Phase-shifting effects of a light pulse interrupting scotophase on locomotor activity rhythm and photoperiodic time measurement for diapause in the onion fly, Delia antiqua

When a light pulse of 1 h duration was given 3 h after lights off in a photoperiod of 11 h light : 13 h dark (LD 11 : 13) at 20°C, the phase of the major peak of locomotor activity rhythm in Delia antiqua was delayed for approximately 0.6 h. In contrast, it was advanced by approximately 0.6 h by a light pulse given 9 h after lights off. It is suggested that in the circadian clock, a pulse falling in the early scotophase is taken as a new dusk and a pulse falling in the late scotophase is taken as a new dawn. Although a sharply defined critical photoperiod did not exist in the diapause response to photoperiod in D. antiqua, the percentage of pupal diapause decreased by these pulses in LD 11 : 13 at 20°C. The effect of a 15 min light pulse on both locomotor activity rhythm and pupal diapause induction was stronger at 3 h than at 9 h after lights off, while a 1 min light pulse was ineffective at both times. The parallel effects of light pulse on locomotor activity rhythm and diapause response might be based on the same chronobiological functions.     

Effect of temperature on circadian rhythm controlling the crepuscular activity of the burying beetle Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae)

Locomotor activity rhythm was examined at various temperatures under a 16 h light : 8 h dark photoperiod (LD 16:8) or LD 12:12 using adults of the burying beetle Nicrophorus quadripunctatus. At 20°C, the locomotor activity of the beetles showed a bimodal daily pattern with two peaks around lights on and lights off under both photoperiods. This bimodal activity rhythm persisted under constant darkness; therefore, the activity of adult N. quadripunctatus is controlled by a circadian clock. Adults showed a bimodal activity pattern for temperatures ranging from 15 to 25°C. The evening peak of the daily activity was earlier at lower temperatures. These findings suggest that in the field, N. quadripunctatus shows crepuscular activity, and is active earlier in the afternoon in cooler seasons. In this species, therefore, temperature appears to play an important role in the determination of daily activity patterns.     

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.     

Significance of Nonparametric Light Effects in Entrainment of Circadian Rhythms in Owl Monkeys (Aotus Lemurinus Griseimembra) by Light-Dark Cycles

In a total of 12 adult Colombian owl monkeys, Aotus lemurinus griseimembra, the significance of nonparametric light effects for the entrainment of the circadian system by light-dark (LD) cycles was studied by carrying out (a) phase-response experiments testing the phase-shifting effect of 30-min light pulses (LPs) of 250 lx applied at various phases of the free-running circadian activity rhythm (LL 0.2 lx) and (b) synchronization experiments testing the entraining effect of 24-h single LP photoperiods consisting of 30-min L of 80 lx and 23.5-h D of 0.5 lx (sP 0.5) and skeleton photoperiods consisting of two 30-min LPs of 80 lx, given against a background illuminance of 0.5 lx either symmetrically at 12-h intervals (PP 12:12) or asymmetrically at 9- and 15-h intervals (PP 9:15). The phase-response characteristics in Aotus, as evidenced by the phase-response curve, generally correspond to those of nocturnal rodents, proving that this neotropical simian primate chronobiologically is a genuine nocturnal species. When free-running with a spontaneous period close to 24 h (24.3 ± 0.1 h), the PP 12:12 produced entrainment in only two of five owl monkeys, whereas the sP 0.5 entrained four of them. The PP 9:15, however, brought about stable entrainment of the circadian rhythms of locomotor activity, feeding activity, and core temperature in all animals tested (n = 8). Changes in phase position of the activity time with the endogenous rhythm entrained by a PP 12:12, by an sP 0.5, or by a PP 9:15 give evidence that both LPs of a skeleton photoperiod contribute to the phase setting of the circadian system. When free-running with a considerably lengthened spontaneous period (τ ≥ 25.5 h), even the sP 0.5 and the PP 9:15 failed to entrain the owl monkeys' circadian rhythms, whereas a 24-h photoperiod with a very long LP of 3 h caused entrainment. The results indicate that in Aotus lemurinus griseimembra, in addition to the nonparametric light effects, parametric light effects play a significant role in the entrainment of circadian rhythms by LD cycles.     

