Circadian rhythm of locomotor activity in the Japanese honeybee, Apis cerana japonica

Abstract.  To reveal circadian characteristics and entrainment mechanisms in the Japanese honeybee Apis cerana japonica , the locomotor-activity rhythm of foragers is investigated under programmed light and temperature conditions. After entrainment to an LD 12 : 12 h photoperiodic regime, free-running rhythms are released in constant dark (DD) or light (LL) conditions with different free-running periods. Under the LD 12 : 12 h regime, activity offset occurs approximately 0.4 h after lights-off transition, assigned to circadian time (Ct) 12.4 h. The phase of activity onset, peak and offset, and activity duration depends on the photoperiodic regimes. The circadian rhythm can be entrained to a 24-h period by exposure to submultiple cycles of LD 6 : 6 h, as if the locomotive rhythm is entrained to LD 18 : 6 h. Phase shifts of delay and advance are observed when perturbing single light pulses are presented during free-running under DD conditions. Temperature compensation of the free-running period is demonstrated under DD and LL conditions. Steady-state entrainment of the locomotor rhythm is achieved with square-wave temperature cycles of 10 °C amplitude, but a 5 °C amplitude fails to entrain.     

The timing of larval wandering and puparium formation in the flesh-fly Sarcophaga argyrostoma

ABSTRACT. In mixed-age cultures of the flesh-fly, Sarcophaga argyrostoma (Robineau-Desvoidy), the initiation of larval wandering (exodus behaviour) occurs as a gated circadian rhythm. In light-dark (LD) cycles, most of this activity occurs in the dark, except in very short nights, or in certain phase relationships between the rhythm and light cycle. When transferred from series of LD cycles into continuous darkness (DD), cultures show a weakly persistent free-running rhythm with a period of about 21 h. However, after transfer of first instar larvae from continuous light (LL) to DD, no such rhythm is observed. In contrast to larval exodus, formation of the puparia occurs at any stage of the LD cycle. The physiological mechanisms underlying this gated exodus behaviour, and its possible selective advantages, are discussed.     

Circadian clock controlling egg hatching in the cricket (Gryllus bimaculatus)

Adult crickets (Gryllus bimaculatus) were maintained under a 12-h light:12-h dark cycle (LD 12:12). After oviposition, their eggs were incubated under different lighting regimens at 23 degrees C, and temporal profiles of egg hatching were examined. When the eggs were incubated in LD 12:12 or in DL 12:12 with a phase difference of 12h from LD 12:12, throughout embryogenesis, 88% to 97% of hatching occurred within 3 h of the dark-light transition on days 17 and 18 of embryogenesis; the phases of the egg-hatching rhythms in the LD 12:12 and DL 12:12 groups differed by about 12 h. In eggs incubated in constant darkness (DD) throughout embryogenesis, a circadian (about 24 h) rhythm of hatching was found, and the phase of the rhythm was similar to that seen in eggs incubated in LD 12:12, but not DL 12:12, throughout embryogenesis. When eggs that had been incubated in DD after oviposition were transferred to DL 12:12 in the middle or later stages of embryogenesis and were returned to DD after three cycles of DL 12:12, the rhythm of hatching synchronized (entrained) to DL 12:12. However, when eggs in the earlier stages of embryogenesis were transferred from DD to DL 12:12 and returned to DD after three cycles, 52% to 94% of hatching did not entrain to DL 12:12. To determine whether photoperiodic conditions to which the parents had been exposed influenced the timing of egg hatching, adult crickets were maintained in DL 12:12, and their eggs were incubated in LD 12:12, DL 12:12, or DD throughout embryogenesis. The egg-hatching rhythm was also found in the eggs incubated under these three lighting regimens. In DD, the phase of the rhythm was similar to that seen in eggs incubated in DL 12:12, not LD 12:12, throughout embryogenesis. The results indicate that in the cricket, the timing of egg hatching is under circadian control and that the circadian rhythm of hatching entrains to 24-h light:dark cycles, but only if the light:dark cycles are imposed midway through embryogenesis. Therefore, by midembryogenesis, a circadian clock has been formed in the cricket, and this is entrainable to light:dark cycles. In addition, the photoperiodic conditions to which the parents (probably the mothers) have been exposed influence the timing of hatching, suggesting that maternal factors may regulate the timing of egg hatching.     

