FOR BS ZOOLOGY STUDENTS MAMMALOGY

1. Naveed Akhtar
Assistant Professor of Zoology

3.  Torpor is a state of decreased physiological activity in
an animal, usually by a reduced body temperature
and metabolic rate.
 Torpor enables animals to survive periods of reduced
food availability.
 The term "torpor" can refer to the time a hibernator
spends at low body temperature, lasting days to
weeks, or it can refer to a period of low body
temperature and metabolism lasting less than 24
hours, as in "daily torpor".

4.  Animals that undergo daily torpor include birds (even tiny
hummingbirds, notably) and some mammals, including
many marsupial species, rodent species (such as mice),
and bats.
 During the active part of their day, such animals maintain
normal body temperature and activity levels, but their
metabolic rate and body temperature drops during a
portion of the day (usually night) to conserve energy.
 Torpor is often used to help animals survive during
periods of colder temperatures, as it allows them to save
the energy that would normally be used to maintain a
high body temperature.

5.  As homeotherms, mammals maintain a constant warm
body temperature (approximately 35 to 38°C) despite
continuous temperature variation in their environment.
 The ability to maintain a constant body temperature has
contributed to the evolutionary success of mammals,
allowing the group to invade unoccupied niches and
become distributed worldwide.
 Some mammals periodically turn down their internal
thermostat and enter torpor as a means to survive
periods of low food availability and then re-warm and
return to a normal level of activity when the environment
becomes favorable.

6.  All animals require energy from food to sustain normal physiology
and behavior.
 The quantity and quality of food provided by the environment might
fluctuate day-to-day or season-to-season such that natural selection
has favored animals adapted to these fluctuations.
 Torpor, a temporary drop in body temperature and metabolic rate
often faced by failure to eat or micturate/defecate, is an adaptation
of endothermic vertebrates that enables them to survive the
energetic demands of cold ambient temperature.
 Torpor, the controlled lowering of metabolic rate, body temperature,
and physical activity is a highly successful adaptation that various
mammals use to cope with periods of low food availability
 This behavior is under environmental control via the endocrine
system

7.  Torpor is the most effective means of energy conservation
available to mammals and birds.
 Torpid mammals can move at low body temperatures from a
torpor site into the sun to passively rewarm and minimize
energy expenditure.
 Social torpor involves coordinated interaction among
individuals, and some species even eat or mate while torpid.
 A decrease in activity and a corresponding increase in torpor
expression can be used to deal with natural disasters such as
fires and storms.
 Behaviors expressed before the torpor season include
selection of suitable hibernacula and storage or sign of
appropriate and sufficient amounts of fuel.

8.  Example:
 In Siberian hamsters, the light: dark cycle entrains
the suprachiasmatic nucleus of the hypothalamus,
the brain structure that controls the onset of torpor.
 Torpor onset is inhibited by testosterone and
prolactin, so torpor in this species occurs only during
winter, when gonads are regressed and Siberian
hamsters are not breeding.

11.  Recent discoveries spanning the metazoa suggest that
sirtuins (a type of protein involved in regulating cellular
processes including the ageing and death of cells and their
resistance to stress.), the mammalian circadian clock,
fibroblast growth factor 21 (FGF21) and lipids are involved in
torpor induction.
 At molecular level, during torpor, metabolism switches from
consuming carbohydrates to consuming lipids.
 The expression of genes that encode metabolic enzymes also
follows a circadian pattern in the brain and liver of mouse
 A key mitochondrial enzyme involved in shutting down
carbohydrate oxidation during the deep torpor associated with
mammalian hibernation, pyruvate dehydrogenase kinase-
isoenzyme 4 (PDK4; also shows a circadian pattern of
expression in mouse liver, aorta, and kidney.

12.  Recent studies in mice demonstrate a connection between
cellular nutrient status and the core molecular machinery of
the mammalian circadian clock.
 Discovery of the link between environmental changes,
metabolism and cellular time-keeping has great potential for
determining the mechanism(s) that induces torpor.
 Both hibernation and daily torpor are often preceded by a
period of fasting or reduced food consumption that alters
cellular nutrient status. Indicators of cellular nutrient status
are the ratios of intracellular [5′-AMP] to [ATP] and [NAD+] to
[NADH].
 Fasting reduces cellular nutrient status and increases both
ratios. The cell can attempt to recover nutrient status by
remodeling metabolism so that stored lipid becomes the
primary source of fuel.

14.  1: nicotinamide phosphoribosyltransferase (NAMPT)
 2. silent mating type information regulation 2 -
homolog 1 (SIRT1) deacetylase
 3. (hypoxia inducible factor-2α; HIF-2α).
 4. adenosine monophosphate kinase (AMPK)
 5: brain and muscle aryl hydrocarbon receptor
nuclear translocator (BMAL1)

17.  References
 https://www.sciencedirect.com/topics/biochemistry-
genetics-and-molecular-biology/torpor
 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC278
8021/
 https://www.researchgate.net/figure/Some-of-the-
major-physiological-events-that-characterize-the-
hibernation-cycle-of-ground_fig1_246862461