When do biological rhythms occur?
When an animal’s physiological activities and behavior patterns can be directly related to environmental features that occur with regular frequency
Types of rhythms
Circadian- day
Circannual- year; reproduction, migration
Circalunar- month
Tidal
Circalunar rhythms (29.5 days)
Nocturnal predators increase activity around the time of a full noon
Tidal rhythm (12.5 hours)
Daily rhythm superimposed on tidal rhythm
How do animals synchronize their behavior and physiology to cyclic changes in the external environment
- direct response to changes in external environment
- biological clock synchronized to changes in external environment
- combination of both
Evidence for existence of biological docks
- rhythm persists in constant conditions of light, temperature
- animals reared in isolation exhibit rhythms
- mutants with altered rhythm
Characteristics of endogenous rhythms
- persist in absence of environmental cues
- period is not exactly that of environmental cycle
- rhythm is entrained by environmental cues
- temperature compensation
Adaptiveness of biological clocks
- synchronize the activities of animals with conditions in their environments
- enabling them to prepare in advance for predictable events such as night, winter
Location and functioning of circadian clock
Master clock located in the brain
Master clock is influenced by light
Melatonin
Hormone produced by pineal gland, regulates circadian rhythm
Circadian rhythms
- varies between individuals
- changes with age