Presence of circadian rhythms in the locomotor activity of a cave-dwelling millipede Glyphiulus cavernicolus sulu (Cambalidae, Spirostreptida)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757-765, 2000)     

Temporal Organization in Locomotor Activity of the Hypogean Loach, Nemacheilus Evezardi, and its Epigean Ancestor

Locomotor activity rhythm in the hypogean population of Nemacheilus evezardi was recorded first under light-to-dark (LD) 12 : 12 h cycle and then DD. The results were compared with that of its epigean counterpart held under comparable regimes. In LD 12 : 12, while hypogean loach exhibited a distinct bimodality in its locomotor activity rhythm, it was altogether absent in the case of epigean population. In hypogean loach, dark-to-light transition peak in LD was observed to free-run under DD. The same was not discernible in case of epigean loach. The locomotor activity rhythm in epigean fish was noticed to free-run in DD either from the dawn peak or dusk peak in LD. It is hypothesized that the hypogean fish still possesses a functional oscillator underlying its overt circadian rhythm in locomotor activity. The ecophysiological significance of these findings is yet to be fully understood.     

Possible evidence for shift work schedules in the media workers of the ant species Camponotus compressus

The locomotor activity rhythm of the media workers of the ant species Camponotus compressus was monitored under constant conditions of the laboratory to understand the role of circadian clocks in social organization. The locomotor activity rhythm of most ants entrained to a 24 h light/dark (12:12 h; LD) cycle and free-ran under constant darkness (DD) with circadian periodicities. Under entrained conditions about 75% of media workers displayed nocturnal activity patterns, and the rest showed diurnal activity patterns. In free-running conditions these ants displayed three types of activity patterns (turn-around). The free-running period (τ) of the locomotor activity rhythm of some ants (10 out of 21) showed period lengthening, and those of a few (6 out of 21) showed period shortening, whereas the locomotor activity rhythm of the rest of the ants (5 out of 21) underwent large phase shifts. Interestingly, the pre-turn-around τ of those ants that showed nocturnal activity patterns during earlier LD entrainment was shorter than 24 h, which became greater than 24 h after 6-9 days of free-run in DD. On the other hand, the pre-turn-around τ of those ants, which exhibited diurnal patterns during earlier LD entrainment, was greater than 24 h, which became shorter than 24 h after 6-9 days of free-run in DD. The patterns of activity under LD cycles and the turn-around of activity patterns in DD regime suggest that these ants are shift workers in their respective colonies, and they probably use their circadian clocks for this purpose. Circadian plasticity thus appears to be a general strategy of the media workers of the ant species C. compressus to cope with the challenges arising due to their roles in the colony constantly exposed to a fluctuating environment.     

Possible Evidence for Shift Work Schedules in the Media Workers of the Ant Species Camponotus compressus

