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1-1986 Ventilation, Gas Exchange, and Aerobic Scope in a Small , gilleni Philip E. Bickler

Roger A. Anderson Western Washington University, [email protected]

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Recommended Citation Bickler, Philip E. and Anderson, Roger A., "Ventilation, Gas Exchange, and Aerobic Scope in a Small Monitor Lizard, Varanus gilleni" (1986). Biology Faculty and Staff Publications. 37. https://cedar.wwu.edu/biology_facpubs/37

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Ventilation, Gas Exchange, and Aerobic Scope in a Small Monitor Lizard, Varanus gilleni Author(s): Philip E. Bickler and Roger A. Anderson Source: Physiological Zoology, Vol. 59, No. 1 (Jan. - Feb., 1986), pp. 76-83 Published by: The University of Chicago Press. Sponsored by the Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology Stable URL: http://www.jstor.org/stable/30156093 . Accessed: 20/01/2015 18:36

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This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions VENTILATION, GAS EXCHANGE, AND AEROBIC SCOPE IN A SMALL MONITOR LIZARD, VARANUS GILLENI' PHILIPE. BICKLER2'3AND ROGER A. ANDERSON Departmentof Biology,University of California,Los Angeles, Los Angeles, California 90024 (Accepted7/11/85) Standardrates of 02 consumption(Vo2) in the darkof Varanusgilleni (mean mass = 30 g) were measuredat 25, 31, 34, and 37 C. At 37 C, the mean value (195 ml 02 STPDkg-' h-') was 22%lower than that predictedby a regressionequation for lizards as a group (Bennett and Dawson 1976). Despite appearingto be asleep, three- to fourfoldelevations in standardVo2 were seen in lizardswith lightweight,transparent respiratorymasks. Vo2 was also measuredduring treadmill exercise at speedsfrom 5 to 15 m min-' and duringbouts of maximalexercise. Varanusgilleni has the highest factorialaerobic scope (27.5) of any lizardexamined to date. The cost of transportin V.gilleni is relativelyhigh and may relateto shortlimb length. Pulmonaryventilation and gas exchange (VE, V02, VC02)were simultaneouslymeasured at 25 C, during warming from 25 to 35 C, and again after several hours at 35 C. Air-convection requirementsfor CO2and 02 were independentof temperature.The patternsof lung ventilation suggestthat arterialPCo2 and pH are constant with rising temperature, behaviorthat is common to that in large varanidsand in contrast to that in other . INTRODUCTION standard Vo2 in larger varanids (Bartholo- Lizards of the family are gen- mew and Tucker 1964; Wood et al. 1978), erally considered to exceed the capabilities but other measurements of standard Vo2 of lizards of other families in the ability to of large varanids fall on the regression of sustain intense aerobic exercise. The var- body mass and Vo2 of lizards as a group anid characteristics of high hematocrit and (Bennett 1972; Gleeson 1980). efficient 02 uptake from lung gas to blood Lung ventilation in large varanids re- and from blood to tissues correlate with sponds to changes in body temperature in their high aerobic scopes for exercise (Ben- a different way than has been reported for nett 1973; Gleeson 198 1). However, data lizards of other families: the ratio of minute for these generalizations come exclusively volume (VE) to Vo2 is independent of tem- from a few large (-- I kg; see Gleeson perature (Wood, Glass, and Johansen 1977; 1981). Currently, it is not known whether Wood et al. 1981). This pattern achieves a these functional capabilities are shared by relatively constant 02 extraction efficiency the smaller members of the family. over a range of temperature as well as a The relationships of body size to standard relatively constant lung P02. It has been oxygen consumption (Vo2) and to Vo2 suggested that the relatively constant lung during maximal exertion in varanids is not PO2serves to support 02 delivery to tissues clear. There are several reports of elevated during activity (Wood et al. 1977). These patterns of ventilation may also produce a relatively constant relationship between 'We wouldlike to thankDavid Morafka and Bob lung Pco2 and body temperature. The con- Drewesfor loanof the lizards. was Equipment gen- stant lung PCO2is reflected in temperature- erouslyloaned by G. A. Bartholomew.This work was arterial and hence in rel- supportedby a Chancellor'sPatent Fund Grant to independent Pco2 P.E.B.from UCLA. atively constant arterial pH despite tem- 2 Presentaddress: Physiological Research Labora- perature changes (Wood et al. 1981). tory, ScrippsInstitution of Oceanography,A-004, The present study was done to see Universityof California, San Diego, La Jolla, California whether 92093. some of the physiological features of 3 Orderof authorshipdecided by coin flip. large varanids are shared by one of the smallest members of the family. The lizard Physiol. Zool. 59(1):76-83. 1986. we studied, the pigmy mulga monitor c 1986 by The University of Chicago. All (Varanus gilleni) is small (<0. I kg), secre- rights reserved. 0031-935X/86/5901-4122$02.00 tive, and thigmothermic (i.e., it obtains heat 76

