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Results for “Biological Clocks”

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PubMed2004

Periodically varying externally imposed environmental effects on population dynamics.

Effects of externally imposed periodic changes in the environment on population dynamics are studied with the help of a simple model. The environmental changes are represented by the temporal and spatial dependence of the competition terms in a standard equation of evolution. Possible applications of the analysis are on the one hand to bacteria in Petri dishes and on the other to rodents in the context of the spread of the Hantavirus epidemic. The analysis shows that spatiotemporal structures emerge, with interesting features which depend on the interplay of separately controllable aspects of the externally imposed environmental changes.

Animals↗
PubMed2005

Steady-state properties of a totally asymmetric exclusion process with periodic structure.

We study the steady-state behavior of totally asymmetric simple exclusion processes (TASEPs) that contain periodically varying movement rates. In this model, particles move to the right at one of two rates: p(2) if the particle occupies one of a periodically arranged set of lattice sites; p(1) otherwise. Approximate mean field approaches are used to study the steady-state currents and bulk densities of this model. These mean field methods are found to provide results in good agreement with data derived from Monte Carlo simulations. Finally, the condition for particle-hole symmetry in the TASEP with periodically varying movement rates is specified, and the changes in the locations of the boundary-limited to maximal-current transition lines due to symmetry violation are investigated.

Animals↗
PubMed2005

Periodicity of mass extinctions without an extraterrestrial cause.

We study a lattice model of a multispecies prey-predator system. Numerical results show that for a small mutation rate the model develops irregular long-period oscillatory behavior with sizeable changes in a number of species. The periodicity of extinctions on Earth was suggested by Raup and Sepkoski [Proc. Natl. Acad. Sci. 81, 801 (1984)], but thus far is lacking a satisfactory explanation. Our model indicates that this might be a natural consequence of the ecosystem dynamics and not the result of any extraterrestrial cause.

Animals↗
PubMed2005

Chaos-induced coherence in two independent food chains.

Coherence evolution of two food web models can be obtained under the stirring effect of chaotic advection. Each food web model sustains a three-level trophic system composed of interacting predators, consumers, and vegetation. These populations compete for a common limiting resource in open flows with chaotic advection dynamics. Here we show that two species (the top predators) of different colonies chaotically advected by a jetlike flow can synchronize their evolution even without migration interaction. The evolution is characterized as a phase synchronization. The phase differences (determined through the Hilbert transform) of the variables representing those species show a coherent evolution.

Animals↗
PubMed2005

Annihilation of limit-cycle oscillations by identification of critical perturbing stimuli via mixed-integer optimal control.

We present a novel model-based mixed-integer optimal control method to automatically identify the strength and timing of critical external stimuli leading to the transient annihilation of limit-cycle oscillators. Biochemical oscillators of this type play a central role in regulating cellular rhythms. Their specific manipulation is a promising perspective to control biological functions by drugs and tailored treatment strategies. We demonstrate our new optimal control approach in an application to a biochemical model for oscillatory calcium signal transduction.

Adenosine Triphosphate↗
PubMed1972

Photoperiodic Entrainment Patterns in the CO(2) Output of Lemna perpusilla 6746 and of Several Other Lemnaceae.

The CO(2) output of Lemna perpusilla 6746 in "skeleton photoperiods" consisting of alternating 10(1/2)-hour and 13-hour dark periods separated by (1/4)-hour illuminations was recorded under stable high and low nitrate conditions. The phase relationship finally attained between light schedule and output is the same regardless of which dark period is given first, but entrainment is more rapid (as is flowering) with an initial 13-hour dark period. In all respects other than bistability-the assumption of two different stable phase relationships depending on the initial dark period-both flowering and the course of CO(2) output conform to Pittendrigh's model derived from Drosophila eclosion rhythms, confirming the view that an endogenous circadian rhythm, or biological clock, underlies the photoperiodic control of flowering in this plant. Experiments with rigorous temperature control show that earlier results with long light exposures were in part due to temperature changes; in consequence, it is clear that entrainment patterns with high nitrate differ even more from those in low nitrate than was previously evident, and not simply by the addition of a "nitrate peak." Other Lemnaceae tested with a few simple light-dark schedules in both types of media show a variety of responses, with no obvious correlation to photoperiodic response type.

Journal Article↗
PubMed1974

Photoperiodism and enzyme activity: towards a model for the control of circadian metabolic rhythms in the crassulacean Acid metabolism.

