Bimodal Circadian Rhythm Research Articles

Time-Dependent Trapping of Pollinators Driven by the Alignment of Floral Phenology with Insect Circadian Rhythms.

Several evolutionary lineages in the early divergent angiosperm family Annonaceae possess flowers with a distinctive pollinator trapping mechanism, in which floral phenological events are very precisely timed in relation with pollinator activity patterns. This contrasts with previously described angiosperm pollinator traps, which predominantly function as pitfall traps. We assess the circadian rhythms of pollinators independently of their interactions with flowers, and correlate these data with detailed assessments of floral phenology. We reveal a close temporal alignment between patterns of pollinator activity and the floral phenology driving the trapping mechanism (termed ‘circadian trapping’ here). Non-trapping species with anthesis of standard duration (c. 48 h) cannot be pollinated effectively by pollinators with a morning-unimodal activity pattern; non-trapping species with abbreviated anthesis (23–27 h) face limitations in utilizing pollinators with a bimodal circadian activity; whereas species that trap pollinators (all with short anthesis) can utilize a broader range of potential pollinators, including those with both unimodal and bimodal circadian rhythms. In addition to broadening the range of potential pollinators based on their activity patterns, circadian trapping endows other selective advantages, including the possibility of an extended staminate phase to promote pollen deposition, and enhanced interfloral movement of pollinators. The relevance of the alignment of floral phenological changes with peaks in pollinator activity is furthermore evaluated for pitfall trap pollination systems.

Seasonal changes of locomotor activity patterns in the desert isopod Hemilepistus reaumuri

The locomotor activity rhythm of the desert woodlouse Hemilepistus reaumurii was monitored as individuals over the four seasons, under entraining and constant darkness conditions. Results indicated that individuals exhibited an endogenous rhythm of locomotor activity with a circadian period longer in spring than the other seasons whatever the regimen. Due to the important inter-individual variability, no significant difference in period was found between seasons as well as between regimens. Periodogram analysis revealed also an ultradian period around 12 h. Activity was mostly confined to the hours of the photophase or to those of subjective day. The activity pattern showed two main peaks. This bimodal circadian rhythm persisted for as long as the experiments were run, and was clearer in summer and autumn than in winter. The most clearly defined rhythms were found in spring and summer recordings, respectively, under entraining and free running conditions. The variation of activity patterns according to the seasons will be discussed.

Ontogeny of daily activity and circadian rhythm in the Iberian lynx (Lynx pardinus)

The aim of this paper is to describe the ontogeny of the circadian activity rhythms in captive-born Iberian lynx (Lynx pardinus) from birth to subadult age and to verify if they develop a bimodal circadian pattern similar to the one they show in the wild. The amount of daily activity and the circadian rhythmicity of 61 Iberian lynx (48 mother-raised and 13 hand-reared) cubs were studied in two breeding centers. During the first month of life, the cubs were active 30% of the day. Activity increased up to 50% during the following two weeks, and then it remained constant until the end of the lynx physical development. The location of the breeding center affected the amount of daily activity of the cubs probably as result of different climatic conditions. Once the lynx cubs had completed their development, there was no difference in the time spent active between wild and captive lynx. Newborns had a constant level of activity throughout the day (24h) during the first month of life. During the second month, once they had developed sufficiently to leave the den, a crepuscular bimodal circadian rhythm started to emerge. This pattern was completely defined by the third month of life. The overlap in circadian activity was over 0.88 when comparing the sexes, breeding centers and rearing methods. However, there was a significant difference between mother-raised and hand-reared cubs – the latter being more active in the morning–, as well as between breeding centers – again due to climate differences. Finally, an overlap of 0.85 in circadian activity pattern was observed between wild and captive lynx, although the wild animals were more active at night.