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions METABOLISM AND VENTILATION IN VARANUS 77 from warmsubstrates) (Pianka 1969). This maintainedat either 25, 31, 34, or 36-37 arborealspecies is found under the barkof C. We weighed the lizards and took their trees in the deserts of central Australia.It cloacaltemperature immediately after each preys principallyon large arthropodsand trial. Rates of oxygen consumption re- small arborealgekkos. Although field-active ported represent the means of values ob- body temperatureshave not been reported tained every 5 min for 2-3 h. The lizards for this species, varanidsof similar ecology appearedto be asleep duringthe entire 2- and bodysize havebody temperatureswhile 3-h period. active of 37-38 C (Pianka 1969). We mea- sured standardVo2, Vo2 during treadmill EXERCISE METABOLISM and maximalexercise, respiratory exchange The lizardswere fasted 2-3 days before ratios, and patternsof pulmonary ventila- exerciseon the treadmill. At the onset of tion at differentbody temperatures. fasting,plastic collarsfor the attachmentof respiratorymasks were glued on to the MATERIAL AND METHODS necks with silicone sealant. Lizards were For 30 days prior to the study in spring then placed in a temperature-controlled 1981, four Varanusgilleni of mass 20-40 cabinet at 35-37 C under the previously g (held in captivity for 1 yr) were kept in established photoperiod. On the day of large glass terrariaunder 12L:12D photo- measurementof V02 duringexercise, clear periods.A 2,000-w photofloodlamp placed plastic masks (snap-capvials) were placed above one end of each terrariumprovided over the head and sealed to the collar. Air light and heat during photophase. Lizards was drawnthrough the masksby the lizards thermoregulatedfreely at a body temper- for the remainderof the day. Flexiblelatex ature (Tb) of - 37 C. At night Tb dropped tubingwas attachedto the mask for routing to ambienttemperature, - 25 C. All lizards of incurrentand excurrentair. The tubes were fed a diet of mealworms,crickets, and were positioned above and in front of the small lizards; water was continuously exercising lizards so that the combined available. weight of the tubing and mask did not in- terferewith locomotion. STANDARD METABOLISM The lizardswere run on a treadmillin a Standardrates of Vo2 (standard meta- 37 C room. All measuresof Vo2 for exer- bolic rate [SMR]) were measured in the cisinglizards were obtainedduring the first dark,during apparent sleeping behavior in half of photophase during a 3-day period. the firsthalf of normal scotophase.The liz- Vo2 was measuredwith the same open-cir- ardswere not fed for 2-3 days beforea trial. cuit systemdescribed for the standardmet- The lizardswere placed unrestrainedin re- abolic rate (SMR) measurements. spiratorychambers 3-4 h before a trial. Each day several treadmill speeds were SMRswere also measuredin lizardstreated usedfor each lizard,the slowestspeed being identically except for being fitted with a used first.Steady V02 values weretypically lightweight,airtight plastic mask fittedwith obtainedafter 3-10 min of running.These inflow and outflowlines. We used an open- steady-statevalues were then recorded at circuit respirometrysystem. Dried, C02- 30-s intervals for the next 4-14 min. If free air was drawnthrough either the respi- steady-statevalues were achieved at the rometry cylinders (8 cm diam. X 20 cm slower speed, then treadmill speeds were length) or the mask of lizards placed into increasedgradually to the next desiredlevel. the cylinders. The flow then passed to a Steady-statevalues were recordedas before. pump, a Brooks Rotameter flowmetercal- Cloacal temperatures of the lizards were ibrated against a Brooks Thermal Mass measuredon cessation of exercise.Lizards Flowmeter,and to the analysis cell of an cooperated if treadmill speeds were not Applied Electrochemistry 02 analyzer changed rapidly and if speeds were set at equipped with dual sensors. Reference flow sustainable levels. Occasionally, a lizard was also dry and CO2 free. Vo2 was cal- could not be coaxed into walking even at culated according to the equations of With- low speed; these trials were discontinued ers (1977). The entire analysis system was for the day. We feel that we were unable to located in a constant-temperature room coax the lizards into attaining their maxi-