Metabolic readjustments after a change from long days to short days appear, in Kalanchoe blossfeldiana, to be achieved through the operation of two main mechanisms: variation in enzyme capacity, and circadian rhythmicity. After a lag time, capacity in phosphoenolpyruvate carboxylase and capacity in aspartate aminotransferase increase exponentially and appear to be allometrically linked during 50 to 60 short days; then a sudden fall takes place in the activity of the former. Malic enzyme and alanine aminotransferase behave differently. Thus, the operation of the two sections of the pathway (before and after the malate step) give rise to a continuously changing functional compartmentation in the pathway. Circadian rhythmicity, on the other hand, produces time compartmentation through phase shifts and variation in amplitude, independently for each enzyme. These characteristics suggest that the operation of a so-called biological clock would be involved. We propose the hypothesis that feedback regulation would be more accurate and efficient when applied to an already oscillating, clock-controlled enzyme system.

Journal Article↗
PubMed1977

Characterization of Photosynthetic Rhythms in Marine Dinoflagellates: II. Photosynthesis-Irradiance Curves and in Vivo Chlorophyll a Fluorescence.

Using data from light-dark cultures of Gonyaulax polyedra entrained to a 24-hour cycle, whole cell absorption curves and photosynthesis-irradiance curves were constructed for various circadian times. While whole cell absorbance and half-saturation constants of photosynthesis showed no statistical difference that could be directly related to the photosynthetic rhythm, the initial slope of the photosynthesis-irradiance curve was a time-dependent parameter which altered in direct proportion to the change in photosynthetic capacity. The results indicated a temporal change in the relative quantum yield of photosynthesis, and the circadian rhythmicity of light-limited photosynthesis was established under constant conditions. Circadian rhythmicity was detected in room temperature chlorophyll fluorescence yield. Low temperature fluorescence kinetics also showed fluctuations. The results suggest that regulation of photosynthesis by the biological clock of Gonyaulax may be mediated through the membrane-bound light reactions and a partial explanation of the underlying mechanism is proposed.

Journal Article↗
PubMed1986

Adaptation to CO(2) Level and Changes in the Phosphorylation of Thylakoid Proteins during the Cell Cycle of Chlamydomonas reinhardtii.

The photosynthetic performance of synchronously grown Chlamydomonas reinhardtii alternated rhythmically during the cell cycle. The activity of the "CO(2) concentrating mechanism" including the ability to accumulate CO(2) internally and the activity of carbonic anhydrase peaked after 6 to 9 hours of light and reached minimum after 6 to 9 hours of dark. Consequently, the apparent photosynthetic affinity to extracellular CO(2) alternated rhythmically. At the end of the dark period the cells behaved as if they were adapted to high CO(2) even though they were continuously aerated with air. Results from experiments in which the light or dark periods were extended bear on the interaction between the internal (cell cycle or biological clock) and the external (light) signal. The observed rhythmical alterations in photosynthetic V(max) may result from changes in PSII activity. The latter may be partly explained by the capacity for phosphorylation of thylakoid proteins, which reached maximum after 9 hours of light and decreased toward the dark period.

Journal Article↗
PubMed1991

Circadian Control of cab Gene Transcription and mRNA Accumulation in Arabidopsis.

An intriguing property of many organisms is their ability to exhibit rhythmic cellular events that continue independently of environmental stimuli. These rhythmic processes are generated by an endogenous mechanism known as the biological clock. We wished to determine whether Arabidopsis thaliana will serve as a model plant system for a molecular genetic dissection of the circadian clock. To this end, we investigated the expression of Arabidopsis chlorophyll a/b-binding protein (cab) genes throughout the circadian cycle. Steady-state mRNA levels of the cab2 and cab3 genes showed a dramatic circadian cycling in plants shifted from light/dark cycles to constant darkness, whereas the cab1 mRNA level exhibited little or no cycling under the same conditions. Analysis of cab promoter fusions in transgenic tobacco revealed that both the cab1 and cab2 5[prime] upstream regions confer circadian-regulated expression on a chloramphenicol acetyltransferase (cat) reporter gene. In vitro nuclear run-on transcription assays also indicated that the transcription of the cab1 and cab2 genes is circadian regulated in Arabidopsis. Taken together, these data suggest that a post-transcriptional mechanism influences cab1 mRNA levels in Arabidopsis. The identification of circadian-regulated cis-acting elements in the cab1 and cab2 upstream regions will provide powerful tools for both molecular and genetic analysis of the higher plant circadian clock.

Journal Article↗
PubMed2004

Generating high-speed dynamic running gaits in a quadruped robot using an evolutionary search.

