Biological rhythms Flashcards
A biological clock
Biological clock:
An innate mechanism that controls the physiological activities of an organism which change on a daily, seasonal, yearly, or other regular cycle.
Zeitgeber:
A rhythmically occurring natural phenomenon which acts as a cue in the regulation of an organisms circadian rhythms. (English = ‘Timegiver’)
Chronobiology
A field of biology that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar- and lunar-related rhythms
Entrainment:
Entrainment:
When the timing of freerunning is synchronised by an external time signal (Zeitgeber)
Freerunning:
Freerunning:
A rhythm that persists in constant conditions
- Phase: A particular time point of a rhythm
- Phase angle: Time difference between two phases
- Phase advance: When a rhythm is altered so that its peak occurs earlier
- Phase delay: When a rhythm is altered so that its peak occurs later
- Phase shifts: General name of both phase delays and phase advances.
- Day (light) and night (dark) cycles:
- DD (constant darkness), LL (constant light) and LD is both light and dark, written as, for example, LD 16:8 (16h light, 8h dark)
- When you take away the light and dark there is something at the molecular level keeps you entrained to what you were used to before
α, ρ and τ
The time spent in a cycle where the organism is active (‘awake’) is Alpha (α)
The time spent in a cycle where the organism is not active (‘resting’) is Rho (ρ)
The length of a cycle of freerunning is its period length, Tau (τ)
- The circadian system plays a role in the measurement and interpretation of day length.
- In marine organisms the response to and role of Alpha, Rho and Tau reflect optimum conditions within a fluctuating environment to aid in survival, feeding and reproduction.
Alpha/Rho significance
Alpha/Rho significance and ratios are often species specific:
nocturnal (night active) or diurnal (day active)
Photoperiodism
Photoperiodism is the physiological reaction of organisms to the
length of day or night. It is vital to both plants and animals and
is important for synchronising seasonally important life history
events.
When do biological rhythms qualify as Circadian Rhythms
- Processes with 24-hour oscillations are often called diurnal rhythms; strictly speaking, they should not be called circadian rhythms unless their endogenous nature is confirmed.
- Although circadian rhythms are endogenous (“built-in”, self-sustained), they are entrained to the local environment by zeitgebers (e.g. light, temperature and redox cycles).
- Present in the sleeping/feeding cycles of animals, and patterns of core body temperature, brain wave activity, hormone production, cell regeneration, and other biological activities.
- In the absence of Zeitgebers, i.e. kept in total darkness for extended periods, animals eventually resort to a free-running rhythm, results in an advanced or delayed phase shift.
Melatonin,
Melatonin, (N-acetyl-5-methoxy tryptamine), is a hormone produced by the pineal gland in vertebrates.
Melatonin is produced from serotonin through two main enzyme steps.
Its rhythmic production provides information on daily and calendar time.
It is used to regulate sleep (timing), blood pressure regulation, seasonal reproduction, and many others.
Types of melatonin production profiles
- A feature of melatonin production is that regardless of whether an animal is diurnal or nocturnal, the peak concentration is at night.
- 3 different types of melatonin profile have been described in fish and vertebrates.
- Type A: peak late in the dark phase.
- Type B: peak during the middle of the dark phase.
- Type C: immediate increase at the start of the dark phase and remain elevated until morning.
- Different peaks times may help coordinate species specific behaviour including spawning.
Melatonin works in coordination with clock genes, which control activity patterns throughout a certain time period.
What are clock genes
Clock genes produce proteins that aid in the generation and regulation of circadian rhythms.
Gene up-regulation drives protein transcription and once protein products reach a certain concentration they inhibit this process.
The result is a endogenous rhythmic cycle, which allows animals adjust their behavioural or metabolic process in order to do everything “on time”.
Melatonin works in coordination with clock genes, which control activity patterns throughout a certain time period.
Clock genes produce proteins that aid in the generation and regulation of circadian rhythms
Gene up-regulation drives protein transcription and once protein products reach a certain concentration they inhibit this process.
The result is a endogenous rhythmic cycle, which allows animals adjust their behavioural or metabolic process in order to do everything “on time”.
Describe seasonal rhythms
- Timely prediction of seasonal periods of weather conditions, food availability, or predator activity is crucial for survival of many species.
- The changing length of the photoperiod is a very predictive environmental cue for the seasonal timing of physiology and behaviour, most notably for timing of migration, hibernation, and reproduction.
- Circannual rhythms can still occur in the absence of zeitgebers (migration)
- Can be detected in gradual but predictable changes (monthly temperatures)
- Can also be significant single periodic annual events (floods, droughts, blooms)
How do circatidal rhythms affect the deep sea?
- The lunar cycle drives water depth, a process that is detectable by organisms at great depth.
- At 1200m in Sagami bay, over 60 days, many deep-sea taxa can be observed reacting to the circalunar tidal cycle.
- Zeitgebers and associated biological rhythms are evidence that the deep-sea and its inhabitants are dynamic.