The locomotor activity rhythm of the media workers of the ant species Camponotus compressus was monitored under constant conditions of the laboratory to understand the role of circadian clocks in social organization. The locomotor activity rhythm of most ants entrained to a 24 h light/dark (12:12 h; LD) cycle and free-ran under constant darkness (DD) with circadian periodicities. Under entrained conditions about 75% of media workers displayed nocturnal activity patterns, and the rest showed diurnal activity patterns. In free-running conditions these ants displayed three types of activity patterns (turn-around). The free-running period (τ) of the locomotor activity rhythm of some ants (10 out of 21) showed period lengthening, and those of a few (6 out of 21) showed period shortening, whereas the locomotor activity rhythm of the rest of the ants (5 out of 21) underwent large phase shifts. Interestingly, the pre-turn-around τ of those ants that showed nocturnal activity patterns during earlier LD entrainment was shorter than 24 h, which became greater than 24 h after 6–9 days of free-run in DD. On the other hand, the pre-turn-around τ of those ants, which exhibited diurnal patterns during earlier LD entrainment, was greater than 24 h, which became shorter than 24 h after 6–9 days of free-run in DD. The patterns of activity under LD cycles and the turn-around of activity patterns in DD regime suggest that these ants are shift workers in their respective colonies, and they probably use their circadian clocks for this purpose. Circadian plasticity thus appears to be a general strategy of the media workers of the ant species C. compressus to cope with the challenges arising due to their roles in the colony constantly exposed to a fluctuating environment.     

Entrainment Properties of the Locomotor Activity Rhythm of Drosophila melanogaster Under Different Photoperiodic Regimens

In this paper we report the results of an experiment to assess how closely repeated brief light pulses (LPs) mimic the effects of 12:12 h light/dark (LD) cycles (PPc). The locomotor activity rhythm of individual fruit flies from a laboratory population of Drosophila melanogaster was monitored under four different photoperiodic regimens, created using 12 h of light and 12 h of darkness or brief light pulses (LPs). The phase relationship (Ψ) and the stability (precision) of the locomotor activity rhythm during entrainment were estimated in order to compare the state of the circadian clocks under the four different photoperiodic regimens. The flies (n = 72) were subjected to four different LD cycles: (i) 12 h of light and 12 h of darkness (complete photoperiod, PPc); (ii) a single brief LP of 15 min duration presented close to the onset of activity (SLP-1); (iii) a single brief LP of 15 min duration administered close to the offset of activity (SLP-2); and (iv) two brief LPs administered 12 h apart (skeleton photoperiod, PPs). The locomotor activity rhythm of the flies was first monitored under constant darkness (DD) for about 10 days and then under the four different photoperiodic regimens for about 10 days, and finally in DD for the remainder of the experiment. The Ψ of the locomotor activity rhythm and its precision under PPc and PPs did not differ significantly, but they were significantly different from the SLP-1 and SLP-2 conditions. The results provide interesting insights into photoentrainment mechanisms of circadian clocks in D. melanogaster, and suggest that skeleton photoperiods, but not single brief LPs, mimic the actions of complete photoperiods.     

Locomotor Activity of the Fiddler Crab, Uca subcylindrica (Stimpson), under Artificial Illumination

Specimens of the fiddler crab Uca subcylindrica (Stimpson) were captured in south Texas (USA) for locomotor rhythm studies. Actographic data were analyzed using Tau™ sofware. Under constant illumination (LL) and darkness (DD), the semiterrestrial crabs express a circadian rhythm of locomotion. When exposed to illumination/darkness cycles (LD_12:12 or LD_14:10), their bouts of activity are entrained to the photoperiod. In LD, activity is generally bimodal with an initial burst about 0.5 h after illumination. A second burst of activity begins 1 to 2 h before the end of illumination. When transferred from LD to LL, a locomotor rhythm with an average period of 24.6 ± 1.0 h (n = 19) is expressed in 89 percent of the crabs. On the other hand, when placed in DD after LD (n = 8), the crabs are either arrythmic or weakly rhythmic (period = 23.8 ± 0.2 h; n = 2). If the onset of illumination is advanced by 6 h, a period of less than 24.0 h is detected in the actogram. If the onset of illumination is delayed by 6 h, a locomotor rhythm with a period greater than 24.0 h appears. The locomotor behavior of this species of fiddler crab, Uca subcylindrica, is not related to the tidal rhythmicities seen in other members of the genus Uca. Rather, it has strong circadian components.     

