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BIO120 Animals at the Extremes Unit 2: Hibernation and Torpor - OPEN University
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Open University
S324_2 14 Hours
Intermediate
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Course Description
This unit is the second in a series of three on Animals in the extreme. In order to get the most from it you should have previously studied
Animals in the extreme: the desert environment (S324_1)
. After completing this unit you might like to complete the series by studying
Animals in the extreme: polar biology (S324_3)
.
By the end of this unit you should be able to:
- define and use, or recognize definitions and applications of, each of the bold terms;
- give
definitions of the terms ‘hibernation’, ‘torpor’ and ‘adaptive
hypothermia’, and the three physiological processes that underlie them;
- give examples of the diversity of the major groups of mammals and birds that contain hibernating species;
- describe the physiological changes occurring during entry to hibernation and at least three of the cues that may trigger entry;
- present evidence to show that hibernating mammals and birds retain physiological control of their T
b;
- explain
the role of brown adipose tissue and mitochondrial uncoupling of
respiration from metabolic energy release in heat generation in mammals;
- describe
the analytical and targeted experimental approaches to the
identification of genes and proteins implicated in hibernation and
arousal, and give examples of them;
- explain the importance of the selection of appropriate metabolic fuel sources in hibernators;
- describe the changes needed to maintain hibernation and survival at cellular level;
- critically
describe experiments designed to evaluate the energy cost of
hibernation as compared with euthermia, and discuss the importance of
three factors that influence whether animals use hibernation as an
energy-conserving strategy;
- suggest why periodic arousals occur and offer a mechanism for them;
- present experimental evidence for the view that control of T
b depends upon temperature-sensitive neurons and suggest where they may be located;
- give
examples of systems of chemical control for the onset and maintenance
of hibernation that operate in the brain and blood circulation;
- describe the relationship between circadian controls of sleep–waking cycles and the maintenance of torpor;
- use diagrams and flow-charts to illustrate physiological and biochemical principles.
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Introduction
 Introduction Resource- This unit is the second in a
series of three on Animals in the extreme. In order to get the most
from it you should have previously studied Animals in the extreme: the
desert environment (S324_1) ....
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Hibernation and torpor: an introduction
- Hibernation and torpor: an introduction Resource
- This unit examines hibernation, a
special form of adaptation that animals can make to the ecological
demands of remaining in a chosen habitat in winter. Hibernation is a
state which enables energy-efficient...
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2 The nature and extent of hibernation and torpor in endotherms
- 2.1 Degrees of torpor Resource
- Adaptive hypothermia occurs in at
least six distantly related mammalian orders (Table 1) and in several
orders of birds. There is a spectrum running from those species which
can tolerate a drop in T b...
- 2.2 Species showing torpor or deep hibernation Resource
- Among the birds, torpor occurs in
a number of species in the orders Apodiformes (hummingbirds and
swifts), Caprimulgiformes (nightjars, nighthawks, goatsuckers and poor
wills) and Coliiformes (mousebirds)....
- 2.3 Hibernators as eutherms Resource
- Hibernating endotherms are not
the easiest animals to study. Thus, until the late 1960s many
biologists believed that mammalian hibernation was a process in which
thermoregulation was simply ‘switched...
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3 Characteristics of hibernation behaviour
- Introduction Resource
- The animal kingdom reveals a
bewildering variety of regulated hypothermic behaviours, which are
characterized by sustained hibernation at one extreme and regular short
bouts of shallow torpor at the other....
- 3.1 Signals for entry Resource
- Despite the fact that hibernation
is reflected in a number of profound and operationally distinct
physiological changes, changes in T b continue to be the recognized
signs of its onset, interruption...
- 3.2 Physiological changes during entry Resource
- Under normal euthermic
circumstances, animals kept in an ambient temperature of 0° C would be
expected to show a marked increase in metabolic rate and adaptive
thermogenesis. However, the response in hibernators...
- 3.3 Maintenance Resource
- Entering hibernation is not a
passive process in response to falling T a. Nor is deep hibernation a
passive process or indeed a uniform state. Figure 13 shows the pattern
of hibernation (as measured...
- 3.4 Arousal Resource
- We can identify three types of
arousal during the hibernation period, on temporal rather than
physiological grounds. The first is alarm arousal, in response to a
major exogenous stimulus such as a sudden...
- 3.4 Arousal (continued) Resource
- What alternatives to shivering might act as a source of heat?
- 3.5 Length of torpor bouts in hibernation Resource
- It is obvious that there is a
very high energetic cost to arousal, and an even higher one to the
periods of euthermic wakefulness prior to re-entering torpor. If an
animal could simply enter torpor once,...