Light and dark rations and the photic entrainment of circadian locomotor activity patterns in the South American Silver Catfish (Rhamdia quelen,Quoy & Gaimard, 1824)

The aim of this study was to evaluate the daily rhythm of locomotor activity in Rhamdia quelen (R. quelen). A total of 30 fish were enrolled in the study and were equally divided in 10 groups and maintained in 100 liters tanks. The locomotor activity was measured in fish maintained under the LD 12:12 photoperiod regime; thereafter, the LD cycle was reversed to DL in order to study the resynchronization and to explore the endogenous pacemaker. Subsequently, the fish were subjected to constant conditions of light to test whether or not locomotor rhythms are regulated by the endogenous circadian clock. The effect of increasing light length and intensity was studied on daily rhythm of locomotor activity of fish. Our results showed that the R. quelen is a strictly diurnal species, the rhythm of locomotory activity resynchronized quickly after inverting the LD cycle and persist under free course LL, suggesting a circadian origin. The light showed a significant masking effect often blocking the expression of the biological rhythm. The strictly diurnal behavior is controlled directly by the photoperiod and maintained even under very dim light (30 lux).     

Phase relations between the circadian leaf movement rhythm and its zeitgeber within the range of entrainment in the cotton plant,Gossypium hirsutum L.

Abstract

The leaf movement rhythm of Gossypium hirsutum L. (cv. Lakshmi) could be entrained to 24 h LD cycles with different photofractions varying from 4 to 20 h such that the night peak position of the rhythm occurred during darkness. The phase angle (ψ) of the rhythm varied in a regular manner with different photoperiods of a 24 h LD cycle. Under 24 h LD cycles with different photoperiods, the leaf movement shows probable evidences for the concurrent participation of a ‘light‐on’ and ‘light‐off rhythm.     

Entrainment to Light of Circadian Activity Rhythms in Tench (Tinca tinca)

The present article analyzes locomotor activity rhythms in Tinca tinca. To that end, three different experiments were conducted on 24 animals (20 g body weight) kept in pairs in 60‐liter aquaria fitted with infrared sensors connected to a computer to continuously record fish movements. The first experiment was designed to study the endogenous circadian clock under free‐running conditions [ultradian 40:40 min LD pulses and constant dark (DD)] and after shifting the LD cycle. Our results demonstrate that tench has a strictly nocturnal activity pattern, an endogenous rhythm being evident in 45.8% of the fish analyzed. The second experiment was conducted to test the influence of different photoperiods (LD 6:18, 12:12, 18:6, and 22:2) on locomotor activity, the results showing that even under an extremely long photoperiod, tench activity is restricted to dark hours. The third experiment examined the effect of light intensity on locomotor activity rhythms. When fish were exposed to decreasing light intensities (from 300:0 lux to 30:0, 3:0, and 0.3:0 lux) while maintaining a constant photoperiod (LD 12:12), the highest percentage of locomotor activity was in all cases associated with the hours of complete darkness (0 lux). In short, our results clearly show that (a) tench is a species with a strictly nocturnal behavior, and (b) daily activity rhythms gradually entrain after shifting the LD cycle and persist under free‐running conditions, pointing to their circadian nature. However, light strongly influences activity rhythms, since (c) the length of the active phase is directly controlled by the photophase, and (d) strictly nocturnal behavior persists even under very dim light conditions (0.3 lux). The above findings deepen our knowledge of tench behavior, which may help to optimize the aquacultural management of this species, for example, by adjusting feeding strategies to their nocturnal behavior.     

Parametric and nonparametric entrainment of circadian locomotor rhythm in the Japanese honeybee Apis cerana japonica

The circadian rhythm of locomotor activity in the Japanese honeybee Apis cerana japonica was studied to determine the involvement of parametric and/or nonparametric entrainment. The rhythm was entrained to a skeleton photoperiod in which a 1-h first light pulse was imposed in the morning along with a second light pulse in the evening, as well as to a complete photoperiodic regime (LD 12:12). However, the timing of peak activity relative to the lights-off in the evening in the skeleton photoperiod was earlier than that in the complete photoperiod. A single daily light pulse in the evening entrained the rhythm, whereas a daily light pulse in the morning allowed free-running as in constant darkness. The free-running period (τ) of locomotor activity in constant light became longer as the light intensity increased. A Winfree's type I phase response curve of the locomotor activity rhythm was obtained using a single 1-h light pulse. The results suggest that both parametric and nonparametric entrainment are involved in the circadian rhythm of individual locomotor activity in this honeybee.     