Locomotor Activity of the Fiddler Crab,Uca subcylindrica (Stimpson), under Artificial Illumination

Specimens of the fiddler crab Uca subcylindrica (Stimpson) were captured in south Texas (USA) for locomotor rhythm studies. Actographic data were analyzed using Tau? sofware. Under constant illumination (LL) and darkness (DD), the semiterrestrial crabs express a circadian rhythm of locomotion. When exposed to illumination/darkness cycles (LD_12:12 or LD_14:10), their bouts of activity are entrained to the photoperiod. In LD, activity is generally bimodal with an initial burst about 0.5 h after illumination. A second burst of activity begins 1 to 2 h before the end of illumination. When transferred from LD to LL, a locomotor rhythm with an average period of 24.6 ± 1.0 h (n = 19) is expressed in 89 percent of the crabs. On the other hand, when placed in DD after LD (n = 8), the crabs are either arrythmic or weakly rhythmic (period = 23.8 ± 0.2 h; n = 2). If the onset of illumination is advanced by 6 h, a period of less than 24.0 h is detected in the actogram. If the onset of illumination is delayed by 6 h, a locomotor rhythm with a period greater than 24.0 h appears. The locomotor behavior of this species of fiddler crab, Uca subcylindrica, is not related to the tidal rhythmicities seen in other members of the genus Uca. Rather, it has strong circadian components.     

PRESENCE OF CIRCADIAN RHYTHMS IN THE LOCOMOTOR ACTIVITY OF A CAVE-DWELLING MILLIPEDE GLYPHIULUS CAVERNICOLUS SULU (CAMBALIDAE,SPIROSTREPTIDA)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757–765, 2000)     

Aging alters properties of the circadian pacemaker controlling the locomotor activity rhythm in males of Drosophila nasuta

Effects of aging on the circadian rhythm of locomotor activity in males of Drosophila nasuta were investigated. The adult life of males was divided in 1-3 stages according to spontaneous changes in free-running period x in constant darkness (DD): stage 1, days 1-19; stage 2, days 20-36; stage 3, days 37-43. Stage 1 was characterized by a bimodal activity pattern with a short light-induced morning peak and a prolonged evening peak when the flies were entrained to light-dark cycles of 12 hours of light, 12 hours of darkness (LD 12:12). The morning peak had a phase angle difference Ψ_m (Ψ, the time from lights on in LD 12:12 cycles to the onset of morning peak) of about 0.1h, while Ψ_e (Ψ of evening peak) was about 9h at stage 1. The transient morning peak was curtailed at the end of stage 1. At stage 2, the Ψ_e was about 10h, and the activity end was delayed by an addition of about 3h of activity in the scotophase. The changes in W during DD free runs were determined in two groups of flies: flies reared in LD 12:12 and flies reared in DD. In both groups, W increased from about 23h at stage 1 to about 25h at stage 2. Stage 3 was characterized by arrhythmicity associated with highest mean activity level (total number of passes/fly/day) in the entrained and both free-running groups. The mean activity level increased significantly from stage 1 to stage 3 in all three groups of flies.     

Rhythmic egg-laying behaviour in virgin females of fruit flies Drosophila melanogaster

Fruit fly Drosophila melanogaster females display rhythmic egg-laying under 12:12?h light/dark (LD) cycles which persists with near 24?h periodicity under constant darkness (DD). We have shown previously that persistence of this rhythm does not require the neurons expressing pigment dispersing factor (PDF), thought to be the canonical circadian pacemakers, and proposed that it could be controlled by peripheral clocks or regulated/triggered by the act of mating. We assayed egg-laying behaviour of wild-type Canton S (CS) females under LD, DD and constant light (LL) conditions in three different physiological states; as virgins, as females allowed to mate with males for 1?day and as females allowed to mate for the entire duration of the assay. Here, we report the presence of a circadian rhythm in egg-laying in virgin D. melanogaster females. We also found that egg-laying behaviour of 70 and 90% females from all the three male presence/absence protocols follows circadian rhythmicity under DD and LL, with periods ranging between 18 and 30?h. The egg-laying rhythm of all virgin females synchronized to LD cycles with a peak occurring soon after lights-off. The rhythm in virgins was remarkably robust with maximum number of eggs deposited immediately after lights-off in contrast to mated females which show higher egg-laying during the day. These results suggest that the egg-laying rhythm of D. melanogaster is endogenously driven and is neither regulated nor triggered by the act of mating; instead, the presence of males results in reduction in entrainment to LD cycles.     

