Etude : effet de la temperature sur un régime en graisses saturées ou non

[Sandrine1308 0]

Voici une autre étude, datant de 2000 sur un des impacts de la température de l'environnement donc du corps du hamster sur son alimentation (graisses saturées ou non).
Pour une fois l'abstract est en anglais et a été traduit en français.
En résumé, en environnement frais (sans être trop froid et donc sans rentrer dans le phénomène de torpeur hivernale), le hamster russe choisit naturellement un régime plus riche en graisses non saturées, et se remet à manger plus de graisses non saturées dès qu'il se trouve à des températures "d'été" (22-25°C).
Cela démontre clairement que la température de son habitat en captivité a un impact, à minima, sur ses besoins alimentaires.
Qu'en conséquence, je me dis qu'à priori, et à étudier plus avant, avoir la possibilité d'augmenter ou de diminuer la température de son habitat pourrait permettre d'adapter, à minima, le régime alimentaire de nos hamsters pour répondre à des situations spécifiques de santé de l'animal (diabète, obésité, maladie, maigreur, etc).
C'est pour cela également que j'ai choisi de prendre un tapis chauffant pour mon futur terra à mettre sous le terra. Je pourrais l'enlever si non adapté.

Voici l'étude complète et l'abstract (résumé des conclusions de l'étude) :


Effect of temperature on preference for dietary
unsaturated fatty acids in the Djungarian hamster
(Phodopus sungorus)
Sara M. Hiebert, Erin K. Fulkerson, Kirstin T. Lindermayer, and Sarah D. McClure
Abstract: Previous studies have shown that hibernators preparing for winter prefer a diet rich in unsaturated fat. This
study was designed to determine if a daily heterotherm, the Djungarian hamster (Phodopus sungorus), shows a similar
preference when given simultaneous access to two diets, one rich in saturated fat and the other rich in unsaturated fat.
In two experiments, hamsters that had been exposed to short days for 8–10 weeks were exposed to 8°C for 10 days.
When half of these animals were moved to a warm environment (26–29°C), they developed a significantly lower preference
for the unsaturated diet than controls that remained at 8°C (P < 0.01). This difference in preference disappeared
when the experimental group was returned to 8°C (P = 0.4). Although mean body temperature (Tb) was significantly
lower (mean difference = 0.35°C) in experimental animals in the cold environment, most animals did not enter daily
torpor at any time during the experiment. Together, these results suggest that the large decreases in core Tb accompanying
torpor, originally assumed to necessitate the incorporation of unsaturated fatty acids into cell membranes of hibernators
and daily heterotherms, are not necessary to stimulate changes in food choice.
Résumé : Des études antérieures ont démontré que les animaux qui entrent en hibernation préfèrent un régime riche en
graisses non saturées. Cette étude a été entreprise dans le but de déterminer si un hétérotherme quotidien, le hamster
Phodopus sungorus, manifeste cette préférence s’il a le choix entre deux régimes, l’un riche en graisses saturées,
l’autre riche en graisses non saturées. Au cours de deux expériences, des hamsters préalablement exposés à des jours
courts pendant 8–10 semaines ont été exposés d’abord à une température de 8°C pour 10 jours. Lorsque la moitié des
animaux ont été placés dans un milieu chaud (26–29°C), ils ont montré une préférence moins marquée pour le régime
riche en graisses non saturées que les hamsters témoins qui sont restés dans le milieu à 8°C (P < 0,01). Cette différence
de préférence est disparue quand les animaux du groupe expérimental ont été retournés au milieu maintenu à 8°C
(P = 0,4). Bien que la température corporelle moyenne (Tb) ait été significativement plus faible (différence moyenne =
0,35°C) dans le milieu froid, la plupart des animaux ne sont jamais entrés en torpeur quotidienne au cours de
l’expérience. Dans l’ensemble, ces résultats indiquent que les diminutions importantes de la température corporelle qui
accompagnent la torpeur, diminutions que l’on croyait nécessiter l’incorporation d’acides gras non saturés dans les
membranes cellulaires des animaux en hibernation et des hétérothermes quotidiens, ne sont pas nécessaires à la stimulation
des changements de choix alimentaires.
[Traduit par la Rédaction] 1368
Introduction Hiebert et al.
