Physiological Responses to Temperature in the obsoletus Author(s): William R. Dawson Source: Physiological Zoology, Vol. 33, No. 2 (Apr., 1960), pp. 87-103 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/30152297 . Accessed: 17/02/2014 18:51

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This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions PHYSIOLOGICALRESPONSES TO TEMPERATURE IN THE LIZARD EUMECES OBSOLETUS

WILLIAM R. DAWSON Department of Zo6logy, University of Michigan1

HEeffectiveness of behavior in al- of hemoglobin.Measurements of the oxy- lowing to maintain body gen capacity of blood from are T temperature at a characteristic also presented.All these things have been level during activity is well known selected for study because the relation of (Cowles and Bogert, 1944;Bogert, 1949a; metabolism to respiratory and circula- Norris, 1953; and Saint-Girons and tory capacities should be of primary im- Saint-Girons, 1956). The fact that this portance in thermal adjustment. level may be similarin congenericspecies existing in different climates, yet differ MATERIALS AND METHODS markedly in of different genera The occurs in a re- within the same habitat (Bogert, 1949b), gion roughly coextensivewith the south- suggests the existence of physiological ern half of the GreatPlains (Fitch, 1955). adjustmentsto particularbody tempera- In desertor forestedportions of its range, tures in lizards, which may differat the this lizard is confined to small areas generic level even within the same en- covered by short, thick grass or com- vironment. parable vegetation, in which flat rocks This study of physiological responses are available for shelter. The to temperaturein the Great Plains skink, used in the present study were ob- Eumeces obsoletus, was undertaken as tained through a commercial collector part of a continuing effort to determine shortly after capture in northeastern the nature and possiblephysiological sig- Kansas from May through July in the nificance of thermal adjustments of liz- years 1955-58. At the time of study they ards. This skink maintains a body tem- weighed between 25 and 35 gm. This re- peratureonly slightly in excess of 300 C. stricted weight range was utilized to re- when abroad and active (Fitch, 1955) duce variation in the results obtained, and succumbsat temperaturesin the nor- arising from differencesin size among the mal activity range for the very heat re- experimentalanimals. sistant desert iguana, Dipsosaurus dor- The skinks were kept in screen cages salis, studied previously (Dawson and except during study. Each of these cages Bartholomew, 1958). The results re- contained an electric light bulb con- ported here concern the effects of tem- trolled by an automatic timer. The pho- on in perature total oxygen consumption, toperiodwas 12 hours. The animalsperi- vivo and in vitro cardiac performance, odically basked under the light and and the affinities breathing rate, oxygen maintained their body temperaturesbe- 1 Work supported in part by grants from the tween 30' and 350 C. Occasionally they Horace H. Rackham School of Graduate Studies, would retirebeneath boards for the University of Michigan, and the National Sci- provided ence Foundation (G-2096). shelter. At night when the lights were off, 87

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 88 WILLIAMR. DAWSON the animals cooled to room temperature cording potentiometer. The electrocar- (23o-280 C.). Food consisting of meal diographic leads were connected to an worms, egg, dogfood, and, occasionally, a.c. preamplifierwhich in turn was con- crickets was regularlyprovided. The in- nected to a channel of a pen-writing animate portionsof this diet were admin- oscillograph.The strain gauge was con- istered by hand. The animals also re- nected to a carrier preamplifierwhich ceived a vitamin mixture weekly. These was connectedto a secondchannel of this arrangements kept the skinks in good oscillograph. condition throughoutthe periodin which As soon as the various leads had been they were studied, judging both by their connected to the appropriate instru- maintenanceof weight and their general ments, the cylinderwith the lizardinside vigor. was placed in a groundedjSreen cage in- side a constant temperaturecabinet. The OXYGEN CONSUMPTION, BREATHING RATE, within this cabinet could be AND HEART RATE temperature controlled to within 0.50 C. of any de- Lizardsto be used in studies of oxygen sired level between 00 and 450 C. When and heart rate were made consumption everything was in position, the cylinder them to 50 C. and then torpid by chilling was connected by tygon tubing into a were securedwith thin of strips masking metabolism circuit. Air was passed to boards fashioned from tape through this circuit from a low pressure wooden A fine ther- tongue depressors. line at approximately100 cc. per minute was mocouple (copper-constantan) in- (not correctedto S.T.P.). After leaving serted the cloaca into the through large the cylinder, this air passed successively intestine of each animal for measurement through an absorbent train which re- or of body temperature. Three silver moved water and CO2 from it, then stainless-steel needle electrodes for elec- through a rotameterwhich measuredthe were then trocardiograms (EKG's) rate of flow, and then through a para- an electrodewas placed intramuscularly; magnetic oxygen analyzer which meas- to each of the front and a attached limbs, ured the fractional concentrationof oxy- third which servedas a electrode, ground, gen in it. Such measurementscombined was placed in the dorsal musculatureof with information on the fractional con- the tail. The animal with electrodes and centration of oxygen in the air entering in in a thermocouple position was placed the metabolism circuit (dried and with with an inner diameter of glass cylinder the CO2removed) made it possible to cal- 6.5 cm. and a of 30 cm. A second length culate the true oxygen consumption of for measurement of air thermocouple the lizards according to a method out- was also in this temperature placed cylin- lined by Depocas and Hart (1957). All der. It was then and the vari- stoppered expressions of metabolic rate are con- led out ous wires through air-tight ports. verted to S.T.P. (00 C. and 760 mm. Hg) In experiments in which breathing rate and refer to individuals that had fasted was also was to be measured,the animal at least 24 hours at 230 C. prior to meas- fitted with a strain gauge which was at- urement. tached to the thoracic cage in such a The over-all arrangement outlined manner that any breathing movement above permitted simultaneous measure- would produce a distortion in this device. ment of the effects of temperature on The thermocouple leads were attached oxygen consumption, heart rate, breath- to a suitably calibrated, multipoint re- ing rate, and EKG pattern. The method

