Energy metabolism and thermoregulation in Chinchilla brevicaudata

Journal of Thermal Biology 28 (2003) 489–495

Energy metabolism and thermoregulation inChinchilla brevicaudata

Arturo Cort!esa,*, Carlos Tiradoa, Mario Rosenmannb

aDepartamento de Biolog!ıa, Facultad de Ciencias, Universidad de La Serena, Casilla 599, La Serena, ChilebDepartamento de Ciencias Ecol !ogicas, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile

Received 6 November 2002; accepted 6 June 2003

Abstract

Chinchilla brevicaudata lives at 3500–5000m, with high ambient temperatures during the day but cold at night. In this

Andean habitat there is also low availability of food and water resources. Physiological attributes that may minimize

their energetic cost as well as the water requirements are: (1) Low values of basal metabolic rate (67.2%) and thermal

conductance (51.0%) compared to predicted values. (2) The aerobic metabolic expansivity was 5.1, while the calculated

theoretical critical lethal temperature was extremely low (�67.8�C). (3) The energetic cost for maintenance of waterbalance was 85.3% of the predicted value for xeric rodents of similar size.

r 2003 Elsevier Ltd. All rights reserved.

Keywords: Chinchilla brevicaudata; Basal metabolism; Maximum metabolism; Thermal conductance; Evaporative water loss

1. Introduction

In xeric environments, the ambient temperature (Ta),

the photoperiod and the availability of food and water

are the main variables that present the largest daily and

seasonal variations (Degen, 1997; Kronfeld-Schor et al.,

2000). Consequently, organisms that live in these

environments should be able to maintain homeostatic

conditions, particularly in their water and energy

equilibrium. In mammals, one of the most utilized

energetic parameters is the basal metabolic rate (BMR),

which is the main component of the energy spent under

laboratory as well as in natural conditions (Cruz-Neto

et al., 2001). For some wild mammals BMR may

represent 50% of the daily energy expenditure (Nagy

et al., 1999; Speakman, 2000).

Variations of BMR among homeotherms have been

basically explained by allometric relations of body mass

(Kleiber, 1961). More recently the residual variance of

this correlation has been applied at taxonomic level

(Hayssen and Lacy, 1985) or in relation to food habits

(McNab, 1986), ambient temperature (MacMillen and

Garland, 1989), and habitat (McNab and Morrison,

1963; Hulbert and Dawson, 1974; Shkolnik and

Schmidt-Nielsen, 1976; Lovegrove, 1986; Lovegrove

et al., 1991).

In nature most homeotherms keep their body tem-

perature (Tb) within certain limits. This condition

depends on some physiological characteristics, such as

the metabolic rate (MR) and thermal conductance (C).

McNab (1979) found that granivorous rodents from xeric

habitats have low BMR, avoiding risks of hyperthermia

and maintaining their water economy by minimizing

evaporative water loss (EWL). This last feature has been

greatly neglected in studies in South American mesic and

xeric rodents, in spite of the fact that EWL plays an

important role in thermoregulation and water balance

(Degen, 1997). A few exceptions are the observations in

some Chilean rodents (Rosenmann, 1977; Cort!es, 1985;

Cort!es et al., 1988, 1990, 2000a, b; Bozinovic et al., 1995).

In rodents, the metabolic water production (MWP)

and the EWL are utilized to evaluate the efficiency

ARTICLE IN PRESS

*Corresponding author.

E-mail addresses: [email protected] (A. Cort!es), mrosen-

[email protected] (M. Rosenmann).

0306-4565/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0306-4565(03)00049-4

of water regulation by means of the relation

Ta@MWP=EWL (MacMillen and Hinds, 1983), where

Ta@ is the ambient temperature when MWP/EWL=1.

If temperature and humidity are kept constant this index

is not affected by the animal’s activity (Raab and

Schmidt-Nielsen, 1972). The efficiency of water regula-

tion has also been expressed considering the energetic

cost of maintenance of water balance (MR-WB), taking

the value of Ta@ that permits the calculation MR-WB

from the relation between MR and the species-specific

ambient temperature (Cort!es et al., 2000b). Further-

more, the value of MR-WB permits the regulatory

efficiency between mesic and xeric rodents to be

determined (Cort!es et al., 2000b).