Over the past several decades, there has been a considerable interest in investigating high-speed dynamic gaits for legged robots. While much research has been published, both in the biomechanics and engineering fields regarding the analysis of these gaits, no single study has adequately characterized the dynamics of high-speed running as can be achieved in a realistic, yet simple, robotic system. The goal of this paper is to find the most energy-efficient, natural, and unconstrained gallop that can be achieved using a simulated quadrupedal robot with articulated legs, asymmetric mass distribution, and compliant legs. For comparison purposes, we also implement the bound and canter. The model used here is planar, although we will show that it captures much of the predominant dynamic characteristics observed in animals. While it is not our goal to prove anything about biological locomotion, the dynamic similarities between the gaits we produce and those found in animals does indicate a similar underlying dynamic mechanism. Thus, we will show that achieving natural, efficient high-speed locomotion is possible even with a fairly simple robotic system. To generate the high-speed gaits, we use an efficient evolutionary algorithm called set-based stochastic optimization. This algorithm finds open-loop control parameters to generate periodic trajectories for the body. Several alternative methods are tested to generate periodic trajectories for the legs. The combined solutions found by the evolutionary search and the periodic-leg methods, over a range of speeds up to 10.0 m/s, reveal "biological" characteristics that are emergent properties of the underlying gaits.

Algorithms↗
PubMed2004

Abolished circadian rhythm of melatonin secretion in sedated and artificially ventilated intensive care patients.

BACKGROUND: Sleep disturbance is common in intensive care patients. Aside from its unpleasantness, there is a correlation with intensive care unit (ICU) syndrome/delirium. Reasons for sleep deprivation appear to be multifactorial, including the underlying illness, an acute superimposed disturbance, medications, and the ICU environment itself. There are reasons to believe that alterations of the 'biological clock' might contribute. Melatonin secretion is one reflection of this internal sleep/wake mechanism. Melatonin levels are normally high during the night and low during daytime, being suppressed by bright light. METHODS: Melatonin levels in blood and urine were studied over 3 consecutive days in eight critically ill patients during deep sedation and mechanical ventilation. Sedation was assessed with the sedation-agitation (SAS) scale and bispectral index (BIS) monitor. RESULTS: The circadian rhythm of melatonin release was abolished in all but one patient, who recovered much more quickly than the others. There was no correlation between melatonin levels and levels of sedation. CONCLUSIONS: This study indicates that dyssynchronization of the melatonin secretion rhythm is common in critically ill and mechanically ventilated patients. It could be hypothesized that an impairment of the melatonin rhythm may play a role in the development of sleep disturbances and delirium in intensive care patients, and that melatonin supply could reduce the incidence of these phenomena.

Aged↗
PubMed2000

Genetic evidence for assortative mating between 13-year cicadas and sympatric "17-year cicadas with 13-year life cycles" provides support for allochronic speciation.

Thirteen-year cicadas of brood XIX from northern Arkansas, Missouri, and southern Illinois (lineage A) are known to be genetically different at two marker loci (mitochondrial DNA and abdominal color) from 13-year cicadas to the south (lineage B) that emerge in the same year. Because 17-year cicadas from all broods (year classes) are indistinguishable from lineage A at these two marker loci, previous workers suggested that the lineage A cicadas of 13-year brood XIX were derived from 17-year cicadas by life-cycle switching (allochrony). Data presented here show that, over the same northern geographic range, lineage A is also present in 13-year cicadas belonging to brood XXIII (which always emerges four years later than brood XIX). Detailed sampling along the putative life-cycle-switching boundary in 13-year brood XXIII revealed a previously unsuspected broad zone of overlap where populations contained individuals of both lineages A and B. Despite this sympatry, and previous reports of a lack of behavioral barriers to interbreeding, a strong correlation between mitochondrial haplotype and abdominal color suggests that assortative mating has taken place. Lineage A 13-year cicadas from both broods XIX and XXIII are only found within a gap in the spatial distribution of 17-year cicadas. This, in combination with the lack of differentiation between lineage A 13- and 17-year cicadas at the marker loci and new behavioral data for 13-year brood XIX, suggests a recent derivation of all northern 13-year cicadas from the 17-year cicadas via life-cycle switching. We discuss the implications of these allochronic shifts for speciation.

Animals↗
PubMed2000

Evolution of temporal isolation in the wild: genetic divergence in timing of migration and breeding by introduced chinook salmon populations.

The timing of migration and breeding are key life-history traits; they are not only adaptations of populations to their environments, but can serve to increase reproductive isolation, facilitating further divergence among populations. As part of a study of divergence of chinook salmon, Oncorhynchus tshawytscha, populations, established in New Zealand from a common source in the early 1900s, we tested the hypotheses that the timing of migration and breeding are under genetic control and that the populations genetically differ in these traits despite phenotypic overlap in timing in the wild. Representatives of families from two populations were collected within a day or two of each other, reared in a common environment, and then released to sea from each of two different rivers, while other family representatives were retained in fresh water to maturity. The date of maturation of fish held in fresh water and the dates of return from the ocean and maturation of fish released to sea all showed significant differences between the two populations and among families within populations. The very high heritabilities and genetic correlations estimated for migration and maturation date indicated that these traits would respond rapidly to selection. Combined with the results of related studies on these chinook salmon populations, it appears that spawning time may not only evolve during the initial phases of divergence, but it may play an important role in accelerating divergence in other traits.