The effects of cold, as well as the adjustments made by
organisms in response to cold exposure, may be observed at
levels of organization ranging from the molecular to the
organismal. At the level of the cell membrane, low temperature
decreases membrane fluidity and may induce phase
transitions, which may in turn affect cell function by affecting
the activity of membrane-associated proteins, the mobility
of molecules within the membrane, and the permeability
of the membrane to water and ions (Cossins et al. 1987;
Aloia 1988; Hazel 1995, 1997; Muramaki et al. 2000). Fluidity
at a given temperature is decreased by the presence of
saturated fatty acyl residues in the phospholipids that comprise
the lipid bilayer and increased by the substitution of
unsaturated fatty acids, which may be obtained in the diet
(Mead et al. 1986; McMurchie 1988) or by enzymatic
desaturation of existing fatty acids. The composition of
lipids outside the plasma membrane may also be important
because depot fats, which in vertebrates are deposited almost
exclusively as triglycerides, need to be fluid to be metabolizable
(Mead et al. 1986; Frank and Storey 1995). Here too,
unsaturated fats tend to counteract the solidifying effects of
low temperature.
Heterotherms, animals that hibernate seasonally or enter
daily torpor, are of particular interest with regard to lipid
composition because body temperature (Tb) in the normothermic
and torpid states differs by a median of 25°C in
daily heterotherms and 37°C in seasonal hibernators (Geiser
and Ruf 1995). Temperature changes of this magnitude would
be expected to affect cell-membrane fluidity and lipid mobilization
substantially. For hibernators, such as the goldenmantled
ground squirrel (Spermophilus lateralis), the
chipmunk (Eutamias amoenus), and the marmot (Marmota
Can. J. Zool. 78: 1361–1368 (2000) 2000 NRC Canada
1361
Received October 13, 1999. Accepted April 20, 2000.
S.M. Hiebert,1 E.K. Fulkerson, K.T. Lindermayer, and
S.D. McClure. Biology Department, Swarthmore College,
500 College Avenue, Swarthmore, PA 19081-1390, U.S.A.
1Author to whom all correspondence should be addressed
(e-mail: shieber1@swarthmore.edu).
flaviventris), consuming the appropriate dietary fatty acids
also has indirect energetic advantages. Individuals consuming
a diet high in unsaturated fatty acids have a greater incidence
of hibernation, lower Tb during bouts of hibernation,
lower metabolic rate, and (or) longer hibernation bouts than
individuals of the same species consuming a diet low in unsaturated
fatty acids (Geiser and Kenagy 1987, 1993; Geiser
1990, 1993; Frank 1992; Geiser et al. 1992, 1994; Florant et
al. 1993; Thorp et al. 1994; but see also Frank and Storey
1995; Hill and Florant 2000).
The necessity of altering lipid composition in seasonal
hibernators is readily apparent because these animals are
torpid for many months at a time. Although hibernators
normally arouse periodically, most of the hibernation season
is spent at very low Tb (Boyer and Barnes 1999). For daily
heterotherms, however, the temporal pattern of torpor is different.
Even though the propensity for entering daily torpor
may be strongly seasonal, daily heterotherms, such as the
deer mouse (Peromyscus maniculatus) and the Djungarian
hamster (Phodopus sungorus), are normothermic for at least
part of each day (Geiser and Ruf 1995). A priori, the need
for altering lipid composition in the case of daily heterotherms
is therefore not as clear as for hibernators, since daily
heterotherms need to function at both high and low temperatures.
Nevertheless, studies on deer mice (Geiser 1991),
Djungarian hamsters (Geiser and Heldmaier 1995), and the
marsupial Sminthopsis macroura (Withers et al. 1996) together
demonstrate that individuals fed a diet high in polyunsaturated
fatty acids (PUFAs) have significantly higher
proportions of these fats in body tissues, including depot fat,
total lipids in leg and brain, heart mitochondrial membranes,
and brown adipose tissue. Furthermore, individuals consuming
PUFA-rich diets increase energy savings during torpor
by one or more of the following means: more frequent bouts
of torpor, longer bouts of torpor, and lower metabolic rate
during torpor.
Although many studies have addressed the question of
whether dietary fatty acid composition affects the torpor patterns
of seasonal and daily heterotherms, far fewer have addressed
the question of whether heterotherms confronted
with a choice of diets containing different proportions of saturated
and unsaturated fatty acids would exercise a preference
for the one containing the seasonally appropriate fatty
acid composition. In a study with ground squirrels (S. lateralis),
Frank (1994) demonstrated that during the fattening
period preceding hibernation, the animals preferred a diet
containing a higher proportion of unsaturated fatty acids
than animals held at high temperatures. The ability of daily
heterotherms to exercise thermally appropriate dietary choice
has not yet been reported.