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions TEMPERATUREIN LIZARDEUMECES OBSOLETUS 89 of restrainingthe animals did not appear anoelectrical transducer tube (RCA to injure them or even disturb them par- 5734). This assembly was then arranged ticularly; minimal rates of oxygen con- so the ventricle was suspended between sumption for such individuals were simi- two platinum electrodes separated by a lar to those observedin unrestrainedani- vertical distance of 2 cm. The electrodes mals at the same body temperature. It were attached to the vertical arm of the was a great convenienceto be able to fol- aerating tube which was arrangedas an low EKG's during these experiments,for inverted L. The horizontal arm of this any activity on the part of the animals aerating tube was clamped to a stand of was indicated by muscle potentials on adjustable height. The apex of the ven- the EKG trace. tricle was connected by its thread to a hook fused to the lower end of CARDIACCONTRACTILITY platinum the vertical arm. A centrifugetube (inner In experiments dealing with the ef- diameter 3 cm.), supportedin a thermos fects of temperatureon ventricularcon- flask and containing Ringer's solution at traction in response to widely spaced 230 C., was positioned so that the elec- electricalstimuli, several steps were nec- trodes and ventricle were immersed in essary to preparethe ventricle for study. this fluid. The centrifuge tube-thermos The thoraciccavity of a pithed skink was flask assembly was supportedon remov- opened along the sternum so that the able wooden blocks so that it could easily heart was exposed. The pericardiumwas be replaced with another containing then carefully slit so that the ligament Ringer's solution at one of the experi- connectingthe apex of the ventricle to it mental temperatures.When the arrange- was not severed. A thread was tied ments outlined above had been com- aroundthis ligament which was then cut pleted, the height of the stand was ad- between the thread and the pericardium. justed so that the ventricle was under a The heart was elevated by the thread slight amount of tension, and the hori- and its vascular connections severed. It zontal arm of the aerating tube was con- was then removedfrom the thoraciccav- nected with rubber tubing to an oxygen ity and placed in Ringer's solution. The bottle. The Ringer's solution used in all heart was allowed to beat until it had ex- the experiments concerned with ven- pelled any blood which it contained. tricular contractility containedper liter: Then the ventricle was separated from 117mM NaC1,4 mM KC1,2 mM CaC12, the auricles, and a V-shapednotch was 1 mM MgSO4,and 2 mM Sorensenphos- cut in its base to removeany possible ac- phate buffermixture (pH 7.2). cessory pace-makingtissue and to facili- The vertical movement of the second- tate the diffusionof oxygen into all parts class lever duringventricular contraction of the muscle. When these preparations was equivalent to less than half a degree were complete, it was placed in well- of arc so that the contractionswere vir- oxygenated Ringer's solution for three tually isometric. The electrical signal hours and checked periodically to make produced by the transducer tube as a sure that spontaneousactivity had been result of contraction was fed through a completely eliminated.At the end of this d.c. amplifierto the Y-axisof an oscillo- period,a second threadwas sewn through scope with a long-persistentscreen. Thus the anteriolateral tips of the ventricle. the tension developed by the ventricle This threadwas then connectedto a sec- could be measuredin terms of the verti- ond-degreelever which actuated a mech- cal deflectionof the electron beam. Cali-

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 90 WILLIAMR. DAWSON bration establishedthat a linear relation OXYGEN CAPACITY OF BLOOD existed between tension applied to the Four-tenths of a cc. of blood was transducer tube and beam deflection. drawn from a lizard by heart puncture. The electrical stimuli used to produce A No. 26 or No. 27 needle connected to contraction by the ventricle were deliv- a 1-cc. syringewas used. Both needle and ered to the ring electrodesby a GrassS- syringe contained crystals of heparin to 4C stimulator generating rectangular inhibit clotting. Despite the relatively wave pulses. Stimuli were twice thresh- small size of the animals, the procure- old voltage and 40 msec. in duration. ment of the blood samples was accom- After all preparationswere complete, plished without difficulty. After the the ventricle was stimulated at 5-min. blood had been drawn into the 1-cc. intervals until tension stabilized. Five syringe, it was chilled and equilibrated with air in this container for 30 the minutes later the centrifuge tube-ther- min., mos the 23' C. air being replaced several times within assembly containing the blood was solution was with one this period. Followingthis, Ringer's replaced warmed to 230C. where it was main- a similarsolution at the initial containing tained for 15 min. Then a few of test After the ventriclehad drops temperature. wereintroduced into the syringe. been in this latter solution -or 5 a mercury min., These served to mix gently the erythro- electrical stimulus was and single given cytes with the mixing is of the tension recorded. there- plasma--such Immediately particular importance with blood from was returned to after the preparation , for their erythrocytes tend to Ringer's solution at 230 C., in which it settle rather rapidly. was allowed to remain for 5 min. Then When the fully oxygenated and well- the centrifuge tube-thermos flask as- mixed blood was ready, its oxygen con- sembly containingthis was replacedwith tent was measured with a Roughton- another containing Ringer'ssolution at a Scholandersyringe analyzer (Roughton second test temperature,and the proce- and Scholander,1943). The rapiditywith dure outlined above was repeated. Solu- which the blood coagulated in the pres- tions were replaced without disturbance ence of certain of the reagents used with of the ventricleexcept in the case of those this device made it critical to commence cooler than 100C. Such solutions when vigorous shaking as soon as they were added. Since each determination re- appliedto the ventricle would cause it to only contract. This thermal stimulation was quired about 40 mm.3 of blood, it was to make several determinations avoidedby brieflysubstituting a solution possible with the blood obtained from a at 12' C. for the one at 230 C. and then given heart puncture, if necessary. applying the still cooler solution. Usu- ally, measurementsof tension develop- OXYGEN EQUILIBRIUM OF HEMOGLOBIN 7 ment were made at 6 or temperatures Blood was drawn from 8 skinks by al- 30-6' C. apart. Temperatures were heart puncture, and the pooled sample ways orderedfrom low to high. All values (4 cc.) was centrifuged and the plasma for tension presentedare expressedas per withdrawn. The original volume of the cent of maximum tension developed by sample was restored by adding Ringer's the particular preparationin the course solution (pH 7.2) to the erythrocytes, of an experiment. which were then resuspended by gentle