Photic entrainment of daily rhythm pattern of locomotor activity in sea bass (Dicentrarcus labrax)

The aim of this study was to evaluate the circadian rhythm of daily locomotor activity in sea bass exposed to three different artificial lighting regimes including 12/12, 24/0, and 0/24 L/D periods, and scheduled daytime feeding. Daily rhythm of locomotor activity during 12/12 L/D was observed, whereas locomotor activity recorded during 24/0 and 0/24 L/D resulted arrhythmic. Statistical differences in mesor values among the photoperiods and between light and dark phases of each photoperiod were found. During the 12/12 and 0/24 L/D, the fish were active mostly during the light phase. During 24/0 L/D, a phase inversion occurred. The results showed that photoperiod is a dominant synchronizer in sea bass, and that the appetite in this fish follows daily rhythms which does not match the imposed feeding schedule, suggesting the absence or the lability of internal process that couples feeding cycles and biological rhythms.     

A circadian clock measures photoperiodic time in the male lizard Anolis carolinensis

Summary Photoperiod plays an important role in controlling the annual reproductive cycle of the male lizard Anolis carolinensis. The nature of photoperiodic time measurement in Anolis was investigated by exposing anoles to 3 different kinds of lighting paradigms (resonance, T cycles, and night breaks) to determine if photoperiodic time measurement involves the circadian system. Both the reproductive response and the patterns of entrainment of the activity rhythm were assessed. The results show that the circadian system is involved in photoperiodic time measurement in this species and that a discrete photoinducible phase resides in the latter half of the animals' subjective night. Significantly, the ability of the circadian system to execute photoperiodic time measurement is crucially dependent on the length of the photoperiod. Resonance, T cycle and night break cycles utilizing a photoperiod 10–11 h in duration reveal circadian involvement whereas these same cycles utilizing 6 or 8 h photoperiods do not.Abbreviation CRPP circadian rhythm of photoperiodic sensitivity     

Photoperiodic time measurement in the male deer mouse, Peromyscus maniculatus

Weanling male deer mice, Peromyscus maniculatus, were exposed for three weeks either to light-dark (LD) cycles with periods (T=L+D) ranging from T=23 (1L:22D) to T=25.16 (1L:24.16D) or to 24-h LD cycles with photoperiods ranging from 1 (1L:23D) to 19 (19L:5D) h. Both the circadian locomotor activity rhythms and the response of the reproductive system to these LD cycles were assessed. The results demonstrate that the photoperiodic effectiveness of light depends on the phase of the light relative to the animal's circadian system, as marked by the circadian activity rhythm. Light falling during the animal's subjective night, from activity onset to at least 11.8 h after activity onset, stimulates growth and maturation of the reproductive system, whereas light falling during the rest of the circadian cycle is nonstimulatory.     

Two Oscillators Might Control the Locomotor Activity Rhythm of the High‐Altitude Himalayan Strain of Drosophila Helvetica

The properties of the pacemaker controlling the adult locomotor activity rhythm of the high‐altitude Himalayan (haH) strain (Hemkund Sahib, 4121 m above sea level) of Drosophila helvetica are strikingly different from those of the low‐altitude Himalayan (laH) strain (Birahi, 1132 m above sea level) of the same species. The haH strain has a unimodal activity pattern with a delayed peak occurring about 4.5 h after lights‐on of the entraining light‐dark (LD) cycle, while the laH strain has a bimodal activity pattern with the morning and evening peaks. It is rather unusual for a wild type strain of any Drosophila species to have a unimodal activity pattern during entrainment as observed in the haH strain. The single activity peak of the haH strain is regarded as a consequence of delayed morning peak merging with the evening one. Three experiments were performed to test this hypothesis. The first experiment examined whether the single activity peak could be dissociated into two components by LD cycles in which photoperiods varied from 10 to 16 h per 24 h. The haH strain again exhibited a unimodal activity pattern with a delayed peak in 10, 12, and 14 h photoperiods but a bimodal activity pattern in 16 h photoperiod. The laH strain had bimodality in 10 and 12 h photoperiods, unimodality in a 14 h photoperiod, but complete arrhythmicity in a 16 h photoperiod.

