Day-night Period Research Articles

VALIDITY CHECKING OF OSCILLOMETRIC AND AUSCULTATORY BLOOD PRESSURE MONITORING IN CLINICAL PRACTICE

Objective: Ambulatory blood pressure monitoring (ABPM) is an out-of-office method of blood pressure (BP) measurement, that could detect pressure with oscillometric or auscultatory devices. According to the 2021 practice guideline, one of the principles of ABPM implementation in routine clinical practice is validity checking, which means result elimination in case of the insufficient number of readings. However, the prevalence of correct ABPM data is unclear in daily practice. The study aimed was to analyze the validation procedure of two algorithms of blood pressure detection (oscillometric and auscultatory). Design and method: We study ABPM patterns in sinus 242 patients (mean age, 62 [95% CI, 60–63] years, 57% men). The day-night period was determined as 24-hour clock-based definitions (nighttime: 01:00 to 05:59). Validity was verified by nalysing readings numbers in awake and night periods (not-valid: < 20 and < 7 readings, respectively). To compare groups, we used Mann-Whitney two-sample statistic (Stata 15). Results: The total number of non-valid readings was 19,8% (48/242) in oscillometric and 45,9% (111/242) auscultatory devices (p < 0,001). Conclusions: The oscillometric devices show better validity checking in daily practice compare to auscultatory. Approximately one-fifth of ABPM results in oscillometric devices have to be repeated due to non-valid readings in daily clinical practice.

Nocturnal surveys reveal novel insights into the community dynamics of an anchialine ecosystem from The Bahamas

Understanding the composition and structure of marine animal assemblages across space and time is essential in the establishment of effective management frameworks, particularly for holistic approaches to ecosystem conservation. Baited remote underwater video (BRUV) surveys are a well-established tool used in assessing relative abundances of marine fauna but are not commonly used in enclosed environments such as lakes. Sweetings Pond is an anchialine lake situated on the island of Eleuthera in The Bahamas that remains relatively undocumented, with only a single census available from 1983, yet has experienced an increase in stress from anthropogenic activity. Here, we investigated differences in community composition between sites and attempted to identify the species/benthic components driving changes using baited video surveys, before exploring differences in community structure between day-night periods. Nine species were identified over the 3780 min of BRUV footage analyzed, which was comparable to 1983 estimates. No difference in animal assemblages was seen between sites and no correlation with benthic composition was present. However, nocturnal replicates displayed higher median animal abundance and species richness than diurnal replicates, potentially resulting from a sequential food web aggregation around the light source. A number of unique, opportunistic feeding behaviors were also observed which opens avenues for future study. Overall, this study presents BRUVS as a viable and streamlined tool for managers of enclosed aquatic ecosystems to rapidly assess the system's macrofauna across day-night periods, supporting the requirements of an ecosystem-based management approach.

Evaluation of Transfusion-Related Hemodynamic Parameters in Patients with Beta-Thalassemia Major by Ambulatory Blood Pressure Monitoring Method

Introduction: There are very few studies on the effects of regular blood transfusions on the hemodynamic organization of patients with Beta-Thalassemia Major (BTM). Ambulatory Blood Pressure Monitoring is method that evaluates fluctuations in day-night periods and life cycle changes. In this study, we aimed to investigate the effects of blood transfusion on hemodynamic parameters by the Ambulatory Blood Pressure Monitoring method on the day of transfusion in patients with a diagnosis of Beta-Thalassemia Major. Material and Methods: This study was conducted in patients who were followed up with a diagnosis of BTM between June 2020 and July 2020. The study consisted of 30 patients. The blood pressure of the patients was measured by auscultation method on the morning of the day when they received routine red blood cell transfusion treatments, and the patients were fitted with an Ambulatory Blood Pressure Monitoring device. With Ambulatory Blood Pressure Monitoring, mean systolic blood pressure, diastolic blood pressure, heart rate, mean arterial pressure, values were calculated for each patient. Statistical analysis was performed by the IBM SPSS Statistics 21 package program. The significance limit for the p-value was accepted as <0.05. Results: There was a significant difference in mean systolic blood pressure and heart rate values between pre-transfusion, transfusion, and post-transfusion periods. In our study, the rate of white coat hypertension was 8.3%, and the rate of masked hypertension was 4.1%. It was observed that 67% of the patients were non-dippers, and the blood pressure burden of one patient was more than 25%. Conclusions: Measurement of hemodynamic parameters with Ambulatory Blood Pressure Monitoring is the gold standard in terms of detection and follow-up of non-dipper patients, indicating increased cardiovascular risk. In practice, Ambulatory Blood Pressure Monitoring should be used more in the follow-up of chronic patients.

