Respiratory Responses to Long-Term Temperature Exposure in the Box Turtle, Terrapene ornata

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J. Comp. Physiol.

Journal of ComParative Physiology' B

l3l, 353 359 (1979)

it) by Springer-Verlag

1979

Glass, l4ogens L., James I{. Hicks and }Iarvin L. Riedesel . L975. Respiratory responses to long-term temperature exposure in the box turtle, Terrapene ornata. J. Cornp. physiol. 111, 353-359. Respiratory Responses to Long-Term Temperature Exposure in the Box Turtle, Terrapene ornat& Mogens L. Glass*, James W. Hicks, and Marvin L. Riedesel Department

ol Biology, University of New Mexico, Albuquerque. New Mexico 87131, USA

Accepted March 9, 1979

Summary. ln late February, seven box turtles were collected with body temperatures between J and9 "C. Ventilation, gas exchange and end-tidal Po. and P6.. were recorded at 5, 10, 15 and 25'C, the animals being at each temperature for 2 to 3 weeks. There was a pronounced diurnal rhythm of breathing frequency at all temperatures. At 5 bC the mean 24-h frequency was only 3.7 breathsh-1. At 15'C the frequency was 16 times higher with a l7-fold increase of ventilation. Oxygen uptake only changed from 3.4 lo l2.l ml .kg 1 .h 1. Consequently, the ratio (ventilation, ml BTPS/Ot uptake, ml STPD) increased from 12.5 ar 5 'C to 48 at 15 oC, but decreased lo 24 at 25 'C. The decrease of this ratio during cold exposure contrasts with an increase of the ratio during cooling earlier reported for fresh water turtles, Pseudemys. Cutaneous COt elimination was important at low temperature. This caused a decrease of the pulmonary gas exchange ratio so that end-tidal P66, remained low at 5'C in spite of an end-tidal Ps, of only 54 Torr.

In many ectothermic vertebrates and in some invertebrates studied, a constant relative alkalinity (i.e. OH /H+ ratio) is maintained when body temperature changes (Rahn, 1966; Reeves, 1972; Howell and Rahn, 1976). With decrease of body temperature, the

plasma pH tends to increase in parallel to pN, the pH of neutral water for which pH:pOH. However, plasma pH is greater than pN, the difference being species dependent. The constant OH /H+ reflects a regulation of the ratio between negative and positive Department

/oli.o,

RT Poro'

(1)

and to the ratio i'u1ito.by the equation

(t"l

) - (iol Vd -

to

as

ln

R eRT f P,1.o.

V.o.:Rn'Vo.

these equations

and

Vu-to:l^

Vr:Iotal ventilation

(2)

volume, Z,

: dead space ventil ation, Vo: alveolar ventilation, Rr: the pulmonary gas exchange ratio, R: the gas constant, and T:the absolute temperature. Increase (and requirements lowers alveolarpH of air convection plasma as P.o, which in turn increases arterial)

Introduction

*

charges on proteins (Reeves, 1972). Thercfore, the optimum pH of various key enzymes increases with decrease of body temperature (Hazel et ai., 1978). In fresh-water turtles, Pseudemys sp. and in Iguana iguana the change of pH with temperature is caused by adjustments of the air convention requirements, i.e. the ratio of ventilation volume, ml BTPS to O, uptake, ml STPD; i"lto. (Jackson, 1971; Kinney et al, 1977 Giordano and Jackson, 1913). Alveolar Pqo, is related ' to the relative alveolar ventilation (VolVro,) by the equation,

of Zoophysiology, University of Aarhus. DK-

8000 Aarhus C. Denmark

shown by the Henderson-Hasselbalch equation: pH

:

pK

-1

HCO; log:- -^- " 1.' L-co.

