Temperature compensation of circasemilunar timing in the intertidal insectClunio

Summary In cultures of a subtropical population of the one-hour midgeClunio tsushimensis, semilunar rhythms of emergence with a period of 15 days can be entrained by using artificial moonlight cycles of 30 days in otherwise invariant 24-h lightdark cycles (0.3 lux over four successive nights every 30 days of LD 1212). After changing to an invariant photoperiod (LD 1212 without the moonlight programme) or even to continuous darkness, freerunning semilunar rhythms were observed for up to 3 months using cultures of a mixed age structure containing all larval instars. The mean period was 14.2 days at 19 °C, i.e. clearly shorter than under entraining conditions (14.7 days in nature, 15.0 days with the artificial zeitgeber). In the range 14°–24 °C (corresponding to the mean seawater temperatures at the place of origin in winter and summer) there was only slight temperature dependence. The Q₁₀ of the circasemilunar period, however, was not significantly different from 1.0. In continuous darkness the freerunning period was about 15.2 days. Both experiments provide supporting evidence for the existence of a temperature-compensated circasemilunar oscillator acting as an endogenous clock mechanism controlling the timing of imaginal disc formation and pupation in the intertidal chironomid.Dedicated to Prof. Colin S. Pittendrigh on the occasion of his 70th birthday, in recognition of his leading and stimulating contributions in the field of biological timing systems     

Circadian range of entrainment in the semilunar eclosion rhythm of the marine insect clunio marinus

The semilunar eclosion of the intertidal chironomid Clunio is controlled by a semilunar timing of pupation in combination with a daily timing of emergence. This results in reproductive activities of a laboratory population every 15 days at a distinct time of day (in nature mostly in correlation with the afternoon low water time on days with spring tides). The entrainment of the timing processes has been tested under various periods of the daily light-dark cycle in order to check the circadian organization of the timing mechanisms as suggested for the perception of the semilunar zeitgeber situation (a distinct phase relationship between the 24 h light-dark cycle and the 12.4 h tidal cycle recurring after every 15th light-dark cycle, named semimonthly zeitgeber cycle) as well as for the daily zeitgeber (the 24 h light-dark cycle). With respect to the semilunar timing, a strong entrainment was only possible in semimonthly zeitgeber cycles with light-dark cycle periods close to the 24-h day (light-dark cycles of 10:10 to 14:14). This limited circadian range of entrainment of an endogenous circasemilunar long-term rhythm (syn. oscillator) conforms with the hypothesis for a circadian clock component as an intrinsic part of the semilunar zeitgeber perception.The range of entrainment for the daily timing was obviously wider which may be discussed either in relation to a multioscillatory circadian organization of the midges or in relation to different coupling characteristics of one circadian oscillator during semilunar and daily timing.     

Entrainment of a semilunar rhythm by a simulated moonlight cycle in the terrestrial crab,Sesarma haematocheir

Summary Sesarma haematocheir is a species of terrestrial crabs inhabiting hillsides and paddy fields near the sea. Females show a semilunar rhythm of zoea-release coinciding with days of spring tides and in addition with the time of high water occurring at the nearby seacoast about dusk. Nature of environmental stimuli or zeitgebers that induce the semilunar rhythm of zoea-release was examined experimentally. In case that a population of males and females was kept under the condition of a 24-h light-dark cycle (LD 14:10) only, females showed a free-running semilunar rhythm of egg-laying and zoea-release synchronized from field conditions. On the other hand, a semilunar rhythm of egg-laying and zoea-release was entrained by the combination of the 24-h LD and a simulated 24.8-hr moonlight cycle of which the phase was shifted in relation to the natural lunar cycle. This result suggests that the 24.8-h moonlight cycle acts as a zeitgeber of a semilunar rhythm. The 12.4-h tidal cycle parallels with the 24.8-h moonlight cycle in the field. On the basis of the perception of a distinct phase relationship between the 24-h LD and the 24.8-h moonlight cycle, it is considered that crabs substitute the 24.8-h moonlight cycle for the 12.4-h cycle of tides as a zeitgeber to synchronize the phase of the semilunar rhythm with a tidal situation.     