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions TEMPERATUREIN LIZARD EUMECES OBSOLETUS 91 agitation and centrifugedagain. The su- the solutions. At the end of the experi- pernatant was drawn off and replaced ment, the hemoglobinsamples were with- with a comparable volume of fresh drawn from the tonometers and their Ringer's solution. The cells were then volumes determined. This information resuspendedand centrifugedagain. This was used in calculationof the oxygen ten- time the supernatant was replacedwith sions within the tonometersin the course distilled water to hemolyze the erythro- of the experiments.The oxygen capacity cytes. Centrifugation was carried out ol the solutions was analyzed with the once more, and the supernatant, now Roughton-Scholandersyringe analyzer. comprising a solution of hemoglobin, This informationalso was needed in the was withdrawn.This solution was mixed calculationof the oxygen tensionswithin with sufficientphosphate buffer mixture the tonometers. It further revealed that (pH 7.2) to produce an M/15 buffercon- the concentrationof the hemoglobinsolu- centration. The bufferedhemoglobin so- tions was approximately2 per cent. lution was then divided between two small cuvettes for a Coleman spectro- RESULTS photometer. The tops of these cuvettes RELATION OF OXYGEN CONSUMPTION had been modifiedto form a ground-glass TO TEMPERATURE joint with a 125 cc. tonometer. Be- Measurementsof rates of oxygen con- fore the cuvettes and their tonometers sumption at rest were carried out on 10 were assembled, this joint was treated skinks at body temperaturesfrom 16Wto with a high-vacuumgrease. 43' C. In the course of these measure- The hemoglobin solutions were de- ments, injury or death from overheating oxygenated by alternately evacuating occurred in some of the animals sub- the atmosphere in the tonometers and jected to body temperaturesbetween 40' replacing it with oxygen-free nitrogen. and 42' C. for 4 to 5 hours, and in all of This procedurewas continued until the those subjected to body temperatures optical density of these solutions, meas- above 42' C. for this period. A straight ured with a Coleman Junior Spectro- line can be fitted to the data for non- photometer (X = 650-70 mp), reached a injurious body temperatures studied maximum. When this occurred, the to- (16W-40'C.) when they are plotted on a nometers were evacuated one final time semilogarithmicgrid (Fig. 1). The equa- and measurementscommenced. The oxy- tion for this line, obtainedby the method gen tension within the tonometer was of least squares, is increased in small steps by injecting known volumes of air in accordancewith log 02 consumption= (7.839 - 10) the technique outlined by Riggs (1951). + 0.046t, Severalspectrophotometer readings were where is taken at each partial pressure to insure oxygen consumption expressed as and t is in that equilibration had taken place. All cc/gm. X hr., temperature volumes of air injectedwere correctedfor degrees centrigrade. The value of the containedwater vapor. Duringthe course slope in this equation, 0.046, corresponds of the experimentsthe tonometers were to a QIoof 2.9. At body temperaturesin maintained in water baths at 28A or excess of 40' C., the data for resting indi- 330 C., only being removed for short pe- viduals prior to the onset of heat injury riods to determinethe optical density of (as determinedby visual observationsof

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 92 WILLIAM R. DAWSON the animal and by analysis of EKG pat- Such suppression did not occur in the tern) tend to lie above the regressionline latter species at body temperatures as fitted to the data for lower temperatures. high as 450 C. A markeddecline of oxygen consumption Comparison also reveals that the correlated with heat injury occurred in Great Plains skink has a significantly most cases when skinks were exposed for higher rate of oxygen consumption at severalhours to temperaturesin excess of 300 C. (P < 0.01) and probably at other 400 C. temperaturesalso than the desertiguana. Comparisons.-It is of interest to com- This comparisonwas made utilizing the pare the relation of oxygen consumption data relating oxygen consumption and to temperaturein the Great Plains skink temperature for the skink (Fig. 1) and with that of the much more heat-resist- oxygen consumptionand body weight at 300 C. for the desert iguana (Vance, per- 1.00 sonal communication).The conservative of ani- .60 EUMECES procedure of using the number . mals ratherthan the numberof observa- 40 I%r- , -e tions in the statistical operationswas em- 20 The relation between the meta- . ee1 ployed. 0" bolic rates of the two lizards suggests oN 0 . 10o r. that the metabolism-temperaturecurve S.06 * for the desert iguana of a given size .04 shouldbe displacedtoward the upperend of the temperature scale from that for .02 skinks of similarbody weight. This would 15 20 25 30 35 40 45 be consistentwith the differencesin ther- 0C. mal relations of these animals in nature. FIG. 1.-The relation of total oxygen consump- It should be noted that lateral displace- tion (corrected to 00 C. and 760 mm. Hg) in ten Eumeces obsoletusweighing from 25 to 35 gm. Data ment of rate-temperaturecurves is one of represent minimal values observed for these lizards the most common forms of temperature at various temperatures. compensation (Scholander et al., 1953; ant desert which has been sub- Bullock, 1955). iguana, These lizards also differ in the inten- jected to the same general measurement of the of their con- procedures as those employed here sity response oxygen to as indicated (Dawson and Bartholomew, 1958) to sumption temperature, by the ascertain whether or not any differences temperaturecoefficients for this proc- exist which might reflect differencesin ess. The relatively high Qio (2.9) of the thermal adjustment. Great Plains skink coupled with its in- One obvious differencebetween these trinsically more rapid oxygen consump- lizard species concernsthe fact that heat tion shouldrender it moreprone to devel- suppressionof metabolism regularly oc- op excessive oxygen demands at high curred in skinks maintained for pro- temperaturesthan the desertiguana with longed periods at a body temperature its lowerQio (2.5) and intrinsicallyslower equivalent to the mean body tempera- consumption. This could contribute to ture, 42.10 C., noted for the desertiguana the conspicuous difference in heat resist- during activity in nature (Norris, 1953). ance characterizing these species.

