Temporal flexibility in activity rhythms of a diurnal rodent,the ice rat (Otomys sloggetti)

ABSTRACT

Diurnality in rodents is relatively rare and occurs primarily in areas with low nighttime temperatures such as at high altitudes and desert areas. However, many factors can influence temporal activity rhythms of animals, both in the field and the laboratory. The temporal activity patterns of the diurnal ice rat were investigated in the laboratory with, and without, access to running wheels, and in constant conditions with running wheels. Ice rats appeared to be fundamentally diurnal but used their running wheels during the night. In constant conditions, general activity remained predominantly diurnal while wheel running was either nocturnal or diurnal. In some animals, entrainment of the wheel running rhythm was evident, as demonstrated by free-running periods that were different from 24 h. In other animals, the wheel running activity abruptly switched from nocturnal to subjective day as soon as the animals entered DD, and reverted back to nocturnal once returned to LD, suggesting the rhythms were masked by light. Wheel running rhythms appears to be less robust and more affected by light compared to general activity rhythms. In view of present and future environmental changes, the existence of more unstable activity rhythms that can readily switch between temporal niches might be crucial for the survival of the species.     

Circadian activity rhythms in BALB/c mice: A weakly‐coupled circadian system?

Abstract

Inbred mouse strains differ in the expression of free‐running circadian activity rhythms. Although previous studies have suggested that BALB/c mice fail to display coherent rhythmicity under constant light, these studies presented only averaged data, and not individual animals’ activity patterns. In the present study, wheel‐running activity rhythms were monitored from individual BALB/c mice during long‐term exposure to constant red light All mice displayed dramatic lability of circadian activity rhythms, characterized by spontaneous alterations in both free‐running period and rhythm coherence. These results suggest that the circadian system in this strain is composed of a population of weakly‐coupled circadian oscillators.     

Synchronization by light of the circadian rhythm of motor activity in the crayfish

Abstract

We have studied the pattern for resetting the circadian rhythm in the spontaneous motor activity of the crayfish. Spontaneous motor activity was recorded continously at a constant temperature and under free running conditions in complete darkness. The effect of single light pulses applied at different circadian times, on the circadian rhythm of motor activity was measured in both transient stage and steady state. The results led us to construct a phase‐transition curve and phase‐response curve which were analyzed to obtain information about the oscillators which underlie the circadian rhythm of motor activity.     

Evidence for an endogenous circadian rhythm of feeding in the trout (Oncorhynchus mykiss)

Abstract

The possible endogenous circadian rhythm in the feeding activity of rainbow trout (Oncorhynchus mykiss) was investigated using individual fish previously trained for self‐feeding. Under LD 12:12 conditions, the fish showed a diurnal behaviour, in many cases with a feeding rhythm with two main peaks of food demand at dawn and dusk, with an 8h interval of low feeding activity, and the actograms showed an expected 24 h rhythm. Fish kept under constant conditions (L : L, 15°±0.5°C), showed free‐running feeding activity for about 12 days. Food demands were concentrated at dawn, with a periodogram of 25.3 hour, under continuous environmental conditions. Results showed evidence for the endogenous origin of the circadian rhythm of feeding in this species.     

Light/dark‐induced effects on behavioral rhythms in suprachiasmatic nucleus‐lesioned rats irrespective of the presence of functional suprachiasmatic nucleus brain implants

Summary

Suprachiasmatic nucleus (SCN)‐lesioned rats which had received a fetal SCN graft were kept in constant red light for three months. After this period it was examined whether those rats that showed a recovered free‐running circadian rhythm could be entrained to light/dark cycles. To this end, they were subjected to a 12 h light/12 h dark schedule, followed by a 12 h light shift and again to dark conditions. In addition, the same regime was imposed on SCN‐grafted rats without recovered circadian rhythms and on sham‐grafted animals with a lesion, which were studied as controls. The presence of an SCN graft was identified immunocytochemically by the presence of vasopressin, vasoactive intestinal polypeptide and somatostatin cells.