Food-deprivation-induced phase shifts in Sminthopsis macroura froggatti

Past research has shown that there is a circadian oscillator in laboratory rats that is entrained by restricted feeding schedules. However, in laboratory rats at least, the light-dark (LD) cycle is the dominant zeitgeber in the entrainment of wheel-running activity rhythms. Given that dasyurid marsupials are predominantly carnivorous, the episodic intake of food in the wild and the high nutritive content of that food suggest that food may be an important zeitgeber in these species. Twelve Sminthopsis macroura froggatti were presented with a daily meal at 0900 hr under an LD 12:12 cycle with lights-on at 0600 hr for 37 days. Activity in anticipation of the meal was observed in most animals. Following this, all animals were exposed to periods of 12-18 days ad lib. food interspersed with 3-day periods of deprivation--a technique used previously to demonstrate persistent meal-associated rhythms. The meal-associated activity rhythms previously observed in rats during the 3-day deprivation period were not seen, but the 3-day deprivation period produced large phase-shifts in the activity rhythms of several S.m. froggatti. It is concluded that meal feeding does not dominate the LD cycle in entraining dasyurid marsupials, but that the frequent observation of phase shifts suggests a different and, perhaps, stronger role for food intake in biological rhythmicity than has been observed previously in laboratory rats.     

Effect of Changing the Light/Dark Schedule, the Time of Onset of the Light or Dark Period, or the Daylength, on Rhythms of Epidermal Cell Proliferation

Rhythms of labeling and mitotic indices were studied in the hindlimb epidermis of the anuran tadpole Rana pipiens under different light/dark (LD) cycles and daylengths in order to examine the role of the various parameters of the lighting regimen in setting the periods of the rhythms and the timing of the cell proliferation peaks. Altering the time of, or inverting, the 12 h light period on a 24 h day resulted in phase shifting of basically bimodal circadian rhythms with peaks in the light and dark. Thus the cell proliferation rhythms were entrained to the LD cycle. These rhythms also entrained to noncircadian schedules since they lengthened on a 15L : 15D cycle and shortened on a 9L : 9D cycle, although the bimodal characteristic of a peak in the light and a peak in the dark remained. Studies of 18L: 6D and 6L : 18D cycles in which either the time of onset of light or dark was changed relative to the 12L: 12D control indicated that the onset of dark may regulate the timing of the labeling index peaks while the onset of light may determine the time of occurrence of mitotic index peaks. Control of the timing of labeling and mitotic index peaks by different parameters of the LD cycle suggests a mechanism for cell cycle regulation by the environmental lighting schedule. Analysis of the rhythms on all the cycles studied suggested that labeling index rhythms equal the length of, or twice the length of, the dark period. Mitotic index rhythms equal the daylfength or a multiple of the length of the dark period.     

Circadian behavioral and melatonin rhythms in the European starling under light-dark cycles with steadily changing periods: evidence for close mutual coupling?

In European starlings exposed to constant conditions, circadian rhythms in locomotion and feeding can occasionally exhibit complete dissociation from each other. Whether such occasional dissociation between two behavioral rhythms reflects on the strength of the mutual coupling of their internal oscillators has not been investigated. To examine this, as well as to elucidate the role of melatonin in this system, we simultaneously measured the rhythms of locomotion, feeding and melatonin secretion in starlings exposed to light-dark (LD) cycles of low intensity with steadily changing periods (T). In birds initially entrained to T 24 LD cycles (12L:12D, 10:0.2 lx), beginning on day 15, T was either lengthened to 26.5 h (experiment 1) or shortened to T 21.5 h (experiment 2) by changing the daily dark period 4 min each day. After 18 and 19 cycles of T 26.5 and T 21.5, respectively, birds were released into constant dim light conditions (LL(dim); 0.2 lx) for about 2 weeks. Locomotor and feeding rhythms were continuously recorded. Plasma melatonin levels were measured at three times: in T 24, when T equaled 26 or 22 h and at the end of T 26.5 or T 21.5 exposure. The results show that, contrary to our expectations, the three rhythms were not dissociated. Rather they remained synchronized and changed their phase angle difference with the light zeitgeber concomitantly and at the same rate. The melatonin rhythm stayed in synchrony with the behavioral rhythms and as a consequence, peaked either during day or at night, depending on the phase relationship between the activity rhythm and the zeitgeber cycle.     