Chinchilla brevicaudata (Waterhouse, 1848) is an hystri-

comorphic nocturnal rodent dwelling between 3500 to

5000m above sea level in the Andes Range (Munoz and

Y!anez, 2000). Due to the special quality of the fur, the

species was intensively hunted and a great part of the

Chilean populations was extinguished or significantly

diminished (Jim!enez, 1996). Currently its distribution is

restricted to Southern Per!u, Northeast Argentina and to

the (I–III Regi!on) of Northern Chile (Redford and

Einsenberg, 1989). Conservation problems have been

noted and it has been considered in critical danger in

Argentina (Garc!ıa et al., 1997) and in risk of extinction in

Chile (Glade, 1993; SAG, 2000). Ecophysiological studies

in C. brevicaudata are few, but some ecological and

conservation aspects have been reported (Jim!enez, 1996).

The combined effects of physiological, morphological,

behavioral and ecological attributes allow desert

rodents to minimize the energetic costs and assure their

survival in these harsh environments (Bozinovic and

Contreras, 1990; Prakash, 2001). Because of the extreme

climatic conditions of the Andean range, we hypothe-

sized that C. brevicaudata would present most, if not all

of these features. To test this idea we measured oxygen

consumption in normal air and under He–O2 (80–20%)

atmosphere. EWL and body temperature (Tb) were also

measured at different ambient temperatures (Ta). In

addition, two indices Ta@ (MWP=EWL), that repre-

sents the efficiency of water regulation, and MR-WB,

representing the energetic cost of maintaining the water

balance, were estimated.

2. Materials and methods

2.1. Experimental animals

Five individuals of C. brevicaudata (2##, 3~~) were

captured with National traps in the locality of El Morro

Negro (25�000S; 69�450W) in the National Park Llul-

laillaco (II Regi !on, South East of Antofagasta, Chile),

between 3000 and 5000m of altitude. This area is

characterized by a perarid climate (di Castri and Hajek,

1976), with an annual precipitation of 20–50mm

(Messerli et al., 1993) and a mean annual temperature

of 2�C (Luebert, 1998). At the site of capture we found

scant vegetation, covering less than 9% of the ground

surface. One of us (AC) found the following proportions

of shrubs and herbs: Baccharis tola (0.05%), Adesmia

eranicea (0.08%), Adesmia caespitosa (0.05%), Cristaria

andicola (0.06%), Fabiana bryoides (5.10%) and Stipa

chrysophylla (3.55%). The captured animals were

transported to the laboratory and maintained under

natural photoperiod in individual cages, with water and

food (barley and alfalfa) ad libitum. At the laboratory,

ambient temperature was 21.073�C, while relative

humidity averaged 60%.

2.2. Energy metabolism

All oxygen consumption measurements were conducted

individually with a modified automatic closed-system

respirometer, based on the manometric design of Morrison

(1951). Animals were in postabsortive state (2–3h after

feeding). Different ambient temperatures (Ta) were main-

tained within70.1�C in a water–glycol bath in which themetabolic chambers were submerged. Average body mass

of our five experimental animals was 454.4762.5 g. Bodytemperature (Tb) was recorded before and after each

ARTICLE IN PRESS

Nomenclature

BMR basal metabolic rate (ml O2/g h)

C thermal conductance (ml O2/g h�C)

CHe thermal conductance in He–O2 atmosphere

(ml O2/g h�C)

EWL evaporative water loss (mg H2O/g h)

mb body mass (g)

MR metabolic rate (ml O2 /g h)

MMR maximum metabolic rate (ml O2/g h)

MWP metabolic water production (mg H2O/g h)

Ta ambient temperature (�C)

Ta@ ambient temperature (�C), when MWP/

EWL=1

Tb body temperature (�C)

Tic calculated theoretical lower critical tempera-

ture (�C)

TLL calculated theoretical lower lethal temperature

(�C)

MR-WB energetic cost of maintaining the water balance

(cal/g h)

DTm minimum thermal differential between Tb and

Tic (�C)

A. Cort!es et al. / Journal of Thermal Biology 28 (2003) 489–495490

metabolic run with a Cole Parmer, Model 8500-40 copper-

constant thermocouple. O2 consumption was also mea-

sured in 80% He–20% O2 atmosphere, which has been

used to obtain the maximum metabolic rate of thermo-

regulation (MMR) (Rosenmann and Morrison, 1974;