Preliminary observations on the natural variation in the endogenous rhythm of the desert Isopod Hemilepistus reaumurii

The desert woodlouse Hemilepistus reaumurii lives in monogamous pairs, together with their offspring, in self-dug burrows. Every burrow contains only one family. This animal is active on the surface from the beginning of spring to autumn. It remains in the burrow during the hottest part of the day, to avoid the heat, but is active at the surface during morning and evening. During the winter, low temperature prevents its above ground activity. Freshly collected animals, from the north of Kairouan (Tunisia) were transferred to a controlled environment cabinet in the laboratory and their locomotor activity monitored as individuals or in male/female pairs, in annular chambers equipped with an infrared activity recording system. For the first 7 days of recording, the animals were kept in a light–dark cycle in phase with the natural diel cycle. For the second 7 days, animals were maintained in constant darkness. The temperature was held constant at 18±1 °C. Analysis of preliminary data indicates that both individuals and pairs exhibit an endogenous rhythm of locomotor activity with a circadian periodicity. Activity was mostly confined to the hours of the photophase (1–7 days) or to those of subjective day (8–14 days). The activity pattern showed two main peaks, around dusk and dawn, respectively. This bimodal circadian rhythm persisted for as long as the experiments were run, and was clearer in individual recording than in pair recording. The characteristics and biological significance of the rhythm are discussed.

Triggers of acute myocardial infarction regarding its site

We have studied the incidence of possible triggers of the myocardial infarction regarding its site in 750 patients with anterior and 731 patients with inferior infarction. Infarctions occurred most frequently without recalling any triggering activity, especially in patients with anterior infarction (67 vs. 44%). Physical effort as the possible precipitator was also more frequent in anterior infarctions (22 vs. 16%). However, the onset of inferior infarction was more frequent during meteorological stress (9 vs. 2%), emotional stress (10 vs. 3%), after overeating (13 vs. 3%) and nicotine abuse (6 vs. 1.5%). These triggers were independent and highly significant ( P<0.02 in each case) discriminators of the site of myocardial infarction. Bimodal circadian rhythm, with primary peak between 6 and 9 h a.m. and the secondary peak between 3 and 6 p.m. was observed in patients which did not recall any triggering activity, and this was more pronounced in patients with inferior infarction. These results support the hypothesis that the influence of the vegetative tone is most pronounced in the onset of myocardial infarction of inferior wall.

Thermal sensitivity during brood care in workers of two Camponotus ant species: Circadian variation and its ecological correlates

Thermal sensitivity during brood care was analysed in two Neotropical Camponotus ant species, related phylogenetically but disparate in ecology. Camponotus mus is dominant in temperate climates, whereas C. rufipes is dominant in subtropical climates. Sensitivity was assessed by first allowing workers to manifest their preference along a thermal gradient, and thereafter increasing the temperature of the nest floor continuously at a rate of 0.2 °C/min. The removal of brood by workers was recorded as an indicative response of upper thermal tolerance. Along a thermal gradient, while C. mus nurse workers exhibited a bimodal circadian rhythm of temperature preference to locate the brood, C. rufipes nurses selected an invariant temperature throughout the day. Irrespective of their thermal preferences, sensitivity to temperature changes in both species showed a conspicuous circadian rhythm. Its endogenous nature was supported by a free-run under constant darkness. In C. mus, instantaneous resetting by the light:dark cycle could also be demonstrated, and experiments suggest the involvement of one oscillator controlling thermal responses. At the middle of the light period when extreme environmental temperatures are expected, C. mus nurses exhibited the highest sensitivity (brood removal after an increase of 0.2 °C), while C. rufipes showed the lowest (removal after an increase of 6.7 °C). For both species, the time-course of thermal sensitivity during brood care suggests an adaptation to the wide and slight daily fluctuations undergone by temperature in temperate and tropical climates, respectively.

Effect of Season and Light Treatment Upon Hot Flashes in a Perimenopausal SAD Patient

A perimenopausal woman with seasonal affective disorder (SAD, winter depression) presented with a 2-year history of hot flashes occurring only in the wintertime. Prospectively documented hot flashes appeared to follow a seasonal rhythm and a bimodal circadian rhythm. The hot flashes decreased with morning, but not evening, light therapy. These observations are discussed in the context of the literature regarding light's possible role in animal and human reproductive functioning.

A free-running bimodal circadian rhythm in the tsetse fly Glossina longipennis

In nature, the tsetse fly, Glossina longipennis Corti, restricts its activity to ∼ 1 h around sunset and a lesser peak at dawn. This markedly crepuscular rhythm was investigated in actographs under constant conditions in the laboratory. In LD 12:12 with 30-min dawns and dusks, the evening activity started as the lights dimmed, peaked in the first hour of darkness, and then declined rapidly to near zero, to peak again for ∼ 1 h at dawn. Virtually no activity occurred through the central 8 light hours of the photophase. In constant darkness, this pattern of a major ‘dusk’ and minor ‘dawn’ peak was repeated in the males for at least three cycles, with a free-running period of ∼ 23 h. This is the first demonstration of a fully endogenous bi-modal rhythm in tsetse flies.

