PSYC388 - Module 3: Evolution & Adaptive Significance of Circadian Rhythms & Clocks

in biology and psychology, scientists distinguish between 2 types of causality:

1. proximate

2. ultimate

what is proximate causality?

the "how"

mechanisms behind processes

ie. how brain cells generate circadian rhythms

ie. how LD cycles sync our internal clocks

how brain cells generate circadian rhythms

a) proximate causality

b) ultimate causality

a) proximate causality

what is ultimate causality?

the "why"

function or purpose of processes

ie "why circadian rhythms evolved and what advantages they provide"

"why circadian rhythms evolved and what advantages they provide"

a) proximate causality

b) ultimate causality

b) ultimate causality

this module (3) focuses on which?

a) proximate causality

b) ultimate causality

b) ultimate causality

circadian rhythms help organisms align with the 24 hour ____________

solar day

circadian rhythms help organisms align with the 24 hour solar day, which are _____________ encoded and have evolved because they provide ______________________

1. encoded

2. survival advantages

t or f: global environmental features are unstable and affect all life on earth

f: they're stable

natural selection favours traits like internal clocks that help organisms....

adapt to both local and global environments

Life began ______ billion years ago

a) 3.5

b) 4.5

c) 5.5

3.5

true circadian clocks are found across all 3 domains of life

what are these domains?

1. Eukaryotes

2. Bacteria

3. Archaea

true circadian clocks possess rhythms that...

persist in constant conditions with 24h periodicity

true circadian clocks are found across all 3 domains of life (eukaryotes, bacteria, archaea) and also across all major kingdoms like....

plants, animals, fungi, protists, chromists, archaebacteria, eubacteria

Circadian clocks are universal across life. They're present in multicellular eukaryotes like...

1. humans

2. mice

3 .fruitflies

4. worms

5. plants

6. fungi

Circadian clocks are universal across life. They're present in unicellular eukaryotes like...

1. algae

2. Euglena

Circadian clocks are universal across life. They're present in prokaryotes like...

1. cyanobacteria

2. human gut bacteria

3. extremophile archaea

what is proof that clocks are ancient and evolved early?

1. primitive organisms like cyanobacteria and archaea have circadian rhythms

2. their widespread across domains and kingdoms = ancient

what is proof that circadian clocks evolved multiple times?

1. different organisms use different clock genes

2. no shared clock genes between bacteria, plants, and animals = independent (convergent) evolution

what is proof that circadian clocks are vital for survival?

their continued presence in organisms implies they play big roles in survival

adapting to the 24 hrs day/night cycle

in regards to the escape from light hyp, what were the 2 main challenges that drove circadian evolution?

1. external coordination

2. internal coordination

in regards to the escape from light hyp, what do we mean by external coordination?

1/2 main challenges that drove circadian evolution

aligning biological functions with day-night cycles of light and temperature

in regards to the escape from light hyp what do we mean by internal coordination?

1/2 main challenges that drove circadian evolution

organizing cellular processes so that incompatible functions happen at different times

explain how sunlight was both useful and harmful for early organisms according to the escape from light hypothesis

provided energy but contained UV radiation which

1. damaged DNA, disrupting transcription

2. was harmful for organisms w/o UV protection

Explain the 2 ways in which circadian clocks were used as a defence mechanisms in early life from light (escape from light hyp)

1. timing: early life restricted vulnerable processes to night time (cell div, gene transcription)

2. movement: mobile organisms could "escape from light" by relocating before sunrise

t or f: many species today still perform critical cellular functions at night (escape from light hyp)

true (evidence for the escape from light hypothesis)

t or f: According to the escape from light hypothesis, light exposure at night causes greater cellular damage, supporting the evolutionary role of circadian clocks in UV protection

true

What was the hypothesis the followed after the "escape from light" hypothesis? for the origin hypothesis of the evolution of circadian clocks

escape from oxygen (radicals)

about ____b years ago, during the great oxidation event, cyanobacteria began producing large amounts of O2 through photosynthesis

a) 1.5b

b) 2.5b

c) 3.5b

b) 2.5b

about 2.5b years ago, during which event did cyanobacteria began producing large amounts of O2 through photosynthesis?