Holloway and Geiser, 2001). For this purpose we used a

Ta range of 5�C to �7.5�C (Bozinovic and Rosenmann,

1989). Metabolic values were determined from the average

of the three minimum periods of 3–5min of each

experimental trial which lasted 1–3h (Rosenmann and

Morrison, 1974). BMR was similarly estimated from the

lowest three MR values when independence of Ta was

determined. Thermal conductance (C) was calculated from

the slope of the regression (MR vs. Ta), below thermo-

neutrality. The lower critical temperature (Tic) was inferred

by the intersection of C with BMR. Values of BMR, C;and the endothermic limit were compared with the

expected values for mammals of similar size using

the relations: BMR=3.42m�0:25b (Kleiber, 1961) and C ¼

1:0m�0:50b (McNab and Morrison, 1963). The ratio BMR/

C that indicates the minimum thermal differential (DTm),

between Tb and Tic; was also calculated: DTm¼ BMR=C

(�C)=3.42m0:25b ¼ Tb2Tic (McNab, 1979).

2.3. Evaporative water loss

Values of EWL were obtained gravimetrically

(70.1mg) from the average of three minimum 5min

periods during 2–3 h of measurements, following the

method of Hainsworth (1968). EWL trials were con-

ducted at different Ta (5�C, 15�C, 20�C, 25�C, 30�C

and 32.5�C), with an air flow of 5 l/min. All measure-

ments started after 1 h of thermal equilibrium (Cort!es

et al., 1990). Results of minimum EWL were compared

with the expected values for mesic (EWL ¼ 7:272m�0:532b )

and desert rodents (EWL ¼ 5:968m�0:416b ) of similar size

(Cort!es et al., 2000b).

2.4. Efficiency of water regulation

To evaluate the efficiency of water regulation we

utilized two indices: Ta@MWP ¼ EWL (MacMillen

and Hinds, 1983) and MR-WB (Cort!es, 2000b). MWP

was assessed from MR data vs. Ta; assuming that 1mlO2 consumed produce 0.62mg of water (Schmidt-

Nielsen, 1979) and 4.8 cal (Schmidt-Nielsen, 1990). The

magnitude of MR-WB was compared with the expected

values for mesic and xeric rodents, using the relations

MR-WB=34.627m�0:339b and MR-WB=68.132m�0:381

b ;respectively (Cort!es et al., 2000b).

2.5. Statistical analyses

Regression equations were calculated using least-

squares analyses (Steel and Torrie, 1985). Values are

given as means7SD.

3. Results


Linear regression of MR vs. Ta; gave the equationMR=1.022–0.0239Ta (Fig. 1). Extrapolation of MR to

0 gave the theoretical body temperature of 42.8�C,

which is 5.2�C higher than the normothermic Tb(37.6�C). The slope of the curve was 0.0239ml O2/

g h�C, and represents the thermal conductance in

normal air. This value is equivalent to 51.0% of that

expected for its body size (McNab and Morrison, 1963).

DTm was 20.8�C. BMR of C. brevicaudata

(0.49870.068ml O2/g h) is equivalent to 67.2% of that

expected (Kleiber, 1961). The lower critical temperature

(Tic) was 22�C. In a He–O2 atmosphere the relationship

of MR vs. Ta was MR (ml O2/g h)=2.28–0.0544Ta;whilst the thermal conductance (CHe) reached 0.0544ml

O2/g h�C (Fig. 1). When Ta was lowered to �7.5�C in

this artificial atmosphere, MR fell 16.9% with respect to

the MMR of 2.5270.005ml O2/g h, indicating that thethermoregulatory capability was exceeded (Fig. 1).

The aerobic metabolic expansivity, calculated as the

ratio MMR/BMR, was found to be 5.1. This figure gives

an indication of the animal’s thermoregulatory ability

under low temperatures. The relation MMR=C ¼Tb2TLL (Bozinovic and Rosenmann, 1988) gave a

theoretical critical lethal temperature (TLL) for this

species of �67.8�C, close to the value of �65.0�Cobtained by extrapolating MMR (He–O2) on the

regression curve of MR vs. Ta in normal air (Rosen-

mann, 1977; Rosenmann and Morrison, 1974).


Minimum values of EWL were found to be

0.49870.014mg H2O/g h within the Ta range of

ARTICLE IN PRESS

Fig. 1. Relationships between oxygen consumption and ambi-

ent temperature in C. brevicaudata under two different atmo-

spheres (normal air (�) and He–O2 (’)).

