Week 2 (Modules 3-4) Flashcards
Proximate causality = ____ or ______ questions
- how
- mechanism
Ultimate causality = _____ or ______ questions
- why
- function
When did life arise on Earth?
~3.5 billion years ago
In which domains of life are circadian rhythms found?
all 3 (eukaryote, bacteria, archaea)
Circadian clocks have ______ several times
evolved
What is the ‘escape from light’ hypothesis?
Ancient organisms may have evolved to perform vulnerable cellular processes at night, so UV rays do not disrupt them
What are the two hypotheses for the origins of circadian rhythms?
- escape from light/oxygen (external coordination)
- internal biochemical coordination
What is the ‘escape from oxygen’ hypothesis?
Ancient anaerobic organisms may have evolved circadian rhythms in order to produce antioxidants during the day, when photosynthesizing organisms produce oxygen
What is the ‘internal biochemical coordination’ hypothesis?
Organisms evolved circadian rhythms in order to be able to temporally separate internal processes that cannot occur at the same time
One of the most important functions of clocks is to anticipate _____
the change from day to night and back
Two uses of being able to predict the changes from night to day are:
- organisms are able to predict when food will be readily available
- organisms can predict when the best time to perform a biological function is
What is FAA?
Food-anticipatory activity - the emergence of activity prior to mealtime
At what time of day can rats and mice anticipate meals?
Any time of day
What are the two different modes of circadian clocks?
- alarm clock mode
- wristwatch mode
What is time-place learning?
When animals can discriminate time of day by learning to go to a particular place at a particular time of day
What is time-compensated sun-compass orientation?
When animals use the location of the sun to navigate, also taking into account the movement of the sun throughout the day
What is ‘swamping’?
When animals wait until a certain time using circadian clocks to perform an action that makes them vulnerable together
What is temporal niche segregation?
When two competitor species in the same niche use a circadian clock to be active during different parts of the day
What is photoperiodism?
When animals use circadian clocks to keep track of days passing, in order to anticipate yearly changes in the environment
Disrupted circadian rhythms have been linked to higher mortality rates of ____
cancer
Most organisms function optimally when _______
there is a match between the period of their circadian clock and the cycles of the environment
Loss of circadian rhythms has been suggested to cause
reduced lifespan
What is an oscillator?
Any device that produces a rhythm
What is a pacemaker?
Controls other oscillators
What is an interval timer?
A clock that is limited to timing one interval, then must be reset
What two problems does entrainment solve?
- Adjusting the timing to fit with a 24-hour interval
- Synchronizing the rhythm with the environment
What is masking?
A direct effect of an environmental stimulus on behaviour
If synchrony to a changed LD cycle is instantaneous, this is probably due to ____
masking
What is the difference between positive and negative masking?
Negative masking suppresses a behaviour, while positive masking stimulates it
What is the non-parametric entrainment model?
The hypothesis that entrainment can occur with small daily phase adjustments (period of the rhythm is not a parameter)
What is a parameter?
A feature of a clock that can be set
What can you predict if you know the tau of a circadian clock and the shape of its phase response curve?
- limits to entrainment
- phase of entrainment
- gradual re-entrainment
What factors determine how long it takes to shift to a new time zone?
- the magnitude of the shift
- the direction of travel
- the timing of light exposure
- parameters (wavelength, amplitude) of the light stimulus
What is the parametric entrainment model?
Hypothesizes that light entrains circadian rhythms by altering both the phase and period of the clock (period is a parameter of the rhythm)
Global environmental features are _______
- enduring
- stable
- nontrivial
From where did circadian clocks likely emerge?
primitive prokaryotic life forms
Where are local oscillators found?
In the specific body part they are responsible for providing a circadian rhythm for
What are three defining characteristics of circadian clocks?
- self-sustaining and have a ~24h period in consistent conditions
- temperature compensated
- entrainable by environmental stimuli