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BREATHING RATE same 10 animals. A straight line can be The breathingrates of 8 resting skinks fitted to the data for temperatures be- were measured at temperaturesranging tween 16' and 40' C. if they are plotted from 190 to 40.50 C. Considerable scatter semilogarithmically(Fig. 3). The equa- is evident in the data, and the relation- tion for this line obtained by the method ship between breathing rate and body of least squares is temperature does not appear to be log of heartrate = 0.86 2 + 0.034t , strictly exponential (Fig. 2). Panting where was not observedeven at 40.50C., and it heart rate is expressedas beats per was also absent in other animalswithout minute, and t is temperaturein degrees The value of the in this strain gauges heated to body tempera- centrigrade. slope to a of tures as high as 43' C. equation, 0.034, corresponds Qio 2.2. Heart rates of lizardsheated Comparisons.-In its failure to pant resting above 400C. tend to lie above the undersevere heat stress, the GreatPlains extrap- skink differsqualitatively from a number of other species of lizards, e.g., the desert 400 iguana (Cowles and Bogert, 1944; Daw- 200 EUMECES 100 ,.,,% ,.;.,. I00 EUMECES 80 606 f) 20 r 40 Cr 1- 20 0 6 4 a: %0 0 0 om 0 " 8 6 0 5 10 15 20 25 30 35 40 45 15 20 25 30 35 40 45 C. oC. FIG. 3.-The relation of heart rate to body tem- FIG. 2.-The relation of breathing rate to body perature in fifteen Eumeces obsoletus. Data for tem- temperature in eight Eumeces obsoletus. The data peratures above 160 C. were obtained during periods were obtained during periods of minimal oxygen of minimal oxygen consumption by ten of the consumption by the animals at various tempera- lizards. Data for temperatures below 160 C. repre- tures. sent minimal heart rates of the other five lizards at various temperatures. son and Bartholomew, 1958) and the chuckawalla, Sauromalus obesus (Dill, olated regression line, as was the case 1938), which pant vigorously when with oxygen consumption. These high heated. The skink might be expected to rates could not be sustainedin most cases be less effective in controllingits rate of over a few hours, and a markeddecline of heating in strong sunlight than these heart rate was correlated with heat in- other species. jury. It was consideredworthwhile to deter- HEART RATE mine the effects of temperatureon heart Measurements of heart rate between rate in skinks at temperatures cooler 160 and 430 C. were carried out simul- than 160C., although it was not feasible taneously with those on oxygen con- to measure oxygen consumption under sumptionpreviously presented, using the such conditions. Therefore measure-

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 94 WILLIAMR. DAWSON ments were made at body temperatures heart, an increase in the utilization coef- between 00 and 160C. on an additional5 ficient (amount of oxygen withdrawnin lizards weighing between 25 and 35 gm., the tissues from a unit volume of blood), under the same general conditions as or, perhaps, a combination of both. If those utilized above, except that meta- either of the first two possibilities,stroke bolic measurementswere omitted. The volume or the utilization coefficient points plotted in Figure3 representmini- would have to be increased approxi- ma for the 5 individuals at the various mately 1.7 times. If the normal utiliza- temperatures to which they were sub- tion coefficientat 200 C. were 5 vol. per jected. These tend to fall along the re- cent, it would rise to 8.5 vol. per cent at gressionline fitted to the data for the 10 400 C., or about two-thirdsof the oxygen animals referred to above at tempera- capacity of the blood (see below). Some tures down to approximately100 C. Be- insight as to which possibility is the cor- low 100C. heart rate is more sensitive to rect one might be afforded by use of temperature, showing a Qio of approxi- some species of larger skinks in which mately 6.5. The range of heart rates in measurementsof oxygen tensions in arte- skinks is impressive, extending from rial and mixed venous blood under a variety of temperatureconditions should TABLE1 be feasible. OXYGENCONSUMPTION PER HEARTBEAT Comparisons.-It is of interest to com- (OXYGENPULSE) AT VARIOUS the effects of on heart TEMPERATURES pare temperature action in skinks and desert 02 Con- iguanas Tempera- sumption OxygenPulse (Dawson and Barthlolmew,1958) under ture (Cc/Gm HeartRate (Cc/Beat conditions.As in the case of XGm) comparable ( C.) XHr) (Beats/Hr) heat of 20...... 0.057 2,088 2.73 X 10-5 oxygen consumption, suppression 30...... 0.166 4,572 3.63 X 10-6 heart rate could be demonstrated in 40...... 0.478 10,020 4.77X10-5 skinks if they were maintained long at about 2.5 beats minute at 00 to 300 enough body temperatures (40' per 430 in the normal for beats minute at be- C.) activity range per temperatures the desert Such did tween 400 and 430 C. iguana. suppression in desert until their The of simultaneousmeas- not appear iguanas availability exceeded 470 C. This urementsof heart rate and con- body temperatures oxygen extreme heat resistance of the desert of skinks as- sumption permits partial to have been of the in which iguana appears purchased sessment way they cope at the of decreasedeffectiveness in with the increased demands price oxygen the cold, for this lizard cannot sustain which their tissues at tem- develop high heart function at low body temperatures peratures.The fact that the Qiofor oxy- to the extent evident in the Great Plains than gen consumption (2.9) is greater skink. Cold suppressionof heart rate was the that for heart rate (2.2) means that apparent in the former when it was amount of oxygen consumedby the ani- cooled below 150C., whereas it was evi- mal per heart beat, the so-called "oxygen dent in the latter only below 100C. (Fig. pulse," will increase with temperature. 3). Furthermore,electrical activity of the Values for this at several temperatures heart was difficult to detect in the desert are indicatedin Table 1. This rise in oxy- iguana below 90 C. and was never ob- gen pulse with temperature demands served below 30 C., although regular either a rise in the stroke volume of the heart action persisted in most skinks

