Transcript ppt檔案 - 國立臺南大學

大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
生物時鐘(Biological clocks)
─動物行為學 (Ethology)
鄭先祐(Ayo)
國立 臺南大學 環境與生態學院
生態科學與技術學系 教授
Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/
Part 1. 動物行為的研究途徑 (個體行為)
 歷史背景 (History of the Study of Animal




Behavior ).
基因分析 (Genetic Analysis of Behavior ).
天擇 (Natural Selection and Behavior ).
學習與認知 (Learning and Cognition.)
生理分析 (Physiological Analysis)


(一) 神經細胞 (Nerve Cells and Behavior ).
(二) 內分泌系統 (The Endocrine System).
 發育(The Development of Behavior ).
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Part 2. 存活 (與環境的互動關係)
 生物時鐘 (Biological Clocks)
 導航機制 (Mechanisms of Orientation and Navigation)
 空間分佈的生態學與演化學 (The Ecology and
Evolution of Spatial Distribution)
 覓食行為 (Foraging Behavior)
 抗掠食行為 (Antipredator Behavior)
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08 生物時鐘 (Biological clocks)
 Clock-controlled rhythms
 Rhythmic behavior
 The clock versus the hands of the clock
 Advantages of clock-controlled behavior
 Adaptiveness of biological clocks
 Organization of circadian systems
 Human implications of circadian rhythms
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Animals have internal clocks
 Hamsters (倉鼠), as well
as all other animals, have
an internal, living clock


Its bouts of activity
alternate with rest
It is so regular that it is
described as an activity
rhythm
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Most animals can measure time
 Biological clocks have been found in every
eukaryotic organism tested

As well as in cyanobacteria
 The rhythmical nature makes sense in the light of
evolutionary principles


Ecological conditions vary tremendously at different
times of the cycle
It is adaptive to predict upcoming changes in a cycle
(i.e. upcoming darkness or winter), rather than just
respond to these events
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Environmental modifications are extreme
but predictable
 Biological clocks have evolved as adaptations to
environmental cycles
 Biological clocks also provide a mechanism to synchronize
various internal processes with other internal processes
 Rhythms have piqued(引發) the interest of scientists studying
 Their adaptive value and evolution
 Genetic underpinnings (基因基礎)
 Hormonal control
 Neural control
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Properties of clock-controlled rhythms
 Biological clocks measure time at the same rate under
nearly all conditions

They can be reset to remain synchronized with
environmental cycles
 In clock-controlled rhythms, cycles continue in the
absence of environmental cues (i.e. light-dark and
temperature cycles)
 Instead, the ability to keep time without external cues is
due to an internal (endogenous) biological clock
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Biological rhythms
 The period (the interval between two identical points
in the cycle) of the rhythm can become longer or
shorter
Circadian rhythm: a daily rhythm (24 hours in nature)
 Circalunidian: a lunar day (tidal) rhythm
 Circamonthly: a monthly rhythm
 Circannual: an annual rhythm
 Free-running period: a circadian period length under
constant conditions
 It is not manipulated by environmental cycles

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Entrainment to environmental cycles
 Biological rhythms are not exactly as long as natural cycles
 A light-dark cycle: the most powerful phase-setting agent in
circadian rhythms
 Nonphotic cues (i.e. social interactions, feeding schedules,
or temperature cycles) also play a part
 Manipulating the light-dark cycle resets (entrain) the
biological clock
 A brief light pulse during early circadian night resets
the clock
 In nature, the clock is reset by light at dawn and dusk
each day
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Light sampling behavior resets the
circadian clock
 Flying squirrels are nocturnal
 Their circadian clock wakes them at twilight (薄暮)
 If it is still light outside, the squirrel returns to its nest
to sleep and its circadian clock is reset
 Activity begins slightly later the next night
 The squirrel’s activity rhythm entrains to the light-
dark cycle with only a few minutes of light exposure

This phase adjustment also causes the squirrel’s onset
of activity to follow sundown as it changes through the
year
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Biological clocks are insensitive to
temperature changes
 If biological clocks were affected by changes in temperature:
They would run at different rates at different times of day
 Cave dwelling, insectivorous bats of the temperate zone roost in
cool, deep caves during the day
 Their body temperature drops while resting to conserve
metabolic energy
 Their temperature rises when they leave the cave to forage
 The biological clock remains accurate