Effects of background light conditions on thermoperiodic eclosion rhythm of onion fly Delia antiqua

To elucidate the effects of light on thermoperiodic regulation of adult eclosion rhythm in the onion fly, Delia antiqua, the responses to two thermoperiods, 29°C (12 h):21°C (12 h) and 25.5°C (12 h):24.5°C (12 h), with different amplitude and same average temperature, were examined in continuous darkness (DD) and continuous light (LL). Irrespective of the temperature step between warm phase (W) and cool phase (C), temperature cycles effectively entrained the adult eclosion rhythm in both DD and LL. Eclosion peaks, however, varied with light conditions and temperature step between W and C. It advanced by approximately 2–3 h in DD than in LL and at smaller temperature step. Background light conditions and temperature step also affect the amplitude of eclosion rhythm. It became lower in LL than in DD and at smaller temperature steps. On transfer to constant temperature (25°C), eclosion rhythm was elicited earliest in the pupae at 8°C temperature step in DD and latest in those at 1°C temperature step in LL. Pupae at 1°C temperature step in DD and at 8°C temperature step in LL demonstrated intermediate responses, but the eclosion rhythm was elicited 1 day earlier in the former than in the latter. This might be ascribed to the interaction between background light and temperature step under thermoperiodic conditions. The results suggest that continuous light and a smaller temperature step weaken the coupling strength between eclosion rhythm and thermoperiod, but the light effect is stronger than the temperature step effect.     

Light and temperature cooperate to regulate the circadian locomotor rhythm of wild type and period mutants of Drosophila melanogaster

In the wild type (Canton-S) and period mutant flies of Drosophila melanogaster, we examined the effects of light and temperature on the circadian locomotor rhythm. Under light dark cycles, the wild type and per(S) flies were diurnal at 25 degrees C. However, at 30 degrees C, the daytime activity commonly decreased to form a rather nocturnal pattern, and ultradian rhythms of a 2 approximately 4h period were observed more frequently than at 25 degrees C. The change in activity pattern was more clearly observed in per(0) flies, suggesting that these temperature dependent changes in activity pattern are mainly attributable to the system other than the circadian clock. In a 12h 30 degrees C:12h 25 degrees C temperature cycle (HTLT12:12), per(0) flies were active during the thermophase in constant darkness (DD) but during the cryophase in constant light (LL). The results of experiments with per(0);eya flies suggest that the compound eye is the main source of the photic information for this reversal. Wild type and per(0) flies were synchronized to HTLT12:12 both under LL and DD, while per(S) and per(L) flies were synchronized only in LL. This suggests that the circadian clock is entrainable to the temperature cycle, but the entrainability is reduced in the per(S) and per(L) flies to this particular thermoperiod length, and that temperature cycle forces the clock to move in LL, where the rhythm is believed to be stopped at constant temperature.     

Active sensing in a freely walking spider: look where to go

The Central American hunting spider Cupiennius salei, like most other spiders, has eight eyes, one pair of principal eyes and three pairs of secondary eyes. The principal eyes and one pair of the secondary eyes have almost completely overlapping visual fields, and presumably differ in function. The retinae of the principal eyes can be moved independently by two pairs of eye muscles each, whereas the secondary eyes do not have such eye muscles. The behavioural relevance of retinal movements of freely moving spiders was investigated by a novel dual-channel telemetric registration of the eye muscle activities. Walking spiders shifted the ipsilateral retina with respect to the walking direction before, during and after a turning movement. The change in the direction of vision in the ipsilateral anterior median eye was highly correlated with the walking direction, regardless of the actual light conditions. The contralateral retina remained in its resting position. This indicates that Cupiennius salei shifts it visual field in the walking direction not only during but sometimes previous to an intended turn, and therefore “peers” actively into the direction it wants to turn.     