(3)

where a:solubility coeflicient for CO, in plasma. The increase ol pH and air convection requirements with cooling has been described to occur within hours (Jackson, 1976). However, long-term or seasonal effects of temperature on ventilation and air convection requirements remain unknown. This is the reason for undertaking a study of ventilation. gas exchange, and end-tidal P6,. and P.o. in hibernating and active box turtles, Teruapene ornata ornota. 0340-1 616 11 9/0 I 3 1 /0353i$01.40

 

354

M.L. Glass et al.: Respiratory Responses to Temperature in the Box Turtle CAII BRATION SYRI NGI

PRESSURE TRAIISDUCTR TRAilSDUCTR II{OICAIOR

RECORDER

02

AI{A I. YZT

R

FLOW

STAEt

ilztR

C0z ATIA LYZTR

Fig. 1. Schen'ratic drawing of the experimental setup

RECO ROT R

Materials and Methods Seven ornate box turtles (Terrapene o. ornata) were collected in the fall and hibernated within an outdoor enclosure. In February the turtles were removed from hibernation sites with a body tempei_ ature

of 7 to 9'C and transferred to an environmental chamber

initially set at

5 "C. Weights ranged from 224 to 390 g (_i:316 g). Experiments were performed in sequence at 5, 10, 15 and 25 "C. The animals were kept at each temperature for 2 to 3 weeks. The turtles were fasting during all measurements, but were initially fed after transfer to 25 'C. Water was available at all times. The experimental setup is shown in Fig. 1. Ventilation was monitored by a plethysmographic technique. A closefitting, gas_ tight mask was constructed for each turtle. For details see Glass etal. (1978). The mask was skintight except for a funnel_shaped extension surrounding the nares (dead space 0.3 ml). The mask was lastened and sealed around the turtle's head with cvanoacrvlate and last setting epoxy glue. Leaks uere prevented b ll,specting the seal through the clear mask material. The funnel-shaped exten_

sion litted tightly and was glued into a hole in the wall of the

plexiglass chamber. The bottom of the chamber was senled with vaseline. As the turtle's body w:rs sealed into the plexiglass chamber, changes body caused inspiration resulted in pressure by which inchambervolume or expiration changes were monitored by a Valydine diflerential pressure transducer (Mp45-1) with a Valydine transducer indicator (CDl2), and recorded with an E & M Physiograph (E & M Instrument Co. Inc., Houston, Texas). Cali_ bration olthe system was achieved during breath-holds by injecting or withdrawing known volumes. Leaks in the mask would occasion_ ally develop, but were detected as a decrease in the amplitude

ol calibration signals.

Catheter tubing placed within the funnel at the nares permitted sampling of end-tidal oxygen and carbon dioxide. A Neuberger pump pulled gases through an 53A oxygen analyzer (Applied E,lectrochemistry) or a LB-1 COr-analyzer (Beckman Instruments). At low flow rates variations in pump activity were reduced by a flow stabilizer vessel (Fig. l). As expired flow rates were low and tidal volumes small (l 7 ml) several precautions were taken to assure that end-tidal Pn, and P.o, wcre obtained. The extension ol the mask served to funnel the expired gas to avoid contamination of the sample. Furthermore, sample flow rates werb reduced to

40 50ml.min '. The small tidal volune only allowed analysis ol one gas at any time (Pn. or- P.,,,). Care was taken to keep dead space at a minimum in the sample inlets of the analyzer pick-up heads. Calibration ol the gas analyzers was perlormed with dry room air or dry commercial standard calibration gases. Sample flow rates were the same during calibrations and measurements. With low flow rates we obtained alveolar plateaus for both O, and COr. As end-tidal gas pressures and mean zrlveolar partial pressures were very close, values for end-tidal p., and p.u, were taken to represent alveolar values. Only end-tidal gas pressures could be recorded at the lower recording speeds which were necessary due to low breathing lrequencies at 1ow temperatures. Endtidal P., or P.,,, was continuously recorcled lor 24-h intervals (Coleman Recorder, Hitachi 165). From the recording it was established that the inspired gas was virtually room air in spite of a dead space of0.3 ml in the funnel. This was due to the continuous pulling of g:rses from the region of the nares. Total Zo, or Z.u, was obtained by placing the turtles in glass jars sealed with vaseline. A small rubber tube inserted through the lid was opened to obtain samples lor gas analysis. Samples were taken repeatedly over 2.{-h periods at intervals that resulted in changes of O, or CO, concentrations of approximately l7o. Oxygen upt:rke was calculated as a mean value for a 24-h period. Cutaneous gas exchange was measured by sampling gases from the plexiglass chamber. The lace mask assured that expired gas did not enter the plexiglass chamber. It is also important that fumes from the glues used for sealing do not interfere with the readings of gas analyzers. The plexiglass chamber was flushed with room air 24 h alter gluing and samples were taken 24 h later. As breathing frequency showed a pronounced diurnal rhythm, ventilation was calculated as a mean value lor a 24 h period. The