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Daily rhythms
 Nocturnal animals are busiest at night
 Hamsters, cockroaches, bats, mice, and rats
 Diurnal animals are active during the day
 Most songbirds and humans
 Crepuscular animals are active primarily at dawn and
dusk
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Lunar day rhythms
 As the moon passes over the surface of the earth, its
gravitational field draws up a bulge in the ocean
waters
 Causing high tides when they reach the shoreline
 There are usually two high tides each lunar day one every 12.4 hours
 The tides cause some dramatic changes in the
environment, Particularly for organisms living on
the seashore
 Rhythms synchronized with tides are lunar day
rhythms
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Fiddler crab activity is synchronized with
tidal changes
 Fiddler crabs are active during low tide
 In search of food and mates
 Before high tide, the crabs return to their burrows
 A fiddler crab’s behavior in the laboratory remains
rhythmic


Periods of activity alternate with quiescence every 12.4
hours
The usual interval between high tides
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 An activity rhythm
of a fiddler crab
(Uca pugnax).
Althouth the crab
was maintained in
constant darkness
and
temperature(20℃).
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Semilunar rhythms
 The gravitational field of the sun also influences the
height of the tides

The highest tides are caused when the gravitational fields
of the moon and the sun operate together
 At new moon and full moon, the earth, the moon, and
the sun are in line

The gravitational fields of the sun and the moon augment
each other
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 The effect of the
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relative positions
of the earth,
moon, and sun on
the amplitude of
tidal exchange.
 (a) at the times of
new and full
moons,
 (b) during the
first and last
quarters of the
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Spring and neap tides
 Spring tides: the highest high tides and lowest low tides
at new and full moons
 Neap tides: periods of lowest high tides and highest low
tides at the quarters of the moon
 Some organisms possess a biological clock that helps
them predict the times of spring or neap tides

In the tiny chironomid midge, emergence of adults from
their pupal cases is programmed to coincide with tidal
changes.
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chironomid midge
 Chironomidae (informally
known as chironomids or nonbiting midges) are a family of
nematoceran flies with a global
distribution.
 Many species superficially resemble mosquitoes but
they lack the wing scales and elongate mouthparts of
the Culicidae.
 This is a large group of insects with over 5000
described species and 700 species in North America
alone.
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Monthly rhythms
 A synodic lunar month: the interval from full moon to full
moon (29.5 days)


The time it takes the moon to revolve once around the earth
Some organisms can program their activities to occur at
specific times during this cycle
 The ant lion shows a monthly rhythm in the size of the pit it
builds



Small arthropods, such as an ant, slide into the pit
At full moon, it constructs larger pits
This is a clock-controlled rhythm - not a response to an
environmental factor
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Pit size of ant lion
 A monthly
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rhythm in the pit
size of the
predatory ant
lion.
 Monthly
rhythms in the
pit size of 50 ant
lions maintained
in constant
condition in the
laboratory.
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Annual rhythms
 Annual biological clocks are important
 In timing migration
 To prepare animals physiologically for migration and
reproduction
 A garden warbler in the laboratory with constant
temperature and unvarying day length (12 hours light 12 dark) lacks obvious seasonal cues


During summer and winter months, it limits activity to
daylight hours
It becomes active at night during autumn and spring, when
it would normally be migrating
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 Annual cycles in migratory
restlessness, body weight, testis
size, and molting in a garden
warbler held in constant lightdark cycle and at a constant
temperature.
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Caged birds have zugunruhe
 Zugunruhe (migratory restlessness): a cage-adapted
nocturnal form of migratory activity
 The timing function is very important for birds
wintering close to the equator

A constant photoperiod and variable rainfall and food
abundance don’t provide proper cues to signal the time
to begin migrating
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The annual clock affects physiology
 It readies birds for migration and reproduction
 A bird gets fatter during winter to provide fuel for the
spring migration
 It molts during winter
 Its testes enlarge for summer reproductive activity
 These cycles are free-running for many years in
constant conditions

The length of the cycle is slightly longer or shorter than a
year
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Circadian vs. annual clocks
 Seasonal changes may be controlled by a response to
the changing photoperiod

Shortening days during winter months and increasing
daylight of spring and summer
 Measuring a change in daylength requires only a
circadian clock

A rhythm controlled by an annual clock continues to be
rhythmic even without changing day length
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Stop and think
 When one wants to determine whether a daily, tidal, or
lunar rhythm is controlled by an endogenous clock,
the organism is placed in constant light or constant
darkness
 When one wants to determine whether an annual
rhythm is controlled by an annual clock, the animal is
kept in a constant photoperiod
 Why are the procedures different?
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Anticipation of environmental change
 Why time an event with a biological clock rather than
responding directly to periodic environmental
fluctuations?