Circadian rhythms of locomotor activity in cockroach nymphs: free running and entrainment

The temporal organization of locomotor activity was investigated in nymphs of the cockroach Leucophaea maderae. Approximately 40% of the animals examined between 1 and 50 days of age exhibited a circadian activity rhythm in constant darkness (n = 172) with an average free-running period of 23.7 +/- 0.68 hr. Twelve of 17 animals in which activity was recorded for most or all of the final instar also exhibited periods of rhythmic activity. The rhythms of the nymphs could be entrained by light-dark (LD) cycles with periods of 22, 24, or 26 hr. In contrast, neither maternal influences during embryogenesis nor hatching from the egg was effective in synchronizing the rhythms. Although adult cockroaches can be readily entrained by temperature cycles, in nymphs temperature appeared at best to be a weak zeitgeber. Embryonic exposure to an LD cycle until 6 days prior to egg hatch was effective in synchronizing the activity rhythms of the nymphs, indicating that differentiation of an entrainable pacemaking system occurs prior to hatching.     

A Lunar Clock Changes Shielding Pigment Transparency in Larval Ocelli of Clunio marinus

Living in the tidal zones of the sea requires synchronization with the dominant environmental influences of tidal, solar, and lunar periodicity. Endogenous clocks anticipate those geoclimatic changes and control the respective rhythms of vital functions. But the underlying mechanisms are only partly understood. While the circadian clocks in animals are investigated employing neurobiological, molecular, and genetic approaches, clocks with a lunar periodicity have been studied with reference to development and behavior only. Sites of their pacemakers, zeitgeber receptors, and coupled endocrine components are unknown. Here, a lunar‐rhythmic change of shielding pigment transparency in the larval ocelli of the intertidal midge Clunio marinus is demonstrated for the first time as a possible access to the neurobiology of lunar timing mechanisms. We studied third instar larvae (Vigo strain) throughout the lunar cycle by light‐ and electron-microscopy as well as by x‐ray fluorescence analysis for the identification of the pigment. Moonlight detection is a prerequisite for photic synchronization of the lunar clock. The larval ocelli of Clunio putatively may function as moonlight receptors and are also controlled by the circalunar clock itself, hence being primary candidates for tracing input and output pathways of the lunar pacemaker. Additionally, the demonstration of a reversible optical change of shielding pigment transparency in Clunio is a novel finding, not reported so far in any other animal species, and reveals a mechanism to enhance photosensitivity under the condition of very dim light. It represents a remarkable change of a sense organ from an imaging device to a radiometer. Its restriction to the developmental stage susceptible to lunar timing elucidates a unique sensory strategy evolved at the level of sensory input. It also raises basic questions about the biochemistry of optically active pigments, like melanin, and their intracellular control.     

On Melatonin Suppression from Polychromatic and Narrowband Light

This study investigates the relative strengths of food and light zeitgebers in synchronization of circadian rhythms of Indian weaver birds and the role of the pineal gland in food-induced synchronization of the circadian activity rhythms. Two experiments were performed. In the first experiment, six birds were concurrently exposed for 10 days to PA 12/12 (12 h food present: 12 h food absent) and LD 12/12 (12 h light: 12 h dark). Then, the PA 12/12 cycle was reversed: food was present during the dark period of the LD 12/12 cycle. After 15 days, birds were released into constant dim light (LL_dim). During exposure to overlapping light and food availability periods, birds were active only during the daytime. When light and food availability periods were presented in antiphase, two of six birds became night active. However, with the removal of the light zeitgeber (i.e., under LL_dim), all birds were synchronized with reversed PA 12/12; hence, they were active during the subjective night (i.e., the period corresponding to darkness [ZT12-0] of the preceding LD 12/12). The second experiment examined whether the pineal contributed to the food-induced synchronization. After two weeks of concurrent PA 12/12 and LD 12/12 exposure, six birds were released into LL_dim for 2.5 weeks. Under LL_dim, five of six birds were synchronized to PA 12/12 with the circadian period (tau, τ)?=?24 h. The LD 12/12 was restored, and after seven days, birds were pinealectomized (pinx). After 2.5 weeks, pinx birds were again released into LL_dim for 2.5 weeks. Under LL_dim, pinx birds did not become arrhythmic; instead, they appeared synchronized to PA 12/12 with τ?=?24 h (n?=?4) or ～24 h (n?=?2). We conclude that both food and light act as zeitgebers, although light appears to be the relatively stronger cue when the two are present together, as in the natural environment. We also found that the pineal is not necessary for food-induced synchronization. The findings suggest that food cycles could act as the synchronizer of circadian rhythmicity in biological functions in individuals held in an aperiodic environment.     