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions 78 P. E. BICKLER AND R. A. ANDERSON mum aerobically sustainable speed since we were expressed on a mass-specific basis. The could never fatigue individual lizards. Their mean + SE Qlo for standard Vo2 between refusal to walk with increased velocity was 25 and 37 C was 1.97 + 0.11. Vo2's from due to their behavioral disposition and not lizards with masks were three to four times to exhaustion. In an attempt to elicit greater than those in lizards without masks. Vo2max, we agitatedthe lizardsby prodding Behaviorally, the masked lizards seemed to and grabbing them repeatedly. Vo2maxwas be asleep, but their bodies were not as limp obtained within the first couple of minutes. as those of the unrestrained lizards.

VENTILATION MEASUREMENTS EXERCISE METABOLISM We simultaneously measured gas ex- Overall, the regression equation relating change (Vo2, Vco2) and ventilation fre- speed to Vo2 was V02 ml kg-l h-' = 3,144 quency (f) and tidal volume (VT) in lizards + 64 m min-' (r = .28; n = 20). When data fitted with masks and placed in a whole- for individual lizards were analyzed sepa- body plethysmograph. A description of this rately, however, velocity was significantly system can be found in Bickler (1981). The related to running speed (fig. 1). The most lizards were fitted with the collars to the complete data set, that for a 37-g male, was masks 2-3 days prior to a trial. Before an described by the equation Vo2 ml kg-' h-' experiment, the lizards were placed in the =1,990 + IIlI m min-' (r = .97; n = 8). plethysmograph and allowed 2-3 h to settle. VO2max for Varanusgilleni was 5.4 liters During this time the Tb of the lizard (mon- 02 kg-l h-l. Table 2 contains a summary itored via a fine thermocouple in the cloaca) of standard and activity metabolism for V. was maintained at 25 C by adjusting the gilleni, other varanids, and the iguanid temperature of the plethysmograph water Dipsosaurus dorsalis. Varanusgilleni has jacket. Ventilation and gas exchange were the highest weight-corrected aerobic capac- then measured for I h at 25 C, during ity (Vo2max factorial aerobic scope) of warming to 37 C (duration of warming any lizard studied to date. = ~-2 h), and 2-3 h after 37 C had been reached. We have not corrected tidal vol- VENTILATION ume and gas exchange values for the dif- Minute ventilation (VE) increased with ferences in body mass among our speci- temperature. This was due to augmentation mens. in both ventilatory rate and tidal volume (fig. 2). Minute ventilation increased uni- with to 37 and RESULTS formly temperature up C, little or no further changes in ventilation STANDARD METABOLISM were noted after 3-4 h at the final temper- Standard Vo2 at different body temper- ature. Thus, steady-state patterns were atures is summarized in table 1. There were reached almost immediately, and no tran- no consistent differences in Vo2 between sient changes were seen with warming. lizards of different mass when these data Corresponding air-convection require-

TABLE 1

MEAN + SE STANDARD OXYGEN CONSUMPTION (Vo2; mi 02 STPD/[kg. h]) IN Varanus gilleni MEASURED AT CONSTANT TEMPERATURES

MEAN + SE Vo2 (N) OF LIZARDS BODY TEMPERATURE (oC) Masked Unrestrained

25-27 372 + 48 (4) 101 + 18 (6) 31.0 126 + 6.6 (3) 34.0 154 + 19.4 (2) 36-37 619 +36 (5) 195 11.4(5)l

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions METABOLISM AND VENTILATION IN VARANUS 79 8

z 7 18.8G,12.3cm

CL 6

- o 28.8G,14.4cM 5 25.5, 138C a3 7.0G, 15.OcM * 4

5 10 15 20 RUNNING SPFED m /min FIG. 1.-Relationship of weight-specific Vo2 to running speed in individual Varanus gilleni (solid symbols). The lower line of stars represents the 25.5-g lizard at a later date. See Results for overall regression formula. Open symbols show Vo02 produced by prodding the lizards to maximal activity; weight and snout-vent length are indicated next to these symbols. ments (VE/Vo2) are shown in figure 3. Hence, ventilation is quickly matched to These ratios were independent of temper- gas exchange,and no time-dependentther- ature(analysis ofcovariance with F-test = P mal acclimationof the respiratorysystem < .001). After reaching 37 C little or no occurs within this range of temperatures furtherchanges in air-convectionrequire- and for these rates of temperaturechange. ments wereseen overthe next severalhours. Mean + SE pulmonary respiratory ex-