breathing frequency was very low and is therefore unconventionally reported as breaths.h 1. The ventilations reported in the following are based on inspired volumes. Expired volumes were less due to cutaneous carbon dioxide elimination. pulmonary gas exchange ratios were calculated lrom the equation (Rahn and Fenn, 1955),

Ro:(Pr.o,)(l -Fro,)l(Pro,-PA6, -Pr.6, 4..) where ,4

:

alveolar (end-tidal)" 1 :

14)

inspired and ,Fr., is the fractional

concentration of inspired oxygen. Alveolar ventilition was calculated from the equation,

 

M.L. Glass

et al.: Respiratory Responses to Temperature in the Box Turtle

355

VA- REV},(RTlPAco),

where R:the

gas constant equal to

BTPS.Torr."K 1 .ml STPD 1 and I

in "K. Dead

2.785 ml is the absolute temperature

space was calculated from the equation. tr/r(.Vt-VoV. Calculation of dead space provided a test that measured total ventilation and calculated alveolar ventilation were in reasonable agreement. As alveolar ventilation was calculated from end-tidal Po, and P6n. (Eq.4 and 5) and oxygen uptake, the comparison also provided an additional method of testing measurements of end-tidal gas pressures.

BO @ a rn

E

:

io

-

-{

z 60c)-n

U)

o-

F 7E

a

(D

j

ui

40

=J

o

Results

of apnea.

Inspirations without expirations would

sometimes precede series of breaths. breath holding relates to shrinkage of the lungs with This probably

o J

^^=

a F

oo'

5rot52025

TEMPERATURE,'C

Fig. 2. Tidal volume and breathing frequency changes with temperature; -t+SE; n:4 al 5 and 25 "C, r-5 at 10 and 15'C

E

(Mithoefer, 1964). The mean 24-h breathing frequency was only 3.7 breaths.h 1 at 5 oC, but at 15 'C the frequency was 16 times higher whereas tidal vol-

-\r'

tion, therefore, changed roughly in proportion to the breathing frequency (Fig. 3). Oxygen uptake at 15 oC was 3.7 times higher than at 5'C (Fig. 4). Because of the larger effect of temperature on ventilation than oxygen uptake, air convection requirements increased from 12.7 ml BTPSiml STPD at 5 'C to 48 ml BTPS/ ml STPD at l5'C (Fig. 5). Oxygen extraction (Eo,) can be estimated from the relationship,

E

umes changed little with temperature (Fig. 2). Ventila-

-<

o o

_,)

There was a pronounced diurnal rhythm in breathing frequency. ln extreme cases at 5'C breathing ceased completely during the night (8 t h) whereas the highest frequency was recorded in the morning. The turtles had individual characteristics as to patterns of breathing, the typical alternatives being single breaths interrupted by regular periods of breath holding or series of breaths separated by longer periods

m o m cz c)

I

a o_ F

(D

.>;

o

z

z a F _)

F

z

UJ

E (1) Eo.:(RTlP,o)(.Vo,lV,:) oC corwhere 1:inspired. The low ir,li,o. at 5

responds to an oxygen extraction of 0.55, i.e. 55% of the inspired oxygen content. Changes of end-tidal P,r, with temperature reflect changes of oxygen extraction (Fig. 6). At 5 'C mean

end-tidal Po, was 55 Torr, but values as low as 15 to 20 Torr were recorded. Assuming a pulmonary gasexchange ratio of 0.75, a mean end-tital Po. of 55 Torr corresponds to a mean end-tidal P6e, of 60 Torr. Surprisingly, end-tidal P.,r. was only 16 Torr (trig. 6), which was not different from the value at 15'C. This was due to extrapulmonary carbon dioxide elimination which was most important at the low temperatures.

ln

contrast, extrapulmonary oxygen

o ) L a o z -J

5ro

oo'

o F Fig.

