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Sharma S.,Center for Biological Rhythm Research | Thakurdas P.,Center for Biological Rhythm Research | Sinam B.,Center for Biological Rhythm Research | Joshi D.,Center for Biological Rhythm Research
Chronobiology International | Year: 2012

Synergic contribution of light and temperature is known to cause a paradoxical masking effect (inhibition of activity by bright light and high temperature) on various rhythms of animals. The present study reports the paradoxical masking effects of 1000-lux photophase at 25°C on the locomotor activity rhythm of Drosophila malerkotliana. Flies were subjected to light (L)-dark (D) 12:12 cycles wherein the photophase was varied from 10 to 1000 lux, whereas the scotophase was set to 0 lux in these and subsequent LD cycles. At 10, 100, and 500 lux, the flies were diurnal; however, at 1000 lux they were nocturnal. Transfer from LD 12:12 cycles to continuous darkness (DD) initiated free-running rhythmicity in all flies. Free-running rhythms of the flies switched from the 10-lux to the 500-lux groups started from the last activity-onset phase of the rhythm following 35 transient cycles, suggesting involvement of the circadian pacemaker. In contrast, the free-running rhythm of the flies of the 1000-lux group began abruptly from the last lights-on phase of the LD cycle, indicating noninvolvement of the pacemaker. Furthermore, all flies showed nocturnal activity in the two types of LD 12:12 cycles when the photophase was 1000 lux. The first type of LD cycles had three succeeding photophases of 100, 1000, and again 100 lux, whereas the second type of LD cycles had only one photophase of 1000 lux, but the LD 12:12 cycles were reversed to DL 12:12 cycles. Apparently, the combined effects of light and temperature caused such paradoxical masking effects. This hypothesis was tested by repeating the above experiments at 20°C. Flies in all experiments exhibited a diurnal activity pattern, even when the photophase was 1000 lux. Thus, the present study demonstrates that the paradoxical masking effect in D. malerkotliana was caused by the additive influence of light intensity and temperature. This strategy appears to have physiological significance, i.e., to shun and thus protect against the bright photophase at high temperature in the field. © 2012 Informa Healthcare USA, Inc. Source


Sinam B.,Center for Biological Rhythm Research | Sharma S.,Center for Biological Rhythm Research | Thakurdas P.,Center for Biological Rhythm Research | Joshi D.,Center for Biological Rhythm Research
Chronobiology International | Year: 2012

Efficacy of the short photoperiod (Spp) and the long photoperiod (Lpp) in accelerating the reentrainment was assessed in Drosophila biarmipes. The Spp accelerated the reentrainment after the phase advance of light-dark (LD) cycles, which was associated with the early activity onset (Ψo) and the short period of free-running rhythm (τ). The Lpp accelerated the reentrainment after the phase delay of LD cycles, which was associated with the late Ψo and the long τ. This study indicates that the photoperiodic modulation of the circadian waveform of the underlying pacemaker that controls activity rhythm influenced the rate of reentrainment in D. biarmipes. (Author correspondence: drdsjoshi08@gmail.com). Copyright © Informa Healthcare USA, Inc. Source


Sinam B.,Center for Biological Rhythm Research | Sharma S.,Center for Biological Rhythm Research | Thakurdas P.,Center for Biological Rhythm Research | Joshi D.S.,Center for Biological Rhythm Research
Naturwissenschaften | Year: 2012

The efficacy of bright photophase (BP) in accelerating the re-entrainment of Drosophila biarmipes rhythm following 8 h phase advance and delay of light-dark (LD) cycle was examined by subjecting the flies to 24 h LD cycles with dim photophase (DP) at 30 lx and BP at 300 lx. Re-entrainment was analysed by using the activity onset, activity offset and the duration of activity. Following LD advance or delay, the BP flies re-entrained faster than the DP flies which was attributed to the enhanced zeitgeber strength of BP. Nevertheless, the re-entrainment was a protracted process even in the BP flies since the activity offsets underwent more transients than the activity onsets. Thus, this study demonstrates that the BP accelerates the re-entrainment in D. biarmipes. It, however, also reveals that the re-entrainment is a prolonged process when the activity onset and offset are regarded as the rhythm markers. © Springer-Verlag 2012. Source


Thakurdas P.,Center for Biological Rhythm Research | Sharma S.,Center for Biological Rhythm Research | Sinam B.,Center for Biological Rhythm Research | Chib M.,Center for Biological Rhythm Research | Joshi D.,Center for Biological Rhythm Research
Chronobiology International | Year: 2010

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 ∼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 (α) 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, α 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. © 2010 Informa UK Ltd. Source


Thakurdas P.,Center for Biological Rhythm Research | Sharma S.,Center for Biological Rhythm Research | Singh B.,Center for Biological Rhythm Research | Vanlalhriatpuia K.,Center for Biological Rhythm Research | Joshi D.,Center for Biological Rhythm Research
Chronobiology International | Year: 2011

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. © Informa Healthcare USA, Inc. Source

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