TABLE 2

SUMMARY OF OXYGEN CONSUMPTION (Vo2), FACTORIALAEROBIC SCOPE (STANDARD METABOLICRATE [SMR]/ MAXIMUM Vo2 [rVo2m]), AND WEIGHT-CORRECTEDVo2. (Vo2.m mr) IN VARANIDS AND Dipsosaurus dorsalis

Factorial Mass Tb SMR Vo2 Aerobic Vo2c "a Species (g) (oC) (ml 02/[g- hi) (ml 02/[g*h]) Scope (ml h]) Reference O2/[g" Varanidae: Varanusgilleni ...... 27.5 37 .195 5.4 27.7 12.14 Presentstudy V. salvator ...... 505 35 .144 1.10 7.6 4.90 Gleeson 1981 V. gouldii ...... 674 35 .10 .76 7.6 3.63 Bennett1972 V. exanthematicus...... 1025 35 .189 1.26 6.7 6.65 Gleesonet al. 1980

35 3.39 W-0'049 8.2 Wood et al. 1978 Iquanidae: D. dorsalis ...... 51.3 40 2.00 15.4 5.75 John-Alder and Bennett1981 35.2 40 .13 2.27 17.5b 5.53 Bennettand Dawson 1972

a was calculated as (go.76 h)-. b 0Vo2. Shocked electrically. Vo2.-

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions S27 7g S23.0 26 130 29.3 110 ,- 22 8 .

18 90 p

6[ 25 30 35 40 25 30 35 40 25 30 35 40 BODYTEMPERATURE 0C FIG.2.-Ventilatory parametersfrom individualVaranus gilleni at 25 C duringwarming to 37 C and after 2-3 h at 37 C. Verticalbars denote SE.

0.7 a0 12828 E 06 - E24 0.5- 20 N o 0.4 16 3 12 ">O 0.2 8> I ,I .

0.8- " 0 E 0.7 -32 H(I

0.6 28 I24 o 0.5 CD I 20 E 0.4 0a " . 03 1 . - 2

I I I -,12 25 30 35 BODY TEMPERATURE OC FIG. 3.-Air-convection requirements for Varanus gilleni at 25 C during warming to 37 C and after 2-3 h at 37 C. Verticalbars denote SE.

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions METABOLISM AND VENTILATION IN VARANUS 81 change ratios (RE; VCo2/Vo2) were 0.75 half the VO2maxof the similarly sized + 0.03 at 25 C and 0.72 + 0.05 at 37 C. No Amblyrhynchuscristatus (Iguanidae; mean significanttransient values in RE were seen mass = 580 g [Gleeson 1979]). duringor after the warming from 25 to 35 Gleeson (1979) presentedthe following C (analysisof covariancewith F-test for P equation for predicting the net cost of < .05). transport for lizards: ml 02 = 3.77 mass-0.25.The predictedvalue for V/gilleni = is DISCUSSION (mean mass 27.5 g) 1.65 ml 02 g-9 km-'. Using velocities close to those for STANDARD METABOLISM which Vo2 was measured for each lizard Our values for standardVo2 at 37 C are (0.3 km h-', 5 m min-'), we performedthe 22%lower (194 ml kg-' h-' vs. 237) than conventional technique for obtaining the values predicted for lizard Vo2 at 37 C cost of transport for each lizard by sub- (log cm2 02 g-' h-' = log 0.424 - 18 log tractingthe y-interceptvalue of Vo2 from g) from Bennett and Dawson (1976). This the Vo2 at 0.3 km h-', then divided that regressionis forlizards as a group.However, value by 0.3 km to obtain the net cost of our values fall within the 95%confidence transport at that speed (John-Alder and limits for that regression. Our values for Bennett 1981). The approximatemean net SMR are somewhat lower than those for cost of transportfor V. gilleni is 2.9 ml 02 some othervaranids previously studied (see g-' h, a value 75% higher than that pre- Bartholomew and Tucker 1964; Louw, dicted (Gleeson 1979). Varanusgilleni has Young, and Bligh 1976;Gleeson, Mitchell, rathershort limbs (20%shorter in front and and Bennett 1980; Gleeson, 1981; and 40%shorter in rear than Dipsosaurusdor- table 3). salis of similarmass), and this may increase In contrastto Bennett (1972), we noted the cost of transport. substantialdifferences between the Vo2'SOf The largest V. gilleni (37.5 g) ran for unrestrainedand masked lizards.Our val- many minutes with no signs of fatigue at ues for masked lizardsat 37 C are approx- 1.0 km/h, a speed greaterthan the 0.8 km/ imately three times those of controls and h maximum aerobicallysustained speed of are near mean values predicted by the D. dorsalis.We could not accuratelydeter- regressionequation given by Wood et al. mine the maximum speed continuously (1978). Wood's lizards were confined in sustainedby aerobicmetabolism in V. gil- cylindersand may not have been relaxed. leni. At present, whether these differences in Largehome rangesand pursuit and ex- SMR between Varanus exanthematicus cavation of vertebrateprey are ecological and unmasked V. gilleni are due to behav- featurescommon to large Varanus (Auf- ioral state or true differencesin physiology fenberg1978; Green and King 1978). Var- is problematic. anus gilleni, in contrast, eats gekkos and insects and is arboreal,secretive, and thig- ACTIVITY METABOLISM mothermic (Pianka 1969). The intense Varanusgilleni exhibits one of the high- male-combatbehavior of V. gilleni (Mur- est factorialaerobic scopes of any vertebrate phy and Mitchell 1974)seems to be the only studied to date, owing, in part, to its rela- factorin this species'behavioral repertoire tively low standardVo2. Therefore,we do that may requirehigh aerobiccapacity. not believethat standardVo2 bearsany di- rectcausal relationship to maximalaerobic PULMONARY VENTILATION capacity in lizards. Another striking ex- Our values for air-convection require- ample is that of the iguanid Dipsosaurus ments (VE/Vo2) in V. gilleni are only dorsalis. Its SMR is comparableto that of - 35%of those in V. exanthematicus(table other iguanids, yet it greatly exceeds other 3). This difference results from roughly family members in its aerobic capacity (ta- comparable mass-specific ventilation values ble 3). At the other end of the spectrum is and much greater mass-specific metabolic Physignathus lesueri (Agamidae; mean rates in V. gilleni. While fhas no apparent mass = 549 g) with a similar resting met- correlation with body mass, VT scales with abolic rate (Wilson 1974) but less than one- mass to the 0.85 power at 37 C (Bennett