Drinking, eating and wheel‐running rhythms were found to synchronize to the light/dark cycles in all rats, not with standing the presence of an SCN graft was. A 12 h light shift was immediately followed by a shift in the three rhythms. Under final dark conditions, free‐running patterns reappeared in rhythm‐recovered animals, without any convincing evidence for entrainment of the rhythms in the pattern of transition.

Behavioral rhythms in SCN‐lesioned rats are apparently masked by 12 h light/dark schedules via other visual pathways than the direct projection from the retina to the SCN.     

Endogenous rhythm in activity of an estuarine amphipod,Talorchestia longicornis

The biological rhythm in activity of the supratidal amphipod Talorchestia longicornis Say was determined under constant conditions. Surface activity was monitored with a time-lapse video system under red light and assessed as the number of animals emerging from their burrows and active on a sand substrate at 0.5?h intervals. The amphipods had a circadian rhythm in which they were active at the time of night at the collection site. The rhythm could be entrained by a light?:?dark cycle and had an average free-running period of 23.7?h. Activity also appeared to be related to tidal times at the collection site because, under constant conditions, surface activity was suppressed at the time of nocturnal high tide and increased at the time of nocturnal low tide. The rhythm is functionally significant for foraging at night to avoid visual predators, desiccation and high temperatures.     

Phase control of circadian activity in the antelope ground squirrel

Abstract

Wheel‐running activity of forty antelope ground squirrels, Ammospermophilus leucurus, was monitored for several months in both an outdoor cage and in the laboratory. The squirrels demonstrated a highly diurnal pattern which persisted in “constant conditions.” After removal from the field the initial free‐running period was close to 24 hrs, but typically lengthened in a nearly linear fashion at least for the first few months. There was no evidence of any difference in this trend for squirrels, in D/D, L/L 100 lx, 250 lx or 1200 lx. Eventually, about 90 percent of the squirrels had periods longer than 24 hrs.

The synchronizing capacity of the natural photoperiod was used to “catch the free‐running rhythm” and thereby demonstrate a response curve. Synchronization occurred by a shortening of the period when the time of sunrise was between 125° and 0° (subjective night) and by a lengthening of the period when the time of sunrise was between 0° and 125° (subjective day).

To more thoroughly examine the underlying mechanisms of phase control, phase‐response curves based on sixty one light‐pulse experiments were constructed. Comparisons of curves based on 6‐hr and 15‐min pulses, showed that the integral action of light is important (i.e., the entire pulse is involved in phase shifting). It was found that light pulses not only affected the phase of the rhythm but also the phase. Large phase shifts were usually associated with decreases in free‐running period. Several hypotheses on the controlling mechanisms were advanced.     

Internal coupling of five functions of rabbits exhibiting a bimodal circadian rhythm

Abstract

By means of a microcomputer‐assisted, electronic recording system five physiological, circadian rhythms of the rabbit were monitored: locomotor activity, hard faeces excretion, food intake, urine excretion and water intake.

During 120 days of continuous light conditions (30 lx) the animals exhibited a free‐running circadian rhythm. After the fading out of aftereffects of the preceding light: dark schedule on day 51 ± 11 the animals ran free with an individually distinct period length of > 24.0 h (τ: 24.48 ± 0.10 (SD) h). Spectral analysis of coherent data of 50–84 days showed that in addition to the circadian period persistent ultradian periods of 6.1, 8.2 and 12.3 h were present. Within each individual the five functions proved to be tightly coupled during the free‐run, during the time of reentrainment and when entrained with the LD 12:12. While during LD 12:12 the animals exhibited a bimodal rhythm, during the free‐run the rhythm was unimodal in all five functions. In one animal a “splitting”; of the free‐running period occurred. Both components ran free with different period length. They fused again after 38 days. The “splitting”; was reflected in all five functions of this animal.

The behavioural characteristics of meal duration and ‐frequency, duration of activity and ‐intervals, of water intake and urination did not show significant differences during the conditions of LD 12:12 and LL.