atur

520

25

TEM PERATURE, "C

Total

(

4 and alveo tar ventilation ( Z, ) cha.nges wlth temper-

.i+sE;n :4 at 5 a nd 25 'C. n:5

at

l0a nd 15'C

uptake was nonexistent or at least immeasurably small. The existence of an extrapulmonary pathway for carbon dioxide elimination caused the pulmonary gas-exchange ratio (Ru) to be less than the ratio for

total steady-state gas exchange (Rr'o'u'). The difference

 

M.L. Glass et al.: Respiratory Responses to Temperature in the Box Turtle

356

o

;o

F-

z

li.

uJ

0

a F z

.E

60

L

3c-x 'ul

Oz or 2^ <H

o

L

N

I

408 -l

LIOE -to 40 O) FIF

?uL

Ld

cr

.>o'a

dE :<

n

colcD

-lEtF

= o^o

c) -J

t.9 gi z

F olI

oN

J F o F

z avm

s

E.

a

E ;--

od TEMPERATURE, "C

TEMPERATURE,"C

Fig.4. Changes in oxygen uptake and carbon dioxide elimination with temperature; ;+SE; n-4 at 5 and 25 "C, n:5 at 10 and 15'C

Fig. 5. Air convection requirements and oxygen extraction changes with temperature; x+SE; n:4 at 5 and 25"C, n:5 at l0 and

t5'c

U

(ts

o z

o

9o E

U,

o

F E

,/'a

(,

UJ

.: N o-o

o ) F

o z I

t

z

rn

z O i

I O

x

I

o

Lrl

-

a (9

 

z o

^-o

E

o

)

f

o_

o z -J

F o F

ro 15

TEMPERATURE, "C Fig. 6, Changes of end-tidal Po, and P..u, with temperature; n:4 at 5 and 25 'C, n:5 at 10 and 15 'C

20

TEMPERATURE."C

r*

SE ;

Fig.7. Changes of pulmonary and total gas exchange ratios with temperature; -+SE; n:4 at 5 and 25'C, n-5 at 10 and 15'C; Rl"t"':Total Gas Exchange Ratio; Rr:pulmonary Gas Exchange Ratio

 

357

M.L. Glass et al.: Respiratory Responses to Temperature in the Box Turtle Table l Extrapulmonary COr-elimination as a percentage of total CO2-elimination at various body temperatures, mean t SE Temperature ("C)

Cutaneous

V.u,(%)

76

10

15

(+8.0) 49 (+3.5)

23

(t1.8)

35 (+6.5)

(trig. 7) at which temperature

was pronounced at 5 'C was 3/o of the total COt CO, elimination cutaneous output (Table 1). At l5'C, only 1/o of the CO2 elimination occurred through extrapulmonary exchange.

The total gas-exchange ratio increased from 0.76 at 5'C to 0.91 at l0'C which is similar to effects of heating in birds and mammals (Chaffee and Roberts, 1971). On transition from 10 to 15'C, there was a transient decrease in the total gas-exqhange-ratio' The ratio increased and reached a steady level after a oC caused other tranweek. Transfer from 10 to 15 sient respiratory responses. Initially, end-tidal Pco. was low, 9 + 3 Torr (t + SD), compared to a mean of 14 Torr two weeks later. The low P.o. was caused by an increase of air convection requirements to STPD.

124 ml values ranging BTPS/ml 48 toVrlZo, was close to 48 ml weeksfrom at 15'C After two BTPS/ml STPD for all the box turtles. Calculated dead space did not change significantly with temperature. The mean of all calculations is Vo:2.04 ml'kg 1 + 0.4 (SE, I/: 18).

Discussion

During winter, box turtles remain in shallow burrows (20 45 cm deep), where they tolerate body temperaoC as a fretures close to the freezing point with 5 quently recorded temperature. They remain inactive during winter and will not emerge in the spring until 1960).

the temperature is at leastbody bodysummer (Legler, 15'C temperature of the preferred During oC, but a variety above 35 'C box turtles is close to 30 of thermoregulatory responses will occur including excessive saliva production (Sturbaum and Riedesel, t97 4).