To anticipate periodic environmental changes
To synchronize behavior with other events
To measure an interval of time
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Anticipation of environmental change
 An animal can anticipate change and prepare for it
 Adult fruit flies emerge from their pupal cases at dawn,
when it is cool and moist
 They can expand their wings with a minimal loss of
water
 If they waited until later, water loss to the arid air could
prevent the wings from expanding properly
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Synchronization of behavior
 Allowing a clock to control an event
allows behavior to be synchronized
with a factor in the environment that
cannot be sensed directly
 Bees time their flights to visit
flowers that are open(開花) only
during certain times

A bee can not use vision or olfaction to determine whether
flowers far from the hive are open
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Bees visit open flowers
 After training, bees visited a feeding station only
during learned hours
 With their biological clock, bees time their visits to
flowers so they arrive when the flower is secreting
nectar

And gather the maximum amount of food with the
minimum effort
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 (b) bees were trained to come
to a feeding dish only at the
specific times at which food
was made available.
 (c) after six days of training,
the feeding dishes were left
empty and the number of
bees arriving throughout the
day was recorded. The bees
arrived at the feeding station
only when food had been
previously present.
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Continuous measurement of time
 Measuring passage of time is crucial to time-compensated
orientation
 A honeybee’s dance indicates the direction to a nectar source
 Telling other bees the flight bearing relative to the sun
 Because the sun is a moving reference point, the honeybee’s
biological clock provides the information for
 The time of day when it discovered the nectar
 How much time has passed since then
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Organization of circadian systems
 A complex nervous system or endocrine system is not
an essential component of the biological clock

Single cells, unicellular organisms and cells that make
up tissues and organs have their own independent
clocks
 There is no such thing as “the” biological clock

Clocks are scattered throughout an animal’s body
 Fruit flies have a multitude of independent clocks
throughout their bodies

They respond to changes in light-dark cycles without
any help from the head
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Fruit flies have multiple clocks
 Glow rhythms indicate per gene activity synchronizes
with light-dark cycles

And continue in constant darkness with a free-running
period length
 Separate cultures of body parts exposed to the same
light-dark cycle glow in unison(一致、合諧)

Each piece of cultured tissue has its own independent
clocks and these clocks have their own photoreceptors
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The insect brain is not needed as a
master clock
 To synchronize rhythms throughout the body.
 Clocks in different cells run at slightly different rates
without a light-dark cycle

Independent clocks gradually become asynchronous
 When exposed to a new light-dark cycle, the clocks
throughout the fly entrain within one cycle and the
glow becomes rhythmic again
 In nature, asynchrony among peripheral clocks is not a
problem


Fruit flies have an environmental light cycle that can
synchronize independent clocks
Because each has its own photoreceptor
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Animals have at least one master clock
 Most rhythmic animals have multiple independent
peripheral clocks throughout the body
 How are an individual’s clocks synchronized so all
rhythmic processes occur at the appropriate time

Relative to one another and the environment’s cycles?
 At least one “master” clock in the brain is entrained
by the light-dark cycle

It regulates other clocks through the nervous and/or
endocrine system
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The master clock: the general scheme
 The general scheme of circadian organization
 One clock or several interacting clocks function as
master clocks to synchronize peripheral clocks
 The output from the master clock(s) can be neural or
hormonal
 The clocks are set to the right time because
photoreceptors convey information on the light-dark
cycle to the clock(s)
 Peripheral clocks generate the rhythmic output, which
may feedback on and affect the master clock(s)
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The master clock: photoreceptors
 What photoreceptors are responsible for entrainment?
 Mammalian eyes contain photoreceptors for light
entrainment
 These photoreceptors are in a different part of the retina
than those involved in vision
 Information about lighting conditions reaches the clock
through the retinohypothalamic tract (RHT)

A bundle of nerve fibers connecting the retina with the
hypothalamus
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The master clock: where is it?
 The circadian system in mammals is a hierarchy of clocks
 The SCN (suprachiasmatic nucleus) is the master
biological clock
 Evidence that the SCN is the master clock
 It is independent: SCN activity remains rhythmic in cultures
 Spontaneous electrical firing of individual neurons is
rhythmic in constant conditions, each of them with a slightly
different period
 The SCN is a self-sustaining oscillator that instills
rhythmicity in other brain regions through neural connections
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The master biological clock of mammals SCN
 The suprachiasmatic nucleus or nuclei (SCN), is a
tiny region on the brain's midline, situated directly
above the optic chiasm. It is responsible for
controlling circadian rhythms. The neuronal and
hormonal activities it generates regulate many
different body functions in a 24-hour cycle, using
around 20,000 neurons.
 The SCN, pine cone shaped and the size of a grain of
rice, interacts with many other regions of the brain. It
contains several cell types and several different
peptides (including vasopressin and vasoactive
intestinal peptide) and neurotransmitters.
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The suprachiasmatic nucleus (SCN) in the brain
 (a) the firing rate of a single neuron from the SCN
continues fo fire rhythmically in tissue culture.
 (b) photoreceptors in the mammalian circadian system
reach the SCN via the retinohypothalmic tract (RHT).
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 Nerve activity in
specific brain
regions (the
caudate and the
suprachiasmatic
nuclei) of a rat
before and after
isolating an “island”
of brain tissue
containing the
SCN.
The SCN instills
rhythmicity
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The master clock regulates other clocks
 When an SCN from a conspecific is transplanted into
rats or hamsters that have been made arrhythmic by
destroying their own SCN


