WATER-BATH STUDIES ON FIELD AND CAPTIVE CITELLUS LATERALIS

7/29/2019 WATER-BATH STUDIES ON FIELD AND CAPTIVE CITELLUS LATERALIS

1/5

t;,1;,f,il"tilj+[i3:ffi ff ;:.ff ,""_.WATERBATH STUDItrS ON FIELD ANDCAPTIVB CITtrLLUS LATERALIS1

J. J. YOUNG AND M. L. RIEDESELDepartment of Biology, University of New Mexico, Albuquerque

INTRODUCTIONATERBATTT experiments wereconducted under field and lab-oratory conditions to inves-tigate the extent to which physiologicalfactors are involved in acclimatizationof field animals to laboratory animalquarters. The waterbath technique pro-vides a uniform surface temperature thatfacilitates quantitative measurement ofthe capacity of an animal to limit theflow of heat from the site of production,or core, to body surface. The tolerance ofCitellus lateral'is to immersion in coldwater has been demonstrated to be pri-marily determined by the extent ofperipheral vasoconstriction and meta-bolic heat production (Yelverton, 1964).The lack of acclimatization followingwaterbath exposures and other advan-tages of this technique have been report-ed by Adolph and Richmond (1956).Acclimatization or preconditioning of

animals very often is the most importantfactor in determining the tolerance ofanimals to environmental stress. Prepa-ration of animals for hibernation repre-sents an extreme example of acclimatiza-tion as hibernation involves changes inessentially all physiological processes(Lyman and Chatfield, 1955). Definitionof mechanisms involved in acclimatiza-tion of mammalian hibernators wouldfacilitate understanding hibernation aswell as acclimatization. However, thel Work supported by National Science Founda-tion grant GB2l6.

importance and characteristics of accli-matization in mammalian hibernatorsare ill defined (Mayer, 1953; Deane andLyman, 1954).MATERIAL AND METHODS

The experimentai animals were golden-mantled ground squirrel s, Citellus lateralis(Say). Collections were made in a 12-sq-mile area, 10 miles east of Cuba onRoute 126, Rio Arriba County, NewMexico, at 8,300-ft elevation. Four col-lecting trips were made to the abovearea between June 28 and JuIy 31,1964.The term "field condition" refers to thedata collected from animals 15 min aftercapture; the term "captive" refers to thesame animals captive 14-62 days. Ineach series of experiments animals werefirst exposed to a given waterbath tem-perature in the field. Animals wereweighed to the nearest gram, and rectalprobe inserted to 6-cm depth prior toimmersion in water for 30 min. Thewaterbath chamber had inside dimen-sions of 32 X 32 X 26 cm and wasplaced in a 25-gal tank of water to facil-itate maintenance of the specified water-bath temperature. After completion ofthe field experiments, the animals wereplaced in individual wire cages withwater and food availablc, and transport-ed within 48 hr to the air-conditionedlaboratory, 24 + 3 C. Later, each animalwas exposed to the same procedure inthe laboratory. Each series is describedas follows: Series I: four animals exposed

189


2/5

J. J, YOUNG ANDmin, 14 days and 48 days after capture25 C water; Series II: five animals15 min, 21 days and 62 dayscapture to 25 C water; Series III:animals exposed 15 min, 14 days anddays after capture to 33 C water;IV: six animals exposed 15 min

28 days after capture to 35 C water.waterbath exposures were of 30-minRecordings of the rectal, water, andtemperatures were made at 2-minfor the first 10 min and at 10-intervals for the next 20 min withtelethermometer, + 0.1 C. During theanimals were confined in af-inch mesh wire. Suspending thefrom a tripod provided constantof immersion, water level approxi-

0.5 cm below the ears.The term "body-heat loss" refers tochange in the heat content, or storedof the animal during the time in-calculated as describedBurton and Edholm (1955). Theheat loss includes the metabolicplus the body-heat loss.The mean metabolic rate of C. lateralisconfined experiments with waterbathof 25-35 C was 5.3 kcal perwith 1.1 sn (Yelverton, 196+).RESULTSA constant rectal temperature indi-a balance between heat gain andloss and implies the existence ofregulation. During the 30-

waterbath exposures, the body-heatin the "field condition" was greaterthe heat loss of the same animalsthe laboratory.The decrease in rectal temperaturethe principal criterion for interpret-the capacity of the animals to toleratecold water. In all exposures, field andthe greatest decrease of rectal

},T. L. RItrDESELtemperature occurred during the first 10min of immersion in the water. Themean decrease in rectal temperature be-tween the 10th and 20th min of immer-sion was 1.6 C with 1.3 sn. The meandecrease in rectal temperature betweenthe 20th and 30th min of immersion was0.3 C with 0.4 sn.The mean decreases in rectal tempera-ture observed during the 30-min expo-sures are given in Figure 1. In Series I(25 C water) the decreases in rectaltemperature of field and 14-day captiveanimals were similar, P ) .3 (Fig. 1).However, the 48-day captive animalslost less heat (p < .001). In Series II(25 C water) the decrease in rectal tem-perature of.2I- and 62-day captive ani-mals was less than recorded for fieldanimals (2 < .OOt). The rectal tempera-ture data on 48- and 62-daY caPtiveanimals were similar (2 > .10). In SeriesIII (33 C water) the 14- and 50-daycaptive animals were able to maintainbody temperatures higher than field ani-mals (2 < .05). In Series IV, the 35 Cwater represented a cold stress for fieldanimals, 1.6 C decrease in rectal temper-ature, whereas 28-day captive animalshad a mean decrease in rectal tempera-ture of 0.6 C (p < .01).The animals consistently gained weightduring captivity; however, the correla-tion between body weight and decreasein rectal temperature was poor, - '377correlation coefficient. Most of the weightdifferences between test groups can be ac-counted for by the rapid gain in weightof young adults, 140-160 g, in the labo-ratory. The effect of the body weight onthe amount of heat lost by animals inthe waterbath was minor, for instancelin the field, the rectal temperature of a151-9 animal decreased I2.5 C during30-min immersion, and the rectal tem-perature of a 210-9 animal decreased