Methods
General methods
Maintenance and care of animals
The Djungarian hamsters in this study were descendents of animals
generously donated to us by Bruce Goldman, whose colony
originated in the laboratory of Klaus Hoffmann. From birth, female
hamsters were kept at 22 ± 2°C, under a photoperiod of 16 h light
(L) : 8 h dark (D). After weaning, hamsters were housed in groups
of two or three in opaque plastic cages (18 × 28 × 13 cm) lined
with cedar shavings. When hamsters were moved to short-day conditions
and ambient temperature (Ta) was reduced to 13°C or less,
bedding was supplemented with cotton batting for added insulation.
Except during experimental diet manipulation during the two
experiments described below, hamsters were fed Purina 5008 rodent
chow and provided with water ad libitum. Animal care and
experimental methods used in these studies conform to the principles
and guidelines of the Canadian Council on Animal Care, as
set forth in the Guide to the Care and Use of Experimental Animals
(1993).
Radio transmitters and implantation surgery
After individual calibration, radio-frequency transmitters (XMFH,
Mini-mitter, Sunriver, Oregon) were implanted intraperitoneally in
hamsters anesthetized with 85 mg/kg pentobarbital sodium (Nembutal
, Abbott Laboratories) supplemented with methoxyflurane vapors
(Metofane, Mallinckrodt) as needed. The abdominal wall was
closed with absorbable suture (Vicryl, Ethicon) and skin incisions
were closed with a surgical adhesive (Vetbond, 3M Animal Care
Products). Nitrofurazone dressing, 0.2% (Fermenta Animal Health),
was applied to the wound closure post surgically and acetaminophen
with codeine phosphate solution (Barre National) was added
to the water supply for several days as a postsurgical analgesic.
Hamsters were kept at 22°C for 4–7 days after surgery and then returned
to 13°C for an additional 5 days before the beginning of the
experiment. Radio-frequency signals were collected, plotted, and
analyzed using Dataquest software (Data Sciences International,
St. Paul, Minnesota).
Experimental diets
Throughout each experiment, hamsters were simultaneously offered
two diets. The diets were prepared by marinating Purina
5001 mouse chow (4.5% crude fat) in an amount of beef fat (high
in saturated fat) or sunflower oil (high in unsaturated fat) sufficient
to produce a 10% increase in pellet mass (Hilditch and Williams
1964; Gunstone et al. 1986; Table 1); this technique was previously
used in experiments testing the effect of dietary fatty acids on torpor
(Geiser and Kenagy 1987, 1993; Geiser 1991; Geiser et al.
1992, 1994; Geiser and Heldmaier 1995; Withers et al. 1996).
Hereinafter, diets will be referred to simply as the unsaturated diet
or saturated diet. After marination, experimental diets were stored
at –4°C to prevent spoilage.
Food hoppers were separated into two compartments by a wiremesh
divider. Half the hamsters in each treatment group received
the saturated diet on the left side of the hopper and the other half
received it on the right side to control for the effects of location
and (or) proximity on food choice. Each day, the pellets remaining
in each compartment were weighed between 16:00 and 17:00, a
time chosen because P. sungorus normally complete their daily
bouts of torpor earlier in the day (Bartness et al. 1989). After
weighing, pellets were added to the hopper to bring the total mass
of pellets in each compartment to 20 g, well over the amount consumed
daily ( 0.08 on all days),
but experimental hamsters consumed significantly less than
controls on every day in phase II (MWU, P < 0.0005 on
each day).
Preference for the unsaturated diet followed the predicted
pattern. In phase I, the unsaturated diet comprised a mean
45.8 ± 1.5% of the total diet of all hamsters. In phase II, after
the hamsters had been divided into treatment groups and
the experimental group had been moved to 29°C, unsaturated
diet accounted for a significantly lower proportion of
the total diet in the experimental group (45.5 ± 5.1%) than in
the control group (62.1 ± 2.3%) (MWU, P = 0.01) (Fig. 1).
In day-by-day comparisons of the treatment groups, diet
preference of experimental and control hamsters did not differ
significantly on any day in phase I. In phase II, differences
tended on some days toward significantly lower preference
for the unsaturated diet by experimental hamsters than by
controls, but there were no significant differences on any
day, nor did the tendencies toward significance follow any
clear temporal pattern (Fig. 1).
Body mass did not change significantly from the end of
phase I (26.9 ± 0.6 g for all hamsters) to the end of phase II
(26.2 ± 0.6 and 26.4 ± 0.9 g for control and experimental
2000 NRC Canada
1364 Can. J. Zool. Vol. 78, 2000
hamsters, respectively) (Wilcoxon, P > 0.5 in both cases),
suggesting that there were no changes in body mass that
could be attributed to the saturation level of the diet.
