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

Abstract

Photic entrainment of animals in the field is basically attributed to their exposure to the dimly lit nights flanked by the dawn and dusk twilight transitions. This implicates the functional significance of the dimly lit nights as that of the twilight transitions. Recently, the authors have demonstrated that the dimly lit night at 0.0006 lux altered the attributes of the circadian rhythm of locomotor activity of Drosophila jambulina. The present study examined whether the durations of such dimly lit nights affect the entrainment and free-running rhythmicity of D. jambulina. Flies were subjected for 10 days to two types of 24-h lighting regimes in which the photophase (L) was at 10 lux for all flies but the scotophase, which varied in duration from 9 to 15 h, was either at 0 lux (D phase) for control flies or 0.0006 lux (the artificial starlight or S phase) for experimental flies. Thereafter, they were transferred to constant darkness (DD) to compare the after-effects of the dimly lit nights on the period (τ) of free-running rhythm in DD with that of the completely dark nights. Control flies were entrained by all LD cycles, but the experimental flies were entrained only by five LS cycles in which the duration of the S phases ranged from 10 to 14 h. The two LS cycles with very short (9 h) and long (15 h) S phases rendered the flies completely arrhythmic. Control flies started activity shortly before lights-on and continued well after lights-off. The experimental flies, however, commenced activity several hours prior to lights-on but ended activity abruptly at lights-off as the result of a negative masking effect of nocturnal illumination. Length of the midday rest was considerably shorter in the control than in the experimental flies in each lighting regime. The active phase in the control flies was predictably shortened; nonetheless, it was invariable in the experimental flies as the nights lengthened. Transfer from lighting regimes to DD initiated robust free-running rhythmicity in all flies including the arrhythmic ones subjected to LS cycles with 9 and 15 h of scotophases. The τ was profoundly affected by the nocturnal irradiance of the prior entraining lighting regime, as it was always shorter in the experimental than in the control flies. Thus, these results indisputably demonstrate the changes in fundamental properties of the circadian pacemaker of D. jambulina were solely attributed to the extremely dim nocturnal irradiance. This strain of D. jambulina is entrained essentially by the dimly lit natural nights, since it is never exposed to the prevailing photic cues such as the twilight transitions or bright photoperiod, owing to the dense vegetation of its habitat.

Study on photoperiodic modulation of the female fertility of Drosophila biarmipes

“…The extremely short or long photoperiods are known to act as a weak zeitgeber, resulting in a poor entrainment, damping of the rhythm, arrhythmicity or miserable physiological performance in most attributes Thakurdas et al 2011;Sinam et al 2012). The results of the present study are in agreement with this hypothesis, as extremely short or extremely long photoperiods drastically reduced the fertility of D. biarmipes.…”

“…Other than the photoperiod, the dark phase or scotoperiod of the entraining light-dark cycles may change the basic properties of the overt rhythms of Drosophila. For example, the dimly lit scotoperiod (9 to 15 h) selectively altered almost all attributes of the entrainment of the locomotor activity rhythm of the males of Drosophila jambulina and subsequent free-running rhythmicity of the locomotor activity rhythm of D. jambulina (Thakurdas et al 2011). Recently, it was elegantly demonstrated that the photoperiod had profound influence on the process of re-entrainment of the adult locomotor activity rhythm of Drosophila biarmipes, wherein the accelerating effects of the photoperiod had strong reliance on the direction of the shift of light-dark cycles (Sinam et al 2013).…”

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

“…The broad spectrum (365–810 nm) white light obtained from the UV-free white light emitting diodes (6 VDC-0.02W, the angle of light emission 20–30°, Ligitek Electronics Co.) was used during the photophase at 300 lx as well as during the dim scotophase at 0.03 lx. The computerized photoelectric method for recording the adult locomotor activity rhythm of Drosophila has been described in details 2 , 15 , 22 . However, the method in brief is as follows.…”

“…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 . Dim nocturnal irradiance in D. melanogaster also advanced the morning peak but delayed the evening peak of activity that rendered the flies completely nocturnal 16 , 17 Moreover, it also altered the clock protein rhythms in the pacemaker neurons of the brain.…”

“…Entrainment in nature is accomplished by exposure of animals to the cycles of day and night, which consist of three powerful photic cues: the daylight, twilight transitions and the natural dim scotopic illumination 1 , 2 . Although the dim illumination failed to evoke any phase shifts or suppress the melatonin secretion in nocturnal rodents, 3 it was regarded as a persuasive photic contributor capable of altering the basic properties of the circadian pacemaker 4 .…”