Their activity becomes rhythmic once again
The period length of the restored activity rhythm
matches that of the transplanted SCN
 The SCN is the clock that provides timing information
 And not just a component needed to make the host’s
clock function
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The genetic basis of circadian timing
 What are the molecular gears that make the clock tick?
 Rhythmic gene activity is involved in the clock
mechanism
 The products of one gene or set of genes activate or
inhibit the activity of other genes


Which in turn affect the activity of the first genes
Creating a self-regulated feedback loop of gene activity
measuring approximately 24 hours
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The genetic basis of the circadian cycle
 Two proteins—Clock and BMAL1—bind together,
forming a complex that enters the nucleus
 The Clock/BMAL1- complex turns on the activity of
the period (per) and the cryptochrome (cry) genes

The protein products of these genes (Per and Cry) bind
with the protein product of the tau gene to form a
complex
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 The genetic basis of circadian timing in mammals consists of
two feedback loops in gene activity.
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A 24-hour feedback mechanism
 The Per/Cry/Tau complexes suppresses action of the
Clock/ BMAL1 complex

Resulting in less activity of per and cry
 With less Per and Cry produced and the degradation of
Per, Cry and Tau

The level of the Per/Cry/Tau complex declines
 With less inhibition of their activity, per and cry are
turned on again
 This cycle takes about 24 hours to complete
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Peripheral clocks
 The SCN may be the master biological clock
 But other circadian clocks throughout the body keep their
own internal time
 Rhythms persist in cell cultures from the SCN, liver, and
lung

And in fibroblasts (generic cells) in cultures
 Perhaps all cells have personal clocks
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 A model of circadian organization in mammals.
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Clock output
 The SCN entrain peripheral circadian oscillators
 So they are correctly set to environmental time
 The phase relationship between rhythmic output of the
SCN and rhythmic clock genes in peripheral tissues
varies


Peak clock gene expression occurs at distinct times of
the day and varies in different tissues
The clock may not directly cause the rhythmic output of
peripheral tissues
 Most neural connections are to the hypothalamus and
autonomic nervous system, which influences hormone
levels
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Signals from the SCN can be neural
 The SCN has at least two neural output pathways that
affect rhythms


One pathway goes to the preoptic nucleus of the
hypothalamus
 Controls the rhythm in ovulation, but not the activity
rhythm
The second pathway leads to the paraventricular
nucleus in the hypothalamus
 Integrates neuroendocrine and autonomic functions
 And then leads to the pineal, which produces
melatonin
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Melatonin (退黑激素)
 退黑激素(Melatonin)有人叫聚黑激素，它是腦部「松
果體」所分泌的一種激素。它可使青蛙皮膚色素細
胞內之黑色素顆粒聚合於細胞核附近（故稱為聚黑
激素），因而使皮膚顏色看起來較淡。
 光線經過視網膜神經細胞再傳至下視丘，再經交感
神經而傳至松果體，抑制退黑激素的分泌。反之，
黑暗則可促使退黑激素的分泌。
 下視丘內之一些細胞有如「生物時鐘」般使松果體
之退黑激素分泌出現晝夜韻律之差異，一般晚上入
睡後其血中濃度為白天的六倍。退黑激素在血中的
半衰期甚短，約為半分鐘至５分鐘之間，主要在肝
臟內代謝而其代謝物則由尿液排出。
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 The influence of light and darkness on circadian rhythms
and related physiology and behavior through the SCN in
humans
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Signals from the SCN can be hormonal
 Reproductive responses to the length of day and
rhythms in hormones require neural connections