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(aside from a couple showing AV block, size class the heart rate-temperature discussed subsequently) at body tem- curve of the desert iguana is displaced peratures down to 00 C. toward the upper end of the temperature With these differencesin mind, it is axis from that for the GreatPlains skink, worthwhile to compare the minimal a condition consistent with the differ- heart rates of the skinks at various body ences in thermal relations evident be- temperatureswith those of desert igua- tween these species. nas under similar conditions, using val- The relation between heart rate and ues obtained from the regression lines oxygen consumption with respect to fitted to the data for these species. How- temperature differs in these two species ever, such a comparison is complicated of lizards. This stems from the fact that by the difference in the mean body in the skink the Qiofor oxygen consump- weights of the experimental groups of tion is higher than that for heart rate, these species. It can be made in a provi- whereas in the desert iguana these coef- sional manner by adjustment of the ob- ficients are similar. Thus the oxygen served heart rates of desert iguanas, pulse of the skink tends to rise with tem- which averaged69 gm. in weight,to levels perature,whereas that of the desert igua-

TABLE 2

HEART RATES OF DESERT IGUANAS AND GREAT PLAINS SKINKS AT SEVERAL TEMPERATURES

DESERT IGUANA Observed "30-gm." GREATPLAINS SKINK TEMPERATURE Heart Rate Heart Rate OBSERVEDHEART RATE b* 1 (0 C.) (Beats/Min) b- (Beats/Min) (BEATS/MIN) 20 20 0.82 -0.18 23 35 25 31 0.93 -0.07 33 52 30...... 49 0.85 -0.15 55 77 35...... 77 0.95 -0.05 80 113

* Values of b, the weight regression coefficient for oxygen consumption, from Vance (personal communication). predicted for animals weighing 30 gm., na remains constant. This suggests that the mean weight for the skinks used in the desert iguana can meet the oxygen this study. This adjustment is based on demands developed at high tempera- the assumption that the weight regres- tures merelyby increasingcardiac output sion coefficientfor heart rate at any tem- through acceleration of heart rate. At perature should approximate b - 1, present it is only possible to speculate where b is the weight regression coeffi- concerningthe functional significanceof cient for oxygen consumption at that the difference between these species of temperature. Dawe and Morrison's lizards. It would appear, however, that (1953) extensive observations show that the desert iguana might have more re- this is the case in mammals at the inter- serve capacity for increasing its oxygen specific level. The determinations of b pulse at high temperatures than the made by Vance (personal communica- Great Plains skink, and this might con- tion) have been used in computing the tribute to its superior capacity for sus- values of b - 1 used in predicting the taining activity at high body tempera- heart rates of 30-gm. desert iguanas tures. It will be of interest to compare (Table 2). These rates are only about simultaneousmeasurements of heart rate two-thirds the correspondingones for the and oxygen consumption in additional skinks, which suggests that within any species of lizards characterizedby other

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 96 WILLIAMR. DAWSON sets of thermal relations than the ones they maintain during activity. Second, consideredhere. the ventricle of the skink develops a higher proportion of its maximum ten- EFFECTS OF TEMPERATURE ON VENTRICULAR sion at between 1' and CONTRACTILITY any temperature 15' C. than does that of the desert igu- The method of preparationeffectively ana. For example, between 00 and 20 C. abolished in the 5 spontaneous activity about 44 per cent is developed in the ventricles of Great Plains skinks used in former, whereas only 20 per cent is these measurements. These ventricles developed in the latter. The differ- maximum tension in developed response ence is statistically significant(P < 0.01). to electrical at widely spaced stimuli, Third, the ventricle of the skink de- between 160 and 26' C. temperatures velops a lower proportion of its maxi- Tension diminished (Fig. 4). markedly mum tension at any temperature be- with decreasing temperature below tween 260 and 350 C. than does that of and about 75 cent of maxi- 160C., per the desert iguana. For example, at 350 C. 76 per cent of maximumtension is devel- z 0-, EUMECES .. oped in the former,whereas about 86 per . 80 - . *' cent is in the latter. The differenceis sta- o_, 60 tistically significant (P < 0.01). Fourth, = the ventricle of the skink con- a 40 appears siderably less resistant to heat under in , 20 vitro conditions than that of the desert 0 0 5 10 15 20 25 30 35 iguana. The elimination of function in *C. the one preparationfrom the formerfol- FIG. 4.-Relation of isometric tension, developed lowing 5 minutes at 460 C. contrasted by the excised ventricle of Eumeces obsoletus in sharply with the fact that contraction response to widely spaced electrical stimuli, to tem- from perature. Tension expressed as per cent of maximum could be produced in preparations tension developed by the particular preparation dur- the latter after 5 minutes at tempera- ing the experiment. Data based on five preparations. tures as high as 500 C. mum tension was developed at 35' C., OXYGENCAPACITY OF BLOOD the highest temperatureat which meas- Measurements of oxygen capacity urements were regularlymade. One ven- were made on blood from 7 Great Plains tricle failed to respondto electricalstim- skinks. The values obtained range from ulation after exposure to 460 C. for 5 10.8 to 14.4 vol. per cent and average minutes. 12.5 vol. per cent (a = 1.4). to Comparisons.-Ventricular response Comparisons.--Thedata obtained in- temperature differs in a number of re- dicate that the blood of this skink can spects between the Great Plains skink carry somewhat more oxygen per unit and the desert iguana. First, the tem- volume than the bloods of most other peraturerange for maximaltension in the reptiles thus far studied (see Prosser, former (16'-260 C.) is lower than that in 1950, for summary). Values obtained for the latter (250-330C.). It is perhaps sig- oxygen capacity in turtles range from nificant that the differencebetween the about 6 to 11 vol. per cent. Those for the mid-pointsof the rangesfor these lizards crocodilians Crocodilus acutus and Alliga- is similar to that which exists between tor mississippiensis range from 8 to 11 the levels of body temperature which and from 7 to 15 vol. per cent, res pec