3/5

WATERBATH STUDIES t9113.0 C under the same conditions. Atr-though some field animais weighed morethan captive animals, the drop in rectaltemperature of fie1d animais was alr,vaysgreater than the acclimated captive ani-mals.

The rectal-temperature measurementsprior to each waterbath exposure demon-strate the range of rectal temperature offield animals to be greater than captiveanimais (Table 1).Shivering was never observed in fietd

0 t448

or 14-day captive anirnals, but vigorousshivering occurred in 25 and 33 C waterby animals captive 2l days or longer.DISCUSSION

The data inCicate limited body-tem-perature regulation by Citellus lateraliscollected during summer months. Iliber-nation and the accompanying loweringof body ternperature and conservationof body stores of energy are recognizedto be important facets of mammalian

o r4bo o zB

e16^. 14=E t2r*t'oo8


4/5

Daysafter

J. J. yOU\TG ANDIn contrast, nurnerous labo-experiments have demonstratedcapacity of mammalian hibernatorshave homeothermic temperature regu-in various environments (Kayser,Suomalainen, 196+). The water-

experiments clearly demonstrateof body temperature of field ani-in contrast to homeothermic tem-regulation by animals main-a neutral thermal environment.

TABLE 1TEMPERATURE op "CtTBLLus LATERA-Lrs" MEASURED pRIoR To WATER-

M. L. RIEDBSELnamely, hypothermia in response to coldenvironments and homeothermia duringmoderate conditions, facilitate conserva-tion of energy and a high rate of activityduring the short summer period availablefor growth and reproduction.

IJnder given conditions, a hetero-thermic hibernator may bc more capableof maintaining a higher core temperaturethan a non-hibernator. Earlier studieshave demonstrated C. spilosoma, a hiber-nator, maintained a higher rectal tem-perature than C.lewcuyis and Dipod,ontysord;i, non-hibernators (Yelverton, 196+) .Apparently, acclimatization and precon-ditioning are as important in defininglimits of temperature regulation as thegenetic characteristics. Kayser in a dis-cussion of awake hibernators duringsummer (Mayer and Van Gelder, 1965)points out that these animals havechemical thermoregulation (heat produc-tion), but their physical thermoregula-tion (heat-Ioss regulation) is insufficient.The responses to acute cold stress, 25 Cwater, suggest that both chemical andphysical thermoregulation are very lim-ited in field animals.Future studies should define the ex-tent of environmental stress which isnecessary to produce homeothermic orheterothermic temperature regulation.Acclimatization or changes in thermo-regulation in response to cold stress mustbe a key factor in preparation for hiber-nation.

SUMMARY1. Acclimation of Citellus lateralisto air-conditioned animal quarters in-volves improved homeothermic tempera-ture regulation as evidenced by a smallerdrop in rectal temperature when im-mersed in 25 or 33 C water.2. Apparently a minimum of 15-21days is required for acclimation and de-velopment of homeothermic temperatureregulation.

Mean Range Differ-ences inExtremes

.....

1141017t488

39.939.438.539. 138.637 .7

37 .6-42.838.2-40.437 .3-s9.638 . 0-40.436 .7-39 .536.7-39 .2

2.22.3a,2.82.5

of pre-experimental environ-conditions should be recognizedfuture studies regarding the body-capacity of mam-species.The lack of homeothermic tempera-regulation in field animals has beenby observation of the wideof rectal temperature (Muilally,Assuming a Qrc ol 2, a 5 C dropbody temperature represents a 50/sin energy expenditure. Theof shivering and apparent in-to limit heat loss by vasocon-in 25 and 33 C water confirmexistence of labile body-temperaturein field conditions. On thehand, during periods of moderatetemperature (21-27 C)animals have homeothermic tempera-

regulation which facilitates maxi-activity. The temperature-regula-characteristics of the mammalianduring summer months,

BATH EXPERIMENTS


5/5

Young, J. J. aad lI. L. Riedesel. L967.Waterbath studles sn field and captiveFhysiological 4_qqlpsy 40: 189-193

3. Ar:elirnntcd animals shivercd during30-min immcrsir:n in 25 anrl 3.j C rvatcr,whereas shivering rvas not observed inficltl animals.

C{tel"1us Latetal"J"s,

\\'ATERBAT'}I ST LIDIES

I,ITER]ITURE CITSD

4. Acclimatization tp therm:rl environ-ment appcars to be an important aspcctin determining the response of mam-malian hibernatnrs to ncute cokl stress"

193

Arcr.Fu, Il, F., ancl J. Rrcuaraxn. 19.56. lltlaptationto cold in golden h*nrsler and ground squirrelrneasured chietly lry rrtes ol body cooling, J.r\ppl. Physiol. e:53-58.BurmN, A, C., anel O. G, E$Eor*e, 1955, Man in ae*ld environment. Edtvar

Documents

WATER-BATH STUDIES ON FIELD AND CAPTIVE CITELLUS LATERALIS