The studies on respiration in Pseudemys sp. recorded higher oxygen uptake than for T. ornata (Jackson, 1971; Kinney et al., 1977). Gatlen (19'74) also reported a generally lower standard metabolic rate in T. ornala than in Pseudemys scripta. The effects of cold exposure on ventilation in Z. ornata deviate

markedly from the effects of cold on breathing in Pseudemys scripta (Jackson, 1971). Whereas mean ventilation in P. suipta changed little with temperatures ranging from 10

to

35

"C, T. ornata increased

ventilation 17-fold when body temperature increased by only 10'C from 5 to 15'C. Kinney etal. (1971) reported an exponential increase of ventilation with increase of body temperature in the turtle, Pseudemys floridana, but ventilation was predicted to increase by a factor of less lhan 2 with an increase of body temperature from 5 to l5 "C. Likewise, the increase of air convection requireoC contrasts ments.with temperatures from 5 to 15 temperature dependence of this ratio in Pseudemys sp. At 10'C the ratio was 76.2mIBTPS/ with ml STPD in P. suipta (Jackson, 1971) and was predicted to be 66 ml BTPSiml STPD in P. .floridana, compared to 21.9 ml BTPS/ml STPD in T. ornata. In the Henderson-Hasselbalch equation (Eq 3), the values for pK and ry for a given animal at a given temperature are constants whereas HCO3 and Ps6, c?n be regulated. Changes of end-tidal Pg6. r€sult from alterations of the relative alveolar ventilation (Eq. 1). lon exchange in the kidneys or intestines could regulate the plasma bicarbonate ion concentration, but most evidence favour a constant HCO3with temperature in reptiles (Howell and Rahn, 1976). Therefore, active pH regulation during temperature changes is generally thought to be mediated through adjustment of the relative alveolar ventilation. This model appears to be valid for fresh water turtles (Pseudemys sp.) exposed to temperatures in the range 10 to 35 oC for hours or days, but in the 5 to 15 "C range Z. ornata air convection requirements increased with temperature (Fig. 8). The pronounced decreases at low temperatures of both breathing frequency and air convection requirements in T. ornata correlate with seasonal cold exposure and inactivity. A low air convection requirement during hibernation is an advantage in terms of energetics because the oxygen cost of breathing in percent of total 26, is a constant times the VulVo. ratio (Kinney and White, 1977). A low ventilation volume in hibernating box turtles limit respiratory water loss. The serve also energy and body water may will to advantages of saving conflict with maintenance of a constant OH /H+ as end-tidal P66, wos relatively constant between 5 and 15 'C, but measurements of plasma pH are necessary for an evaluation of the problem. ln the range of temperatures within which 7. ornata is active the values for air convection requirements agree well with previous studies on chelonians (trig. 8). The differences between effects of low

temperature

on respiration of T. ornata

and

Pseudemys seems explainable. Only this study reports on ventilation and Or-uptake of a reptile at low body temperature associated with inactivity during the winter season. Other studies involved measurements over active P. scripta and inverse reladays. hours or In

 

358

M.L. Glass et al.: Respiratory Responses to Temperature in the Box Turtle

o oF a

9pji9ie$

. - Voronus exonihemolicus4 . - lgwno iguonos .-

b

e

r

-Coluber rovergieriS

o ".-

Locerlo spp

a

o-

F co

Vipero poloesiinoe8

Spoleropphis c|ffordiS Aspris cerosles8

Acrtrhordus jovonicus9

E

a F

z

A

trJ UJ

E f

\\*

O

UJ

E.

z.

\

IF

O ul z.

o C)

a'

E

5 to t5 20253035 TEMPERATURE.'C

5 ro t5 20253035 TEMPERATURE,"C

5 ro

15

20253035

TEMPERATURE,9C

Fig'8. Air convection requirements reported lor various repllles (Chetonions, Saurians and, OptLidians); rGlass etal., present study; Jackson 3calculated