Biodiversitas ikan padang lamun di perairan Tanjung Tiram, Konawe Selatan, Sulawesi Tenggara

Research on fish biodiversit yof seagrass bed has been carried out in Indonesian waters, and the results vary between water locations. This study aims to determine the biodiversity of fish based on seagrass density in the day and night period. This research was conducted in the waters of Tanjung Tiram, South Konawe from February to March 2018. Fish sampling based on seagrass density in the day and night period using gillnets with mesh size of 0.75, 1.25 and 1.50 inch. Fish biodiversity found in this study consisted of 42 species from 24 families with an abundance of 1000 individuals. Fish biodiversity in densely seagrass beds was higher than low seagrass beds.Labridae family was the most doimnan fish during the daytime while at night is dominated by the family Plotosidae. The status of fish biodiversity based on seagrass density was categorized as moderate to high and stable diversity while based on the day-night period was classified as moderate diversity with unstable to stable conditions, and the level of dominance of both was low.

Perils of nighttime dining

Nutrition There's a lot of debate in the health media not just about what to eat but also about when to eat whatever is decided is best to eat. Humans, like all mammals, have day-night metabolic rhythms (circadian cycles), approximately tuned to a 24-hour day-night period. Kelly et al. put individuals between 51 and 63 years of age separately into a room calorimeter that contained facilities for daily life, such that minute-by-minute energy expenditure of the room's occupant was measured very precisely. Each individual was given three meals a day, with nutritionally equivalent meals in the morning and late evening. The authors discovered that the late evening snack resulted in less lipid oxidation than breakfast and was more likely to be stored as adipose tissue. PLOS Biol. 18 , e3000622 (2020).

Abstract TMP71: Marked Circadian Variation in Number and Type of Hyperacute Strokes During the 24 Hour Day-Night Cycle

Background: Circadian variations in stroke onset provide critical information for allocation of prehospital and hospital resources in clinical care and clinical trials. Studies of stroke circadian timing have had conflicting findings, and understanding would benefit from analysis confined to patients with defined onset in waking and clearly distinguished ischemic and hemorrhagic stroke subtypes. Methods: We analyzed all patients enrolled in the NIH FAST-MAG phase 3 trial of field-initiated neuroprotective agent in patients with hyperacute stroke within 2h of onset (last known well). Onset times were analyzed in 1h time blocks throughout the 24h day-night cycle. Patient demographic and clinical features, medical history, imaging characteristics, and stroke deficit severity were evaluated for association with onset times. Results: Among 1632 patients, final diagnoses were acute cerebral ischemia in 76.2% and intracranial hemorrhage in 23.7%. Hourly circadian variation in onset is shown in the Figure. Acute cerebral ischemia (ACI) had a unimodal distribution with peak onset at midday (12:00-12:59); intracerebral hemorrhage (ICH) a bimodal distribution with peaks at mid-morning (08:00-08:59) and early evening (18:00-18:59). Events were markedly reduced in early morning, with only 3.4% starting in the 25% of the day between 00:00-05:59. The proportion of events that were hemorrhagic was higher in the first 8h of the day (00:00-07:59) than the remaining 16h, 33.3% vs 22.5%, p=0.006. Both among ACI and ICH patients, vascular risk factors, presenting deficit severity, and initial brain imaging findings were fairly homogenous throughout all day-night time periods. Conclusion: There is marked, more than 10-fold, circadian variation in onset of acute cerebrovascular disease, and circadian variation in the ratio of ischemic to hemorrhagic neurovascular events. These findings can inform resource planning for regional systems of acute stroke care.