The results support Pittendrigh's model of two systems of oscillators, selectively susceptible to the transitions of dark : light and light : dark. Our results suggest that in the rabbit the five functions are governed in common by both oscillator‐systems.     

Free‐running circadian rhythm of plastid movements in individual cells of pyrocystis lunula (dinophyta)

Abstract

Pyrocystis lunula, a dinoflagellate lacking periodicity in spontaneous bio‐luminescence, shows a characteristic circadian rhythm of plastid movements which can be monitored photographically in individual cells. The rhythm persists under free‐running conditions in constant dim light (40–50 Ix), but is damped out already in LL of 100 lx.     

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.     

Endogenous rhythm in activity of an estuarine amphipod, Talorchestia longicornis

The biological rhythm in activity of the supratidal amphipod Talorchestia longicornis Say was determined under constant conditions. Surface activity was monitored with a time-lapse video system under red light and assessed as the number of animals emerging from their burrows and active on a sand substrate at 0.5 h intervals. The amphipods had a circadian rhythm in which they were active at the time of night at the collection site. The rhythm could be entrained by a light : dark cycle and had an average free-running period of 23.7 h. Activity also appeared to be related to tidal times at the collection site because, under constant conditions, surface activity was suppressed at the time of nocturnal high tide and increased at the time of nocturnal low tide. The rhythm is functionally significant for foraging at night to avoid visual predators, desiccation and high temperatures.     

Light control of the circadian activity rhythm in mouse‐eared bats (Myotis myotis Borkh. 1797)

Abstract

The aim of this study was to analyse the effect of light respectively illumination cycles on the activity rhythm of the insectivorous bat Myotis myotis (M.m.). A new electronic registration system devised for this purpose can be applied almost universally in recording the activity of terrestrial animals.

M.m. is a strictly dark‐active species with a bimodal activity pattern of bigeminus character. Under constant conditions, M.m. reveals a free running circadian activity rhythm. Its period length varies between 22.6 and 27.8 h and is positively correlated with the intensity of illumination. The range of entrainment of the circadian activity rhythm of M.m. is unusually wide. Accordingly, M.m. resynchronizes very quickly after phase shifts of the Zeitgeber LD. Activity maxima in the range of 10^‐4 lx occur in LD 12:12 with constant illumination in L and varied illumination in D as well as in LL with varying intensity.

It is to be discussed whether the wide variability of different parameters in the circadian system of M.m. compared with those of other Chiroptera can be interpreted as an adaptation to ecological factors.     

Freerunning and entrained circadian rhythms in activity,eating and drinking in the cat

Abstract

Because cats with pontile lesions exhibit an abnormal behavior that is under photoperiodic control, and because circadian rhythms are implicated in photoperiodic control mechanisms, an effort was made to detect circadian rhythms in the cat. Cats were isolated from all extraneous stimuli in soundproof chambers for extended periods of time. Photocells were used to monitor activity, eating and drinking in different LD cycles, in constant light at two intensities, and in constant dark. Freerunning circadian rhythms were found in the constant conditions, and entrained nocturnal patterns occurred in most of the LD cycles. The higher intensities of ambient illumination disrupted the freerunning rhythms. The freerunning rhythms were always greater than 24 h, ranging from 24.2 to 25 h. Measurements of food intake of cats living in a large colony room, obtained by weighing the food, revealed that a nocturnal pattern of entrainment was not present in the majority of the cats. Instead, most cats in the colony exhibited a random pattern of eating throughout the light and dark period of the LD cycle. However, the variation among the cats in the colony was considerable, extending from nocturnal to diurnal patterns of eating. A diurnal pattern of human activity was present in the colony and may account for the disruption of a basic nocturnal pattern. The presence of circadian rhythms in the cat leads us to consider the coincidence models for photoperiodic induction as possible explanations of the photoperiodic control of the lesion‐induced abnormal behavior.     

