[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

FW: 6th International Congress of Comparative Physiology and Biochemistry (long)

Forwarded to the list from a "chronic archives-lurker".

(note: downloaded from online version of the journal Comparative
Biochemistry and Physiology, vol. 134 supplement 1 [Feb 2003] via
Science Direct)

Sixth International Congress of Comparative
Physiology and Biochemistry

Program and Abstracts, Mt. Buller, Australia, 2?7 February 2002

23. Paleophysiology

23.1. Respiration and reproduction in theropod dinosaurs

1Ruben, J., and 2Jones, T.D.

1Zoology Department, Oregon State University, Corvallis, OR 97331-2914,
USA; 2Department of Biology, Stephen F. Austin
State University, Nacadoches, TX 75962, USA


In theropod dinosaurs, narrow nasal passages and extensive accessory
rostral sinuses are inconsistent with the presence of
respiratory turbinates, structures which are causally-linked to high
lung ventilation rates in all nostril-breathing birds and
mammals. Thus, although dinosaurs were almost surely homeothermic, the
absence of nasal respiratory turbinates in theropods
indicates that they were likely to have maintained reptile-like
(ectothermic) metabolic rates during periods of rest or routine
activity. Nevertheless, the likely utilization of diaphragm breathing in

these dinosaurs also suggests that they might have had
exercise-related aerobic capacities that exceeded those of extant

In spite of occasional inferences to the contrary, clutch incubation by
dinosaurs was likely to have been more reptile- than
bird-like. This is based on persistent in vivo nest-burial and apparent
lack of egg turning in these animals. Similarly, conventional
wisdom notwithstanding that there is little, if any, reliable data
consistent with some dinosaur young having been helpless and
nestbound (altricial) at hatching. There is no credible evidence that
dinosaur reproduction differed markedly from that of extant

23.2. The evolution of pelvic aspiration in archosaurs

Farmer, C.G., and Carrier, D.R.

Department of Biology, University of Utah, 257 South 1400 East, Salt
Lake City, UT 84112, USA


Ventilatory mechanics of recent crocodilians are highly derived in that
a ventral rotation of the pubis about a movable joint (the
pubic-ischial symphysis) occurs during inspiration; the pubis rotates
dorsally during exhalation. The inspiratory movement is
correlated with electrical activity in two pelvic muscles, the
ischiopubis and ischiotruncus. During expiration contraction of the
rectus abdominis and transversus abdominis rotates the pubes dorsally.
Birds also use dorso-ventral movements of the pelvis to
facilitate ventilation. Based on the evidence that the two extant groups

of archosaurs use the pelvis for ventilation, and that
numerous features of the pelvic girdle and abdominal region of extinct
archosaurs are not readily explained by clear locomotor
functions (e.g. the extremely elongated pubis of many theropods,
elaborate cuirassal baskets) we suggest that pelvic aspiration is
plesiomorphic for archosaurs. Pelvic aspiration appears to facilitate
lung ventilation during vigorous locomotion in crocodilians.
We suspect that it may also have allowed breathing during vigorous
locomotion in extinct archosaurs such as pterosaurs, and
theropod and ornithischian dinosaurs.

23.3. Theropod agility?

Carrier, D.R.

Department of Biology, University of Utah, 201 South Biology Building,
Salt Lake City, UT 84112, USA


