Chong et al, 1973), we elected to perform the gaping measurements during the same time of the day, between 10.00·h and 16.00·h. Lizards were given time to acclimate to the new temperature, as well as for the box to reach hypoxic levels if necessary.…”

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

“…Variability, however, did not appear to be a problem in our study due to the paired, repeated nature of the experimental design and the fact that we assessed percentage time spent gaping to estimate the ET 50 threshold (Fig.·2). Previous studies have used the first attempt at gaping as the gaping threshold (Chong et al, 1973;Dupré et al, 1986;Heatwole et al, 1973;Parmenter and Heatwole, 1975). It is possible that assessing a simple value such as the initial gape has much more variability inherent in the estimate, particularly if the response is truly sigmoidal, as we have demonstrated.…”

“…Panting thresholds have been shown to be altered by dehydration (Parmenter and Heatwole, 1975), circadian rhythms (Chong et al, 1973) and the rate or source of heating . The direction of these changes reflects the constraints of other physiological processes on thermoregulation; to conserve water, lizards do not gape until higher temperatures, and, since daily metabolic demand decreases at night in many reptiles (Rismiller and Heldmaier, 1987), a concomitant decline in the threshold for gaping occurs as the thermoregulatory set-point (T set ) is reduced along with the reduced metabolic requirements (Rismiller and Heldmaier, 1982).…”

“…Since it has been shown that lizards have different gaping thresholds between night and day (Chong et al, 1973), we elected to perform the gaping measurements during the same time of the day, between 10.00·h and 16.00·h. Lizards were given time to acclimate to the new temperature, as well as for the box to reach hypoxic levels if necessary.…”

Lizard thermal trait variation at multiple scales: a review

“…amphibians, fish and insects; Johnson 1972Johnson , 1976Kelty and Lee 2001). For CT max , Chong et al (1973) found that the panting threshold, the body temperature at which the mouth first opens to lower T b via evaporative effects (Heatwole et al 1973), fluctuated daily with lowest thresholds at night in the agamid Amphibolorus muricatus (heating ramping rate of 1°C/min). However, no significant differences were found during daytime trial periods.…”

No consistent effect of daytime versus night-time measurement of thermal tolerance in nocturnal and diurnal lizards

“…However, despite the large presence of thermal tolerance in the thermal physiology literature ( Bennett et al , 2021 ), little research has been carried out on the existence of diel variation in CTLs, especially for lizards ( Clusella-Trullas and Chown, 2014 ). In the Australian agamid Jacky lizard, the lowest panting thresholds—the Tb at which animals begin to rapidly breathe with their mouths gaping to increase evaporative cooling ( Taylor et al , 2021 )—were observed at night, during the resting phase of this diurnal species ( Chong et al , 1973 ). Other examples from other taxa largely focus on single species in specific locations.…”

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

“…Variability, however, did not appear to be a problem in our study due to the paired, repeated nature of the experimental design and the fact that we assessed percentage time spent gaping to estimate the ET 50 threshold (Fig.·2). Previous studies have used the first attempt at gaping as the gaping threshold (Chong et al, 1973;Dupré et al, 1986;Heatwole et al, 1973;Parmenter and Heatwole, 1975). It is possible that assessing a simple value such as the initial gape has much more variability inherent in the estimate, particularly if the response is truly sigmoidal, as we have demonstrated.…”

“…Panting thresholds have been shown to be altered by dehydration (Parmenter and Heatwole, 1975), circadian rhythms (Chong et al, 1973) and the rate or source of heating . The direction of these changes reflects the constraints of other physiological processes on thermoregulation; to conserve water, lizards do not gape until higher temperatures, and, since daily metabolic demand decreases at night in many reptiles (Rismiller and Heldmaier, 1987), a concomitant decline in the threshold for gaping occurs as the thermoregulatory set-point (T set ) is reduced along with the reduced metabolic requirements (Rismiller and Heldmaier, 1982).…”