Experiment 2
Food consumption
During phase II, mean total daily food consumption for all
hamsters was 5.16 ± 0.14 g. As in phase II of experiment 1,
total daily food consumption averaged over all of phase II
was significantly lower in experimental hamsters at 29°C
(3.12 ± 0.16 g) than in control hamsters remaining at 8°C
(5.20 ± 0.16 g) (MWU, P < 0.0001). Averaged over all of
phase III, total daily food consumption of experimental hamsters
was again statistically indistinguishable from that of
control hamsters (MWU, P = 0.07) (Fig. 2).
Day-by-day comparisons of total food consumption
showed that during phase I, there were no significant differences
between treatment groups on any day (MWU, P >
0.05 on all days). During phase II, experimental hamsters
consumed significantly less food than controls on all but
2 days (MWU, P < 0.002 for significant differences and P ³
0.06 for nonsignificant differences). During phase III, total
daily food consumption was significantly lower in experimental
than control hamsters on days 1 and 3 (MWU, P <
0.003) but not on any of the remaining days (MWU, P ³
0.02 in all cases), suggesting that adjustment of total food
intake in a new thermal environment is not immediate but
may take several days.
During phase I, the mean percentage of unsaturated diet
consumed by all hamsters over all 10 days was 72.2 ± 4.3%.
During phase II, the mean percentage of unsaturated diet in
the control group at 8°C remained in this range (68.5 ± 4.5%),
whereas that of the experimental group at 29°C was significantly
lower (46.5 ± 5.6%) (MWU, P = 0.005) (Fig. 2).
In phase III, when experimental hamsters were returned to
8°C with the control hamsters, there was again no significant
difference in diet preference between the control group (63.5 ±
3.6% unsaturated diet) and the experimental group (57.3 ±
6.5% unsaturated diet) (MWU, P = 0.83) (Fig. 2). Day-byday
comparisons of diet preference between the two treatment
groups showed no significant differences on any day in
phase I. In phase II, a significantly lower preference for the
unsaturated diet by the experimental hamsters than by the
controls did not remain stable until after day 10 (Fig. 2). In
phase III, significant differences were again absent on all
days, suggesting that dietary adjustments made in response
to a sudden shift to high temperature require longer exposure
than dietary adjustments made in response to a sudden shift
to low temperature.
Body temperature
In phase I, mean Tb of all hamsters was 36.45 ± 0.05°C.
In phase II, however, mean Tb of the experimental group at
26°C (36.57 ± 0.09°C) was slightly but significantly higher
than the mean Tb of the control group at 8°C (36.22 ±
0.08°C) (two-sample t test, P = 0.01) (Fig. 2). For the 20
hamsters for which at least partial data were available in
phase III, there was again no significant difference in mean
Tb between the control (36.37 ± 0.10°C) and experimental
(36.32 ± 0.12°C) animals (two-sample t test, P = 0.79).
In all three phases of experiment 2, temperature records
showed only two bouts of torpor, here defined as excursions
of Tb below 28°C (Heldmaier and Steinlechner 1981). Both
of these bouts were exhibited by one hamster in the experimental
group during phase II, when the experimental group
was held at 26°C.
Pelage and body mass
Pelage color index of all 30 hamsters increased significantly
(i.e., fur became lighter) from phase I (1.7 ± 0.1) to
phase III (2.0 ± 0.2) (P = 0.04). There was no difference in
fur color between treatment groups at the end of phase III
(P = 0.8), indicating that the balanced fur color of the treatment
groups that was present when the animals were assigned
to treatment groups at the beginning of phase II
persisted until the end of the experiment.
There were no significant differences in body mass between
the two treatment groups at any time during the experiment
(ANOVA, P = 0.99), but the increase between
initial body mass (before the experiment began (26.1 ±
0.5 g)) and subsequent measurements (29.4 ± 0.7 g at the
end of phase I, 29.5 ± 0.7 g at the beginning of phase III,
and 29.8 ± 0.6 g at the end of phase III) (P < 0.0001) was
significant, suggesting that the addition of fat (either saturated
or unsaturated) to the diet results in significant mass
gain.
Discussion
The results of these experiments demonstrate that Ta influences
diet choice in Djungarian hamsters exposed to short
days in such a way that there is a greater preference for a
diet high in unsaturated fatty acids at low Ta than at high Ta.
Development of diet preference requires at least several days
of exposure to a higher Ta and is reversible by returning the
animals to a low Ta.