Contrary to recent media depictions, the agility of theropod dinosaurs
may have been severely limited by the large rotational
inertia of their horizontal trunks and tails. Bodies with mass
distributed far from the axis of rotation have much greater rotational
inertia than bodies with the same mass distributed close to the axis of
rotation. In this study, we increased the rotational inertia
about the vertical axis of human subjects by 9.2-fold, to match our
estimate for theropods the size of humans, and measured the
subjects' ability to turn. To determine the effect of the increased
rotational inertia on maximum turning capability, five subjects
jumped vertically while attempting to rotate as many degrees as possible

about their vertical axis. This test resulted in a decrease
in the average angle turned to 20% of the control value. We also tested
the ability of nine subjects to run as rapidly as possible
through a tight slalom course of six 90° turns. When the subjects ran
with a 9.2-fold greater rotational inertia, the average
velocity through the course decreased to 77% of the control velocity.
When the subjects ran the same course but were
constrained as to where they placed their feet, the average velocity
through the course decreased to 65% of the control velocity.
These results are consistent with the hypothesis that rotational inertia

may have limited the turning performance of theropods.
They also indicate that the effect of rotational inertia on turning
performance is dependent on the type of turning behavior.
Characters such as retroverted pubes, reduced tail length, decreased
body size, pneumatic vertebrae, and absence of teeth
reduced rotational inertia in derived theropods, and therefore probably
improved their turning agility. To reduce rotational
inertia, theropods may have run with an arched back and tail, an
S-curved neck, and forelimbs held backwards against the

23.4. Paleontological fallacies: the pitfalls of not knowing how animals


1Hicks, J.W., and 2Jones, D.R.

1Department of Ecology and Evolutionary Biology, University of
California, Irvine, Irvine, CA, USA; 2Department of Zoology,
University of British Columbia, Vancouver, Canada V6T 1Z4


Over 30 years ago, the image of the dinosaur changed dramatically, from
sluggish, reptilian behemoths to `fast, agile, energetic
creatures' powered by an endothermic metabolism. The `dinosaur
renaissance' immediately became controversial, and evidence
for and against endothermy in dinosaurs continues to be `hotly' debated.

For comparative physiologists looking from outside the
debate, the intensity of the controversy seems, at times, out of all
proportion to the actual question. Clearly, hypotheses
concerning the metabolic status of a living vertebrate would hardly be
debatable given our ability to directly measure both body
temperature and metabolism in the face of changes in environmental
temperature. However, for the paleontologist, the metabolic
status of dinosaurs must be inferred from the evidence left behind in
the fossil record and through comparisons of this evidence
with the anatomy and physiology of living animals. Interpretations of
fossil evidence can have alternative explanations and be
experimentally untestable, consequently leaving the animal physiologist
`cold' and generally uninterested in participating in the
ongoing debate. The recent report of the discovery of a fossilized
`four-chambered, single aorta' dinosaur heart using
computerized tomography (CT) scans of the chest region of a previously
discovered ornithischian dinosaur, Thescelosaurus has
received enormous attention in the non-scientific media. Several
paleontologists, including the authors, have trumpeted the
finding as providing cardiovascular evidence for intermediate and
perhaps high metabolic rates. The basic argument is that an
avian or mammalian heart design is the only one capable of ensuring
separation of oxygenated and de-oxygenated blood while
at the same time generating high enough blood pressures to ensure
adequate blood flow to metabolizing tissues. In our view, the
major flaw of the report in Science is the failure to interpret or
speculate about structure/function relationships of
Thescelosaurus within the context of current physiological information
on reptiles. The notion that reptiles are both behaviorally
and metabolically sluggish as a result of their `inefficient' heart and
circulations is antiquated and a product of paleontological

23.5. A case for endothermic ancestors of crocodiles at the stem of
archosaur evolution

Seymour, R.S.

Department of Environmental Biology, University of Adelaide, Adelaide
5005, SA, Australia


In living endotherms, there is a functional nexus between high rates of
metabolism, high systemic blood flow rates, and high
systemic (but low pulmonary) blood pressures produced by thick-walled,
four-chambered hearts. The hearts of crocodiles are
equivocal: they are four-chambered, but are relatively small and feature

low blood pressure and a capacity for right-to-left
shunting. Recent crocodiles are definitely ectotherms, but there is
paleontological, embryological, anatomical and physiological
evidence that their ancestors may have been highly active, endothermic
predators. By invading an aquatic, ambush predator
niche, one descendent line may have become ill-suited for endothermy and

reverted to ectothermy, which may have prevented
their extinction at the end of the Mesozoic. Endothermy in stem
archosaurs has implications for the metabolic status of both
saurischian and ornithischian dinosaurs.

