Lecture 5:
Thermoregulation
and Resting
Metabolism
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Ectotherm - organism that relies on external
sources of heat
Endotherm - organism that produces enough heat
by its own metabolic processes to affect its own
body temperature; can increase metabolic rate in
response to reduced ambient temperature
Poikilotherm - organism that experiences variable
body temperature, often closely tracking ambient
temperature
Homeotherm - organism that experiences
(relatively) constant body temperature (e.g., + 2 C)
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Fig. 17-9
Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.
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Endotherm Tb and Metabolic Rate vs. Ambient Temperature
Note:
slight typo
in figure,
TNZ goes
from LCT
to UCT
Summit
metabolism
(e.g.,
evaporative
cooling by
sweating or
panting)
Fig. 17-21
Lower C.T.
Upper C.T.
Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.
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Controlling Heat Loss within the TNZ
Takes little energy.
Vasomotor responses - regulate blood flow
between the periphery and core
Insulation adjustments - pilomotor muscles
can raise ("fluff") or lower hairs or feathers
(human "goose bumps" are a vestige of this)
Postural changes - body shape or orientation
affects heat exchange via radiation,
conduction, convection
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High Insulation gives Low Conductance and vice versa
Fig. 17-25
Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.
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Combining Terms in Thermoregulation
Endothermic Homeotherm - most birds and
mammals; some insects; some large fishes
(tuna, sharks); brooding pythons;
a few plants (example later in this lecture …)
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Combining Terms in Thermoregulation
Ectothermic Poikilotherm - most marine
invertebrates; arthropods; amphibians;
fishes; "reptiles" (not a good name, with respect
to phylogenetic relationships, e.g., birds are
"reptiles" in the old sense of the term)
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Terms for Exceptions to "Rules"
Inertial Homeotherm - relatively constant Tb
because of large body size:
e.g., some dinosaurs?
Trivial Homeotherm - constant Tb because of
constant environmental temperature:
e.g., animals in the deep sea,
by hydrothermal vents,
pupfish living in thermal hot springs
Heterotherm - homeotherm whose body
temperature varies somewhat, either over time
or regionally (regional heterothermy)
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Other Important Exceptions
Regional Heterothermy
Fig. 17-24
Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.
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Other Important Exceptions
Regional Heterothermy
Humans also do
this, but not to
such a degree
(pun intended).
Fig. 17-24
Randall, D., W. Burggren, and K. French. 2002. Eckert animal physiology: mechanisms and adaptations. 5th ed. W. H. Freeman and Co., New York.
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Other Important Exceptions
Many lizards maintain high and stable body
temperatures (35-40 C) when active.
Many birds and mammals, especially small
ones, undergo regulated hypothermia and
hypometabolism:
Daily torpor in hummingbirds
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Other Important Exceptions
Many lizards maintain high and stable body
temperatures (35-40 C) when active.
Many birds and mammals, especially small
ones, undergo regulated hypothermia and
hypometabolism:
Daily torpor in hummingbirds
Seasonal hibernation
in small mammals
and the Poorwill
(only bird)
http://www.earthrangers.com/wildwire/top-10/top-ten-hibernating-animals/
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Seasonal hibernation in the Poorwill, discovered by Dr.
Edmund C. Jaeger in 1946 in the Chuckwalla Mts. of CA
http://www.jaeg
er.ws/index.html
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Other Important Exceptions
Many lizards maintain high and stable body
temperatures (35-40 C) when active.
Many birds and mammals, especially small
ones, undergo regulated hypothermia and
hypometabolism:
Daily torpor in hummingbirds
Seasonal hibernation in small mammals
and the Poorwill (only bird)
Seasonal estivation in response to heat
and/or lack of water, e.g., round-tailed
ground squirrel in Mojave desert
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Basal Metabolic Rate - Originally defined for
human beings, used as an index of thyroid
function.
The "minimal" metabolic rate of an endotherm
under fasting conditions,
in the thermal-neutral zone,
undisturbed,
during its normally inactive time of 24-hour period
(but for human beings is done during day).
Standard Metabolic Rate - similar to BMR, but in
an ectotherm at a specified temperature.
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What is Basal or Standard Metabolic Rate?
Summation of all energy-consuming processes
A high met. rate (i.e., per unit time) indicates that
~ all physiological processes are working fast
Can measure by heat production = direct
calorimetry, e.g., by amount of ice melted
Usually measured as O2 consumption = indirect
calorimetry:
O2 is final electron acceptor;
technique works because most vertebrates
use aerobic metabolism almost exclusively
when resting under normal conditions.
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Can also convert to an energy equivalent:
C6H12O6 (glucose) + 6 O2 ---> 6 CO2 + 6 H2O
+ 2,820 kilojoules/mole of O2
Metabolic
Water
Production
varies with
Diet
Conversion factor depends on fuel being utilized
(carbohydrate, fat, protein).
Usually assume mixed diet and use
20.1 KJ/liter of O2 consumed.
(1 calorie = 4.1868 joules)
Can measure CO2 instead, but is a less reliable
indicator of heat production.
Measuring both allows best estimate of heat prod.
But most studies just report O2 consumption.
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Endothermy in Plants
Was discovered over 200 years ago by Lamarck!
Has now been documented in 9 different families.