And also small molecules that diffuse to their target
 Activity rhythms are caused by the SCN’s release of
chemical signals to other parts of the brain without
neural connections
 In mammals, the rhythmic production of two hormones
(melatonin and glucocorticoids) entrain peripheral
oscillators
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糖皮質激素（Glucocorticoid）
 糖皮質激素（Glucocorticoid），學名叫做「腎上
腺皮質素」，由於可用於一般的抗生素或消炎藥
所不及的病症，如SARS、敗血症……等，是由
腎上腺皮質分泌的一類甾體激素，具有調節糖、
脂肪、和蛋白質的生物合成和代謝的作用，還具
有抗炎作用，稱其為「糖皮質激素」是因為其調
節糖類代謝的活性最早為人們所認識。
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Hormones entrain peripheral oscillators
 Neural connections from the SCN cause the pineal to
produce melatonin

Melatonin amplifies the body temperature rhythm,
facilitates sleep, and controls photoperiodic responses
 Neural connections from the SCN to the anterior
hypothalamus initiate hormonal events


Glucocorticoids were produced by the adrenal gland
Glucocorticoids: steroid hormones that control many
physiological functions
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Stop and think
 Light cannot reset the clock in the SCN of people who
are totally blind


Consequently, their sleep-wakefulness rhythms drift out
of phase with the day-night cycle
They are often sleepy during the day or wide awake at
night
 In one experiment, blind people were able to set their
clocks by taking a dose (10 mg) of melatonin at
bedtime

Why do you think this is possible?
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Human circadian rhythms: jet lag
 Jet lag: the most familiar way circadian clocks affect
humans


A syndrome of effects that includes decreased mental
alertness and increased gastric distress
Caused by a disruption of circadian timing
 After traveling across time zones, your biological clocks
are still set to the local time of your home
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The clocks gradually adjust to the day-night cycle in the
new locale
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Resetting biological clocks takes time
 After traveling, it may take several days to reset your
biological clock
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The more time zones crossed, the longer it takes to reset
the clock
 Not all body functions adjust at the same rate
 Phase relationships in physiological processes are upset
 Your body time is out of phase with local time
 Your rhythms may peak at inappropriate times
 You suffer psychological and physiological disturbances
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Stop and think
 If you were traveling from Tampa Florida to San
Diego California to compete in an important athletic
event, what steps could you take before you left to
minimize jet lag?
 If you could choose the time of the event, would you
choose morning or afternoon? Why?
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Human circadian rhythms: human health
 Nearly every physiological process in humans is
rhythmic

Each process peaks at the appropriate time of day
 Certain acute medical conditions occur at a certain
time of day
 Most heart attacks and strokes occur between 6 AM
and noon

Blood pressure rises, platelets become stickier and
more likely to form blood clots, and the mechanism that
breaks down blood clots is least active
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Human circadian rhythms: human health
 Asthma (氣喘) attacks mostly occur at night

Levels of epinephrine (a hormone that causes the air
tubules to dilate), and cortisol (a hormone that
suppresses the immune system) are low
 The hormone leptin decreases appetite and ghrelin
increases appetite

Sleep-deprived humans have low leptin levels and
high ghelin levels, giving them a heartier appetite than
usual
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Circadian rhythms, sleep and energy
 The clock gene is part of the circadian mechanism in
mammals

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Clock mutant mice eat more than normal mice
They gained weight, developed high cholesterol, blood
sugar and triglycerides, low insulin, and bloated fat cells
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New possibilities for treating diseases
 Discovering the link between the circadian clock and
metabolism has opened new possibilities for treating
diabetes and obesity


The activity of a gene called SIRT1 is clock controlled
It is modulated by how many nutrients a cell is
consuming
 SIRT1 responds to the energy state of a cell and
transmits that information to the clock by binding to
the BMAL1-Clock complex

Helping to explain why lack of sleep can increase
hunger and lead to obesity and diabetes
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Summary
 Clocks evolved as adaptations to environmental cycles
 Periods are called circadian, circalunidian, or circannual
 The free-running period: the period length in constant
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conditions
Entrainment adjusts the period length and the rhythm’s phase
Daily rhythms can be entrained to light-dark and temperature
cycles
Rhythmic processes match geophysical periods and are
caused by an internal biological clock
Processes become rhythmic when coupled to the biological
clock
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Summary
 A biological clock measures time for:
(1) anticipation of the environmental changes
 (2) synchronizing the behavior with unsensed events
 (3) continuous measurement of time
A functional clock enhances survival
One or more master clocks (SCN) regulates other, slave clocks
The master clock regulates activity through nerves and chemicals
The genetic basis of circadian clocks involves feedback loops
The SCN controls the pattern of gene expression in tissues
The human circadian clock is related to health in several ways
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問題與討論
[email protected]
 Ayo 台南 NUTN 站
http://myweb.nutn.edu.tw/~hycheng/
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