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions TEMPERATUREIN LIZARDEUMECES OBSOLETUS 97 tively. Direct expressionsof oxygen ca- owing to the electrode orientation em- pacity seem to be lacking for lizards,and ployed. the followingvalues have been calculated Analysis of the effects of temperature from data on hemoglobinconcentrations on EKG time relations was based upon for several species: Lacertamuralis, 12.2 measurements of the P-R, S-T, and vol. per cent; L. agilis, 7.8 vol. per cent; Pi-Tf intervals as defined by Dawe and Anguis fragilis, 15.8 vol. per cent (the Morrison (1953); the wave designations three preceding values calculated from conventionally used in electrocardiogra- data given in Prosser, 1950); Heloderma phy have been applied in the following suspectum,9.7 to 11.9 vol. per cent (Ed- discussion to the EKG's of the skinks. wards and Dill, 1935); and Sauromalus The P-R interval extends from the peak obesus,10.1 to 12.7 vol. per cent (Dill et of the P- to the peak of the R-wave. This al., 1935). These calculatedvalues do not provides an acceptably close approxima- include the small amount of oxygen car- tion of auriculoventricular(AV) conduc- ried by the blood in solution. The oxygen tion time without requiring determina- capacity of skink blood falls somewhat tion of the exact starting points of the P-

FIG. 5.-Electrocardiogramsof the same Eumeces obsoletus at two body temperatures,17.4' C. (left) and 28.6' C. (right).Measurements obtained with needle electrodesimplanted in the forelimbs. Vertical bar,one millivolt.Horizontal bar, one second.Records read fromleft to right, the initial wave in each case being the P-wave. Three completeEKG's are evidentin the recordfor the highertemperature. above the lower limits of values reported and the R-waves, as would have been re- by Prosser (1950) for adult birds (10.5 quired for measurementof the conven- vol. per cent) and by Burke (1953) for tional P-R interval. These starting adult mammals (11.7 vol. per cent). points were frequently difficultto locate. The S-T interval extends from the peak ELECTROCARDIOGRAMS of the S- to the peak of the T-wave. Al- Electrocardiogramsof Great Plains though this interval does not represent skinks were obtained using an electrode the full extent of the repolarizationpe- arrangement comparable to that em- riod, it does indicate a precisely defined ployed for standard limb lead I, as and easily measuredsegment of this pe- pointed out previously. They generally riod, which does not require location of consisted of deflectionscorresponding to the exact terminations of the S- and T- the P-, R-, S-, and T-wavesin the EKG's waves, one or both of whichwere difficult of mammals (Fig. 5), althoughthe S or T to find on many records. The Pi-Tf in- component was absent from a few rec- terval extends from the beginning of the ords. A deflection correspondingto the P- to the end of the T-wave. These refer- Q-wave was observed in less than 5 per ence points could not be preciselylocated cent of the records obtained, perhaps in all the recordsavailable. The Pi-Tf in-

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 98 WILLIAMR. DAWSON terval representsthe duration of electri- gests incipient difficultiesof AV conduc- cal activity of the heart during a given tion, and, indeed, two skinks with body cardiac cycle. temperatures of 2.50C. showed AV The effects of temperatureon the three block; only about a quarter of the P- intervals in 9 skinks is shown in Figare 6. waves recorded in these animals were Between 12.50and 40' C., a straight line followed by signs of ventricular excita- can be fitted to each set of data when tion. No signs of AV dissociation were they are plotted on a semilogarithmic noted at low body temperatures,such as grid, indicating an inverse exponential are commonly detected in the EKG's of relationship between the durations of hibernatingmammals (Lyman and Chat- these intervals and temperature. The field, 1956). Qio's for the reciprocals of these intervals At temperatures above 41' C., the EKG's of skinks were generally so com- plex as to defy quantitative analysis. 6.00 This arose from 4.00 complexity principally the coincidenceof the T- and suc- 2.00 partial 2. ceeding P-waves. At high body tempera- 1.00 tures, auricularexcitation apparentlybe- - .60 0 0 - 6.00 gins to the completion of ventricu- O .40 4.00 prior | lar repolarization.

L 06 *0 0 .60 Comparisons.- The EKG of the Great .10 10000 Plains skink differs profoundly in rela- 0 .06 . tive time characteristicsfrom those of .04 .40 mammals of size studied " EUMECESST .20 comparable by 02 .20 Dawe and Morrison(1953). In the skink .02 the S-T interval is the major segment of 0 5 10 15 20 25 30 35 40 45 the EKG, representingsomewhat more C.o than half of Pi-T7. The P-R interval FIG. 6.-The relation of the duration of various only comprises a third of the latter. In EKG intervals to body temperature in nine Eumeces the mammals (Peromyscus, Clethrio- obsoletus weighing 25 to 35 gm. Reference points the for the intervals defined in the text. The lines for nomys,and Mus), on the other hand, the data on the P-R and S-T intervals were fitted P-R interval is the major segment of the by eye. EKG, comprising a third to a half of Pi-Tf. The S- T interval only amountsto all 2.1. Consequent- closely approximate about a tenth to a quarter of the latter. ly the proportions of Pi-Tf represented It would be of interest to know to what constant be- by P-R and S-T remain extent the differencesrelative to Pi-Tf tween 12.5' and 400 C. despite profound are associated with the obvious differ- of changes in the absolute durations ences in cardiac morphology between these intervals. These proportionsare 33 lizards and mammals. and 55 per cent, respectively. Differences in absolute time dimen- Below 12.5' C. the Qiofor the recipro- sions between the EKG's of skinks at a cal of the P-R interval exceeds 4, but body temperature of 370 C. and those of that for the S-T interval remainsat 2.1. the mammals referredto above are very The increasedsensitivity of the P-R in- great. The durations of the P-R, S-T, terval to temperature below 12.50 C. sug- and P-Tf intervals in the lizards are 4,

