Circadian Rhythm-clock

• sexual selection

• mating systems

• parental care

• migration

• dispersal

(underlying all this is a clock)

• animals need to know when to eat

• when to disperse

• what season it is —> mating and migration

(prep time)

concept of “clock”

1729 French astronomer

• mimosa plant —> moved towards sun moved back straight at night

John jack and sun plant

• put the plant in total darkness —> plant still moved, implies there are no external light cue, meaning there is some eudeogenous clock

behavior = free running

maintenance of daily rhythm in absence of cue

2017 Nobel prize 3 scientists

circadian rhythm

circa= latin = about

dian = day

sunlight —> external trigger(cue) —> predictable

SCN (suprachiasmatic nuclei)

• where clock is located

• period gene (PER) protein

• Timeless gene (TIM)protein

Self-sustain negative feedback loop in cytoplasm and nucleus 

• 24hr cycle

1. period makes PER

2. PER transfereed to cytoplasm

3. TIM appears in cytoplasm later than PER (PER is responsible for negative feedback loop)

4. At some point in day there is enough TIM in cytoplasm to bind w/ PER= dimer PER-Tim

5. PER-TIM can now go back and enter nucleus (PER can’t go back and enter nuncles alone)

6. PER-TIM are in nucleus 

• PER —> inhibit period gene —> PER concentration drops 

7. At some point —> NO PER NO TIM NO Dimer in cytoplasm

8. makes PER again (back to step 1)

Research —> fruit flys

wild type = 24hrs

3 mutants = no rhythm —> arthytmic

• single gene mutant -short 19hr period -long 28hr period

Actogram

measure of activity bar on top shows L:D Tim (light & dark)

D:Df

free running: Strats to drift

arrhtymitc = no pattern

Sage grouse

start liking at 4 am —> stop at 9am b/c predator

• predatory hawks —> large birds, need thermal air to fly effectively

• around 9 am 

Fruitfly clock = 23.75

Human clock= 24hrs + 11 min

• adjust for environmental change of sunrise and sunset

Why are clocks important

Hibernation

• sleep

• do not eat

• no poop

• no pee

• low metabolism

• for about 7 months

have to eat before hand >5 00lbs pre-hibernation

salmon spawning =may-sept

bear starts eating = july

bear hibernates oct/nov —> apr/may

Timing for forging + predator avoidance

• food = ephemeral resource

• link in clocks

• unpredictable, comes and goes

Nocturnal animals

cue to sunset —> bats —>predators by large birds

• bats on avg. emerge 20-30 min after sunset

Mating Calls

Teleogryllus -cricket

males call —> attract females

• nocturnal

Expt 1. L:D cricket

captured males —> breeding season

• about 2 hrs before lights out

• natural cycle 

• sync to darkness

Expt 2. L:L cricket

• kept on calling for serval hours each day —> 25-26hrs

Whether timing mechanism have a built-in schedule that acts independently of any environment cues?

OR

Animals alter relationship of the command center in nervous system strictly on feedback gathered from environment?

Conclusion: environment independent

internal = circadian

Naked mole rat

no circadian rhythm

nocturnal, feed on roots and tubers

• social group

Research 1994

• very reduced vision —> ni light activation (SCN)

• brief episodes  activities and large episodes of inactivities

How does the mole rat know whats going on?

temp? rainfall>

temp —> tunnel —> high above 33 degrees Celsius increase activity to stay warm 

rainy season—> soil moist = easier to dig

Migration

• prep activity beforehand, feeding to prep for travel

• birds —> active —> daytime

• birds —> migrate —> night

Zygymnuke (German)

migratory restlessness

• agitation prior to migratory