2. Evolution and advantages of endothermy

2.1. The age of endothermy??evidence from fossils

Hillenius, W.J.

Department of Biology, College of Charleston, 66 George Street,
Charleston, SC 29424, USA


Endothermy is one of the major achievements of vertebrates. Providing
both endurance and thermal independence, endothermy
is largely responsible for the present success of mammals and birds in
aquatic, aerial, and terrestrial environments. Traditionally,
however, this physiological attribute has been very difficult to
demonstrate in fossils: it results from an aggregate of `soft
anatomy' features that leave a poor, and usually non-existent, fossil
record. Consequently, the origin of endothermy among the
ancestors of mammals and birds has long remained obscure. Recent studies

identify two approaches that provide some insight
into the metabolic physiology of extinct forms. The first addresses
chronic (resting) metabolic rates, and emphasizes the
presence of respiratory turbinates in virtually all extant endotherms.
These convoluted projections in the nasal cavity are
associated with recovery of respiratory heat and moisture in animals
with high resting metabolic rates. The fossil record of
non-mammalian synapsids suggests that at least two Late Permian lineages

possessed incipient respiratory turbinates. In
contrast, examination of non-avian dinosaurs has so far failed to
uncover evidence of respiratory turbinates, and nasal
morphology suggests that these structures were probably absent in
non-avian dinosaurs and the earliest birds. The second
approach addresses the capacity for maximal aerobic capacity, and
examines lung structure and the mechanisms of lung
ventilation. There is no credible evidence to support the reconstruction

of a derived, avian-like parabronchial lung/air sac system
in dinosaurs. Dinosaur lungs were most likely heterogeneous,
multicameral septate lungs with conventional tidal ventilation,
although evidence from some theropods suggest that at least this group
may have had a hepatic piston mechanism of
supplementary lung ventilation. This suggests that dinosaurs generally
lacked the capacity for high, avian-like levels of sustained
activity, although the aerobic capacity of theropods may have exceeded
that of extant ectotherms. The avian parabronchial
lung/airsac system appears to be an attribute of ornithurine birds.

2.2. Evolution and consequences of endothermy in fishes

Dickson, K.A.

Department of Biological Science, California State University Fullerton,

800 N State College Blvd., Fullerton, CA, 92834,


Regional endothermy (the ability to conserve metabolically derived heat
to maintain the temperature of certain tissues elevated
above ambient temperature) has evolved independently among several fish
lineages, including lamnid sharks, billfishes, and
tunas. All are large, active, pelagic species that undertake
long-distance migrations and move vertically within the water column,
thus encountering a range of water temperatures. Based on phylogenetic
comparisons between the endothermic tunas and their
ectothermic sister taxa (bonitos and mackerels) and fossil evidence, an
evolutionary sequence of character state changes that
have resulted in endothermy has been proposed to have occurred in
response to changing oceanographic conditions. Among
scombrid fishes, only the tunas possess internalized aerobic locomotor
muscle, which is perfused by vascular counter-current
heat exchangers, and an elevated standard metabolic rate, and some tuna
species can elevate the temperature of the eye and
brain and the viscera. These specializations have also evolved in the
lamnid sharks by convergence. The hypothesized
advantages of endothermy in fishes include niche expansion and elevation

of tissue metabolic rates to increase tissue aerobic
capacity, the rate of lactate processing, and growth rates. In addition,

maintaining visual acuity in cool water, increasing the rates
of digestion and assimilation of food, and increasing muscle contraction

rates to increase swimming performance are the
hypothesized benefits of maintaining elevated temperatures in the eye
and brain, viscera, and locomotor muscle, respectively.
However, a consequence of endothermy in tunas may be a higher SMR and a
higher cost of transport, even though these fishes
need only conserve the heat generated by continuous swimming to elevate
locomotor muscle temperature and retain the heat
associated with digestion to elevate visceral temperature. Thus, the
benefits of endothermy in fishes may be offset by significant
energetic costs.