In the second experiment, the haH flies were transferred from LD 16∶8 to LL at 5 lux to confirm whether the bimodality of this strain in LD 16∶8 cycles was not the result of masking by the long photoperiod of 16 h. Bimodality of the haH strain persisted in LL too; moreover, the morning component free‐ran with period (τ) <24 h, while the evening component free‐ran with τ>24 h. The third experiment examined the LL‐induced splitting of activity peak of the haH strain. Flies were transferred from LD 12∶12 cycles to LL at 0, 1, 5, and 15 lux. The haH strain was rhythmic in LL at 0 and 1 lux with a unimodal activity pattern. It was also rhythmic in LL at 5 lux, but the single activity peak was split into two discrete components; the morning component free‐ran with τ<24 h, while the evening component free‐ran with τ>24 h. This strain, however, was completely arrhythmic in LL at 15 lux. The laH strain was uniformly arrhythmic in LL at all levels of light intensity. These results suggest that the single but late activity component of the haH strain during entrainment appears to be the consequence of merging the delayed morning peak with the evening one as an adaptation to the environmental conditions at the altitude of origin of this strain, where these flies begin activity in the forenoon owing to non‐permissible low temperature in the morning.     

Photoperiod influences endogenous rhythm of ambient temperature selection by the honeybee Apis mellifera

The aim of this study was to evaluate whether the day–night cycle phase is a critical factor modulating diurnal rhythm of isolated honeybee's thermal preference or other factors are involved. The insects were exposed to standard (LD 12:12) and reversed (DL 12:12) photoperiods as well as to constant light and constant darkness conditions. Thermal preference and motor activity of honeybees were recorded for 3–5 days in a thermal gradient system. Under the standard (control) photoperiod conditions mean values of temperature selected by honeybees changed rhythmically within the period of about 24 h. Honeybees, exposed to the modified light–darkness cycle distinctly modified their rhythm of thermal preference. Under the reversed photoperiod conditions period of selected ambient temperature was much longer than before, until a complete reversal of the circadian oscillation was established at the end of the experiment. Experiments performed under constant light and constant darkness yielded undisturbed 24 h rhythms of both ambient temperature selection and locomotor activity. Under these conditions only a slight, nonsignificant flattening of the temperature selection curves was noticed. Both lack of substantial changes in the amplitude and occurring phase shifts of the rhythm, recorded in our experiments suggest its endogenous character. Our results prove that diurnal rhythm of ambient temperature selection by bee workers may be entrained by light–dark cycles. This implies a critical role of photoperiod in the modulation of nychthemeral oscillations of thermal preference in honeybees.     

Formal properties of the circadian rhythm of locomotor activity in Japanese quail

Summary Japanese quail have a circadian rhythm of locomotor activity whose free-run period () in constant darkness (DD) was 22.5±0.1 h (45). A phase response curve of typical form was obtained by illuminating the free-running rhythm with single 1 h light pulses. Using entrainment theory a derived phase response curve was calculated from the phase relationships between the locomotor rhythm and 1 h light periods in light-dark cycles of various lengths (T). Although the limits of entrainment to theseT cycles differed slightly from those predicted, there was a close correlation between the two phase response curves. The phase relationships between the locomotor rhythm and 1–9 h photoperiods in 24 h cycles were in general accord with a prediction based on the short free-run period and the relative sizes of the delay and advance portions of the phase response curve for 1 h light pulses.     

Behavioral and neurochemical sources of variability of circadian period and phase: studies of circadian rhythms of npy-/- mice

The cycle length or period of the free-running rhythm is a key characteristic of circadian rhythms. In this study we verify prior reports that locomotor activity patterns and running wheel access can alter the circadian period, and we report that these treatments also increase variability of the circadian period between animals. We demonstrate that the loss of a neurochemical, neuropeptide Y (NPY), abolishes these influences and reduces the interindividual variability in clock period. These behavioral and environmental influences, from daily distribution of peak locomotor activity and from access to a running wheel, both act to push the mean circadian period to a value < 24 h. Magnitude of light-induced resetting is altered as well. When photoperiod was abruptly changed from a 18:6-h light-dark cycle (LD18:6) to LD6:18, mice deficient in NPY were slower to respond to the change in photoperiod by redistribution of their activity within the prolonged dark and eventually adopted a delayed phase angle of entrainment compared with controls. These results support the hypothesis that nonphotic influences on circadian period serve a useful function when animals must respond to abruptly changing photoperiods and point to the NPYergic pathway from the intergeniculate leaflet innervating the suprachiasmatic nucleus as a circuit mediating these effects.     

