Abstract:
For centuries, it has been observed that behavioral and physiological processes of most organisms occur in a rhythmic manner with different periodicities (see Daan, 2010). Trees flower and fruit at species-specific seasons every year, marine organisms with inter-tidal habitats show behavioral processes that occur periodically according to tidal rhythms, petals of flowers open and close rhythmically at particular times of the day, different animal species remain active at specific times of the day, and so on (Dunlap et al., 2004). These biological rhythms were thought to arise as a result of the organism’s response to the cyclic temporal changes in its environment.
One of the first systematic documentations of the possible endogenous origins of such a biological rhythm was done by a French astronomer De Mairan in 1729 (De Mairan, 1729; Pittendrigh, 1965) who studied the daily, rhythmic movement of leaves in the Mimosa plant. Persistence of rhythmic leaf movements in an environment devoid of cyclic changes in light suggested that this rhythmic behaviour has an endogenous origin and is not a simple passive response to periodic changes in the environment. Subsequently, experiments over decades have provided support for the endogenous nature of such rhythms (Kleinhoonte, 1929; Bunning and Stern, 1930; see also, Daan, 2010).