Because the energy content of both lipid-enhanced diets
was 20 kJ/g (Geiser and Kenagy 1987), the saturation level
of dietary fats explains the observed preference better than
direct energetic considerations. The potential benefits of this
preference are that unsaturated fats, when incorporated into
fat depots and cell membranes, should increase fat mobilizability
and offset the viscosity-increasing effects of low
temperature on cell membranes, respectively. Although a mechanism
has not yet been elucidated, previous studies have demonstrated
that incorporation of unsaturated fats into somatic
tissues also has an indirect energetic benefit because an increase
in unsaturated fatty acid content results in increased
energy savings during torpor, both in hibernators (Geiser and
Kenagy 1987; Geiser et al. 1992, 1994; Frank and Storey
1996) and in daily heterotherms (Geiser 1991; Geiser and
Heldmaier 1995; Withers et al. 1996). The hamsters in the
present study did not benefit in this way, however, because
they did not enter torpor.
Torpor is not necessary for the expression of dietary
fatty acid preference
It was originally hypothesized that the large decreases in
Tb during hibernation and daily torpor necessitated adjustments
to counteract the viscosity-increasing effects of cold
on somatic lipids in fat depots and cell membranes (Raison
2000 NRC Canada
Hiebert et al. 1365
and Lyons 1971; Geiser and Kenagy 1987; Geiser 1991). In
general, one might propose that reduced physiological function,
brought about by increases in membrane viscosity and
(or) solidification of depot fats, could be the proximate cue
that initiates desaturase activity and (or) stimulates changes
in preference for unsaturated dietary fatty acids. The results
of the present experiment, however, show that torpor is not
necessary for the expression of temperature-influenced
changes in preference for dietary-fat composition. This finding
may be interpreted in several ways: (1) even very small
decreases in Tb (in the present study, less than 0.5°C) are
sufficient to stimulate a change in diet preference; (2) a
large decrease in Ta (in this study approximately 20°C) is the
proximate cue stimulating a change in diet preference; or
(3) the regional heterothermy that develops in endotherms
during cold exposure, in which skin and appendage temperatures
fall well below core Tb (Irving et al. 1957), affects
membrane function and (or) lipid mobilization sufficiently
to stimulate a change in diet preference. In any case, this
finding leads to the prediction that seasonal changes in preference
for unsaturated dietary fats should be evident in a
wide range of endotherms, not just in those entering daily
torpor or seasonal hibernation.
Low incidence of torpor
Although the lack of torpor observed in this study was unexpected,
it does not detract from the general conclusion that
thermal environment affects dietary fatty acid choice. Nevertheless,
this observation raises the question of why the animals
in this study failed to enter torpor more frequently, as
observed in other studies of short-day Djungarian hamsters
(e.g., Heldmaier and Steinlechner 1981; Bartness et al. 1989;
Geiser and Heldmaier 1995). We propose several explanations.
First, one might propose that the animals did not have sufficient
time to develop spontaneous daily torpor. Prior to
each of the experiments reported here, however, hamsters
had already been exposed to short days for 8 (experiment 2)
or 10 (experiment 1) weeks, which should have been sufficient
to induce the expression of torpor (Bartness et al. 1989).
Second, the hamsters in this study were exposed to extremely
long days (16 h L : 8 h D) before being introduced
to short-day conditions in this experiment, and recent studies
have shown that such a photoperiodic history may increase
the incidence of short-day nonresponsiveness (Gorman and
Zucker 1997). Because nonresponders fail to regress the gonads
in response to short-day exposure, they continue to
maintain high levels of reproductive hormones, such as
prolactin and testosterone, which are known to inhibit daily
torpor in P. sungorus (Ruby et al. 1993). The significant
change in fur color of our animals, however, argues that the
animals were responding to short days. Nevertheless, even
the animals with the lightest pelage were not entering torpor.
One explanation for this combination of observations could
be that different components of the winter phenotype (e.g.,
pelage color and spontaneous daily torpor) are under separate
control, so that some traits can be more responsive to
short days than others (Hoffmann 1978; Wade and Bartness
1984; Hall and Lynch 1985; Blank and Desjardins 1986;
Bartness and Goldman 1988; Smale et al. 1988; Gorman et
al. 1993).
Third, saturated fat in the diet has been shown to reduce
the incidence of torpor in a hibernator (Geiser and Kenagy
1987) as well as in daily heterotherms (Geiser and Heldmaier
1995; Withers et al. 1996). In the experiments reported here,
all animals consumed some of the saturated diet.