(1971); from Kinney et al. (1917);1wo;d et u,t. (1973); 8calculated from Dmi'el (1472); ',GIass and Johansen (1976)

tionship between Vrl Vo. and body temperature was recorded during transient temperature changes (Jackson, 1971; Jackson and Kagen, 1976). Respiratory responses to low temperature may not be immediate or the applied temperature range may have been insufficient to detect a frequency decrease at low temperature in P. scripta. Unfortunately, an inconsistent picture emerges from studies on air convection requirements versus temperature when non-chelonian reptiles are considered. In the saurians lguana iguana ald Lacerta sp., air convection requirements increase with cooling, but in Sauromalus this ratio decreases with lower temperatures. In varanids the ratio remains constant between 25 to 35'C (Fig. 8). In ophidians air convection requirements change little with temperatures between 20 and 30'C, but tend to decrease at higher temperatures (trig. 8). Consistency and better agreement with the relative alkalinity concept would probably result from experiments including: l) a wide range of temperature consistent with the ecology of the reptiles, 2) measurements of the time courses of respiratory and other regulatory responses to temperature, 3) measurements of plasma bicarbonate ion concentrations and pH along with air convection requirements. The feeding status of a reptile can influence both pH (Coulson and Hernandez, 1964) and end-tidal P"o. (Glass et a1., in press). This largely neglected aspect of reptilian physiology may also aicount some inconsistency. Moreover, specialized modesfor of

1tolll;

sGiordano and Jackson (1973); 6Nielsen

iflorl; tB.;;;t

life will influence respiratory responses to temperature and can cause deviations from otherwise common rules. In the aquatic snake Ac'rochordu,s .jauanicus air convection requirements were nearly the same at 20 and 30 'C (Fig. 8). In this snake ventilation is primarily adjusted to meet oxygen demands, as a large fraction of the COr-elimination takes place through the

skin (Standaert and Johansen, 1974; Glass and Johansen, 1976). In the lizard Varanus exanthematicus, arterial pH did not change between 25 and 35'C and the Vnl Vo.-ratio was virtually temperature indepen-

dent (Wood et al., l9ll, Fig. 8). Varanid lizards are unusual among reptiles in being " mammal-like " in

Johansen, many and 1974; leatures Wood et(Bennett, al., 1971;1973; press). GlassMillard et al., in The temperature effects on end-tidal P1r, in T. ornota are similar to changes of ventricular Po, in P. scripta (Frankel et al., 1966) although the ventricular P6. values are generally lower. Whereas ventricular P6e, in P. scripta increased with temperatures from 5 to 35'C, the end-tidal P"o, of T. ornata did not increase until body temperature exceeded 15 oC. Decrease of the pulmonary-gas-exchange ratio (Rs) with low temperature reflects the nature of cutaneous respiration. As early as 1904 Krogh pointed out that extrapulmonary gas exchange tends to be constant in spite ol large variations in total gas exchange. Consequently, if total exchange decreases, the extrapul-

exchange monary more imporrelativelylowers will become tant (Table l). Cutaneous respiration blood

 

M.L. Glass et al.: Respiratory Responses to Temperature in the Box Turtle

P66, and conversely, as stated by Dejours (1915), "the more an animal is a pulmonary breather, the higher is its blood CO, pressure". Therefore, at low temperatures end-tidal Ps6. refiiained low in spite of a low end-tidal Po,. As total gas exchange increases with temperatures from 5 to 15'C, the pulmonarygas-exchange ratio (Ru) approaches the total-gas-exchange ratio (R.totor). At 25 'C, the difference between the total and the pulmonary gas exchange ratios is oC increase 15 greater corresponding togas than at anexchange of the importance of extrapulmonary (Table 1). This may correlate with an increase of endtidal P.o, with increase of temperature from 15 to 25 "C as increased blood P.,r, promotes cutaneous COr-elimination (Crawford and Schultetus, 1910). Cutaneous gas exchange is common in aquatic reptiles, but may also occur in terrestrial species (Standaert and Johansen, 1914). The values measured at oC 15 and 25 for T. ornata are rather high. Experimental error may have given an overestimate of cutaneous COr-elimination. It is nevertheless certain that cutaneous COr-elimination is very important in preventing high blood P.,r. in T. ornata at iow temperatures.

The respiratory dead space volume (V") of

thana 2.04+0.4 lowerthan t), but islarger ml.kg-t (2.6 ml'kg graeca (SE) in T. ornata for Testudo

Vp of 0.6 ml .kg-1 1976).

