Biological Clocks Flashcards by Shannon Davis

what is biological clock theory

Animals have a timing mechanism with an endogenous, built in schedule, independent of environment

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What is environment response theory

Relationships between command centers are modified by feedback from the environment… behavior changes as conditions change

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What is the environment response theory for crickets

If cricket calling is controlled by environment, crickets in constant light should never call

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What was the first cricket calling experiment

Grow crickets in lab under constant temperature/brightness, record calling

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What were the results of the first cricket chirp experiment

Crickets continue calling in absence of environmental cue

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What was the interpretation of the cricket chirp experiment

Mate calling is a free-running cycle, supporting idea that internal clock controls behavior

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What is the time period of a circadian rhythm

“about a day”

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What was the second cricket calling experiment

Grow crickets in lab on 12 hour light dark cycle and record calling

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What were the results of the second cricket calling experiment

Crickets use the cue of darkness to adjust their calling so that it begins about 2 hours before lights off and ends about 2.5 hours before lights on

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What was the interpretation of the second cricket calling experiment

Calling is reset/entrained each day to darkness, which matches the natural behavior

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What hypothesis was supported by the cricket experiments and why

Both hypotheses: calling can occur independent of environment based on an internal clock but is normally reset each day during nightfall

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What is the circadian rhythm pathway?

Sunlight/environmental cue -> sensory receptors -> pacemaker -> observed rhythms

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What are sensory receptors considered

Clock-setting pathway

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What is the pacemaker considered

Clock mechanism

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What are the 4 observed rhythms in circadian rhythms

Locomotory patterns
Feeding behaviors
Hormone release patterns
Other rhythms

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What structure is the “mammalian pacemaker”

Superchiasmatic nucleus (SCN)

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What is the input to the SCN

Retina

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What happens when SCN is removed from rodents

Arrhythmic patterns of locomotion, hormone secretion, feeding

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What happens during transplant of SCN but noth other tissues

Locomotion, hormone secretion, feeding restored

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what happens during transplant of mutant SCN

Mutant period length (shorter/longer than 24 hours)

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What does the SCN do when removed from the brain

Maintains rhythmic secretions

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*Research clock/per gene and add it to this

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What is the evidence for per as a timing gene (4)

Fruitfly mutations
Normal honeybee levels vary with behavior
Humans with a per mutation have altered sleep cycles
Gene is highly conserved and expressed in SCN

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Explain honeybee per variation

Young nurse bees have low per and are active all day/night
Adult foragers, who go out during day, have higher per levels and exhibit defined circadian rhythms

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What are the three expectations of the biological clock

Molecule relaying clocks instructions should be regulated by clocks genes Molecule should be secreted and there should be a receptor for secretions in target behavior mediating tissue Experimental manipulation of chemical should disrupt timing of behavior

What are the 2 candidate molecules for the "biological clock"

Melatonin and PK2

What is melatonin

Hormone released by hypothalamus at dusk that promotes sleep

What is PK2

Prokineticin 2. Found in mRNA

Why is PK2 thought to potentially be biological clock

Amount found in mRNA increased in beginning/end of day and decreases in middle of day

What are the three pieces of evidence for PK2 as the circadian clock signal

Mice with mutations in per and tim lack cyclic production of PK2 Only certain structures produce a PK2 receptor Injections of PK2 during the night, when levels are normally low and rats are active, leads to cessation of activity and sleep (daytime behavior)

What are the two adaptive values of circadian rhythms

Individuals do not always have to check environment to see what time it is Individuals CAN use environment to subtly adjust their clock to changing conditions

Which animals do not have circadian clocks

Animals that do not use a day-night cycle

How does reproductive physiology correspond to hibernation

Molting corresponds to decrease in testicle width

How do white-crowned sparrows know spring is coming

Males fly north in spring, courts females, defends territory, and fights rivals Gonads grow from the winter state

What is the hypothesis for determining what the biological clock is

Clock exhibits a daily change in sensitivity to light that is reset every day at dawn

Explain the clock's daily change in sensitivity to light

Insensitive for the first 12 hours of light, then steadily rises to a peak around 16-20 hours after the start of the cycle, then fades again

What happens to the clock if days are less than 12 hours

System will not be activated because no light is present during photosensitive period

What is the hypothesis for the photosensitive hypothesis experiment

You should be able to trick the clock by manipulating day/night

Describe the photosensitive hypothesis experiment

Start with 8 hours of light, 16 hours of dark: no stimulation during photosensitive period (days are short, testes dont grow) then switch to 8 hours of light and 28 hours of dark

What were the results of the photosensitive hypothesis experiment

8L:28D causes testicle growth

What are some reasons why photoperiod does not always reliably predict access to food or mates

Dry winter, delayed thaw

What is a more reliable predictor of resources than photoperiod

Rainfall

Which animal bases its habits off of rainfall

Arizona sparrow

How does the Arizona sparrow base its habits off rainfall

Testes grow in March, as days lengthen, but following a dry winter, they dont breed Rainfall during the July monsoons trigger production of LH, which stimulates testes to release testosterone, increasing song production and reproductive behaviors

What type of cue are rainfall signals

Proximate cues

What type of behavioral cue do Red crossbill finches use

Food abundance

How do red crossbill finches use food abundance cues

Take advantage of good conditions regardless of season

What is one thing that food abundance cues do not control in red crossbill finches?

Breeding

When is breeding lowest in red crossbill finches

December and January (even with abundant food)

What else suggests an internal clock regulates physiology

Under constant conditions, testes shrink and hormone levels decline from October to December, consistent with the photoperiod sensitivity exhibited by other temperate birds

What happened when crossbill finches were caged with females

Underwent faster reproductive growth than males kept alone

What happened when crossbill finches were exposed to a female for 60 minutes

Testosterone levels were raised and singing was initiated

How does the moon impact feeding

Decreased belly size with higher luminosity (full moon)

When do male mice become infanticidal

About three weeks after mating

What is a possible reason for how the infanticidal timing is determined

Internal timing device counting off from time of last meeting

What is the hypothesis for how infanticidal timing is determined

We should be able to manipulate the infanticidal period by altering the perceived length of a day

What was the fast day in infanticide behavior experiment

11L:11D

What was the fast day in infanticide behavior experiment

13.5L:13.5D

What were the results of the infanticide behavior experiment

Fast and slow day males continue habits based on how many days they percieved

What are the implications of the results of the infanticide behavior experiment

Timing device in males detects number of light-dark cycles since last mating and could potentially control male hormones

What are the two male hormones

Testosterone and progesterone

What does high testosterone lead to

high aggression and infanticide

What does high progesterone lead to

Suppression of parental behavior

What is the hypothesis for the mechanism for infanticide experiment

If progesterone is key to infanticide, then males lacking progesterone receptors should not kill pups

What is the mechanism for infanticide experiment

Generate a genetic knock out of the PR gene, expose males to new pups

What were the results of the mechanism for infanticide experiment

PR-/- males do not kill pups Levels of Progesterone and Testosterone are the same as in wild type mice