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4 Physiological adaptations – molecules and cells
- 4.1 Scientific approaches Resource
- Even after many years of
research, the phenomenon of hibernation continues to be a mystery to
scientists. Despite coming nearer to an understanding of how and why it
happens, some fundamental questions...
- 4.2 Arresting protein synthesis Resource
- The regulation of T b in
hibernators has traditionally been viewed as the fundamental
physiological process in hibernation. But recently, questions have been
raised about whether thermal changes...
- 4.3 Cellular changes Resource
- Hibernation can result in the
deposition of fat in adipose tissue. In tissues of finite size which
are important sources of energy and sites for fuel metabolism, changes
in cell structure (redistribution...
- 4.4 Cell survival mechanisms Resource
- Physical damage is not the only
danger that faces cells recovering from low temperatures in the absence
of oxygen (due to a 90% drop in blood flow to the brain) and energy
supplies. A universal sign of...
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5 Physiological adaptations – respiration and energy provision
- Introduction Resource
- The change in BMR observed in all
hibernators has traditionally been viewed as a passive response that is
a consequence of hypothermia. However, many studies have provided
evidence for temperature-independent...
- 5.1 Energy sources in torpor and hibernation Resource
- For animals that show daily
torpor, such as Siberian hamsters (Phodopus sungorus) and Djungarian
hamsters (Phodopus campbelli) (Figure 28), blood glucose remains the
respiratory fuel for several hours...
- 5.2 Mitochondrial adaptations Resource
- During the winter months, whilst
hibernating vertebrates maintain a very low metabolic rate, major
reorganization of mitochondrial metabolism occurs. The phenomenon has
been studied in some detail in frogs...
- 5.3 Inspiratory drive Resource
- The supply of oxygen to tissues
such as the heart, liver and WAT is, under euthermic conditions,
invariably linked to and dependent upon local blood flow and pulmonary
function. However, as we have already...
- 5.4 Energy budgeting – the benefits of hibernation and torpor Resource
- Studies performed on ground
squirrels in the wild and in the laboratory have allowed estimates to
be made of energy expenditure in hibernating and euthermic animals over
similar periods (Wang, 1987). The...
- 5.5 The importance of size and habitat Resource
- The use of hibernation to gain
energetic advantage must be weighed against a number of considerations,
particularly animal size and behaviour, biogeographic distribution and
habitat. Small animals, which...
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6 Control systems
- Introduction Resource
- Measurements of thermoregulation,
respiration and metabolic depression in the edible dormouse (Myoxus
glis) during the early stages of torpor, hibernation and aestivation,
indicate remarkable similarities...
- 6.1 The hypothalamus as central regulator Resource
- Research in the past 30–40 years
has established that the hypothalamus, which lies below the thalamus
and above the optic nerve chiasma and the pituitary gland in the brain,
fulfils all of the functions...
- 6.2 Metabolic regulation and the midbrain Resource
- As you found in the last section,
the physiological evidence points to the likelihood that different
components of regulation may be regulated separately. The hypothalamus,
which appears to be central...
- 6.3 Rapid-response genes and rhythmic neuronal activity Resource
- Reactive changes in the brain are
usually marked by changes in neuronal electrical activity. If these
changes are to be of long duration, adjustments in neuronal electrical
behaviour may be made through...
- 6.4 The neurotransmitters histamine and serotonin: a role for chemical signalling between neurons of the hypothalamus Resource
- As in all other regions of the
brain, the integration of physiological change in the hypothalamus,
conducted by the dialogue between many thousands of nerve cells, is the
result of transmissions across...
- 6.5 Hormones and hibernation Resource
- Syrian hamsters, which display
pronounced circadian temperature fluctuations before hibernation, lose
these circadian cycles on entry to hibernation, and start to regain
them shortly before arousal. Cycles...
- 6.6 Sleep, the brain and hibernation Resource
- There has been a popular
misconception that hibernating animals are asleep when dormant, and
that arousal during or at the end of hibernation involves waking
analogous to that following deep sleep. Sleep...
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Questions
- Questions Resource
- Describe three measures of
physiological regulation central to hibernation. Using these measures
as definitive criteria state why the Svalbard reindeer is not a
hibernator.
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References and Acknowledgements
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Copyright 2007,
by the Contributing Authors.
Cite/attribute Resource.
administrator. (2010, January 03). BIO120 Animals at the Extremes Unit 2: Hibernation and Torpor - OPEN University. Retrieved September 04, 2010, from Free University Courses OCW Courses OpenCourseWare Freeversity Foundation Web site: http://www.freeversity.org/science-and-mathematics/biology/bio120-animals-at-the-extremes-unit-2-hibernation-and-torpor-open-university.
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