Ultradian and circadian compartmentalization of respiratory and metabolic exchanges in small laboratory vertebrates

Carbon dioxide emission (VCO2) taken as an index of respiratory and metabolic exchanges, was continuously recorded during 4-30 consecutive days in 100 quail, 87 chicks, 347 rats, 665 mice and 70 guinea-pigs which were under controlled environmental parameters. Harmonic analysis, fast Fourier transform, chi-square periodograms, peak and trough intervals were computed with VCO2 values obtained with CO2 concentrations sampled every 20 min on the CO2 recordings. In LD 12:12 alternation, circadian rhythms were observed in all quail, chicks, rats and mice, but only in 80% of the guinea-pigs. Ultradian VCO2 rhythms, with periods which show statistically significant interspecies differences, were assessed. For each of the 5 species these computed periods, which were the same in LL and DD, were: 1.17 h for quail and chickens, 1.25 h for rats, 1.50 h for mice and 1.0 h for guinea-pigs. In LD 12:12 these periods were different during L and D in quail, chicks, rats and mice, but not in guinea-pigs. The amplitudes of these ultradian variations were, according to the species, 10-20% of their mean VCO2 levels. These ultradian rhythms persist in the absence (or masking) of circadian rhythms, e.g. in LD 12:12 in 20% of guinea-pigs and in LL in 87% of Japanese quail and in 23% of Sprague-Dawley rats. Moreover, these ultradian rhythms persist during starvation, locomotor activity restraint and ageing. These ultradian VCO2 cycles which are related to rest-activity variations appear to be basic physiological rhythms with a genetic origin.     

Die Temperaturabhängigkeit semilunarer und diurnaler Schlüpfrhythmen bei der intertidalen MückeClunio marinus (Diptera,Chironomidae)

On Helgoland (North Sea), the imagines ofClunio emerge during two seasonal periods (late spring and summer) from water temperatures of 8°–18 °C. The temperature dependence of the known semilunar eclosion rhythm ofClunio (correlated in nature with the spring tides every 14–15 days) was tested in the laboratory. Between 15° and 23 °C the semilunar eclosion maxima varied by only one day within the artifical 15-day zeitgebercycle, below 15 °C they were delayed up to 8 days at 8 °C. However, the days of pupation were approximately independent of the temperature level. One can conclude the existence of a temperature-independent physiological switch inducing the pupation only within a few days of the semilunar zeitgeber-cycle. Moreover, a semilunar synchronized differentiation of the imaginal discs already starts in the preceding larval instar, indicating an additional physiological switch. A model is suggested in which the semilunar eclosion rhythm and its relatively slight temperature dependence is explained by the action of two physiological switches which are coupled with the endogenous temperature-compensated lunar timing mechanism on the same days of the 15-day zeitgeber-cycle. In the laboratory, the diurnal eclosion and its underlying circadian timing mechanism (correlated on Helgoland with the time of spring low water in the late afternoon) also proved to be temperature independent between 12° and 20 °C. A comparison of field and laboratory data showed very similar results at temperatures around 18 °C (summer swarming period). In contrast, the midges emerged on all days of the semimonthly cycle of springs and neaps during the spring swarming period. This lack of semilunar synchronization may be the consequence of fluctuating temperatures during the larval and pupal development in spring time due to a general rise in the water temperature (4°–8 °C) and to short temperature rises up to 18 °C during exposure of the intertidal habitat at about low tide. Since some higher parts of theClunio habitat suitable for egg deposition are exposed on almost every day of the semimonthly cycle, even such animals that undergo lunar unsynchronized metamorphosis can reproduce within the short imaginal life duration (ca 2 h) if they emerge just about the time of low water. In correspondence with the daily delay in the times of low water by about 50 min, the diurnal eclosion rhythm was in fact modified with the tides during the spring period resulting in shifts of the diurnal eclosion time of up to 12 hours within the semimonthly cycle of springs and neaps.     

Interruption of the rat circadian clock by short light-dark cycles

Ninety male Sprague-Dawley rats were exposed to 1:1-h light-dark (LD1:1) cycles for 50-90 days, and then they were released into constant darkness (DD). During LD1:1 cycles, behavioral rhythms were gradually disintegrated, and circadian rhythms of locomotor activity, drinking, and urine 6-sulfatoxymelatonin excretion were eventually abolished. After release into DD, 44 (49%) rats showed arrhythmic behavior for >10 days. Seven (8%) animals that remained arrhythmic for >50 days in DD were exposed to brief light pulses or 12:12-h light-dark cycles, and then they restored their circadian rhythms. These results indicate that the circadian clock was stopped, at least functionally, by LD1:1 cycles and was restarted by subsequent light stimulation.     