МОРФО-ФУНКЦІОНАЛЬНИЙ СТАН ЕПІФІЗА ТА СУПРАХІАЗМАТИЧНОГО ЯДРА ГІПОТАЛАМУСА ЩУРІВ ЗА РІЗНИХ РЕЖИМІВ УВЕДЕННЯ ЕКЗОГЕННОГО МЕЛАТОНІНУ

In modern society increase of digitalization associated with grown exceed level of light at night – a new type of pollution. Presence of light at night inhibited endogenous melatonin synthesis by pineal gland, that influence on circadian system work cycles, so organism oftenbroken regime of wake/sleep, meals, physical activity. Also, a lack of melatonin in some certain time of dayand low melatonin concentration both, were shown take some intervention in diseases development through incorrect regulation of clock-depended genes expression. In connect with this, some latest clinical protocol in therapy or clinical trials of many different pathologies (for example, insomnia, metabolic syndrome, cardiovascular diseases, central nervous and immune system trouble, cancer, viral infection, etc.) include exogenous melatonin usage. As melatonin perform his function via endocrine and paracrine ways in variety types of cell, his application take place in wide range of doses and in different time of day (chronotherapeutic approach). Therefore, important to control state of circadian system central elements – pineal gland (main producer of endogenous melatonin) and suprachiasmatic nucleus (SCN) of hypothalamus (central pacemaker of circadian rhythm) in conditionsof exogenous melatonin treatment. Thus, the main goal of our research were analysis of rats pineal gland and hypothalamic SCN morpho-functional state after different time (morning, evening and continuously with drinking water) melatonin daily administration. Melatonin was administered by gavage for 7 weeks in dose 30 mg/kg 1 h before lights-off (M ZT11, evening), or 1 h after lights-on (M ZT01, morning), or continuously with drinking water during day-night period (MW). After melatonin use only in MW group pineal gland demonstrates changes in morphology (pinealocytes nucleus had mild basophilic color) and morphometric (increased cross-sectional area of the pinealocytes nucleus in compare with control group) analysis data. Besides, some similar changes were observed in SCN: the cross-sectional area of the SCN neurons nucleus grown in case of usage each of regime melatonin administration, while morphology characteristic remains without any alteration. In general, it suggesting about having by melatonin non-inhibiting features in context of circadian system feedback loop and supposing wide potential for melatonin use with absent huge side effect on central elements of above mentioned system.

Seamount effects on the diel vertical migration and spatial structure of micronekton

We examined the diel vertical migration (DVM) behavior and vertical spatial structure of sound-scattering layers (SLs) at two seamounts (Condor and Gigante) in the Azores and in surrounding open-waters. Active acoustic data were recorded day and night during nine cruises conducted in spring, summer and autumn between 2009 and 2011. SLs were permanent features with two main layers, shallow scattering layers (SSLs) and deep scattering layers (DSLs). Over seamount plateaus, SSLs aggregated close to the seafloor during the day and in slightly shallower waters at night. Backscatter intensity on plateaus varied little between day and night and was consistently higher than in SSLs above slopes or in open-waters. DSLs found over slopes and open-waters migrated towards the surface at dusk and returned to their daylight depths at dawn but an intense DSL persisted overnight in deep open-waters. Variograms showed that SSLs and DSLs were not uniformly distributed but amount of spatial heterogeneity varied between seamount plateaus, slopes and open-waters, and day-night periods. Taken together, these findings suggest that (1) Condor and Gigante Seamounts host a resident micronekton community, (2) there is an influx of vertically migrating organisms over the plateaus at night, and (3) seamount topography affects the DVM behavior of the DSL. Physical processes, such as Taylor cap effect, along with topographic blockage and lateral advection of migrating organisms, may play a role in transporting micronekton from open-waters to seamount plateaus. These findings are critical to understanding the ecology of seamount communities and the function of seamount habitats in oceanic ecosystems.

Beta diversity of ant-plant interactions over day-night periods and plant physiognomies in a semiarid environment

Despite the growing knowledge regarding biotic interactions, the diversity and turnover of species interactions is one of the least understood and explored components in studies dealing with species interaction networks. Since the spatial and temporal distribution of animals and plants is unequal, their pairwise interactions are also expected to vary or rewire, generating dissimilarities among species interaction networks. In this study, we evaluated the structure of ant-plant interaction networks and described its dissimilarities by assessing species and the turnover of their interactions between day and night periods across two plant physiognomies in a semiarid Neotropical environment of central Mexico. We found that even though the emergent nested structure of networks remains invariant, the great majority of ant-plant interactions are reassembled in less than one day. Moreover, we observed that, between day-night periods, the interaction turnover was mainly driven by rewiring of interactions while, between plant physiognomies, this was generated by both interaction rewiring and species turnover. We postulate that interaction rewiring across the studied habitats could be influenced by the turnover of the central core of highly interacting species. Furthermore, we highlight that both interaction rewiring and species turnover shape ant-plant interactions turnover over day-night periods and plant physiognomies.