A. Cort!es et al. / Journal of Thermal Biology 28 (2003) 489–495 491

p20�C (Fig. 2), while the averages of EWL at 25�C,

30�C and 32.5�C were 0.604, 0.820 and 1.105mg H2O/

g h, representing increases of 20%, 65% and 120%,

respectively, over the minimum. At the highest experi-

mental temperature EWL was equivalent to only 24.6%

of the basal rate of heat production (2.39 cal/g h). The

low cooling capability was reflected in a Tb increase of

1.1�C above the normothermic condition (38.7�C vs.

37.6�C) (Fig. 2).


Fig. 3 shows the relation of LogMWP/EWL vs.

Ta; which gave the equation MWP=EWL ¼ 1:705�ð0:951ÞTa : Taking MWP/EWL=1, we obtained a valueof 10.6�C, that represents the efficiency index of

water regulation for C. brevicaudata (see Hinds and

MacMillen, 1985). Replacing Ta ¼ 10:6�C in the regres-sion equation (MR=1.022–0.0239Ta), we obtained a value

of 3.71 cal/gh, that is the energetic cost of maintaining the

water balance (MR-WB) (Cort!es et al., 2000b).

4. Discussion


C. brevicaudata showed an average BMR of

0.49870.068ml O2/g h, which is equivalent to 67.3%of the predicted value for a mammal of similar size

(Kleiber, 1961) and to 34% of the average given for

South American octodontid and murid rodents (Rosen-

mann, 1977; Bozinovic and Rosenmann, 1988; Bozino-

vic, 1992; Bozinovic et al., 1995); but in these

comparisons we should consider that our species is

twice the body size of the largest octodontid measured.

A comparison with a closer species indicated that BMR

in C. brevicaudata reached up to 75% of that reported

for Chinchilla lanigera (Cort!es et al., 2000a). Both

species are herbivorous (Cort!es et al., 2002), and

following the proposition of McNab (1986), their

BMR should be somewhat higher than that expected

for granivorous heteromyids and murids from North

American and Australian deserts (McNab, 1979; Daw-

son, 1955; Carpenter, 1966; MacMillen and Lee, 1970),

and also higher than some murids from Asian deserts

(Shkolink and Borut, 1969). Our data did not confirm

McNab’s proposition. Here BMR values were similar to

those reported for the other groups of desert rodents.

The fact that some species may possess a lower than

expected BMR is favorable for the maintenance of

energy and water balance, especially for those species

inhabiting arid environments with extreme climatic

conditions as found in the highlands of Northern Chile

ARTICLE IN PRESS

Ambient Temperature (ºC )

0 5 10 15 20 25 30 35

Eva

pora

tive

Wat

er L

oss

(mg/

g h )

0.0

0.5

1.0

1.5

2.0

Bod

y T

empe

ratu

re (

ºC)

37

38

39

40

Eva

pora

tive

Hea

t L

oss

(% o

f he

at p

rodu

ctio

n)

0

10

20

30

40

Normothermic37.6 + 0.28ºC.

Fig. 2. Relationships between evaporative water loss, evapora-

tive heat loss, body temperature and ambient temperature in

C. brevicaudata.

Ambient Temperature (ºC)

0 5 10 15 20 25

MW

P/E

WL

0.4

0.6

0.8

1

1.2

1.4

MWP/EWL = 1.705 (0.951)Ta

r = - 0.88 (P < 0.01)

Ta @ = 10.6ºC

Fig. 3. Relation between MWP/EWL and ambient temperature

in C. brevicaudata.

A. Cort!es et al. / Journal of Thermal Biology 28 (2003) 489–495492

where C. brevicaudata dwells. A low thermal conduc-

tance was also found in this species (C ¼ 0:0239ml O2/g h�C), equivalent to half of that predicted for body size

(McNab and Morrison, 1963). In fact, this is the lowest

conductance reported for South American rodents,

including murids, octodontids and chinchillids (Rosen-

mann, 1977; Bozinovic and Rosenmann, 1988; Bozino-

vic, 1992; Bozinovic et al., 1995; Cort!es et al., 2000a).