The internal synchronization of five circadian functions of the rabbit

Five different physiological functions of the rabbit (hard faeces and urine excretion, food and water intake and locomotor activity) were registered during LD 12:12 and during continuous light conditions (LL).

(1) In LD 12:12 a strong synchronization of the five parameters existed. The minima of all functions consistently occurred during the hours of light. The nocturnal percentage of overall 24-hr events was increased significantly in 'hard faeces excretion' (66±8 (S.D.) %), 'water intake' (64±15 (S.D.) %) and 'urine excretion' (58±10 (S.D.) %). The nocturnal percentage of locomotor activity was significantly increased during the dark-hours in 9 out of 14 animals. In the other five individuals prominent peaks were present even during the photoperiod. On the average of all 14 animals 5S±13 (S.D.) % of the 24 hr events of locomotor activity occurred during the night. Despite a trough during the cessation of hard faeces excretion the events of food intake were not elevated significantly during the dark hours.

(2) During LL the synchronization of the five functions within each animal persisted during the complete 90-day LL period. A free-running circadian rhythm with-: = 24.8±0.5 (S.D.) hr was present in the four rabbits kept in LL conditions within 5-16 days after the withdrawal of the zeitgeber.

(3) In addition to the circadian period the power spectrum analysis of data obtained during LD 12:12 revealed significant ultradian periods of an average period length of 11,6 hr (hard faeces and urine excretion), 8 hr (food and water intake, locomotor activity) and 4 hr (food intake, locomotor activity). During the free-run ultradian periods of 8 and 3.2-4.2 hr were significant in almost all parameters.

(4) During LL the level of locomotor activity was reduced for 13±16 (S.D.) %, the events of food intake were increased for 17±12 (S.D.) %.

(5) The reinserted LD 12:12 zeitgeber re-entrained the circadian rhythms within 25-45 days.

(6) These results provided evidence of a predominant nocturnality of the rabbits under investigation.     

Effects of Choline Depletion on the Circadian Rhythm in Neurospora crassa

One approach to identifying components of the circadian oscillator is to screen for clock defects in mutants with known biochemical lesions. The chol-1 mutant of Neurospora crassa is defective in the first methylation step of phosphatidylcholine synthesis, the conversion of phosphatidylethanolamine to phosphatidylmonomethylethanolamine, and requires choline for normal growth. Choline depletion of this mutant inhibits growth and lengthens the period of the rhythm of conidiation. On high levels of choline (above 20 µM), the growth rate and the period of the rhythm are normal. Below about 10 µM choline, the growth rate and period length depend on the choline concentration, and the period is about 58 h on minimal medium without choline. Choline depletion decreases period stability, and replicate cultures do not remain in phase due to variability in period within each culture. At intermediate levels of choline (around 10 µM) cultures are often arrhythmic. The choline requirement for growth can be met by the phosphatidylcholine precursors monomethylethanolamine and dimethylethanolamine, and these supplements also restore a normal period. Choline depletion of the chol-1 strain exaggerates the rhythm in growth rate previously reported in a chol + strain. Growth rate during formation of a conidial band (measured as forward advance of the mycelial front) is less than half of the maximum rate during non-conidiating interband formation. Choline-depleted cultures can be entrained to light/dark (LD) cycles with periods near to their free-running periods. Cultures on 10 µM choline (with a free-running period of about 25 h) can be entrained to a 24 h (12:12) LD cycle, but not to a 36 h (18:18) or 48 h (24:24) LD cycle. Cultures on 0.5 µM choline (free-running period of about 52 h) or minimal medium (free-running period of about 58 h) can be entrained to 18:18 and 24:24 LD cycles, but not a 12:12 cycle. The phase relationship of the conidiation rhythm to the zeitgeber for low-choline cultures in LD 24:24 is similar to high choline cultures in LD 12:12. Continuous light abolishes rhythmicity in choline-depleted cultures. These results may indicate a role for membrane phospholipids, and the metabolites of phosphatidylcholine in particular, in the control of the period of the circadian oscillator in Neurospora .     