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions al et figs.2 in 1977 1973 study ReferenceWood Bennett Present shown are

STPD) a a 2.6 3.8 3.0a warming + + + 39.5 25.3 53.9 VE/VO2 during BTPS/ml 38.1 14.4 13.4 (ml gilleni V.

a these min) 4.1 3.9a for + + VE 34.8 73.8 23.3 100.5 LIZARDS (ml/kg. 45.5 85.0 parameters

VARANID 4.9a 4.3a 1.0a 1.3a FROMVT + + 6.3 8.5 + + (ml/kg) gas-exchange 20.5 24.3 12.2 15.7 3 and

PARAMETERS TABLE f 2.5 3.0 6.2 20.03.7 5.5 ventilatory (min') in

VENTILATORY OF Changes

(0C) 25 35 25 35 25 35 masks. Temperature COMPARISON respiratory

30 Mass(g) NS 674 lightweight with

...... fitted specified. lizards not = Species SE.from ...... + exanthematicus

MeansCollected3. gouldii gillenib NOTE.-NSa b Varanus V V and

This content downloaded from 140.160.178.72 on Tue, 20 Jan 2015 18:36:46 PM All use subject to JSTOR Terms and Conditions METABOLISM AND VENTILATION IN VARANUS 83 1973). Our tidal volume estimates for V. Values for arterial Pco2 calculated in this gilleni fall within the 95% confidence limits way for V. gilleni at 25 and 37 are 43.8 and of Bennett's (1973) regression. The oxygen 42.0 torr. Our temperature-independent extractionefficiency (Eo2) was 68.6%at 25 VE/VCo2 values are consistent with the C and 63.8% at 35 C as calculated by the nearly constant arterial Pco2 and pH values expression EO2 = (V02/VE) (100%/Cio2), that have been reported for V. exanthe- where C1o2 is the concentration of 02 in maticus (Wood et al. 1977, 1981). Constant inspired air (Dejours 1981). In light of the blood PCo2 with rising temperature means spectacular aerobic capacity of V. gilleni, that the total CO2 content of the blood de- measurements of 02 extraction during ac- creases with rising temperature. Changes in tivity would be of interest. the respiratory exchange ratio were not The VA/Vo2 (VA = alveolar minute seen, however. This suggests that changes ventilation) value for V. exanthematicus in the total CO2 content of the various from Wood et al. (1977) is 45.8 at 25 C and body-fluid compartments, if they indeed 38.1 ml BTPS ml-' at 35 C, implying that occur, must involve exchanges between arterial PC02 was 17.1 torr at 25 C and 21.8 compartments rather than net changes in torr at 35 C, as calculated from the gas total CO2 content between the and equation and assuming a Vco2/Vo2 of 0.80. environment via the respiratory system.