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21, and 5 times longer, respectively,than ported for various mammalian hemo- the correspondingintervals in the mam- globins at pH's near neutrality, e.g., mals. The observationthat Pi-Tf is only sheep, -8.2 kcal. (Paul and Roughton, a fifth as long in the homeothermsis of 1951) and ox, -9.4 and -10.0 kcal. particular interest in view of the fact (summarizedin Wyman, 1948). that the heart rates of the mammals The only informationthat does appear (500-675 beats per min.) were 4 or 5 to be available on a reptilianhemoglobin times more rapid than that of the lizard in solution is that of Wilson (1939) for at 37' C. (130 beats per min.). the turtle Pseudemys scripta. This pig- ment was observed to have a of 14 OXYGEN EQUILIBRIUM OF HEMOGLOBIN Pso mm. Hg at 250C. and pH 7.4. Its dissoci- Oxygendissociation curves were deter- ation curve was hyperbolic. This is con- mined for the hemoglobin of the Great sistent with the fact that the oxygen dis- Plains skink at 280 and 330 C., using 2 per cent solutions containingM/15 phos- 10.0 phate buffer,pH 7.2. The curvesfor both Ioo ECUMECES are in with temperatures sigmoid shape, zo 80 the one for 330 C. displaced to the right, 1.0 660 o as would be expected, from the one for 280 C. (Fig. 7). The pso's for 28' and 40 -0 330 C. are 19 and 24 mm. 20 Hg, respec- 0.1 tively. Use of these values as the equi- 10 20 40 librium constants at the two tempera- 0 10 20 30 40 50 60 70 80 TENSION (mm tures allows calculation of an apparent 02 HG) heat of oxygenation (AH') for the hemo- FIG. 7.-The oxygen dissociation curves of Eu- of this lizard The meces obsoletus hemoglobin at pH 7.2. Unshaded globin (Wyman, 1948). data for 280 C. Shaded for 330 is -8.9 kcal. circles, circles, data C. value obtained Information Arithmetic coordinates are for the sigmoid curves. permitting determination of the true Logarithmic coordinates are for the straight lines. heat of oxygenation (AHo) is not cur- rently available. sociation curves for whole blood of most The sigmoid characterof the dissocia- turtles are also hyperbolic (Southworth tion curves suggests heme-hemeinterac- and Redfield, 1926; Gaumer and Good- tion. A measureof this is providedby the night, 1957). Sinceliberation of the skink constant n in Hill's equation,which is the hemoglobin into solution would, if any- slope of the line relating the log of y/ thing, tend to reducethe value of n, from (100 - y) to the log of the partial pres- the level pertaining within the erythro- sure of oxygen, y representing the per cyte, it is reasonableto assume that this cent saturation of the pigment at a par- pigment under physiological conditions ticular partial pressure.The values for n would show a sigmoiddissociation curve, at 280 and 33' C. are identical (Fig. 7), as do those of the lizards Sauromalus equaling 2.2. (Dill et al., 1935) and Heloderma(Ed- Comparisons.-No information on wards and Dill, 1935). Therefore the heats of oxygenation of hemoglobins of blood pigments of lizards would appear other reptiles seems to be available. How- closer in the extent of their heme-heme ever, the AH' for that of the skink does interaction under such conditions to the fall within the general range of those re- hemoglobin of the crocodile Crocodilus

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 100 WILLIAMR. DAWSON acutus (Dill and Edwards, 1931) than to kept at 16WC. for three weeks had sig- those of the turtles. nificantly higher rates of oxygen con- sumption at 330 C. than those which had DISCUSSION been maintained at the latter tempera- Evidence concerning adjustments for ture for a similar period, but the lateral temperature in the physiology and be- displacementof the metabolismtempera- havior of reptiles falls into two cate- ture curves one from the other only gories: one concerningadult-phenotypic amounted to 30 C. modifications of temperature response, Some examples of adult-phenotypic which seem primarily dependent upon modifications of functions other than the thermal history of the animal, and metabolism are also known for reptiles. one concerninginterspecific differences in The heat resistanceof the lizard Urosau- temperature response which, presum- rus ornatus is improved from levels ob- ably, are genetically fixed. served in animals adjusted to spring con- Several studies of adult-phenotypic ditions in their habitat, by exposure to modificationsof temperatureresponse in 350 C. for 7-9 days. The body tempera- reptiles have dealt with metabolic rate. ture at which locomotor disability first Vance (1953) found that lizards of the develops is elevated 1.40C. and the sur- species Urosaurus ornatus which had vival time at 440 C. is doubled (Lowe and been maintained at 350 C. had signifi- Vance, 1955). Muscle contraction in the cantly lower rates of oxygen consump- turtle Chrysemyspicta is influenced by tion at 150C. than did those which had the recent thermalhistory of the animal. been kept for a comparable period at Brown (1957) noted that skeletal muscle 80 C. Subsequently, Gelineoand Gelineo from animals that had lived for approxi- (1955) reported that the metabolism- mately 4 months in cold water (5- temperaturecurves for the lizardsLacer- 100C.) developed a higher proportionof ta m. melisellensis and L. m. galvagnii its maximum tension in vitro at 00 C. following maintenancefor several weeks than did that from ones that had lived at approximately240 C. were displaceda for a similar period in warmer water remarkable100 C. toward the upper end (200-25' C.). Cardiac muscle from the of the temperature scale from the cor- turtle Pseudemysscripta also reflects the responding ones for individuals of these recent thermalhistory of the animal; the subspecies following maintenance for a optimal temperaturefor tension develop- similarperiod at 130C. The extent of this ment in vitro is higher in auricles from lateral displacementindicates nearly per- warm-acclimatedturtles than in those fect compensationof metabolismfor tem- from cold-acclimated ones (J6bsis, per- perature in these animals; individuals sonal communication).The observations acclimated to the lower temperature thus far presented serve to indicate that would have virtually the same metabolic a capacity for adult-phenotypic modifi- rate at 130C. as those acclimated to the cations of temperatureresponse exists in higher temperaturewould at 240C. This reptiles.However, they are inadequateto is noteworthy, for as Fry (1958) points permit any generalizations concerning out, compensation is usually only par- the role of these modificationsin the life tially effective. This is certainly the case of the animals in nature. It would be of in the lizard Sceloporus occidentalis particular interest to examine the physio- (Dawson and Bartholomew, 1956). Indi- logical responses of various species to viduals of this species which had been temperature using individuals freshly