Several hypotheses for the ecological relevance
(selective importance = ultimate causation) of
elevated temperatures in plants:
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protect flowers from freezing
enhance rate of flower development
provide a direct energy reward for insect
pollinators
increase diffusion rates of CO2 and volatilization
of specific chemicals that attract pollinators
enhance growth of the pollen tube
assure reproductive success (seed set)
achieve mimicry of mammalian faeces and carrion
to attract scavengers and carrion flies
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Family Rafflesiaceae, Rhizanthes zippelii
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Distribution of Family Rafflesiaceae
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Patiño, S., J. Grace, and H. Bänziger. 2000.
Endothermy by flowers of Rhizanthes lowii
(Rafflesiaceae). Oecologia 124:149-155.
Abstract: Rhizanthes lowii (Beccari) Harms
(Rafflesiaceae) is a parasitic plant that
grows in the understory of the rainforest in
South-East Asia. This plant does not have
leaves, stems, or photosynthetic tissue and
is characterised by the emission of a strong
odour that attracts the natural pollinators,
carrion flies. Flowers that volatilise odorous
compounds and attract carrion flies, beetles
and other insects ...
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… are often thermogenic. Here we present
evidence of both thermogenesis and
thermoregulation in R. lowii from
microclimate and tissue temperatures … in
natural conditions in Brunei, Borneo.
Endothermy was detected in young and
mature buds as well as in blooming flowers
and even in decaying tissues 3 or more days
after blooming. Tissue temperatures were
maintained at 7-9 K above air temperature, in
both female and male flowers, at all stages
of floral development.
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Stopped here 22 Jan. 2013
Extra
Slides
Follow
Started here 24 Jan. 2013
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As of Winter 2006 in the 174 course, Ted has more
that can be added from his 161B lectures. These have
confusing names, but do not seem to overlap with
each other:
161B-04-Spr-L2-Eck02ch16.ppt = locomotion, UK 1989
Talk, mice on metabolic wheels, r-K continuum -whole ppt file is expanded into these two:
161B-04-Spr-L3-Eck02ch16_Part_1.ppt
161B-04-Spr-L3-Eck02ch16_Part_2.ppt
161B-04-Spr-L4-Eck02ch17.ppt = thermoregulation,
costs/benefits of endothermy
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Fig. 1. The energetic
consequences of different
ambient temperatures.
Metabolism is fully governed by
intrinsic factors only within a
narrow zone of ambient
temperatures – the
thermoneutral zone (indicated
by the area between the dashed
lines, i.e. the lower and upper
‘critical’ temperatures) (calling
these temperatures ‘critical’
may be considered misleading
but this is the current
nomenclature in thermal
physiology). In mice, the
thermoneutral zone lies at
approximately 30°C. At ambient
temperatures outside the
thermoneutral zone, a large
fraction of total energy is used
for thermoregulation; already at
normal animal house conditions
(18–22°C), this fraction is an
additional 50–100% above the
basal metabolic rate. The
shaded area indicates the extra
metabolism required for body
temperature defence. BMR,
basal (or resting) metabolic
rate. Oxygen consumption
rates are arbitrary units. Based
on data on wild-type mice
published previously
(Golozoubova et al., 2004).
Cannon, B., and J. Nedergaard. 2011. Nonshivering thermogenesis and its adequate measurement in metabolic
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studies. J Exp Biol 214:242-253.
Fig. 2. The effects of exceeding the
ambient temperature survival limits.
Principal figure extended from data in
Fig. 1. Dashed lines indicate the lower
and upper temperature survival limits.
TB, body temperature.
Cannon, B., and J. Nedergaard. 2011. Nonshivering thermogenesis and its adequate measurement in metabolic
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studies. J Exp Biol 214:242-253.
Fig. 4. The effect of increased
insulation on the thermoneutral zone.
As seen, animals with a better
insulation (a smaller slope of the line)
must necessarily also obtain a
broader thermoneutral zone, because
the line must extrapolate to the same
defended body temperature.
Cannon, B., and J. Nedergaard. 2011. Nonshivering thermogenesis and its adequate measurement in metabolic
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studies. J Exp Biol 214:242-253.
Heterotherm - homeotherm whose body
temperature varies somewhat, either over time or
regionally (regional heterothermy)
Trivial Homeotherm - deep sea organisms by
hydrothermal vents, desert pupfish
Inertial Homeotherm - experiences fairly constant
TB because of large size, e.g., large dinosaurs
Basal Metabolic Rate - "minimal" metabolic rate of
an endotherm under fasting conditions, in the
thermal-neutral zone, undisturbed, during its
normally inactive time of the 24-hour period
Standard Metabolic Rate - similar to BMR, but in
an ectotherm at a specified temperature
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Some Terms from the Student Survey
(plus or minus a few ...):
Serves as Partial Review for Midterm 1
on Tuesday, 30 Jan. 2007
Ecology - study of relationships between
organisms and their environments, including both
biotic (i.e., other organisms) and abiotic (i.e.,
physical factors)
Evolution - change;
more specifically, heritable, cross-generational
changes in populations of organisms
Physiology - study of how organisms work
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Phenotype - physical characteristics of an
organism resulting from gene expression modified
by environmental factors
Genotype - genetic material possessed by an
individual organism, usually in the form of DNA
Natural Selection - correlation between variation in
one or more phenotypic traits and Darwinian
fitness (~ lifetime reproductive success)
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