Seasonal changes in the circadian activity rhythm of light-dark (LD) and completely dark (DD) regimen in the mouse submandibular gland in the presence of light-dark (LD) and completely dark (DD) regimen

Influence of seasons on circadian activity changes and the influence of one and six weeks of DD upon these changes of acid phosphatase (AP) and beta-acetylglucosaminidase (AM) was studied in the submandibular gland of sexually mature male mice. Total enzyme activity was determined in tissue homogenates at four-hour intervals in March, June, October, and February under standard LD12/12 conditions and after one and six weeks of the DD regime. The rhythms were analysed according to cosinor method. Under constant lighting conditions the seasonal differences in the AM circadian activity rhythm were found. AP activity was considerably less influenced by seasonal changes. Both enzyme activity changes were independent of each other and each rhythm was differently influenced by DD. In the case of AM the most pronounced circadian activity changes had the highest amplitude and mesor occurred in summer. The strongest influence of DD upon this enzyme activity rhythm was observed in spring and summer especially after the first week, after six weeks the acrophase returned to the LD group value (spring). In autumn and winter the reaction to DD was different to that of summer and spring. For AP the circadian changes of activity were non-rhythmic in spring, whereas in all other seasons the acrophases occurred almost at the same time in the afternoon. In DD the activity rhythm significantly changed after six weeks. In all seasons, except spring the circadian rhythm of activity was not observed after six weeks of DD. An attempt was made to explain the observed results by the certain kind of genetic memory present in laboratory animals the neurohormonal system of which is influenced by seasonal changes.     

LIGHT AT NIGHT ALTERS THE PARAMETERS OF THE ECLOSION RHYTHM IN A TROPICAL FRUIT FLY,DROSOPHILA JAMBULINA

We investigated the effects of natural light at night (LAN) in the field and artificial LAN in the laboratory on the circadian rhythm of pupal eclosion in a tropical wild type strain of Drosophila jambulina captured at Galle, Sri Lanka (6.1^oN, 80.2^oE). The influence of natural LAN, varying in intensity from 0.004 lux (starlight intensity) to 0.45 lux (moonlight intensity), on the entrainment pattern of the circadian rhythm of eclosion at 25^o?±?0.5^oC was examined by subjecting the mixed-aged pupae to natural cycles of light and darkness at the breeding site of this strain in the field. The eclosion peak was ～2?h prior to sunrise, and the 24?h rhythmicity was the most robust. Effects of artificial LAN at 25^o?±?0.5^oC were determined in the laboratory by subjecting pupae to LD 12:12 cycles in which the light intensity of the photophase was 500 lux in all LD cycles, while that of the scotophase was either 0 lux (complete darkness, DD), 0.5, 5, or 50 lux. In the 0 lux LAN condition (i.e., the control experiment), the eclosion peak was ～2?h after lights-on, and the 24?h eclosion rhythm was not as strong as in the 0.5 lux LAN condition. The entrainment pattern in 0.5 lux LAN was strikingly similar to that in the field, as the 0.5 lux LAN condition is comparable to the full moonlight intensity in the tropics. LAN at 0.5 lux dramatically altered both parameters of entrainment, as the eclosion peak was advanced by ～4?h and the 24?h eclosion rhythm was better than that of the control experiment. LAN at 5 lux, however, resulted in a weak eclosion rhythm that peaked in the subjective forenoon. Interestingly, the 50 lux LAN condition rendered the eclosion events unambiguously arrhythmic. After-effects of LAN on the period (τ) of the free-running rhythm and the nature of eclosion rhythm were also determined in DD by a single LD 12:12 to DD transfer. After-effects of the LAN intensity were observed on both the τ and nature of the eclosion rhythm in all four experiments. Pupae raised in 0.5 lux LAN exhibited the shortest τ (20.6?±?0.2?h, N?=?11 for this and subsequent values) and the most robust rhythm, while pupae raised in 50 lux LAN had the longest τ (29.5?±?0.2?h) and weakest rhythm in DD. Thus, these results demonstrate the intensity of LAN, varying from 0 to 50 lux, profoundly influences the parameters of entrainment as well as free-running rhythmicity of D. jambulina. Moreover, the observed arrhythmicity in LD 12:12 cycles caused by the 50 lux LAN condition appeared to be the masking effect of relatively bright light at night, as the LD 12:12 to DD transfer restored the rhythmicity, although it was rather weak. (Author correspondence: drdsjoshi08@gmail.com)     