Great Oxidation Event

about 2.5b years ago, during the great oxidation event, _______________ began producing large amounts of O2 through photosynthesis

cyanobacteria

about 2.5b years ago, during the great oxidation event, cyanobacteria began producing large amounts of O2 through photosynthesis

what are cyanobacteria?

ancient, photosynthetic bacteria that produce oxygen

live in various environments

play a key role in ecosystems

can also cause harmful algal blooms.

about 2.5b years ago, during the great oxidation event, cyanobacteria began producing large amounts of ______ through photosynthesis

oxygen

about 2.5b years ago, during the great oxidation event, cyanobacteria began producing large amounts of O2 through what process?

photosynthesis

the process where organisms make their own food using sunlight, carbon dioxide, and water, and it produces oxygen as a result.

about 2.5b years ago, during the great oxidation event, cyanobacteria began producing large amounts of O2 through photosynthesis

what did this lead to?

rise of aerobic metabolism, which produces harmful reactive oxygen species (ROS) as byproducts

the Great Oxidation event led to the rise of aerobic metabolism

this process produced something a bit harmful, what was it?

harmful reactive oxygen species (ROS) as byproducts (ie. H202)

the Great Oxidation event led to the rise of aerobic metabolism

what is this?

the process your cells use to make energy from food using oxygen, and it produces a lot of energy along with carbon dioxide and water as byproducts.

the Great Oxidation event led to the rise of aerobic metabolism, which produced ROS (bad)

how did organisms fight this?

circadian clocks evolved to anticipate daytime oxygen production and activate anti-oxidants in advance to neutralize ROS

evolutionary advantage, more efficient and resilient

in the "escape from oxygen hypothesis", the rise of aerobic organisms led to the extinction of many _______________

anaerobic organisms

Anaerobic organisms live and grow without oxygen and may even be harmed by it, while aerobic organisms need oxygen to survive and make energy.

Oxygen metabolism produces ______________ like hydrogen peroxide (H202)

ROS (reactive oxygen species)

Why are ROS (reactive oxygen species) harmful?

highly reactive and can damage cells - liked to aging and disease like cancer

what was needed to neutralize the effects of ROS?

anti-oxidant systems

photosynthesis and ROS production happen during

a) the day

b) night

a) day

Because photosynthesis and ROS production happen during, what did organisms evolve into to defend themselves against the harm of ROS?

1. activate anti-oxidant production in advance

2. shut it down at night when no longer needed

What was hypothesis 2? for the evolutionary origins of circadian clocks?

Internal biochemical coordination hypothesis

Explain how plants and cyanobacteria evolved using the Internal biochemical coordination hypothesis

Some organisms needed ammonia to keep them healthy

to make ammonia, they took nitrogen from the air and used nitrogen fixation to turn it into ammonia

this process required enzyme nitrogenase

the issue was oxygen, made during photosynthesis destroys nitrogenase

so these 2 processes cant happen at the same time

so as a solution, organisms used time: photosynthesis for the day, nitrogen fixation for the night

their circadian clock controls this switch

the process where cells take nitrogen from the air and turn it into ammonia:

nitrogen fixation

nitrogen fixation, the process where cells take nitrogen from the air and turn it into ammonia: requires an enzyme called:

nitrogenase

what was stopping organisms form producing ammonia?

the oxygen produced during photosynthesis destroys nitrogenase, which is required for nitrogen fixation, which is used to make ammonia

photosynthesis was basically stopping organisms from making ammonia and keeping themselves healthy

what did they do as a solution?

