Behavioral and genetic analyses of fruit fly drosophila melanogaster populations selected for morning and evening adult emergence

Abstract

Almost all living organisms on the earth perceive robust 24-hr cycles of abiotic variables such as light, humidity and temperature, which occur as an inevitable consequence of unceasing rotation of the earth around its axis. Unicellular organisms such as bacteria to complex living systems such as human beings exhibit 24-hr rhythms in various behavioral and physiological processes. These rhythms persist under constant laboratory conditions with near 24-hr periodicity (hence circadian; circa - about, dies - day), which indicates that daily rhythms are not simply passive responses to 24-hr environmental cycles, but are the expression of some endogenous rhythm-generating systems (Dunlap et al., 2004). Scheduling of biological functions at specific time of the day is believed to be the primary function of these endogenous oscillators (Roenneberg et al., 2003a), which they achieve by using various environmental time cues such as light, temperature, social cues through a process known as entrainment (Johnson et al., 2003). The system comprising of core endogenous oscillators, mechanisms to sense environmental time cues (zeitgebers) and transduction mechanisms by which the oscillators regulate circadian rhythms are collectively known as “circadian clocks”.