Effects of Photophase and Altitude on Oviposition Rhythm of the Himalayan Strains of Drosophila Ananassae

The effects of varying photophase and altitude of origin on the phase angle difference (Ψ) of the circadian rhythm of oviposition during entrainment to light‐dark (LD) cycles and the aftereffects of such photophases on the period of the free‐running rhythm (τ) in constant darkness (DD) were evaluated in two Himalayan strains of Drosophila ananassae, the high‐altitude (HA) strain from Badrinath (5,123 m above sea level=ASL) and the low‐altitude (LA) strain from Firozpur (179 m ASL). The Ψ (i.e., the hours from lights‐on of the LD cycle to oviposition median) of both strains was determined in LD cycles in which the photophase at 100 lux varied from 6 to 18 h/24 h. The HA strain was entrained by all LD cycles except the one with 6 h photophase in which it was weakly rhythmic, but the LA strain was entrained by only three LD cycles with photophases of 10, 12, and 14 h, but photophases of 6, 8, 16, and 18 h rendered it arrhythmic. Lights‐off transition of LD cycles was the phase‐determining signal for both strains as oviposition medians of the HA strain occurred～6 h prior to lights‐off, while those of the LA strain occurred～1 h after lights‐off. The Ψ of the HA strain increased from～2 h in 8 h photophase to～11 h in 18 h photophase, while that of the LA strain increased from～11 h in 10 h photophase to～15 h in 14 h photophase. The aftereffects of photophase of the prior entraining LD cycles on τ in DD were determined by transferring flies from LD cycles to DD. The τ of the HA strain increased from～19 to～25 h when transferred to DD from LD 8:16 and LD 18:6 cycles, respectively, whereas the τ of the LA strain increased from～26 to～28 h when transferred to DD from LD 10:14 and LD 14:10 cycles, respectively. Thus, these results demonstrate that the photophases of entraining LD cycles and the altitude of origin affected several parameters of entrainment and the period of the free‐running rhythm of these strains.     

Temperature dependent eclosion rhythmicity in the high altitude Himalayan strains of Drosophila ananassae

The circadian pacemaker controlling the eclosion rhythm of the high altitude Himalayan strains of Drosophila ananassae captured at Badrinath (5123 m) required ambient temperature at 21°C for the entrainment and free-running processes. At this temperature, their eclosion rhythms entrained to 12h light, 12h dark (LD 12:12) cycles and free-ran when transferred from constant light (LL) to constant darkness (DD) or upon transfer to constant temperature at 21°C following entrainment to temperature cycles in DD. These strains, however, were arrhythmic at 13 or 17°C under identical experimental conditions. Eclosion medians always occurred in the thermophase of temperature cycles whether they were imposed in LL or DD; or whether the thermophase coincided with the photophase or scotophase of the concurrent LD 12:12 cycles. The temperature dependent rhythmicity in the Himalayan strains of D. ananassae is a rare phenotypic plasticity that might have been acquired through natural selection by accentuating the coupling sensing mechanism of the pacemaker to temperature, while simultaneously suppressing the effects of light on the pacemaker.