In Varanus

in P. scripta (Crawford et a1., exanthematicus V j decreased with

low temperature because a decrease of breathing frequency increased the time available for intrapulmonary diffusion of gases (Wood eI al., 1977). The temperature-independent values for Ve rn T. ornata are probably due to a generally low breathing frequency. L. Glass was supportcd by a lellowship awarded by Thc University ol Aarhus, Denmark. The authors are indebted to Professors Stephen C. Wood and Kjell Johansen for encouragement and support, and to Raymond B. Smith for making the drawing in trig. l. Mogens

References Bennett, A.F.: Ventilation in two species of lizards during rest and activity. Comp. Biochem. Physiol. 46A, 653 671 (\973) Chaffee, R.R.J., Roberts, J.C.: Temperature acclimation in birds and mammals. Ann. Rev. Physiol. 33, 155 202 (1971) Coulson, R.A., Hernandez, T.: Biochemistry of the Alligator: A study of metabolism in slow motion. Baton Rouge: Lor.risiana State Univ. Press 1955

Crar'vford, E.C., Jr., Gatz, R.N., Magnussen, H.. Perry, S.F., Piiper. J.: Lung volumes, pulmonary blood flow and carbon monoxide dilfusing capacity of turtles. J. Comp. Physiol. 107,

169 178 (1976) Crarvford, E,.C., Jr., Schultetus, R.R.: Cutaneous gas exch:rnge in the lizard Saurontalus obesls. Copeia 1910, 179 180 (1970) Dejours, P.: Principles of comparative respiralory physiology. Amsterdam: North-Holland Publishing Company 1975 Dmi'el, R.: E,fflect of activity and temperature on metabolism and .T. Physiol loss in snakes. Am. (1972) water H.M., of temperature J.: Effects516 Frankel, Steinberg, G., Gordon, .223,510

359

on blood

gases, lactate and pyruvate

scripta elegan,s,

in turtles,

Pseudemys

in vivo. Comp. Biochem . Physiol. 19,219

283

( l e66)

Gatten, R.E.: Effects of temperature and activity on aerobic and anaerobic metabolism and heart rate in the twlles Psettdemys scripta and Terrapene ornuto. Comp. Biochem. Physiol. 48A, 619 648 (1974) Giordano, R.V., Jackson, D.C.: The eflect of temperature on \entilation in the green iguana. Comp. Biochem. Physiol. 45, 235 238 (1973) Glass, M.L., Johansen, K.: Control of breathing in Acrochordus jaranicus, and aquatic snake. Physiol. Zool. 49,328 340 (1976) Glass, M.L., Wood, S.C., Johansen, K.: The application of pneumotachography on small unrestrained animals. Comp. Bio-

chem. Physiol. 594,425'427 (1918) Glass, M.L., Wood, S.C., Hoyt, R.W., Johansen, K.: Chemical control of breathing in the lizard, Varanus ex(mthemati(:us. Comp. Biochem. Physiol. (in press) (1979)

Hazel, J.R., Garlick, W.S., Scllner, P.A.: The ellects of :rssay temperature upon the pH optima of enzymes from poikilotherms: A test of the imidazole alphastat hypothesis. .T Con]p. Physiol. 123,9t 104 (1918) Howell, B.J., Rahn, H.: Regulation of acid-base balance in reptiles. In: Biology of the Reptilia, Vol. 5, Physiology A. Gans, e , Dawson, W.R. (eds.), pp. 335 365. London: Academic Press r91 6

Jackson.

D.C.: The effect of temperature on ventilation in

Inrrle, Pseudeml,-s scripta elegun,s.

(le7l)

Resp. Physiol. 12, 131

Jackson, D.C.. Kagen, R.D.: Elfects

the 140

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on gas exchange and acid-base status of turtles. Am. J. Physiol. 230. 1389 1393 (1976) Kinney,.l.S., White, F.N.: Oxidative cost olventil:rtion in a trLrtle, PseLrdemys.floridana. Resp. Physiol. 31,327 332 (1977) Kenney, .T.S., Matsuura, D.T., White, F.: Cardiorespiratory effects of temperature in the turtle. Pseudem,vs florirlana. Resp. Physiol

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