Nocturnal Illumination Dimmer Than Starlight Altered the Circadian Rhythm of Adult Locomotor Activity of a Fruit Fly

Abstract

The effects of nocturnal irradiance tenfold dimmer than starlight intensity on the locomotor activity rhythm of Drosophila jambulina were investigated in two types of light-dark (12 h:12 h) cycles, in which light intensity of the photophase was 10 lux while that of the scotophase was either 0 lux for control flies or 0.0006 lux for experimental flies. Activity onset in the experimental flies was approximately 5.4 h prior to lights-on, so it occurred around midnight. However, activity onset of the control flies coincided almost with the lights-on. Nevertheless, activity offset was the same in both groups, occurring at lights-off. Duration of the active phase (alpha) and activity passes/fly/cycle (APC) in the experimental flies was far greater than in controls. After-effects of the nocturnal illumination of the light-dark cycles when the flies were transferred to constant darkness were evident as the period of the free-running rhythm was shortened, alpha was lengthened, and APC was enhanced in the experimental compared to control flies. Thus, very low photic sensitivity of these flies appears to be a physiological adaptation to dim-light ambiance in its natural breeding site in the field.

Varying the Length of Dim Nocturnal Illumination Differentially Affects the Pacemaker Controlling the Locomotor Activity Rhythm ofDrosophila Jambulina

“…For example, bright nocturnal irradiance adversely affected several aspects of the circadian physiology and behavior of humans (Kloog et al, 2011;Siegelova et al, 2006) and social voles, Microtus socialis (Zubidat et al, 2007). Similarly, dim nocturnal irradiance varying from starlight to moonlight intensity modified many features of the circadian locomotor activity rhythm of bats (Erkert et al, 1976;Joshi & Chandrashekaran, 1982;Vanlalnghaka et al, 2006), hamsters (Evans et al, 2005;Gorman & Elliot, 2004;Gorman et al, 2003Gorman et al, , 2006, and fruit fly, Drosophila (Bachleitner et al, 2007;Hirsh et al, 2010;Kempinger et al, 2009;Thakurdas et al, 2009Thakurdas et al, , 2010. Thus, several studies have reported the effects of the intensity of nocturnal illumination on the circadian rhythms of animals.…”

“…Besides, the detection of the extremely dim scotophases used in the present experiments is not a herculean task for this strain of D. jambulina. This is because it is already endowed with exceptionally diminished circadian photic threshold for entrainment by virtue of its adaptation to the dim natural photic ambience at its breeding site in the Sapota orchard (Thakurdas et al, 2010).…”

“…Methods for the monitoring the circadian rhythm of the locomotor activity of adult D. jambulina and for data analysis have been previously described in detail (Thakurdas et al, 2010). Briefly, locomotor activity was monitored with the Chronobiology Kit (Stanford Software Systems, Santa Cruz, CA, USA).…”

“…Two groups of flies were subjected to cycles of 12 h of light at 10 lux and 12 h of scotophase at 0 and 0.0006 lux for control and experimental flies, respectively. The morning peak of the experimental flies was advanced by ∼5 h during entrainment, and the period of free-running rhythm (τ) was considerably shortened in subsequent constant darkness (DD) when compared with the control flies (Thakurdas et al, 2010). The objectives of the present study were to examine whether or not the durations of such a dimly lit night (0.0006 lux) affect the pacemaker controlling the locomotor activity rhythm of this strain.…”

Dim scotopic illumination accelerates the reentrainment following simulated jetlags in a diurnal experimental model, Drosophila

“…For example, the dim natural and artificial nighttime illuminations altered the attributes of entrainment and free-running rhythm of the pupal eclosion of D. jambulina 14 . In the same species, the nocturnal illumination at 0.0006 lx advanced the activity onset by several hours, extended the activity duration, enhanced the activity level and shortened the period of free-running rhythm 15 . Varying durations (9–15 h) of the dim scotophase at 0.0006 lx modulated the fundamental properties of the circadian pacemakers that controlled the adult locomotor activity rhythm of D. jambulina 2 .…”