photosynthesis occur in day

nitrogen fixation for night (O2 production stops)

explain how humans use internal biochemical coordination as an evolutionary advancement

glucose storage in liver:

after eating, liver stores sugar using enzyme glycogen synthase

when not eating, body needs sugar back into blood, and it does this using enzyme glycogen phosphorylase

these enzymes do opposite jobs so they're made at diff times of the day based on circadian clock

humans and internal biochemical coordination:

after eating, the liver stores sugar using an enzyme called:

glycogen synthase

humans and internal biochemical coordination:

when not eating, our bodies need sugar back in blood and does this using an enzyme called;

a) glycogen synthase

b) glycogen phosphorylase

glycogen phosphorylase

"The only reason for time is so that everything doesn't happen at once" -Einstein

what does this mean?

supports the internal biochemical coordination:

Some important things your cells need to do can't happen at the same time because they interfere with each other, thus our clocks help solve this

Circadian clocks were thought to help organisms _____________________ for predictable daily environmental changes like transition from night to day. temp, & humidity

anticipate and prepare

circadian clocks were thought to help organisms anticipate and prepare for predictable changes

these close evolved independently in different organisms and are widely conserved across specied due to their survival benefits

what do we mean by "widely conserved"?

something (like a gene, trait, or system) has remained similar across many different species over time because it’s important for survival and evolution has kept it.

what are examples of organisms that use circadian clocks for anticipatory benefits

1. nematodes (worms)

2. fruit flies

3. photosynthetic organisms

explain how nematodes (worms) evolutionarily used circadian clocks for anticipatory benefits

use clocks to time vertical movement in soil, avoiding extreme heat or dryness

explain how fruit flies evolutionarily used circadian clocks for anticipatory benefits

they come out of their cocoons around dawn, when it's best for their wings to dry.

Their internal clock keeps working while they change into adults and stays in sync with light.

Explain how photosynthetic organisms evolutionarily used circadian clocks for anticipatory benefits

use clocks to produce enzymes ahead of sunrise, maximizing efficiency

explain the importance of the "reliability of dawn" in regards to how organisms evolutionarily used circadian clocks for anticipatory benefits

dawn is a consistent environmental cue

its more dependable than temp or humidity

which organisms use to time crucial behaviours

t or f: food availability isn't really a key rhythm animals adapt to

false: its a key daily rhythm they adapt to

What does FAA mean and why is it important?

Food-anticipatory activity

animals can learn and remember the time of day that food is provided if predicable from day to day

Rats/mice show increased activity _____ hours before predictable meals

a) 1-2h

b) 2-4h

c) 4-6h

a) 1-2h

t or f: FAA persists even when meals are skipped

true

FAA persists even when meals are skipped

what does this imply?

implies the use of internal clocks, not just hunger or external cues

t or f: animals can anticipate meals in constant light or darkness

true

t or f: animals can anticipate multiple meals per day, possibly up to 4

true

Provide evidence that animals can remember when and where food appears?

honey bees:

use circadian clocks like an alarm clock to start/stop foraging

use clocks like a wrist watch to remember specific times and places

can recall up to 9 meal times tied to distant locations even w/o time cues

honey bees can remember when and where food appears

what is this ability called? Why is this ability important?

zeitgedächtnis (memory for time)

enables efficient foraging

t or f: birds and rodents are the only organisms that cannot demonstrate time-place learning

false: Birds and rodents also demonstrate time-place learning, though rats require more training.

birds, bees, and butterflies navigate using the _____

sun

birds, bees, and butterflies navigate using the sun, which moves ___ degrees an hour

a) 12

b) 15

c) 20

b) 15

birds, bees, and butterflies navigate using the sun, which moves 15 degrees an hour

to navigate accurately, animals adjust their orientation based on:

time of day using a circadian clock

bees use the _________________ to communicate distance and direction of food relative to the sun

waggle dance

bees use the waggle dance to communicate distance and direction of food relative to the sun

and clocks help them do what?

compensate for sun movement

bees use the waggle dance to communicate distance and direction of food relative to the sun

and clock helps them compensate for sun movement

what does this all mean?

Bees perform a special movement called the waggle dance to tell other bees where to find food.

The dance shows:

1. Direction of the food (based on the angle to the sun).

2. Distance to the food (based on how long they "waggle").

bees also use an internal clock to adjust their dance if the sun moves across the sky.

ex. if sun has shifted since the bee found the food, the bee changes the angle of the dance accordingly.