The estrous cycle in golden hamsters: a circadian pacemaker times preovulatory gonadotropin release

In a population of cycling female hamsters entrained to an LD 6:18 light cycle (lights 1000-1600 hours), preovulatory release of luteinizing hormone and follicle-stimulating hormone occurred in some animals at 1300-1400 hours and in others at 1900 hours. In every case peak release was phase-locked (2-3-hour positive phase angle) to the circadian rhythm of locomotor activity. The pattern of entrainment of gonadotropin release on LD 6:18 is fully explicable in terms of the hamster's phase response curve to light. We conclude that periodic gonadotropin release in cycling females is timed by a circadian oscillator (biological clock) that is probably the same oscillator driving the circadian rhythm of locomotor activity.     

The daily rhythms of melatonin and free fatty acids in goats under varying photoperiods and constant darkness

The purpose of the study was to explore parallel and divergent features of the daily rhythms of melatonin and plasma free fatty acids (FFA) in goats exposed to different lighting conditions. From these features, we attempted to analyze whether the endogenous melatonin rhythm plays any role in the maintenance of the FFA rhythm. Seven Finnish landrace goats were kept under artificial lighting that simulated the annual changes of photoperiod at 60°N (longest photoperiod, 18 h; shortest, 6 h). The ambient temperature and feeding regimen were kept constant. Blood samples were collected 6 times a year at 2 h intervals for 2 d, first in the prevailing light‐dark (LD) conditions and then after 3 d in constant darkness (DD). In LD conditions, the melatonin levels always increased immediately after lights‐off and declined around lights‐on, except in winter (18 h darkness), when the low daytime levels were restored clearly before lights‐on. The FFA levels also displayed a consistent rhythmicity, with low levels at night and a transient peak around lights‐on. In DD conditions, the melatonin profiles were very similar to those found in the habitual LD conditions, but the rhythm tended to advance. The FFA rhythm persisted also in DD, and the morning peak tended to advance. There was an overall parallelism between the two rhythms, with one significant exception. In winter in LD conditions, the morning rise in FFA levels coincided with lights‐on and not with the declining phase of melatonin, whereas in DD conditions, the FFA peak advanced several hours and coincided with the declining phase of melatonin. From this finding and comparisons of the calculated rhythm characteristics, i.e., phase‐shifts, phase differences, and correlations, we conclude that the daily rhythm of FFA levels is most probably generated by an endogenous oscillator, primarily adjusted by dawn, whereas the melatonin rhythm in this species is regulated by an oscillator primarily adjusted by dusk. The results did not exclude a modulatory effect of melatonin on the daily FFA profiles, but melatonin secretion, alone, does not explain the patterns sufficiently.     

Characteristics of the circadian activity rhythm in common marmosets (Callithrix j. jacchus)

The circadian activity rhythm of the common marmoset, Callithrix j. jacchus was investigated by long-term recording of the locomotor activity of 15 individuals (5 males, 10 females) from 1.5 to 8 years old, both under constant illumination and under LD 12:12. The mean period of the spontaneous circadian rhythm was 23.2 ± 0.3 h. Neither sex-specific differences nor a systematic influence of light intensity on the spontaneous period were observed, but the period was dependent on the duration of the trial and on the age of the individual. Due to the short spontaneous period, in LD 12:12 there was a distinct advance of the activity phase with respect to the light time and a masking of the true onset of activity by the inhibitory direct effect of low light intensity during the dark time. After an 8 h delay shift of the LD 12:12, re-entrainment of the circadian activity rhythm required an average of 6.8 ± 0.7 days; the average re-entrainment time after an 8 h phase advance of the LD cycle was 8.6 ± 1.3 day. This directional effect is ascribed to characteristics of the phase-response curve. No ultradian components were observed, either in the LD-entrained or the free-running circadian activity rhythm.     

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.