Diet choice in the natural environment
Must free-living rodents preparing for winter exercise dietary
fatty acid choice in nature? The plants on which these
rodents feed are constrained in similar ways by Ta, with the
result that exposure to the cold induces an increase in PUFA
content; overwintering plant parts, such as seeds, typically
have higher PUFA content than other parts of the plant
(Hilditch 1951; Gunstone et al. 1986). Thus, a change in diet
could conceivably be accomplished without any choice on
the part of the animal; it could simply continue eating whatever
plant foods were available in the environment and these
would increase in PUFA content as winter approached. Dietary
shifts toward increased consumption of foods high in
unsaturated fats in autumn, such as those reported for pygmy
possums (Burramys parvus; Smith and Broome 1992), goldenmantled
ground squirrels (Frank 1994), and chipmunks (Tevis
1953), may represent a passive process based primarily on
availability in the environment. Only by comparing the composition
of gut contents with the composition of foods available
in the environment can behavioral preference be implicated
in seasonal dietary shifts. It could also be argued that seasonal
shifts in dietary preference are driven primarily by
high reproductive requirements for protein rather than by
fatty acid saturation. According to this argument, animal
foods, which incidentally also contain higher proportions of
saturated fatty acids, would be more strongly preferred in
spring and early summer than in late summer and early autumn.
There is evidence, however, that hibernators in nature
may play an active role in selecting foods with enhanced unsaturated
lipid content in preparation for winter. Yellowbellied
marmots (Marmota flaviventris) are reported to extend
their home range specifically to include the cow parsnip,
Heracleum sp. (Armitage et al. 1976), the plant highest
in PUFAs in the marmot’s natural environment (Florant et al.
1990).
The present laboratory study is the first to show that daily
heterotherms exercise active choice for dietary fatty acid
saturation and that choice is influenced by Ta. The question
of whether such choice is regularly exercised in nature has
yet to be demonstrated. Unlike hibernators, many of which
discontinue eating and rely primarily on body fat stores for
energy during the winter, daily heterotherms continue to eat
during the winter, in many cases consuming food that has
been cached in or near the burrow. Previous considerations
of food choice for caching have focused on factors such as
energy content, nutritional value, perishability, and the energetic
costs of acquisition and handling (Smith and Reichman
1984). Evidence from the present and other studies suggests
that fatty acid saturation should be included as a criterion influencing
food choice for caching. Interestingly, some of the
least perishable foods (seeds) also tend to have the highest
unsaturated fatty acid content; thus, preference that may previously
have been attributed to low perishability may in fact
be driven primarily by natural selection favoring the con-
2000 NRC Canada
1366 Can. J. Zool. Vol. 78, 2000
sumption of unsaturated fats by rodents in cold winter climates.
Acknowledgements
Cynthia Ristine and Rory Alarcon provided excellent animal
care and Jessica Cuni oversaw experiment 1 during a
holiday break. We are also grateful to Jocelyne Noveral,
who assisted with project oversight, John Kelly, who kept
our equipment working, and Phil Everson, who provided statistical
consulting. The Swarthmore College Biology Department
provided funding for supplies and animal care.
Generous contributions from the Howard Hughes Medical
Institute supported the purchase of the environmental chamber
and Mini-mitter data-acquisition system.
References
Aloia, R.C. 1988. Lipid, fluidity, and functional studies of the
membranes of hibernating mammals. In Physiological regulation
of membrane fluidity. Edited by R.C. Aloia, C.C. Curtain,
and L.M. Gordon. Alan R. Liss, New York. pp. 1–39.
Armitage, K.B., Downhower, J.F., and Svendsen, G.E. 1976. Seasonal
changes in weights of marmots. Am. Midl. Nat. 96: 36–
51.
Bartness, T.J., and Goldman, B.D. 1988. Peak duration of serum
melatonin and short-day responses in adult Siberian hamsters.
Am. J. Physiol. 255: R812–R822.
Bartness, T.J., Elliot, J.A., and Goldman, B.D. 1989. Control of
torpor and body weight patterns by a seasonal timer in Siberian
hamsters. Am. J. Physiol. 257: R142–R149.
Blank, J.L., and Desjardins, C. 1986. Photic cues induce multiple
neuroendocrine adjustments in testicular function. Am. J.
Physiol. 250: R199–R206.
Boyer, B.B., and Barnes, B.M. 1999. Molecular and metabolic aspects
of mammalian hibernation. BioScience, 49: 713–724.
Canadian Council on Animal Care. 1993. Guide to the care and use
of experimental animals. 2nd ed. Vol. 1. Bradda, Ottawa, Ontario.
Cossins, A.R., Behan, M.K., Jones, G., and Bowler, K. 1987.
Lipid-protein interactions in the adaptive regulation of membrane
function. Biochem. Soc. Trans. 15: 77–81.
Duncan, M.J., and Goldman, B.D. 1984. Hormonal regulation of
the annual pelage color cycle in the Djungarian hamster,
Phodopus sungorus. I. Role of the gonads and pituitary. J. Exp.