This keeps the directions accurate even as time passes.

t or f: birds and butterflies, like bees, use time-compensated navigation during long-distance migrations

true

circadian clocks allow for complex behaviours like:

timing, memory, and spatial navigation

t or f: humans are the best at circadian clock complex behaviours like timing, memory, and spatial navigation

false: bees outperform humans here

overall, internal clocks enhance survival by allowing animals to

optimize behaviour without relying solely on external cues

mating success increases when males and females:

are active at the same time

mating success increases when males and females are active at the same time

this is achieved by:

aligning rest-activity cycles to shared environmental cues

explain how blind mole rats, despite living underground, have true circadian rhythms entrained to LD cycles

light-sensitive eyes under their skin that detect light and connect to brain's circadian clock

exposed to light when digging

15 mins of light per day is enough to entrain their rhythms

despite living underground, they have true circadian rhythms entrained to LD cycles

Even in animals that live underground (like blind and naked mole rats), circadian rhythms can still be entrained by very limited light exposure—especially in individuals with specific roles (like digging).

explain how naked mole rats entrain their clocks

tunnel digging workers get occasional light exposure which may help them entrain their clocks

Even in animals that live underground (like blind and naked mole rats), circadian rhythms can still be entrained by very limited light exposure—especially in individuals with specific roles (like digging).

explain how dispersers maintain genetic diversity through outbreeding

Dispersers are a special type of individual in some eusocial animals (like naked mole rats) whose job is to leave their home colony and go find a new one—or even start a new one themselves.

Workers = day-active

Dispersers = night-active

Likely because dispersal occurs at night when it’s safer for vulnerable individuals.

“You don’t belong here anymore—it’s your job to go out, find new mates, and keep the species strong.”

t or f: circadian clocks synchronize behaviour across sexes/species for optimal survival and reproduction

true

t or f: circadian clocks synchronize behaviour across sexes/species for optimal survival and reproduction, and even blind or underground species rely on light cues to regulate these rhythms

true

how do naked mole rats' social roles support division of labour and maintain survival strategies?

they align with distinct circadian patterns

Explain how Guillemot chicks survive with circadian clocks (demonstrating avoidance)

they leave the nest when mature (fledge) which is risky due to predators

they fledge in large groups at night when light is low

this behaviour is regulated by circadian clock

this strategy is known as swamping which overwhelms predators

what is swamping?

strategy where prey fledge (leave the nest) in large groups to overwhelm predators

this behaviour is controlled by circadian clock

another ie. fruit flies emerge at down

explain how desert rats use circadian rhythms to avoid competition, not predators (demonstrating temporal niche segregation)

only the dominant larger species stay nocturnal

smaller ones become dinural to avoid conflict

temporal niche segregation: sharing the same space but using different times to reduce competition

what is temporal niche segregation?

sharing the same space but using different times to reduce competition

demonstrates how animals use circadian rhythms to avoid competition

explain how malaria parasites use circadian timing to maximize transmission and avoid immune attack

-live in mosquito vectors infect hosts during bites

-after maturing in liver cells, they enter bloodstream in evening when mosquitoes are active

-return to liver in morning to hide from immune system

what are the 2 benefits that circadian control offers for malaria parasites?

1. maximizes transmission to mosquitoes (evening emergence)

2. swamps the hosts immune system (which cant kill them all at once)

releasing many at once to overwhelm predators or immune defenses

swamping

what are the 3 ways circadian clocks help animals in avoidance

1. timing predator avoidance (fledging)

2. avoiding competition (temporal niche segregation)

3. timing transmission and immune evasion

t or f: even tiny organisms like parasites rely on circadian rhythms for survival strategies

true

What is photoperiodism?

1. tracking day length to anticipate seasonal changes

2. relies on circadian clock as internal calendar

3. common in both plants and animals

t or f: photoperiodism is a unique feature only found in plants

f: plants and humans