Both the high thermal insulation as well as the low Ticshould allow this nocturnal species to maintain a normal

Tb at low ambient temperatures. We should note that

the mean annual Ta at the capture site is about 2�C

(Luebert, 1998). The high thermal insulation is also

reflected by a DTm ¼ 22�C. This figure is 16�C and

6.4�C higher than the minimum and maximum DTmvalues reported for cricetids from South America

(Bozinovic and Rosenmann, 1988), and also higher than

the reported for some North American heteromyids

(Hinds and MacMillen, 1985). The aerobic metabolic

expansivity, (MMR/BMR) in C. breviaudata, was 5.1,

somewhat lower than the value of 5.8 reported for

C. lanigera (Cort!es et al., 2000a), and is clearly lower

than 8.2, found in the Andean murid Calomys ducilla

(Rosenmann and Morrison, 1974), but is of similar

magnitude to the values reported for Microtus oecono-

mus (5.1), Uromys caudimaculatus (4.7) (Hinds et al.,

1993) and the octodontid Octodon degus (4.9) (Rosen-

mann, 1977).

The critical lethal temperature that was calculated

for C. brevicaudata (TLL ¼ �67:8�C), was similar to theone for C. lanigera (�65.5�C) (Cort!es et al., 2000a), butwas 51.8�C lower than that (TLL¼ �16�C) given forC. ducilla (Rosenmann and Morrison, 1974).


Minimum EWL in our chinchilla was 0.498mg H2O/

g h (Fig. 2). This value is within that expected for xeric

rodents (Cort!es et al., 2000b). It is probable that similar

morphological respiratory nasal adaptations occur as

reported for other xeric and desert rodents (Cort!es et al.,

1990). In any case, the low EWL may have unfavorable

consequences at high temperatures where evaporative

heat loss is important; for example, at Ta ¼ 32:5�C,C. brevicaudata was able to loose by EWL only 14 of the

metabolic heat production, which was reflected by a Tbincrease of 1.1�C. This moderate increase was seen to

affect its normal conditions. Similar responses to

moderate high temperatures have been reported in

O. degus (Rosenmann, 1977) and in C. lanigera

(Cort!es et al., 2000a). The low EWL of the chinchilla

may appear unfavorable at high temperatures, but this

physiological response is valuable for the maintenance

of body water, considering that this species inhabits

highly xeric environments where the only water source

may be found in the few plants that are normally

consumed (e.g., S. chrysophylla, A. eranicea, F. bryoides,

C. andicola and B. tola). In the same context, it is quite

likely that the high ambient temperatures occurring

around noon may not have significant consequences on

the animal’s thermoregulation, because of the nocturnal

habits described in this chinchilla (Munoz and Y!anez,

2000). Moreover, one of us (AC) found during several

summer days a relatively stable Ta range of 20–25�C

inside the dens or shelters, which are build under or

between large (2–3m) rocks.


A Ta@ of 10.6�C was calculated for C. brevicaudata

(Fig. 3). This value may indicate a slightly lower

efficiency compared with other Chilean rodents from

mesic and xeric habits: Abrothrixs olivaceus (18.6�C), A.

andinus (12.5�C), Phyllotis darwini (14�C), P. magister

(10.5�C), P. rupestris (12.1�C), Oligoryzomys longicau-

datus (12.1�C), C. lanigera (12.7�C) and O. degus

(16.6�C) (Cort!es et al., 2000b). Nevertheless, the

energetic cost of maintaining the water balance, MR-

WB=3.71 cal/g h, was similar or lower than the values

reported for the other rodent species. In fact, the

energetic cost in our studied chinchilla is the lowest so

far described, being only 82% of the predicted value

(Cort!es et al., 2000b). Because of the extreme environ-

mental conditions endured by C. brevicaudata (low

availability of food and water), we found that this

physiological feature was not surprising.

Acknowledgements

We thank the Corporaci !on Nacional Forestal (CON-

AF, II Regi !on, Chile) for logistic assistance, mainly to

the wildlife keepers Rodrigo Araya and Alfonso Tapia

(Parque Nacional Llullaillaco). We also thank Dr. Jaime

Jim!enez (Universidad de Los Lagos) for his valuable

collaboration in the field. This work was financed by the

projects FONDECYT 5960017, Programa Sectorial

Biomas y Climas del Norte de Chile, Comisi !on Nacional

de Investigaci !on Cient!ıfica y Tecnol !ogica de Chile

(CONICYT), and Project FONDECYT 1981122.

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Energy metabolism and thermoregulation in Chinchilla brevicaudata

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