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drawn from their respective habitats at peraturesbeing abroadearlier in the day various seasons of the year. than those with higher ones. The known Insofar as interspecific differencesin mean activity levels of body temperature physiologicaland behavioralresponses to for lizards span a range of nearly 200C., temperatureare concerned,the most ex- ranging from 25.80C. for the alligator tensive informationavailable pertains to lizard, Gerrhonotus multicarinatus (Bo- lizards, and the following discussion is gert, personal communication), to confined to them. Three types of differ- 42.1 C. for the desert iguana (Norris, ences exist among these animals, which 1953). relate, respectively, to: the body tem- Differences in heat resistance which peratures which they maintain by be- seem correlatedin a generalway with the havioral regulationduring activity; their differencesin levels at which body tem- resistance to high body temperatures; perature is regulated during activity and various aspects of their physiological have been documented in a number of performanceat particularbody tempera- cases. Cole (1943) found that the respec- tures. tive temperaturesat which several spe- The ability of most lizards for con- cies of the family Iguanidae were in- trolling body temperaturethrough utili- capacitatedby heat rangedfrom 41.7' to zation of the heat affordedby solarradia- 48.40 C. Interspecific differences in these tion allows them under favorable condi- temperatureswere also noted by Cowles tions to achieve a measure of independ- and Bogert (1944). The fact that in the ence of air temperature (Bogert, 1949a, present studies the Great Plains skink b: Saint-Gironsand Saint-Girons, 1956; died if maintained for several hours at and others) and establish a level of body temperatures in the normal activity temperaturepresumably optimal for ac- range for the desert iguana further illus- tivity. The effectiveness of this behav- trates the profounddifferences in heat re- ioral regulation of body temperatureis sistance which seem to characterizeliz- indicated by Pearson's (1954) observa- ards differingin the levels at which they tions of the andeanlizard Liolaemus mul- regulate body temperatureduring activ- tiformis, which he found capable of ity. maintaining body temperature near Detailed information on how the 300 C. by basking, even though nearby physiological responses to temperature shade temperatures were at or below compare among lizards which differ in freezing. The level at which lizards regu- their thermalrelations is very scarce,and late body temperature appears fixed it is in this area that the data presented within fairly narrowlimits at the generic in this and a previous report (Dawson level; congeneric species, even though and Bartholomew, 1958) representa be- they may live in markedly different ginning. These data establish that differ- habitats, tend to maintain similar tem- ences in physiologicalperformance with peratures during activity. However, this respect to temperature are evident be- level commonly varies from genus to tween the Great Plains skink and the genus, even though their representatives desert iguana at both the tissue and sys- may occur in the same habitat. In very temic levels of organization. These dif- hot climates differences in times of activ- ferences, which have been reviewed in ity during the day seem to stem from detail in a previous part of this report, such differences in thermal relations-- concern the position of the metabolism- species with relatively low activity tem- temperature and heart rate-temperature

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions 102 WILLIAMR. DAWSON curves on the temperatureaxis, the tem- increasedwith temperature,but the rela- perature range over which cold suppres- tionship was not strictly exponential. sion of heart rate occurs, the lower tem- Panting was not observed even at tem- perature at which electrical activity of peratures high enough to be injuriousto the heart is abolished,breathing patterns the animals with prolongedexposure. at high temperatures, and the tension- Measurements of heart rate between temperaturerelationship of excised ven- 16' and 430 C. were carried out simul- tricles. Their nature provides tentative taneouslywith the measurementsof oxy- support for the view that physiological gen consumption.The Qiofor heart rate adjustments favoring efficient physio- between 100 and 40' is 2.2. The physio- logical performancein particular ranges logical implications of the dissimilarity of temperatures underly the observed between this value and that for oxygen differencesin levels at which body tem- consumptionare considered.Between 0O peratureis regulatedin various species of and 100C., the Qiofor heart rate is 6.5. lizards. Relative ventriculartension developed The pattern of temperature adapta- in responseto field stimulationwas great- tion evident in lizards is of interest from est between 160and 26' C. the standpoint of comparative physiol- The oxygen capacity of the blood of ogy, for it appearsto have developedpri- the Great Plains skink is 12.5 vol. per marily with referenceto behaviorallyes- cent (0 = 1.4). This is higher than most tablished rather than environmentally of the other values available for reptiles. imposed body temperatures,in contrast Analysis was made of the time rela- to the situation which appearsto pertain tions of the P-R, S-T, and Pi-Tf inter- among many aquatic poikilotherms. vals of electrocardiograms,at various temperatures.The Qio'sfor the recipro- SUMMARY cals of the P-R and S-T intervals ap- As part of a continuingeffort to under- proximate 2.1 between 12.50 and 40' C. stand the nature and significance of However, below 12.50C. the Qio for the of the P-R interval exceeds 4 physiological adjustments of lizards to reciprocal whereas that for the of the temperature, a study has been made of reciprocal the effects of this factor on total S-T interval remains at 2.1. Indications oxygen of AV block were noted in the electro- consumption, breathing rate, heart rate, cardiogramsof some skinks at low body in vitro ventricular contraction, and the temperatures. oxygen affinity of hemoglobin in the The oxygen dissociation curves of 2 Great Plains skink, Eumeces obsoletus. per cent hemoglobinsolutions buffered at The of the blood of this oxygen capacity pH 7.2 were determinedat 280and 330 C. animal was also determined. The Great The P50'sfor these temperaturesare 19 less heat resistant than Plains skink is and 24 mm. Hg, respectively. The AH' the desertiguana, Dipsosaurusdorsalis, a calculated from these results is -8.9 previously studied lizard with which it is kcal. The dissociation curves at both comparedextensively in this report. temperatures are sigmoid in shape and The increase in oxygen consumption the values of n for both approximate2.2. by the Great Plains skink between 16W Evidence concerning adjustments for and 40' C. showed a Qioof 2.9. temperature in the physiology and be- Between 190 and 40.50 breathing rate havior of reptiles is reviewed both at the

This content downloaded from 207.233.74.102 on Mon, 17 Feb 2014 18:51:29 PM All use subject to JSTOR Terms and Conditions TEMPERATURE IN LIZARD EUMECES OBSOLETUS 103 adult-phenotypic and specific levels. iguana reveals differencesin physiologi- Comparisonof the results obtained for cal responses to temperature consistent the Great Plains skink and the desert with their thermal relations in nature.

LITERATURE CITED

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