Zool. 230: 89–95.
Florant, G.L., Nuttle, L.C., Mullinex, D.E., and Rintoul, D.A.
1990. Plasma and white adipose tissue lipid composition in marmots.
Am. J. Physiol. 258: R1123–R1131.
Florant, G.L., Hester, L., Ameenuddin, S., and Rintoul, D.A. 1993.
The effect of a low essential fatty acid diet on hibernation in
marmots. Am. J. Physiol. 264: R747–R753.
Frank, C.L. 1992. The influence of dietary fatty acids on hibernation
by golden-mantled ground squirrels (Spermophilus lateralis).
Physiol. Zool. 65: 906–920.
Frank, C.L. 1994. Polyunsaturate content and diet selection by
ground squirrels (Spermophilus lateralis). Ecology, 75: 458–463.
Frank, C.L., and Storey, K.B. 1995. The optimal depot fat composition
for hibernation by golden-mantled ground squirrels
(Spermophilus lateralis). J. Comp. Physiol. B, 164: 299–305.
Frank, C.L., and Storey, K.B. 1996. The effect of total unsaturate
content on hibernation. In Adaptations to the cold. Edited by F.
Geiser, A.J. Hulbert, and S.C. Nicol. University of New England
Press, Armidale, N.S.W., Australia. pp. 211–216.
Geiser, F. 1990. Influence of polyunsaturated and saturated dietary
lipids on adipose tissue, brain, and mitochondrial membrane
fatty acid composition of a mammalian hibernator. Biochim.
Biophys. Acta, 1046: 159–166.
Geiser, F. 1991. The effect of unsaturated and saturated dietary
lipids on the pattern of daily torpor and the fatty acid composition
of tissues and membranes of the deer mouse Peromyscus
maniculatus. J. Comp. Physiol. B, 161: 590–597.
Geiser, F. 1993. Dietary lipids and thermal physiology. In Life in
the cold: ecological, physiological and molecular mechanisms.
Edited by C. Carey, G.L. Florant, B.A. Wunder, and B. Horwitz.
Westview Press, Boulder, Colo. pp. 141–153.
Geiser, F., and Heldmaier, G. 1995. The impact of dietary fats,
photoperiod, temperature and season on the morphological variables,
torpor patterns, and brown adipose tissue fatty acid composition
of hamsters, Phodopus sungorus. J. Comp. Physiol. B,
165: 406–415.
Geiser, F., and Kenagy, G.J. 1987. Polyunsaturated lipid diet
lengthens torpor and reduces body temperature in a hibernator.
Am. J. Physiol. 252: R897–R901.
Geiser, F., and Kenagy, G.J. 1993. Dietary fats and torpor patterns
in hibernating ground squirrels. Can. J. Zool. 71: 1182–1185.
Geiser, G., and Ruf, T. 1995. Hibernation versus daily torpor in
mammals and birds: physiological variables and classification of
torpor patterns. Physiol. Zool. 68: 935–966.
Geiser, F., Stahl, B., and Learmonth, R.P. 1992. The effect of dietary
fatty acids on the pattern of torpor in a marsupial. Physiol.
Zool. 65: 1236–1245.
Geiser, F., McAllan, B.M., and Kenagy, G.J. 1994. The degree of
dietary fatty acid unsaturation affects torpor patterns and lipid
composition of a hibernator. J. Comp. Physiol. B, 164: 299–305.
Gorman, M.R., and Zucker, I. 1997. Environmental induction of
photononresponsiveness in the Siberian hamster, Phodopus
sungorus. Am. J. Physiol. 272: R887–R895.
Gorman, M.R., Ferkin, M.H., Nelson, R.J., and Zucker, I. 1993.
Reproductive status influences odor preferences of the meadow
vole, Microtus pennsylvanicus, in winter day lengths. Can. J.
Zool. 71: 1748–1754.
Gunstone, F.D., Harwood, J.L., and Padley, F.B. 1986. The lipid
handbook. Chapman and Hall, New York. p. 554.
Hall, E.S., and Lynch, G.R. 1985. Two daily melatonin injections
differentially induce nonshivering thermogenesis and gonadal
regression in the mouse (Peromyscus leucopus). Life Sci. 37:
783–788.
Hazel, J.R. 1995. Thermal adaptation in biological membranes: is
homeoviscous adaptation the explanation? Annu. Rev. Physiol.
57: 19–42.
Hazel, J.R. 1997. Thermal adaptation in biological membranes: beyond
homeoviscous adaptation. Adv. Mol. Cell Biol. 19: 57–
101.