Coordinated gene expression between Trichodesmium and its microbiome over day-night cycles in the North Pacific Subtropical Gyre.

Trichodesmium is a widespread, N2 fixing marine cyanobacterium that drives inputs of newly fixed nitrogen and carbon into the oligotrophic ecosystems where it occurs. Colonies of Trichodesmium ubiquitously occur with heterotrophic bacteria that make up a diverse microbiome, and interactions within this Trichodesmium holobiont could influence the fate of fixed carbon and nitrogen. Metatranscriptome sequencing was performed on Trichodesmium colonies collected during high-frequency Lagrangian sampling in the North Pacific Subtropical Gyre (NPSG) to identify possible interactions between the Trichodesmium host and microbiome over day-night cycles. Here we show significantly coordinated patterns of gene expression between host and microbiome, many of which had significant day-night periodicity. The functions of the co-expressed genes suggested a suite of interactions within the holobiont linked to key resources including nitrogen, carbon, and iron. Evidence of microbiome reliance on Trichodesmium-derived vitamin B12 was also detected in co-expression patterns, highlighting a dependency that could shape holobiont community structure. Collectively, these patterns of expression suggest that biotic interactions could influence colony cycling of resources like nitrogen and vitamin B12, and decouple activities, like N2 fixation, from typical abiotic drivers of Trichodesmium physiological ecology.

Inferred fish behavior its implications for hydroacoustic surveys in nearshore habitats

Population availability and vessel avoidance effects on hydroacoustic abundance estimates may be scale dependent; therefore, it is important to evaluate these biases across systems. We performed an inter-ship comparison survey to determine the effect of vessel size, day-night period, depth, and environmental gradients on walleye (Sander vitreus) density estimates in Lake Erie, an intermediate-scaled system. Consistent near-bottom depth distributions coupled with horizontal fish movements relative to vessel paths indicated avoidance behavior contributed to higher walleye densities from smaller vessels in shallow water (i.e., <15m), although the difference decreased with increasing depth. Diel bank migrations in response to seasonally varying onshore-to-offshore environmental gradients likely contributed to day-night differences in densities between sampling locations and seasons. Spatial and unexplained variation accounted for a high proportion of total variation; however, increasing sampling intensity can mitigate effects on precision. Therefore, researchers should minimize systematic avoidance and availability related biases (i.e., vessel and day-night period) to improve population abundance estimates. Quantifying availability and avoidance behavior effects and partitioning sources of variation provides informed flexibility for designing future hydroacoustic surveys in shallow-water nearshore environments.

Assessment of conservative force models from GRACE accelerometers and precise orbit determination

The accuracy of the conservative force-models is not clear and the new space accelerometers provide a unique opportunity for their validation. In this paper, the conservative-force model deficiencies are investigated via Principal Component Analysis (PCA) using 4 years of GRACE measurements (2006–2009). The deficiencies are assessed by comparing the accelerometer readouts with the differences between the conservative force-model and the precise orbit accelerations. Within this scheme, the spatiotemporal data analysis is synthesized in a time-series of grids whose latitudinal and longitudinal variations are respectively influenced by the half orbital period and the equatorial orbit shift. With maximum amplitude of 50 nm/s2, the mean map shows a positive overestimation in Canada and Brazil and negative in Greenland. Explaining the 74% of the variability, the two first pairs of PCA modes show un-modeled patterns with amplitudes maxima of 80 nm/s2 and 50 nm/s2. Their periodic behavior and wave-length of degree-6 and degree-11s spherical harmonics strongly suggest an additional modeling and improvement. As for the long-term variations, our results show a latitudinal variation of 15 nm/s2 maximum amplitude correlated with the day-night periods. Performing a combined analysis of ascending and descending orbits, a trend of 3 nm/s2yr in the Indian Ocean is also observed. Our new approach for orbital force-models validation can be considered crucial for the current state-of-the-art of precise orbit determination (POD) and Time–Varying Gravity (TVG) modeling.

Secondary metabolite gene expression and interplay of bacterial functions in a tropical freshwater cyanobacterial bloom.