Influence of Light Intensity on Plasma Melatonin and Locomotor Activity Rhythms in Tench

Melatonin production by the pineal organ is influenced by light intensity, as has been described in most vertebrate species, in which melatonin is considered a synchronizer of circadian rhythms. In tench, strict nocturnal activity rhythms have been described, although the role of melatonin has not been clarified. In this study we investigated daily activity and melatonin rhythms under 12∶12 light‐dark (LD) conditions with two different light intensities (58.6 and 1,091 µW/cm²), and the effect of 1 h broad spectrum white light pulses of different intensities (3.3, 5.3, 10.5, 1,091.4 µW/cm²) applied at middarkness (MD) on nocturnal circulating melatonin. The results showed that plasma melatonin in tench under LD 12∶12 and high light conditions displayed rhythmic variation, where values at MD (255.8±65.9 pg/ml) were higher than at midlight (ML) (70.7±31.9 pg/ml). Such a difference between MD and ML values was reduced in animals exposed to LD 12∶12 and low light intensity. The application of 1 h light pulses at MD lowered plasma melatonin to 111.6±3.2 pg/ml (in the 3.3–10.5 µW/cm² range) and to 61.8±18.3 pg/ml (with the 1,091.4 µW/cm² light pulse) and totally suppressed nocturnal locomotor activity. These results show that melatonin rhythms persisted in tench exposed to low light intensity although the amplitude of the rhythm is affected. In addition, it was observed that light pulses applied at MD affected plasma melatonin content and locomotor activity. Such a low threshold suggests that the melatonin system is capable of transducing light even under dim conditions, which may be used by this nocturnal fish to synchronize to weak night light signals (e.g., moonlight cycles).     

Circadian Pattern of Wheel‐Running Activity of a South American Subterranean Rodent (Ctenomys cf knightii)

Circadian rhythms are regarded as essentially ubiquitous features of animal behavior and are thought to confer important adaptive advantages. However, although circadian systems of rodents have been among the most extensively studied, most comparative biology is restricted to a few related species. In this study, the circadian organization of locomotor activity was studied in the subterranean, solitary north Argentinean rodent, Ctenomys knightii. The genus, Ctenomys, commonly known as Tuco‐tucos, comprises more than 50 known species over a range that extends from 12°S latitude into Patagonia, and includes at least one social species. The genus, therefore, is ideal for comparative and ecological studies of circadian rhythms. Ctenomys knightii is the first of these to be studied for its circadian behavior. All animals were wild caught but adapted quickly to laboratory conditions, with clear and precise activity‐rest rhythms in a light‐dark (LD) cycle and strongly nocturnal wheel running behavior. In constant dark (DD), the rhythm expression persisted with free‐running periods always longer than 24 h. Upon reinstatement of the LD cycle, rhythms resynchronized rapidly with large phase advances in 7/8 animals. In constant light (LL), six animals had free‐running periods shorter than in DD, and 4/8 showed evidence of “splitting.” We conclude that under laboratory conditions, in wheel‐running cages, this species shows a clear nocturnal rhythmic organization controlled by an endogenous circadian oscillator that is entrained to 24 h LD cycles, predominantly by light‐induced advances, and shows the same interindividual variable responses to constant light as reported in other non‐subterranean species. These data are the first step toward understanding the chronobiology of the largest genus of subterranean rodents.     

Expression of circadian rhythmicity in Djungarian hamsters under constant light: Effects of light intensity and the circadian system's state

Summary Djungarian hamsters (Phodopus sungorus), were exposed to constant light with increasing intensities (20, 60, 350 lux), and wheel running activity was recorded. With increasing light intensity the percentage of hamsters showing a split in their daily activity pattern increased and the free running period was lengthened for both the unsplit and the split state. The fact that the free running period of both states depended on the light intensity together with the observation that the highest incidence of acircadian activity occurred under 350 lux, provoked the idea that the emergence of splitting or acircadian rhythmicity is a direct consequence of the light induced lengthening of the free running period. However, analysis of the data failed to support the idea that emergence of a split or acircadian activity is a threshold phenomenon with respect to the free running period.Due to differences in circadian function some Djungarian hamsters do not exhibit photoinduction following short day exposure. In these individuals splitting also occurred but required exposure to a higher light intensity than in photo-responsive hamsters. This observation is in accordance with the idea that the two phenotypes differ in the interaction of the two component oscillators underlying circadian rhythmicity.Abbreviations LD long day photoperiod - LL constant light - SD short day photoperiod - free running period     

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.     