Heldmaier, G., and Steinlechner, S. 1981. Seasonal pattern and
energetics of short daily torpor in the Djungarian hamster,
Phodopus sungorus. Oecologia, 48: 265–270.
Hilditch, T.P. 1951. Biosynthesis of unsaturated fatty acids in ripening
seeds. Nature (London), 167: 298.
Hilditch, T.P., and Williams, P.N. 1964. The chemical constitution
of natural fats. John Wiley, New York.
Hill, V.L., and Florant, G.L. 2000. The effect of a linseed oil diet
on hibernation in yellow-bellied marmots (Marmota flaviventris).
Physiol. Behav. 68: 431–437.
2000 NRC Canada
Hiebert et al. 1367
Hoffmann, K. 1978. Effect of castration on photoperiodically induced
weight gain in the Djungarian hamster. Naturwissenschaften,
65: 494.
Irving, L., Schmidt-Nielsen, K., and Abrahamsen, N.S.B. 1957. On
the melting points of animal fats in cold climates. Physiol. Zool.
30: 93–105.
McMurchie, E.J. 1988. Dietary lipids and the regulation of membrane
fluidity and function. In Physiological regulation of membrane
fluidity. Edited by R.C. Aloia, C.C. Curtain, and L.M.
Gordon. Alan R. Liss, New York. pp. 189–237.
Mead, J.F., Alfin-Slater, R., Howton, D., and Popjak, G. 1986.
Lipids: chemistry, biochemistry, and nutrition. Plenum, New
York.
Muramaki, Y., Tsuyama, M., Kobayashi, Y., Kodama, H., and Iba,
K. 2000. Trienoic fatty acids and plant tolerance of high temperature.
Science (Washington, D.C.), 287: 476–479.
Raison, J.K., and Lyons, J.M. 1971. Hibernation: alteration of mitochondrial
membranes as a requisite for metabolism at low
temperature. Proc. Natl. Acad. Sci. U.S.A. 68: 2092–2094.
Ruby, N.F., Nelson, R.J., Licht, P., and Zucker, I. 1993. Prolactin
and testosterone inhibit torpor in Siberian hamsters. Am. J.
Physiol. 264: R123–R128.
Smale, L., Nelson, R.J., and Zucker, I. 1988. Daylength influences
pelage and plasma prolactin concentrations but not reproduction
in the prairie vole, Microtus ochrogaster. J. Reprod. Fertil. 83:
99–106.
Smith, A.P., and Broome, L.S. 1992. The effects of season, sex and
habitat on the diet of mountain pygmy-possums (Burramys
parvus). Wildl. Res. 19: 755–768.
Smith, C.C., and Reichman, O.J. 1984. The evolution of food caching
by birds and mammals. Annu. Rev. Ecol. Syst. 15: 329–351.
Sokal, R.R., and Rohlf, F.J. 1995. Biometry. 3rd ed. W.H. Freeman
and Co., New York.
Tevis, L. 1953. Stomach contents of chipmunks and mantled
ground squirrels in northeastern California. J. Mammal. 34:
316–334.
Thorp, C.R., Ram, P.K., and Florant, G.L. 1994. Diet alters metabolic
rate in the yellow-bellied marmot (Marmota flaviventris)
during hibernation. Physiol. Zool. 67: 1213–1229.
Wade, G.N., and Bartness, T.J. 1984. Effects of photoperiod on
food intake, body weight and body composition in Siberian
hamsters. Am. J. Physiol. 246: R26–R30.
Withers, K., Billingsley, J., Hirning, D., Young, A., McConnell, P.,
and Carlin, S. 1996. Torpor in Sminthopsis macroura: effects of
dietary fatty acids. In Adaptations to the cold. Edited by F.
Geiser, A.J. Hulbert, and S.C. Nicol. University of New England
Press, Armidale, N.S.W., Australia. pp. 217–222.

[Sandrine1308 0]

ooppsssss.....
"et se remet à manger plus de graisses saturées dès qu'il se trouve à des températures "d'été" (22-25°C)."
j'a n'a écris une carabistouille.... Désolée...

[Sandrine1308 0]

Il s'agit également d'une étude sur le hamster russe, également appelé djungarian hamster.
J'avais oublié de le préciser...

[Mio 0]

Le pavé !

[Sandrine1308 0]

sorry... j'ai mis toute l'étude mais on peut ne regarder que l'abstract qui en est le résumé avec ses conclusions, et qui est au début de l'étude.
Dites moi si vous preferez que je ne mette que l'abstract ou toute l'étude, et je ferais selon vos souhaits.