2.3. The evolution of models of evolution of endothermy in birds and

Koteja, P.

Institute of Environmental Biology, Jagiellonian University, ul.
Ingardena 6, 30-060 Kraków, Poland


Warm-blooded animals, mammals and birds, are unique not because they are

endothermic in the strict sense of the term, i.e.
thermoregulate by generating metabolic heat, but because they employ an
extravagant economy: they have high energy budgets
and spend most of their energy resources on basic maintenance. Although
the advantages of endothermy are easy to indicate,
mechanisms behind evolution of such a wasteful life strategy remain
unclear. For two decades the `aerobic capacity model' has
been recognized as the most promising hypothesis. The breakthrough idea
was that high rates of heat production evolved not in
a response to direct selection for maintaining high or constant body
temperature, but as a side-effect of selection for perpetual
locomotor activity. The concept catalyzed a new direction in ecological
and evolutionary physiology-studying correlated
evolution of behavioral and morpho-physiological traits. Recently, two
alternative models have been proposed, both of which
see evolution of high metabolic rates in birds and mammals as an element

in evolution of intensive parental care. According to
the models, the cost of elevated metabolic rate of adults is paid back
as an increased growth rate, better survival, and better
quality of their offspring. Unlike previous models, which treated
individuals as static objects of fixed properties, the new
hypotheses explicitly incorporate life histories into
evolutionary?physiology research program. Forty years ago one would ask
`what were the climatic conditions that favored an internally maintained

homeothermy?'; 20 years ago the question became
`what were the properties of potential predators and prey that favored
intensive locomotor activity?'; today, we have to ask
`what was the population structure and age-related mortality pattern
that favored K-type life history strategy?'. Unfortunately,
an answer to the last question is the most difficult one to verify
against paleontological data. Assumptions and predictions of the
new models are compared with those of the aerobic capacity model, and
methodological difficulties associated with testing the
models are discussed.

2.4. Thermal background of mammalian and bird evolution: forces,
trade-offs and constraints
along the ectotherm??endotherm continuum

Pörtner, H.O.

Alfred-Wegener-Institut für Polar- und Meeresforschung, Ökophysiologie,
D-27515 Bremerhaven, Germany


Current concern about climate change and its effect on marine and
terrestrial ecosystems has brought into focus the mechanisms
by which environmental temperature and its oscillations shape
biogeography. At the same time, such information would help to
understand how climate oscillations in earth history may have influenced

the ways and directions of evolution. The physiological
mechanisms need to be identified that have shaped the
temperature-dependent success or failure of animals from a bio-energetic

point of view. The comparison of extant, water and air breathing animal
species from various climates provides a cause and
effect understanding of how body temperature, animal performance and
cellular design are interrelated. Most importantly, the
setting of mitochondrial densities and their energetic capacities,
together with the adjustment of membrane properties reflects a
high cost of functional adaptation to fluctuating temperatures,
especially in the cold. The trade-offs and constraints observed
support an understanding of why metazoan evolution led to the
development of high energy turnover life forms, why dinosaurs
were able to live in subpolar climates, and also give access to the
benefits and trade-offs involved in the evolution of constant
body temperature maintained by endothermia, and set to between 32 and 42

°C in mammals and birds.

2.5. Role for membranes and molecular activity in the evolution of

1Else, P.L., 1Turner, N. and 2Hulbert, A.J.

