No axial constraint Gular pumping 800 Axial constraint EE 600 Gular pumpin disabled 0 Speed (km/h) → Recovery Effects of gular pumping in lizards. (a)THEORY: The axial constraint hypothesis predicts that, above a threshold speed, ventilation, measured by expired gas volume (VE), will decrease with increasing speed, and only reach a maximum during the recovery period after lo- comotion ceases. Without axial constraint, ventilation should reach its maximum during locomotion. ()EXPERIMENT: Monitor lizards typically show no axial constraint while running. Axial constraint is evident, however, if gular pumping of air is disabled. So, it seems that ome species of monitor lizards are able to use gular pumping to overcome the axial constraint on ventilation The Experiment value up to a speed of 1 km/hr. The value began to decrease Brainerd set out to test this gular pumping hypothesis. gular between 1 and 2 km/hr indicating that there was constraint pumping occurs after the initial inhalation because the lizard on ventilation. During the recovery period, VE increased as closes its mouth, sealing shut internal nares(nostril-like struc- predicted by the axial constraint hypothesis, because there was no longer constraint on the intercostal muscles. Ve in- tures).Air is thus trapped in the gular cavity. By contracting creased to pay back an oxygen debt that occurred durin the lungs. This process can be disrupted by propping the period of time when anaerobic metabolism took over g the muscles that compress the gular cavity, this air is forced into mouth open so that, when the gular cavity is compressed, its Comparing the VE measurements under control and ex- perimental conditions, the researchers concluded that moni- air escapes back out of the mouth. The lizards were trained tor lizards are indeed subject to speed-dependent axial con to run on a treadmill. A Plastic mask was placed over the ani- straint just as theory had predicted, but can circumvent this mal's mouth and nostrils and air was drawn through the mask The mask permitted the measurement of oxygen and Co constraint when running by using an accessory gular pump levels as a means of monitoring gas consumption. The ex- to enhance ventilation. When the gular pump was experi- pired gas volume (Ve was measured in the last minutes of lo- mentally disrupted, the speed-dependent axial constraint comotion and the first minute of recovery at each speed. The condition became apparent. Although the researchers have not conducted a more speeds ranged from 0 km/hr to 2 km/hr. The maximum run- complete comparative analysis using the methods shown To disable gular pumping, the animals mouth was here, they have found correlations between gular pumpin ind increased locomotor activity. Six highly active species propped open with a retainer made of plastic tubing. In exhibited gular pumping while six less active species did not parallel exper riments that allow gular pumping, the same exhibit gular pumping in lung ventilation. It is interesting animals wore the masks, but no retainer was used to disrupt the oral seal necessary for gular pumping to speculate that gular pumping evolved in lizards as a neans of enhancing breathing to allow greater locomotor endurance. The gular pumping seen in lizards is similar to The results the breathing mechanism found in amphibians and ai Parallel experiments were conducted on monitor lizards breathing fish. In these animals, the air first enters a cavity with and without gular pumpin close and the buccal cavity collapses, forcing air into the pumping alloz en t lar pumping lungs. The similarities in these two mechanisms suggest mechanism was not obstructed, the VE increased to a maxi- that one might have arisen from the oth mum at a speed of 2 km/hr and decreased during the recov- ery period(see blue line in graph b above). This result is predicted under conditions where there is no axial con- straint on the animal(see graph a above). To explore this experiment furthe er. go to 2. Gular pumping disabled. When the gular pumping tualLabatwww.mhhe.com/raven6/vlab13.mhtml mechanism is obstructed, VE increased above the restingThe Experiment Brainerd set out to test this gular pumping hypothesis. Gular pumping occurs after the initial inhalation because the lizard closes its mouth, sealing shut internal nares (nostril-like struc￾tures). Air is thus trapped in the gular cavity. By contracting muscles that compress the gular cavity, this air is forced into the lungs. This process can be disrupted by propping the mouth open so that, when the gular cavity is compressed, its air escapes back out of the mouth. The lizards were trained to run on a treadmill. A plastic mask was placed over the ani￾mal’s mouth and nostrils and air was drawn through the mask. The mask permitted the measurement of oxygen and CO2 levels as a means of monitoring gas consumption. The ex￾pired gas volume (VE) was measured in the last minutes of lo￾comotion and the first minute of recovery at each speed. The speeds ranged from 0 km/hr to 2 km/hr. The maximum run￾ning speed of these lizards on a treadmill is 6.6 km/hr. To disable gular pumping, the animal’s mouth was propped open with a retainer made of plastic tubing. In parallel experiments that allow gular pumping, the same animals wore the masks, but no retainer was used to disrupt the oral seal necessary for gular pumping. The Results Parallel experiments were conducted on monitor lizards with and without gular pumping: 1. Gular pumping allowed. When the gular pumping mechanism was not obstructed, the VE increased to a maxi￾mum at a speed of 2 km/hr and decreased during the recov￾ery period (see blue line in graph b above). This result is predicted under conditions where there is no axial con￾straint on the animal (see graph a above). 2. Gular pumping disabled. When the gular pumping mechanism is obstructed, VE increased above the resting value up to a speed of 1 km/hr. The value began to decrease between 1 and 2 km/hr indicating that there was constraint on ventilation. During the recovery period, VE increased as predicted by the axial constraint hypothesis, because there was no longer constraint on the intercostal muscles. VE in￾creased to pay back an oxygen debt that occurred during the period of time when anaerobic metabolism took over. Comparing the VE measurements under control and ex￾perimental conditions, the researchers concluded that moni￾tor lizards are indeed subject to speed-dependent axial con￾straint, just as theory had predicted, but can circumvent this constraint when running by using an accessory gular pump to enhance ventilation. When the gular pump was experi￾mentally disrupted, the speed-dependent axial constraint condition became apparent. Although the researchers have not conducted a more complete comparative analysis using the methods shown here, they have found correlations between gular pumping and increased locomotor activity. Six highly active species exhibited gular pumping while six less active species did not exhibit gular pumping in lung ventilation. It is interesting to speculate that gular pumping evolved in lizards as a means of enhancing breathing to allow greater locomotor endurance. The gular pumping seen in lizards is similar to the breathing mechanism found in amphibians and air￾breathing fish. In these animals, the air first enters a cavity in the mouth called the buccal cavity. The mouth and nares close and the buccal cavity collapses, forcing air into the lungs. The similarities in these two mechanisms suggest that one might have arisen from the other. Speed (km/h) Axial constraint No axial constraint VE max VE max Recovery Speed (km/h) Recovery Expired gas volume (VE) VE (ml/min/kg) 1000 800 600 400 200 0 0 1 Gular pumping allowed Gular pumping disabled 2 (a) (b) Effects of gular pumping in lizards. (a) THEORY: The axial constraint hypothesis predicts that, above a threshold speed, ventilation, measured by expired gas volume (VE), will decrease with increasing speed, and only reach a maximum during the recovery period after lo￾comotion ceases. Without axial constraint, ventilation should reach its maximum during locomotion. (b) EXPERIMENT: Monitor lizards typically show no axial constraint while running. Axial constraint is evident, however, if gular pumping of air is disabled. So, it seems that some species of monitor lizards are able to use gular pumping to overcome the axial constraint on ventilation. To explore this experiment further, go to the Vir￾tual Lab at www.mhhe.com/raven6/vlab13.mhtml