Circadian Rhythms

SS, mating systems, PC, migration, dispersal, all occur due to …

an internal clock

an animal needs to know …

when to feed, when to dispose, what season is it

diurnal:

active in the day time

nocturnal:

active in the night time

concept of “clock” came from a …

1729 French astronomer

‘concept of “clock”’: mimosa plant moves towards the sun, during the day, and …

straight back to normal during the night 

‘concept of “clock”’: putting the mimosa plant in darkness led to the discovery that …

it followed the sun, even in internal darkness, meaning there was some sort of internal clock at play

‘concept of “clock”’: endogenous clock =

no external light cue

‘concept of “clock”’: behavior is “free running behavior” …

maintenance of daily rhythm in absence of cues 

SCN is …

suprachiasmatic nuclei

SCN contains 2 genes:

Period gene (PER protein) & Timeless gene (TIM protein)

PER and TIM are a part of a …

self-sustaining negative feedback loop

PER and TIM are located in the …

nucleus

1). Period makes …

PER protein

2). PER transfers to …

cytoplasm 

3). TIM appears in cytoplasm …

later than PER

PER is responsible for the …

negative feedback loop

4). ASP, in day —> there is enough …

TIM in the cytoplasm to bind with PER, forming a dimer

5). Dimer PER-TIM can …

enter the nucleus

PER alone is …

inhibited from entering the nucleus (a need for PER-TIM dimer)

6). Once PER-TIM are in nucleus …

PER inhibits Period gene, inhibiting further PER production and causes level of PER in cytoplasm to drop

7). ASP —> if there is no PER or TIM in the cytoplasm …

there is no dimer and no more PER than can inhibit the Period gene

The whole PER-TIM cycle lasts for …

24 hours

the external signal of the PER-TIM cycle is …

sunlight (predictable)

Inhibition of Period gene is …

removed around 4 am and can now make more PER

from 4 am to 2 pm …

PER and TIM levels continue to rise in the cytoplasm 

At 2 pm, PER and TIM …

become a dimer and go back into the nucleus

At around 10 pm, the PER and TIM levels …

start to lower

We are awake when …

PER and TIM are in the cytoplasm (sleepy when they aren’t)

Human Circadian Rhythm: at 6 am …

cortisol is released

Human Circadian Rhythm: between 6 am and 12 pm …

• fastest increase in blood pressure

  • high alertness

Human Circadian Rhythm: between 12 pm and 6 pm …

• best coordination

  • fastest reaction times 

Human Circadian Rhythm: at 6 pm …

highest body temp

Human Circadian Rhythm: between 6 pm and 12 am …

• highest blood pressure

  • melatonin secretion

Human Circadian Rhythm: between 12 am and 6 am …

• deep sleep

  • lowest body temperature

wild type of fruit flies have a …

24hr cycle

3 mutants of fruit flies have …

no rhythm (arrhythmic)

a single gene in a fruit fly …

short and has a 19 hr period

in mutants …

there is a 28 hours period

actogram:

measure of activity (light and dark timings)

the 24 hr period is a …

human construct

the internal clock of a fruit fly is …

23.74 hours

for the sage grouse, they start leking at …

4 am - 9 am

predator hawks are large birds that need thermal air to fly effectively …

meaning that their clocks start after 9 am

during hibernation …

animals don’t eat, defecate, or pee; and only sleep

salmon start spawning …

May-Sept

brown bears regain activity in …

july

bears hibernate between …

Oct/Nov and Apr/May

clocks are important since food is an …

epheremerod resource, meaning it is unpredictable and comes & goes

in teleogryllus (crickets), males call to attract females but …

they are noctural

what animal has no circadian rhythm?

naked mole rat (totally nocturnal, feeds on roots)

in 1994, they found that reduced vision means that …

no light activated SCN

birds are active in the daytime and …

migrate at night

a second experiment with crickets were done which involved crickets that kept calling for several hours of each day, leading to the conclusion that …

enviroment independent interval (circadian)