The following points highlight the five main types of endogenous rhythms seen in animals. The types are: 1. Circadian Rhythm 2. Circa-Tidal Rhythm 3. Circannual Rhythm 4. Circa-Lunar Rhythm 5. Semilunar Rhythms.
Endogenous Rhythm: Type # 1. Circadian Rhythm:
This rhythm is matched with the 24 hour cycle of day and night. We ourselves provide a good example, as we tend to wake up almost at the same time every day in the morning and start feeling sleepy at night. Such circadian rhythms are exhibited by diurnal as well as nocturnal animals.
Endogenous Rhythm: Type # 2. Circa-Tidal Rhythm:
This rhythm is the 12-4 or 24-8 hour tide cycle synchronized with the low and high tides. Organisms living in the intertidal zone (shore crabs, fiddler crabs etc.) are alternately submerged in water and exposed to air. Due to this, pressure, salinity, food supply, temperature and predation also undergo changes. Therefore, animals inhabiting such areas show behavioural periodicity associated with the tides.
Endogenous Rhythm: Type # 3. Circannual Rhythm:
This has been defined as an approximately 365 day physiological pattern that regulates annual changes in activities. This may also be represented in terms of seasonal rhythms (summer, autumn, winter etc.). Circannual rhythms are widespread amongst animals and plants. Different physiological annual rhythms are breeding cycle, hibernation, diapause, migration etc.
Endogenous Rhythm: Type # 4. Circa-Lunar Rhythm:
ADVERTISEMENTS:
Circa-lunar or circa-synodic rhythms are synchronized with the phases of the moon. This is the 29.5 days’ lunar cycle. Such circa-lunar rhythm are common among marine invertebrates and insects. For example, the annelid palolo worm (Eunice viridis) of the Pacific Ocean (southern hemisphere), rises to the surface to spawn in great numbers when the moon is full during October/November, but the Atlantic palolo worm of the northern hemisphere similarly spawns in the last quarter of the moon in July. Worms isolated in the laboratory produce their gametes at the correct time, showing that this activity is controlled by biological clock of the palolo worm.
Another example is provided by the Jamaican fruit bats that have a pattern of feeding that involves leaving the day roost in the evening and feeding throughout the dark nights during the period of new moon.
However, during full moon they depart from their day roost at the normal time in the evening, but return, back when the moon is high, even when obscured by clouds, suggesting that they make use of an endogenous lunar clock to time their foraging and feeding behaviour.
Endogenous Rhythm: Type # 5. Semilunar Rhythms:
It is the biological rhythms which are synchronized with the fortnightly cycle of spring tide (high tide) and neap tide (low tide). It is also known as circasyzygic or circa-semilunar clocks. Such rhythm is exhibited by periwinkle (Littornia rudis). They show a marked 15 day periodicity in their locomotory activity. The species live high up on the shore and is only covered by the high water of spring tide.