Metabolic Research Centre, Department of 1Biomedical Science, and
2Department of Biological Science, University of
Wollongong, Wollongong, NSW 2522 Australia


Molecular activity is simply the rate at which individual enzymes
turnover substrate. For the Na+, K+-ATPase (i.e. the sodium
pump) substrate turnover ranges from 1000 to 25 000 ATP/min in a variety

of tissues from a variety of organisms. In three
models of metabolism (ecto- vs. endothermic vertebrates, young vs. adult

endotherms, and large vs. small endotherms) a
general positive relationship exists between molecular activity and
metabolism. Changes in molecular activities involve
predictable changes in membrane composition, with higher molecular
activities (and rates of metabolism) associated with higher
levels of membrane unsaturation. Based on these observations, it is
worth considering the relationship between molecular
activity, membrane composition and the evolution of endothermy. Some
tissues of ectotherms, such as glands that specialise at
sodium pumping, display high molecular activities. These tissues are
normally from cold water species that display high levels of
unsaturation as a consequence of cold adaptation. If the evolution of
endothermy involved the antecedents of mammals and
birds moving into colder niche environments, this would couple membrane
unsaturation, higher molecular activities and the
potential for increased metabolism.

2.6. Body temperature in free ranging dromedary camels

1Dorges, B., 1Heucke, J.F., 1Coventry, J., 2Coppock, G.A., 3Beard, L.A.
and 3Grigg, G.C.

1c/- NT Department of Business Industry and Resource Development, P.O.
Box 8760, Alice Springs, NT 0871, Australia;
2Newhaven Station via Alice Springs, NT 0870, Australia; 3Zoology,
School of Life Sciences, The University of Queensland,
Brisbane, Q4072 Australia


Body temperature was monitored in dromedary camels free ranging in a
large fenced area (1600 ha) on Newhaven Station, 280
km NW of Alice Springs in Australia's arid region in the period
1998?2000. The animals were fed on available forage, and
water was supplied at a trough in one corner of the paddock. The region
has large daily and seasonal temperature changes. Five
male and five female camels were each fitted with a radio-tracking
collar plus a surgically implanted temperature-sensitive
transmitter and data logger. Behavioural observations were made with
binoculars in all seasons, and showed differences
between winter and summer that are consistent with thermoregulatory
considerations. Preliminary analysis of body temperature
shows small daily cycles of 1?2 °C, with small but significant seasonal
and gender differences. Males were cooler than females
in summer, and females were cooler in winter than in summer. Activity
higher than normal led to increased temperature. Males in
rut, usually in winter, showed much larger daily variations in
temperature (3?4 °C), a consequence of lower daily minima rather
than higher daily maxima. We suggest that these low minima, which occur
in the mornings, represent strategic hypothermia in
anticipation of heat production from higher activity levels associated
with the rut. As such, they may be analogous to the low
daily minima described in water-deprived dromedaries by Knut
Schmidt-Nielsen in his seminal work nearly 50 years ago.

2.7. Pressure and flow separation between the systemic and pulmonary
circulation in Python

1Wang, T., 2Altimiras, J., 3W. Klein, 4Axelsson, M.

1Zoophysiology, University of Aarhus, Denmark; 2Biology, IFM, University

of Linköping, Sweden; 3Zoology, University of
Bonn, Germany; and 4Zoophysiology, University of Gothenburg, Sweden


Evolution of pressure separation by virtue of a two-chambered ventricle
evolved independently in mammals and birds from a
reptilian ancestor with a single ventricle and allowed for high systemic

perfusion pressure, while protecting the lungs from
oedema. The increased oxygen transport was essential for the evolution
of endothermy. Within non-crocodilian reptiles,
ventricular pressure separation has only been observed in varanid
lizards and has been regarded as a unique adaptation to an
active predatory lifestyle and high metabolic rate. The cardiac anatomy
of Python resembles varanids where the systemic and
pulmonary sides of the ventricle are well separated by the muscular