Cyanobacterial harmful algal blooms (cyanoHABs) appear to be increasing in frequency on a global scale. The Cyanobacteria in blooms can produce toxic secondary metabolites that make freshwater dangerous for drinking and recreation. To characterize microbial activities in a cyanoHAB, transcripts from a eutrophic freshwater reservoir in Singapore were sequenced for six samples collected over one day-night period. Transcripts from the Cyanobacterium Microcystis dominated all samples and were accompanied by at least 533 genera primarily from the Cyanobacteria, Proteobacteria, Bacteroidetes and Actinobacteria. Within the Microcystis population, abundant transcripts were from genes for buoyancy, photosynthesis and synthesis of the toxin microviridin, suggesting that these are necessary for competitive dominance in the Reservoir. During the day, Microcystis transcripts were enriched in photosynthesis and energy metabolism while at night enriched pathways included DNA replication and repair and toxin biosynthesis. Microcystis was the dominant source of transcripts from polyketide and non-ribosomal peptide synthase (PKS and NRPS, respectively) gene clusters. Unexpectedly, expression of all PKS/NRPS gene clusters, including for the toxins microcystin and aeruginosin, occurred throughout the day-night cycle. The most highly expressed PKS/NRPS gene cluster from Microcystis is not associated with any known product. The four most abundant phyla in the reservoir were enriched in different functions, including photosynthesis (Cyanobacteria), breakdown of complex organic molecules (Proteobacteria), glycan metabolism (Bacteroidetes) and breakdown of plant carbohydrates, such as cellobiose (Actinobacteria). These results provide the first estimate of secondary metabolite gene expression, functional partitioning and functional interplay in a freshwater cyanoHAB.

Circadian molecular clocks and cancer

Physiological processes such as the sleep-wake cycle, metabolism and hormone secretion are controlled by a circadian rhythm adapted to 24h day-night periodicity. This circadian synchronisation is in part controlled by ambient light decreasing melatonin secretion by the pineal gland and co-ordinated by the suprachiasmatic nucleus of the hypothalamus. Peripheral cell autonomous circadian clocks controlled by the suprachiasmatic nucleus, the master regulator, exist within every cell of the body and are comprised of at least twelve genes. These include the basic helix-loop-helix/PAS domain containing transcription factors; Clock, BMal1 and Npas2 which activate transcription of the periodic genes (Per1 and Per2) and cryptochrome genes (Cry1 and Cry2). Points of coupling exist between the cellular clock and the cell cycle. Cell cycle genes which are affected by the molecular circadian clock include c-Myc, Wee1, cyclin D and p21. Therefore the rhythm of the circadian clock and cancer are interlinked. Molecular examples exist including activation of Per2 leads to c-myc overexpression and an increased tumor incidence. Mice with mutations in Cryptochrome 1 and 2 are arrhythmic (lack a circadian rhythm) and arrhythmic mice have a faster rate of growth of implanted tumors. Epidemiological finding of relevance include ‘The Nurses’ Health Study’ where it was established that women working rotational night shifts have an increased incidence of breast cancer. Compounds that affect circadian rhythm exist with attendant future therapeutic possibilities. These include casein kinase I inhibitors and a candidate small molecule KL001 that affects the degradation of cryptochrome. Theoretically the cell cycle and malignant disease may be targeted vicariously by selective alteration of the cellular molecular clock.

Effects of N-applications and photosynthesis of maize (Zea mays L.) on soil respiration and its diurnal variation

In order to understand the relationship of soil respiration to N-applications and photosynthesis, a soil pot experiment of planting maize with two N-applications was conducted. During the trumpeting stage, maize plants were shaded for three days and soil respiration was sampled by static chamber method and measured by gas chromatography. A clear diurnal cycle of soil respiration rate (SRR) showed a single peak curve in which the rate crested at about 14:00 during a day-night period and the daily average SRR was very close to that between 18:00 and 21:00. The SRR increased with soil N-application and the measured average SRR in three days was 29% higher in high N-application (HN, 300 mg·kg−1 of N) than that in low N-application (LN, 150 mg·kg−1 of N). The shaded plants significantly decreased the SRR and its diurnal variation. The soil respiration within the first, second and third day-night decreased to about 21%, 50% and 65%, respectively compared with the un-shaded plants. Under non-shading treatments, the exponential relativity of SRR was significantly dependent on temperature but not on time, while in shaded plants, it was significantly dependent on both temperature and shading time, with the relative coefficient to shading time significantly higher than that to temperature. In summary, soil N-application could increase the soil respiration, while the shaded plants not only decreased the SRR and its diurnal variation but also altered the relationship between the SRR with temperature, thus the soil respiration during maize growth was mainly derived from the recent photosynthates. Photosynthesis, together with temperature, are the key factors controlling the diurnal variation of soil respiration.