Effects of Choline Depletion on the Circadian Rhythm in Neurospora crassa

One approach to identifying components of the circadian oscillator is to screen for clock defects in mutants with known biochemical lesions. The chol-1 mutant of Neurospora crassa is defective in the first methylation step of phosphatidylcholine synthesis, the conversion of phosphatidylethanolamine to phosphatidylmonomethylethanolamine, and requires choline for normal growth. Choline depletion of this mutant inhibits growth and lengthens the period of the rhythm of conidiation. On high levels of choline (above 20 µM), the growth rate and the period of the rhythm are normal. Below about 10 µM choline, the growth rate and period length depend on the choline concentration, and the period is about 58 h on minimal medium without choline. Choline depletion decreases period stability, and replicate cultures do not remain in phase due to variability in period within each culture. At intermediate levels of choline (around 10 µM) cultures are often arrhythmic. The choline requirement for growth can be met by the phosphatidylcholine precursors monomethylethanolamine and dimethylethanolamine, and these supplements also restore a normal period. Choline depletion of the chol-1 strain exaggerates the rhythm in growth rate previously reported in a chol + strain. Growth rate during formation of a conidial band (measured as forward advance of the mycelial front) is less than half of the maximum rate during non-conidiating interband formation. Choline-depleted cultures can be entrained to light/dark (LD) cycles with periods near to their free-running periods. Cultures on 10 µM choline (with a free-running period of about 25 h) can be entrained to a 24 h (12:12) LD cycle, but not to a 36 h (18:18) or 48 h (24:24) LD cycle. Cultures on 0.5 µM choline (free-running period of about 52 h) or minimal medium (free-running period of about 58 h) can be entrained to 18:18 and 24:24 LD cycles, but not a 12:12 cycle. The phase relationship of the conidiation rhythm to the zeitgeber for low-choline cultures in LD 24:24 is similar to high choline cultures in LD 12:12. Continuous light abolishes rhythmicity in choline-depleted cultures. These results may indicate a role for membrane phospholipids, and the metabolites of phosphatidylcholine in particular, in the control of the period of the circadian oscillator in Neurospora.     

THERMOCYCLIC AND PHOTOCYCLIC ENTRAINMENT OF CIRCADIAN LOCOMOTOR ACTIVITY RHYTHMS IN SLEEPY LIZARDS,TILIQUA RUGOSA

Australian sleepy lizards (Tiliqua rugosa) exhibit marked locomotor activity rhythms in the field and laboratory. Light-dark (LD) and temperature cycles (TCs) are considered important for the entrainment of circadian locomotor activity rhythms and for mediating seasonal adjustments in aspects of these rhythms, such as phase, amplitude, and activity pattern. The relative importance of 24 h LD and TCs in entraining the circadian locomotor activity rhythm in T. rugosa was examined in three experiments. In the first experiment, lizards were held under LD 12:12 and subjected to either a TC of 33:15?°?C in phase with the LD cycle or a reversed TC positioned in antiphase to the LD cycle. Following LD 12:12, lizards were maintained under the same TCs but were subjected to DD. Activity was restricted to the thermophase in LD, irrespective of the lighting regime and during the period of DD that followed, suggesting entrainment by the TC. The amplitude of the TC was lowered by 8?°?C to reduce the intensity and possible masking effect of the TC zeitgeber in subsequent experiments. In the second experiment, lizards were held under LD 12.5:11.5 and subjected to one of three treatments: constant 30?°?C, normal TC (30:20?°?C) in phase with the LD cycle, or reversed TC. Following LD, all lizards were subjected to DD and constant 30?°?C. Post-entrainment free-run records revealed that LD cycles and TCs could both entrain the locomotor rhythms of T. rugosa. In LD, mean activity duration (α) of lizards in the normal TC group was considerably less than that in the constant 30?°?C group. Mean α also increased between LD and DD in lizards in the normal TC group. Although there was large variation in the phasing of the rhythm in relation to the LD cycle in reversed TC lizards, TCs presented in phase with the LD cycle most accurately synchronized the rhythm to the photocycle. In the third experiment, lizards were held in DD at constant 30?°?C before being subjected to a further period of DD and one of four treatments: normal TC (06:00 to 18:00 h thermophase), delayed TC (12:00 to 00:00 h thermophase), advanced TC (00:00 to 12:00 h thermophase), or control (no TC, constant 30?°?C). While control lizards continued to free-run in DD at constant temperature, the locomotor activity rhythms of lizards subjected to TCs rapidly entrained to TCs, whether or not the TC was phase advanced or delayed by 6 h. There was no difference in the phase relationships of lizard activity rhythms to the onset of the thermophase among the normal, delayed, and advanced TC groups, suggesting equally strong entrainment to the TC in each group. The results of this experiment excluded the possibility that masking effects were responsible for the locomotor activity responses of lizards to TCs. The three experiments demonstrated that TCs are important for entraining circadian locomotor activity rhythms of T. rugosa, even when photic cues are conflicting or absent, and that an interaction between LD cycles and TCs most accurately synchronizes this rhythm. (Author correspondence: david.j.ellis@adelaide.edu.au)     