Circadian distribution of onset of acute myocardial infarction in subgroups from analysis of 10,791 patients treated in a single center

A circadian variation of symptom onset in acute myocardial infarction (AMI) with an increased frequency in the late morning and possibly also in the evening has been found in several studies. It has been suggested that different circadian rhythms may exist in various subgroups of patients. This possibility was examined in a population of 10,791 patients collected between 1973 and 1987 in a continuously operating register of patients with AMI in Malmö, Sweden. In 6,763 patients (63%) in whom a distinct symptom onset could be established, symptom onset occurred with an increased frequency between 6:01 A.M. and 12:00 noon (30.6%) and between 6:01 P.M. and 12:00 midnight (26.9%). Similar bimodal circadian rhythms were seen in patients aged >70 years (n = 2,923), ≤70 years (n = 3,840), men (n = 4,528), women (n = 2,235), smokers (n = 2,458), hypertensives (n = 1,999), diabetics (n = 653), patients with (n = 1,872) and without (n = 4,891) a history of previous AMI, and in patients with recent non-Q-wave AMI (n = 333). In 455 patients receiving cardioselective β blockers the circadian distribution did not differ from a random, whereas in patients taking nonselective β blockers or calcium antagonists significant bimodal rhythms were found. Statistically significant interactions were found between symptom onset and age dichotomized at 70 years, and between patients with and without a history of previous AMI. In a multivariate analysis only these variables (age ≤/>70 years; ± history of a previous AMI) were found to modify the circadian rhythm of symptom onset in the population. It is suggested that only minor differences in symptom onset between various subgroups exist within the same population, and that these differences probably are unable to explain differences in circadian rhythm of symptom onset between different populations.

Rhythmic changes in the activities of NAD kinase and NADP phosphatase in the achlorophyllous ZC mutant of Euglena gracilis klebs (strain Z)

NAD kinase and NADP phosphatase activities were detected in the supernatant and the pellet fractions prepared by sonication and centrifugation of the achlorophyllous ZC mutant of the phytoflagellate Euglena gracilis. A detailed study of substrate concentration-velocity curves enabled us to define the saturating substrate concentrations that were used in the enzyme assays. An analysis of the reproducibility of the entire assay procedure indicated that the pooled standard error was about 14%. We report circadian variations in the activities of NAD kinase and NADP phosphatase in the soluble and membrane-bound fractions of both synchronously dividing and nondividing cultures maintained in constant darkness. Bimodal circadian rhythms in total NADP phosphatase activity were found in dividing cells (peaks at circadian times [CT] 00 and 12). The peak observed at CT 00–03 disappeared when the cells had ceased dividing, a result that suggests that it might be regulated by the cell division cycle. NAD kinase activity displayed unimodal circadian rhythms (peak at CT 12) in dividing cells, which persisted with the same phase after the culture entered the stationary phase of growth. Results are discussed with reference to a model ( K. Goto, D. L. Laval-Martin, and L. N. Edmunds, Jr., 1985, Science 228, 1284–1288 ) in which we have proposed that the Ca 2+-transport system, Ca 2+, calmodulin, NAD kinase, and NADP phosphatase could represent clock “gears” that might constitute a self-sustained circadian oscillating loop.

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 daylength or a multiple of the length of the dark period.

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.

Effect of digestible energy on nitrogen and energy balance in rainbow trout

The utilization by rainbow trout of high protein diets, incorporating 30% of either gelatinized (diet AG) or natural starch (diet AC) was studied. Compared with a commercial diet, both these diets were more efficiently utilized. Food and protein utilization were higher in trout fed the diet AG than in those fed the diet containing the raw starch. Body composition was similar in both groups except for fat content which was elevated in those fed the natural starch. Relative liver weight and post-prandial plasma glucose levels were higher in those fed the diet containing gelatinized starch than in those fed raw starch. Patterns of post-prandial ammonia and total free amino nitrogen levels in the plasma did not differ between the two groups but the levels were consistently higher in those fed diet AC. A bimodal circadian rhythm was found with a maximum at 6 and 9 h and a second peak at 17 and 20 h after the morning meal in trout fed AC and AG diets, respectively. In fasted trout, only one maximum was observed, corresponding to the second peak in fed animals. Nitrogen excretion, following a meal, was much lower in trout fed the AG diet than in those fed either the AC diet or the control diet. Balance studies confirmed the more efficient utilization of protein and energy by trout fed the more digestible starch than by those in the other groups.