LITERATURE CITED AUFFENBERG,W. 1978. Social and feeding behavior in the lizards Varanus and Iguana. Am. J. Physiol. of Varanus komodoensis. Pages 301-331 in N. 239:R174-R 179. GREENBERG and P. P. MACLEAN, eds. Behavior GREEN,B., and D. KING. 1978. Home range and ac- and neurology of lizards. U.S. Dept. of Health, Ed- tivity patterns of the sand Varanus gouldii ucation, and Welfare, National Institute of Mental (Reptilia: Varanadae). Aust. J. Wildl. Res. 5:417- Health, Rockville, Md. 424. BARTHOLOMEW,G. A., and V. A. TUCKER.1964. Size, JOHN-ALDER,H. B., and A. F. BENNETT.1981. Ther- body temperature, thermal conductance, oxygen mal dependence of endurance and locomotory consumption, and heart rate in Australian varanid energetics in a lizard. Am. J. Physiol. 241:R342- lizards. Physiol. Zool. 37:341-354. R349. BENNETT, A. F. 1972. The effect of activity on oxygen Louw, W. G., B. A. YOUNG, and J. BLIGH. 1976. consumption, oxygen debt, and heart rate in the Effect of thyroxine on thermoregulation, cardiac lizardsVaranus gouldii and Sauromalushispidus. rate, and oxygen consumption in the monitor lizard J. Comp. Physiol. 79:259-280. Varanusalbigularis albigularis. J. Therm.Biol. 1: . 1973. Ventilation in two species of lizards 189-193. during rest and activity. Comp. Biochem. Physiol. MURPHY,J. B., and L. A. MITCHELL.1974. Ritualized 46A:653-671. combat behavior of the pygmy mulga monitor liz- BENNETT,A. F., and W. R. DAWSON. 1972. Aerobic ard, Varanus gilleni (Sauria: Varanidae). Herpe- and anerobic metabolism during activity in the liz- tologica 30:90-97. ard Dipsosaurus dorsalis. J. Comp. Physiol. 81: PIANKA,E. R. 1969. Notes on the biology of Varanus 289-299. caudolineatusand Varanusgilleni. West. Aust. Nat. . 1976. Metabolism. Pages 477-504 in C. GANS 11:76-82. and W. R. DAWSON,eds. Biology of the reptilia. WILSON,R. J. 1974. The relationship of oxygen supply Vol. 5. Academic Press, New York. for activity to body temperature in four species of BICKLER,P. E. 1981. Effects of temperature on acid- lizards. Copeia 1974:920-934. base balance and ventilation in desert iguanas. J. WITHERS,P. C. 1977. Measurement of o2, VCO2and Appl. Physiol. 51:452-460. evaporative water loss with a flow-through mask. DEJOURS,P. 1981. Principles of comparative respi- J. Appl. Physiol. 42:120-123. ratory physiology. 2d ed. Elsevier/North-Holland, WOOD,S. C., M. L. GLASS,and K. JOHANSEN.1977. Amsterdam. Effects of temperature on respiration and acid-base GLEESON, T. T. 1979. Foraging and transport costs in balance in a monitor lizard. J. Comp. Physiol. 116: the Galapagos marine iguana, Amblyrhynchus 187-196. cristatus. Physiol. Zool. 52:549-557. WOOD,S. C., K. JOHANSEN,M. L. GLASS,and R. W. . 1980. Metabolic recovery from exhaustive ac- HOYT. 1981. Acid-base regulation during heating tivity by a large lizard. J. Appl. Physiol. 48:689- and cooling in the lizard, Varanus exanthematicus. 694. J. Appl. Physiol. 50:779-783. . 1981. Preferred body temperature, aerobic WOOD, S. C., K. JOHANSEN,M. L. GLASS, and scope, and activity capacity in the monitor lizard, G. M. O. MALOIY.1978. Aerobic metabolism of Varanus salvator. Physiol. Zool. 54:423-429. the lizard Varanus exanthematicus: effects of ac- GLEESON,T. T., G. S. MITCHELL,and A. F. BENNETT. tivity, temperature and size. J. Comp. Physiol. 127: 1980. Cardiovascular responses to graded activity 331-336.

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