Forced desynchronization model for a diurnal primate

The circadian system is organized in a hierarchy of multiple oscillators, with the suprachiasmatic nucleus (SCN) as the master oscillator in mammals. The SCN is formed by a group of coupled cell oscillators. Knowledge of this coupling mechanism is essential to understanding entrainment and the expression of circadian rhythms. Some authors suggest that light-dark (LD) cycles with periods near the limit of entrainment may be good models for promoting internal desynchronization, providing knowledge about the coupling mechanism. As such, we evaluated the circadian activity rhythm (CAR) pattern of marmosets in LD cycles at lower limits of entrainment in order to study induced internal dissociation. To that end, two experiments were conducted: (1) 6 adult females were under symmetrical LD cycles T21, T22 and T21.5 for 60, 35 and 48 days, respectively; and (2) 4 male and 4 female adults were under T21 for 24 days followed by 18 days of LL, back to T21 for 24 days, followed by 14 days of LL. The CAR of each animal was continuously recorded. In experiment 1, vocalizations were also recorded. Under Ts shorter than 24 days, a dissociation pattern was observed for CAR and vocalizations. Two simultaneous circadian components emerged, one with the same period as the LD cycle, called the light-entrained component, and the other in free-running, denominated the non-light-entrained component. Both components were displayed in the CAR for all the animals in T21, five animals (83.3%) in T21.5 and two animals (33.3%) in T22. Our results are in accordance with the multioscillatory nature of the circadian system. Dissociation is partial synchronization to the LD cycle, with at least one group of oscillators synchronized by relative coordination and masking, while another group of oscillators free runs, but is also masked by the LD cycle. Since only T21 promoted the emergence of both circadian components in the circadian rhythms of all marmosets, it was considered the promoter period of circadian rhythm dissociation in this species, and is proposed as a good animal model for forced desynchronization in non-human diurnal primates.     

Circadian Rhythm in Pineal N-Acetyltransferase Activity: Rapid Phase Reversal and Response to Shorter than 24-Hour Cycles (IV)

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is responsible for circadian rhythms in melatonin. The NAT activity rhythm has circadian properties such as persistence in constant conditions and precise control by light and dark. Experiments are reported in which chicks (Gallus domesticus), raised for 3 weeks in 12 h of light alternating with 12 h of dark (LD12:12), were exposed to 1-3 days of light-dark treatments during which NAT activity was measured in their pineal glands. (a) In LD12:12, NAT activity rose from less than 4.5 nmol/pineal gland/h during the light-time to 25-50 nmol/pineal gland/h in the dark-time. Constant light (LL) attenuated the amplitude of the NAT activity rhythm to 26-45% of the NAT activity cycle in LD12:12 during the first 24 h. (b) The timing of the increase in NAT activity was reset by the first full LD12:12 cycle following a 12-h phase shift of the LD12:12 cycle (a procedure that reversed the times of light and dark by imposition of either 24 h of light or dark). This result satisfies one of the criteria for NAT to be considered part of a circadian driving oscillator. (c) In less than 24-h cycles [2 h of light in alternation with 2 h of dark (LD2:2), 4 h of light in alternation with 4 h of dark (LD4:4), and 6 h of light in alternation with 6 h of dark (LD6:6)], NAT activity rose in the dark during the chicks' previously scheduled dark-time but not the previously scheduled light-time of LD12:12. In a cycle where 8 h of light alternated with 8 h of dark (LD8:8), NAT activity rose in both 8-h dark periods, even though the second one fell in the light-time of the prior LD12:12 schedule.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic adaptation in emergence time ofClunio populations to different tidal conditions