Circadian Rhythms of Locomotor Activity in Lycosa tarentula (Araneae,Lycosidae) and the Pathways of Ocular Entrainment

Lycosa tarentula is a ground-living spider that inhabits a burrow where it awaits the appearance of prey or conspecifics. In this study, circadian rhythms of locomotor activity were examined as well as the ocular pathway of entrainment. Thirty-three adult virgin females were examined under constant darkness (DD); all of them exhibited robust circadian rhythms of locomotor activity with a period averaging 24.1h. Fourteen of these spiders were studied afterwards under an LD 12:12 cycle; they usually entrained to in the first or second day, even when the light intensity was as low as 1 lx. During the LD cycle, locomotor activity was generally restrained to the darkness phase, although several animals showed a small amount of diurnal activity. Ten males were also examined under LD; they were also nocturnal, but were much more active than the females. Seven females were examined under constant light (LL); under this they became arrhythmic. Except for the anterior median eyes (OMAs), all the eyes were capable of entraining the locomotor activity to an LD cycle. These results demonstrate that under laboratory conditions and low light intensities locomotor activity of Lycosa tarentula is circadian and in accordance with Aschoff's 'rule'. Only OMAs are unable to entrain the rhythm; the possible localization of circadian clock is therefore discussed.     

Effect of different lighting conditions on circadian developmental rhythms and behaviour in Ephestia kuehniella Zell

Abstract

A study was made on the developmental rhythms of Ephestia kuehniella during different photoperiods: constant lighting (L/L), under conditions of 12 hours light per day (L/D) and in constant darkness (D/D). Observations were made every 2 hrs, for 3 successive 24‐hr periods, of the number of wandering larvae emerging from food, the number of pupations and of imaginai moults. Emergence of wandering larvae is rhythmic only under L/D conditions, and in addition this is also affected by the density of the larvae. Rhythm is least apparent with greatest density of the larvae. Pupation in E. kuehniella is a non‐rhythmic process with each of the photoperiods examined, whereas the imaginai moult is characterized by an endogenous (existing under D/D conditions) rhythm. Emergence of imagines is non‐rhythmic under L/L, and also when pupae under L/D fail to receive the final period of darkness. The rhythm of the imaginai moult is possibly controlled by the biological clock, which stops under conditions of constant light.     

Tidal,Daily, and Lunar‐Day Activity Cycles in the Marine Polychaete Nereis virens

The burrow emergence activity of the wild caught ragworm Nereis virens Sars associated with food prospecting was investigated under various photoperiodic (LD) and simulated tidal cycles (STC) using a laboratory based actograph. Just over half (57%) of the animals under LD with STC displayed significant tidal (～12.4 h) and/or lunar‐day (～24.8 h) activity patterns. Under constant light (LL) plus a STC, 25% of all animals were tidal, while one animal responded with a circadian (24.2 h) activity rhythm suggestive of cross‐modal entrainment where the environmental stimulus of one period entrains rhythmic behavior of a different period. All peaks of activity under a STC, apart from that of the individual cross‐modal entrainment case, coincided with the period of tank flooding. Under only LD without a STC, 49% of the animals showed nocturnal (～24 h) activity. When animals were maintained under free‐running LL conditions, 15% displayed significant rhythmicity with circatidal and circadian/circalunidian periodicities. Although activity cycles in N. virens at the population level are robust, at the individual level they are particularly labile, suggesting complex biological clock‐control with multiple clock output pathways.