Animals↗
PubMed1976

The diurnal rhythm of enzymes in human red cells.

The activities of glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP oxidoreductase, G6PD), 6-phosphogluconate dehydrogenase (6-phospho-d-gluconate: NADP oxidoreductase, 6PGD), hexokinase (ATP:D-hexose 6-phosphotransferase, HK), lactic dehydrogeanse (L-lactate: NAD oxidoreductase, LDH) and aspirate aminotransferase (L-aspartate: 2-oxoglutarate aminotransferase, Asp.T) were determined in red blood cells of 11 healthy individuals. The determinations were carried out on samples drawn every 4 h over a 24 h period. The activities of G6PD, 6PGD, LDH and Asp.T exhibited a semi-circadian rhythm, namely, two peaks of activity during 24 h while HK activity demonstrated a true circadian rhythm. In addition a polymorphism of the G6PD and LDH activity patterns was observed. The implications of a biological clock in enucleated cells are discussed.

Aspartate Aminotransferases↗
PubMed1995

Bilateral lesions of the suprachiasmatic nuclei alter the nocturnal melatonin secretion in sheep.

The hypothalamic suprachiasmatic nuclei (SCN) constitute both the biological clock of many circadian rhythms, and the first relay in the transmission of light cues from the retina to the pineal gland, which releases, via nocturnal melatonin secretion, an endocrine expression of the daylength. The aim of the present work was to investigate the precise role of the SCN in the entrainment of the nocturnal rhythm of melatonin (MEL) in sheep. Bilateral lesions of the SCN were performed via a transsinusal surgical approach in 10 adult rams submitted to a constant photoperiod (16:8D). Lesioned rams were compared to 4 sham and 2 control animals. Blood samples were collected 8 days before, 8 days after, and one month after surgery. Plasma MEL levels were estimated using direct radioimmunoassay. At the end of the experiment, histology and immunohistochemistry of the suprachiasmatic area were performed, and the extent of lesions was evaluated using a computerized image analysis system. Six rams exhibited a complete lesion of the SCN, and in the four remaining animals, the lesions were restricted to the anterior part of the SCN. For all animals, the nocturnal melatonin secretion was altered, but depending on the extent of the lesion, two types of results were observed: Eight days after surgery, in 3 of the 4 rams bearing anterior lesions of the SCN (SCNx-), a nocturnal increase in melatonin secretion still occurred at dusk, but the duration of this secretion extended beyond the end of the night. One month after surgery, melatonin profiles were once again normal, as compared to sham animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Larval growth rates of the blowfly, Calliphora vicina, over a range of temperatures.

Blowfly larvae (Diptera: Calliphoridae) fulfil an important ecological function in the decomposition of animal remains. They are also used extensively in forensic entomology, predominantly to establish a minimum time since death, or a minimum post-mortem interval, using the larval length as a 'biological clock'. This study examined the larval growth rate of a forensically important fly species, Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) at temperatures of between 4 degrees C and 30 degrees C, under controlled laboratory conditions. The laboratory flies had been trapped initially in London, U.K. The minimum developmental temperature was estimated to be 1 degrees C and 4700 accumulated degree hours (ADH) were required for development from egg hatch to the point of pupariation. Lines fitted to the laboratory larval growth data were found to adequately explain the growth of larvae in the field. The nature of variation in growth rates from geographically isolated populations is discussed.

Animals↗
PubMed1989

Gangliosides in normal human serum. Concentration, pattern and transport by lipoproteins.

The total content and pattern of gangliosides were determined in the unfractionated sera of 11 healthy human adults and in isolated lipoproteins. The total content of lipid-bound sialic acid was 10.5 +/- 3.2 nmol/ml serum. The ganglioside profile consisted of more than ten different components. The major ganglioside was GM3, followed by GD3, GD1a, GM2, GT1b, MG-3 (sialosyllactoneotetraosylceramide), GD1b and GQ1b. Traces of four additional gangliosides could not be quantified reliably. Ganglioside patterns did not vary in sera taken from healthy adults of different age and sex. Approximately 98% of human serum gangliosides were transported by serum lipoproteins, predominantly by LDL (66%), followed by HDL (25%) and VLDL (7%). The quantitative distribution of individual gangliosides in VLDL and LDL was almost the same as that in the unfractionated serum; some differences existed with the ganglioside profile in HDL.

Adult↗