Circadian rhythms in accessory sex gland function in the male rat.

Alterations in various parameters of accessory sex gland function were monitored during two separate 24 h periods in adult male rats, and compared to fluctuations in the circulating levels of testosterone, prolactin, corticosterone and LH. Bimodal circadian rhythms in ventral prostate prolactin binding, cytosolic oestrogen binding and seminal vesicle weight could be discerned which appeared to be related to a similar rhythmicity in circulating testosterone levels, but with a phase shift of 3 h. Prostatic membrane bound adenylyl cyclase activities (basal and hormone stimulated) and prostatein concentrations followed different patterns possibly correlated to other endocrine changes.

The effect of light regimes on the circadian rhythm of flight activity in the mosquito Aedes taeniorhynchus.

ABSTRACT The flight activity patterns of groups and individuals of sugar-fed A. taeniorhynchus females have been studied under different light regimes, by recording of flight sound as an indicator of flight activity. In an LD 12:12 regime, flight activity occurs both at light-off and light-on, forming a bimodal ‘alternans’ pattern. This basic pattern of flight activity persists with a periodicity of 23.5 h under continuous DD, but under continuous LL is masked over by irregular excessive outbursts of activity. The flight activity rhythm originates for the first time in the adult stage, and it is not carried over from rhythms of developmental stages. Flight activity rhythms can be entrained to a new light regime within 24 –36 h which is rather fast. An early light-off does not reset the phase of the rhythm, but a delayed light-off does. The flight activity rhythm can be entrained to 24 h light regimes other than LD 12:12. But a single stimulus of less than 12 h is not effective in initiating the bimodal circadian rhythm. Frequency demultiplication within certain limits can entrain the flight activity rhythm to 24 h. This flight activity rhythm of A. taeniorhynchus is compared with the activity rhythms of Aopheles gambiae and Culex pipiens pallens. It is concluded that the basic bimodal alternans pattern of flight activity is a persistent property of the circadian oscillating system, which suggests that other activity rhythms involving flight are dependent on the same rhythm.

Circadiane Rhythmik von Drosophila-Speicheldrüsen in vivo, in vitro und nach Ecdysonzugabe

Nuclear and nucleolar volumes of Bouin-fixed salivary glands of Drosophila larvae show a bimodal circadian rhythm (12 : 12 hr light-dark régime, 20°C). The phasing of this rhythm relative to the light-dark ‘Zeitgeber’ changes in the course of ontogeny, i.e. from day 4 to day 7 during larval development. The rhythms of nuclear and nucleolar volumes seem to follow the same pattern. Living nuclei from salivary glands freshly prepared at different times of day show a bimodal rhythm very similar to the rhythm of fixed salivary glands of the same developmental age. The transverse profiles of all data under normal and inverse light-dark conditions reveal significant differences between maxima and minima. Volumes of single nuclei from salivary glands cultured up to 10 days in a chemically defined medium also oscillate in a bimodal circadian rhythm (12 : 12 hr light-dark régime, 25°C); differences between maxima and minima extend to about 10 per cent of the mean volume. The rhythm of these nuclei measured longitudinally over 36 to 48 hr coincides with the rhythm of the fixed and living nuclei in the transverse profiles. Varying relative K + and Na + concentrations of the medium have no remarkable influence on the rhythm. The rhythm persists in constant light of about 200 lx for at least 4 days; it is phase-shifted by a 6 hr ‘Zeitgeber’ shift during larval development. Pulse- or stepwise addition of ecdysone-containing medium between 13 and 18 hr caused a phase shift of the nuclear rhythm in vitro: after a small maximum at 24 hr (coinciding with the controls) phase differences of 3 to 9 hr relative to the normal and control groups can be observed later. The addition of ecdysone between 9 to 12 hr failed to shift the rhythm.