“…Since it has been shown that lizards have different gaping thresholds between night and day (Chong et al, 1973), we elected to perform the gaping measurements during the same time of the day, between 10.00·h and 16.00·h. Lizards were given time to acclimate to the new temperature, as well as for the box to reach hypoxic levels if necessary.…”

Lizard thermal trait variation at multiple scales: a review

“…amphibians, fish and insects; Johnson 1972Johnson , 1976Kelty and Lee 2001). For CT max , Chong et al (1973) found that the panting threshold, the body temperature at which the mouth first opens to lower T b via evaporative effects (Heatwole et al 1973), fluctuated daily with lowest thresholds at night in the agamid Amphibolorus muricatus (heating ramping rate of 1°C/min). However, no significant differences were found during daytime trial periods.…”

No consistent effect of daytime versus night-time measurement of thermal tolerance in nocturnal and diurnal lizards

“…However, despite the large presence of thermal tolerance in the thermal physiology literature ( Bennett et al , 2021 ), little research has been carried out on the existence of diel variation in CTLs, especially for lizards ( Clusella-Trullas and Chown, 2014 ). In the Australian agamid Jacky lizard, the lowest panting thresholds—the Tb at which animals begin to rapidly breathe with their mouths gaping to increase evaporative cooling ( Taylor et al , 2021 )—were observed at night, during the resting phase of this diurnal species ( Chong et al , 1973 ). Other examples from other taxa largely focus on single species in specific locations.…”

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

“…Variability, however, did not appear to be a problem in our study due to the paired, repeated nature of the experimental design and the fact that we assessed percentage time spent gaping to estimate the ET 50 threshold (Fig.·2). Previous studies have used the first attempt at gaping as the gaping threshold (Chong et al, 1973;Dupré et al, 1986;Heatwole et al, 1973;Parmenter and Heatwole, 1975). It is possible that assessing a simple value such as the initial gape has much more variability inherent in the estimate, particularly if the response is truly sigmoidal, as we have demonstrated.…”

“…Panting thresholds have been shown to be altered by dehydration (Parmenter and Heatwole, 1975), circadian rhythms (Chong et al, 1973) and the rate or source of heating . The direction of these changes reflects the constraints of other physiological processes on thermoregulation; to conserve water, lizards do not gape until higher temperatures, and, since daily metabolic demand decreases at night in many reptiles (Rismiller and Heldmaier, 1987), a concomitant decline in the threshold for gaping occurs as the thermoregulatory set-point (T set ) is reduced along with the reduced metabolic requirements (Rismiller and Heldmaier, 1982).…”

“…Since it has been shown that lizards have different gaping thresholds between night and day (Chong et al, 1973), we elected to perform the gaping measurements during the same time of the day, between 10.00·h and 16.00·h. Lizards were given time to acclimate to the new temperature, as well as for the box to reach hypoxic levels if necessary.…”

Lizard thermal trait variation at multiple scales: a review

“…amphibians, fish and insects; Johnson 1972Johnson , 1976Kelty and Lee 2001). For CT max , Chong et al (1973) found that the panting threshold, the body temperature at which the mouth first opens to lower T b via evaporative effects (Heatwole et al 1973), fluctuated daily with lowest thresholds at night in the agamid Amphibolorus muricatus (heating ramping rate of 1°C/min). However, no significant differences were found during daytime trial periods.…”

No consistent effect of daytime versus night-time measurement of thermal tolerance in nocturnal and diurnal lizards

“…However, despite the large presence of thermal tolerance in the thermal physiology literature ( Bennett et al , 2021 ), little research has been carried out on the existence of diel variation in CTLs, especially for lizards ( Clusella-Trullas and Chown, 2014 ). In the Australian agamid Jacky lizard, the lowest panting thresholds—the Tb at which animals begin to rapidly breathe with their mouths gaping to increase evaporative cooling ( Taylor et al , 2021 )—were observed at night, during the resting phase of this diurnal species ( Chong et al , 1973 ). Other examples from other taxa largely focus on single species in specific locations.…”