Summary 1. The emergence times of intertidalClunio-species (Diptera, Chironomidae) are correlated with special tidal conditions in such a way that the immediately following reproduction of the short-lived imagos can take place on the exposed habitat.2. If the habitat of aClunio-species is situated in the middle tidal region and exposed twice a day by the tidal cycle (T = 12.4 h), a tidal rhythm of emergence with an average period of 12.4 hours may result (example:Clunio takahashii).3. If the habitat is located in the lower tidal zone, exposed only at about the time of the spring tides, a semilunar rhythm of emergence is expected (examples:Clunio marinus andClunio mediterraneus). These semilunar rhythms are correlated with certain conditions of low tide which occur at the coastal locations every 15 days at about the same time of day. The semilunar rhythm is therefore exactly characterized by two dates: the lunar emergence time (a few successive days around full and new moon) and the diurnal emergence time.4. According to experimental investigations on the control of the emergence rhythm, the midges are able to determine both dates in advance.5. Coastal populations differ in their lunar and diurnal emergence times. These differences correspond to the time of low tide which exists at each location during the emergence days of the semilunar rhythm.6. Crossbreeding between stocks of different populations showed that the differences in diurnal emergence time are gene-controlled.

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Genetische Adaptation der Schlüpfzeiten vonClunio-Populationen an verschiedene Gezeitenbedingungen

Kurzfassung Die Schlüpfzeiten der in der Gezeitenzone lebendenClunio-Arten (Diptera, Chironomidae) sind mit bestimmten Wasserstandsbedingungen synchronisiert, und zwar derart, daß die unmittelbar anschließende Fortpflanzung der kurzlebigen Imagines auf dem trockengefallenen Habitat stattfinden kann. Wenn das Habitat einerClunio-Art in der mittleren Gezeitenzone liegt und parallel zu dem halbtägigen Gezeitenzyklus (T = 12,4 h) zweimal täglich auftaucht, dann kann sich eine 12,4stündige Schlüpfperiodik einstellen (Beispiel:Clunio takahashii). Wenn das Habitat in der unteren Gezeitenzone liegt und nur um die Zeit der Springtiden auftaucht, dann ist eine 15tägige (semilunare) Schlüpfperiodik zu erwarten (Beispiele:Clunio marinus undC. mediterraneus). Diese 15tägige Schlüpfperiodik ist synchronisiert mit bestimmten Niedrigwasserbedingungen, die an einem Küstenort alle 15 Tage jeweils um die gleiche Tageszeit auftreten. Sie wird daher durch zwei Daten eindeutig gekennzeichnet: (1) die lunaren Schlüpftage (wenige aufeinanderfolgende Tage um Voll- und Neumond) und (2) die tägliche Schlüpfzeit. Wie experimentelle Untersuchungen über die Steuerung der Schlüpfperiodik zeigten, können die Tiere beide Daten richtig vorausbestimmen. Die einzelnen Küstenpopulationen unterscheiden sich allerdings in Anpassung an die örtlichen Gezeiten- und Standortbedingungen recht auffällig in ihren lunaren und täglichen Schlüpfzeiten. Kreuzungsversuche zwischen Laboratoriumsstämmen verschiedener Populationen belegen, daß die Unterschiede in der täglichen Schlüpfzeit genkontrolliert sind.

     

Effects of moonlight exposure on plasma melatonin rhythms in the seagrass rabbitfish, Siganus canaliculatus

Influences of light-dark (LD) cycle and moonlight exposure on plasma melatonin rhythms in the seagrass rabbitfish, Siganus canaliculatus, a lunar synchronized spawner, were determined by time-resolved fluoroimmunoassay (TR-FIA). When the fish were exposed to a natural LD (12:12) cycle, plasma melatonin levels exhibited a clear daily rhythm, with higher levels at midnight and lower levels during the day. These rhythms were not evident under either constant light (LL) or constant dark (DD) conditions. Plasma melatonin levels under LL condition were low and high under DD condition. These results indicate that plasma melatonin rhythms are driven by LD cycle in this species. When the fish were exposed to the 4 lunar phases, plasma melatonin levels around the new moon were significantly higher than during the first quarter moon and the full moon. Exposure to experimental new moon and full moon conditions caused significant increases and decreases of plasma melatonin levels, respectively. The synchronous rhythmicity of melatonin levels in the plasma support the hypothesis that the seagrass rabbitfish perceives moonlight intensity and responds with secretion of melatonin into the bloodstream.