In unanaesthetised Python molurus, systemic blood pressure exceeded
pulmonary pressure almost even times (75.7±4.2 vs.
11.6±1.1 cm H2O). Intraventricular pressures, measured in anaesthetised
snakes, showed an overlap in the pressure profile
between the pulmonary side of the ventricle (cavum pulmonale) and the
pulmonary artery, while the higher pressure in the
systemic side of the ventricle (cavum arteriosum) overlapped with the
pressure in the right aortic arch. This verifies that the
pressure differences originate within the ventricle, indicating that the

large muscular ridge separates the ventricle during cardiac
contraction. An astonishing degree of flow separation was revealed from
in situ perfusion of python hearts, which also
documented that the systemic side can sustain higher output pressures
than the pulmonary side of the heart [J. Exp. Biol. 205
(2002) 2715?2723].

Python molurus is an inactive sit-and-wait predator with a lower maximal

oxygen uptake than varanid lizards, but exhibit
substantial and long-lasting increases in oxygen uptake during digestion

and when using shivering thermogenesis to incubate their
eggs. It is possible that the increased metabolic demand during these
situations have led to the evolution of a functionally divided

Supported by The Danish Research Council and The Swedish Research

2.8. The relationship between basal and maximum metabolic rates in the
bank vole, Clethrionomys

Labocha, M., Sadowska, E., Baliga, K., Semer, A., and Koteja, P.

Institute of Environmental Biology, Jagiellonian University, ul.
Ingardena 6, 30-060 Kraków, Poland


Many experiments have been performed to test a hypotheses that basal
(BMR) and maximum aerobic metabolic rates (V2
max) are functionally linked. One reason why several of them failed to
show the expected correlation could be a large random
error of the estimates or temporal changes of the traits, both resulting

in low repeatability. If this was the case, the intrinsic
functional relation between the traits could actually be stronger than
the observed correlation. We measured BMR (at +30 °C,
after 6 h of food deprivation) and V2 max in males of a small rodent,
the bank vole (Clethrionomys glareolus; average body
MASS=21.5 g). The maximum metabolic rate was measured as the highest
1-min oxygen consumption during exercise trials
(MEmax; swimming at +30 °C for 15 min) and during forced thermogenesis
trials (MTmax; in completely soaked individuals
placed in a wet chamber for 15 min at +23 °C). In one group of animals
(N=108) MEmax, BMR and MTmax were measured on
3 successive days, and measurements of MEmax and MTmax were repeated
12?29 days later. In another group (N=64) BMR
was measured twice in a 30-day span. BMR (52 ml O2/h), MEmax (273 ml
O2/h), and MTmax (285 ml O2/h) all increased with
body mass. Repeatability of mass-independent values (residuals from
regression on body mass), measured as coefficient of
intraclass correlation (), was very high for BMR (=0.617; P<0.001), high

for MEmax (=0.494; P<0.001), and moderate for
MTmax (=0.290; P<0.001). Pearson's correlations between absolute values
of BMR and MEmax (r=0.297, P=0.003) as well
as of BMR and MTmax (r=0.227, P=0.015) were significant. However, after
accounting for effect of body mass, the partial
correlations were not significant, and the values of the coefficients
were even negative (MEmax: r=-0.080, P=0.443; MTmax:
r=-0.109, P=0.247). The results are inconsistent with the hypothesis
that basal and maximum aerobic metabolic rates are
strongly linked in mammals, and undermine a fundamental assumption of
the `aerobic capacity model' of the evolution of

2.9. Marsupials, muscles, and the development of endothermy

1Kabat, A.P., Rose, R.W. and 2West, A.K.

1School of Zoology, University of Tasmania, G.P.O. Box 252-05, Hobart,
Tasmania, 7001, Australia; and 2NeuroRepair
Group, Discipline of Biochemistry, University of Tasmania, G.P.O. Box
252-58, Hobart, Tasmania, 7001, Australia


Marsupials are born at a rudimentary level of maturity with the majority

of physiological development completed in the pouch
post-partum. In many species, the ability to maintain homeothermy is one

aspect of development that is not completed until late
in pouch-life. This study attempted to discern what physiological
mechanisms develop during pouch life allowing endothermy to
be achieved in the Tasmanian Bettong (Bettongia gaimardi) a rat kangaroo

with a 15-week-long pouch life. During several
key age groups, we investigated the metabolic and EMG response of pouch
young in different thermal conditions (control 35
°C, or cold stress 20 °C), with and without injection of the -agonist
norepinephrine (NE). We also used molecular techniques
to investigate the possible expression of uncoupling proteins 1, 2 and 3

(UCP1, 2 and 3), and any association these may have
with the timing of development of endothermy. We also investigated, from

the same key time points, changes in total and
subcutaneous body fat. Combining new data with our published results, we

are able to confirm that prior to the 8th week, the
pouch young bettong had a low metabolism and was completely unable to
thermoregulate. However, after the 8th week, the
pouch young developed the ability to shiver but was still unable to
maintain core temperature for long durations. At
approximately the 10th week, shivering was observed but lasted only a
finite duration until tapering off completely, and body
temperature began to decline. It was at this time that the expression of

UCP2 was first seen. It was not until the 12th week,
however, that the pouch young were able to maintain body temperature for

the duration of the cold stress. At this point in
development, several other factors converged; total body fat increased
by approximately 300%, fur was beginning to appear,
plasma thyroid levels were at their highest, a definitive response to NE

was first seen, UCP2 was upregulated, and shivering
stopped being the main source of thermogenesis. Thus, we propose that
UCP2 has an association with thermogenesis.

2.10. Nest-building behaviour and maximum cold-induced rate of food
consumption in house mice
(Mus domesticus)

1Koteja, P., 2Carter, P.A., 3Swallow, J.G. and 4Garland, T., Jr.

1Institute of Environmental Biology, Jagiellonian University, ul.
Ingardena 6, 30-060 Kraków, Poland; 2Washington State Univ.,
Pullman, WA 99164, USA; 3University of South Dakota Vermillion, SD
57069, USA; 4University of California, Riverside, CA
92521, USA


C.B. Lynch and collaborators demonstrated that thermoregulatory
nest-building behavior in mice, measured as the amount of
cotton used by an individual to build a nest, is correlated with other
traits related to thermoregulatory capabilities. For example,
wild mice from northern US populations build larger nests, and have a
lower rate of food consumption at moderately low
ambient temperature, compared to mice from southern populations, which
indicates their better ability to conserve energy. On
the other hand, it could be expected that the maximum rate of food
consumption (Cmax) achieved under severe cold-exposure,
which sets an upper limit to energy budgets, should be higher in mice
from colder climates. Thus, a question arises: is the
nest-building behavior in mice correlated positively or negatively with
Cmax? We measured nest-building behavior and (approx.
2 month later) food consumption in laboratory house mice from eight
lines: four selected for high voluntary wheel-running
behavior and four random-bred, control lines. Previously, we reported
that mice from the selected lines build smaller nests, but
tend to have higher food consumption at room temperature, at least with
access to wheels. Here, we report that at the level of
variation among individuals within the lines, nest-building was not
correlated with the maximum rate of food consumption
achieved at -5 to -10 °C after a cold acclimation (females, r=0.06,
P=0.65, N=59; males, r=-0.09, P=0.51, N=65; partial
correlations with the effect of body mass controlled). At the level of
variation among adjusted means of the eight lines, nest
building was negatively correlated with Cmax in females (r=-0.75;
P=0.03), but not in males (r=0.03, P=0.94). The result
obtained for females indicate that the lines of mice may employ
alternative strategies of dealing with low ambient temperatures:
an `economy' strategy of energy-conserving or a `power' strategy of high

metabolic heat production supported by high capacity
of acquiring energy from food.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796