Melatonin therapy to improve nocturnal sleep in critically ill patients: encouraging results from a small randomised controlled trial

IntroductionSleep disturbances are common in critically ill patients and when sleep does occur it traverses the day-night periods. The reduction in plasma melatonin levels and loss of circadian rhythm observed in critically ill patients receiving mechanical ventilation may contribute to this irregular sleep-wake pattern. We sought to evaluate the effect of exogenous melatonin on nocturnal sleep quantity in these patients and, furthermore, to describe the kinetics of melatonin after oral administration in this patient population, thereby guiding future dosing schedules.MethodsWe conducted a randomised double-blind placebo-controlled trial in 24 patients who had undergone a tracheostomy to aid weaning from mechanical ventilation. Oral melatonin 10 mg or placebo was administered at 9 p.m. for four nights. Nocturnal sleep was monitored using the bispectral index (BIS) and was expressed in terms of sleep efficiency index (SEI) and area under the curve (AUC). Secondary endpoints were SEI measured by actigraphy and nurse and patient assessments. Plasma melatonin concentrations were measured in nine patients in the melatonin group on the first night.ResultsNocturnal sleep time was 2.5 hours in the placebo group (mean SEI = 0.26, 95% confidence interval [CI] 0.17 to 0.36). Melatonin use was associated with a 1-hour increase in nocturnal sleep (SEI difference = 0.12, 95% CI -0.02 to 0.27; P = 0.09) and a decrease in BIS AUC indicating 'better' sleep (AUC difference = -54.23, 95% CI -104.47 to -3.98; P = 0.04). Results from the additional sleep measurement methods were inconclusive. Melatonin appeared to be rapidly absorbed from the oral solution, producing higher plasma concentrations relative to similar doses reported in healthy individuals. Plasma concentrations declined biexponentially, but morning (8 a.m.) plasma levels remained supraphysiological.ConclusionIn our patients, nocturnal sleep quantity was severely compromised and melatonin use was associated with increased nocturnal sleep efficiency. Although these promising findings need to be confirmed by a larger randomised clinical trial, they do suggest a possible future role for melatonin in the routine care of critically ill patients. Our pharmacokinetic analysis suggests that the 10-mg dose used in this study is too high in these patients and may lead to carryover of effects into the next morning. Reduced doses of 1 to 2 mg could be used in future studies.Trial registrationCurrent Controlled Trials ISRCTN47578325.

Glial fibrillary acidic protein immunoreactivity in the rat suprachiasmatic nucleus: circadian changes and their seasonal dependence

The pacemaker of the biological clock, the suprachiasmatic nucleus (SCN) of the hypothalamus, was studied in intact male rats to determine its immunoreactivity to glial fibrillary acidic protein (GFAP), a specific marker of astrocytes. Animals were kept under 12-h light-dark cycles in synchrony with day-night periods. Immunohistochemical reactions were carried out at midday and late at night in both winter (January) and summer (July). In winter, GFAP immunoreactivity was found to be low during the day and high at night. The findings were reversed in summer, when GFAP immunoreactivity was high during the day and low at night. Increased GFAP immunoreactivity appeared in the form of an abundance of thick immunopositive fibres rather than of cell bodies. This was interpreted as a hypertrophy of pre-existing astrocytes due to alternating photic stimulation conveyed by retinofugal fibres to the SCN. The observed seasonal reversal in the direction of GFAP oscillations raises the possibility that a circannual timer exists outside the SCN.

Kinetics and rhythm of body contractions in the spongeTethya wilhelma(Porifera: Demospongiae)

Sponges of the species Tethya wilhelma display rhythmic body contractions, which were analyzed by digital timelapse imaging and semi-automated image analysis. For the first time, differential, quantitative data on sponge behaviour could be obtained. The sponges are able to reduce their body volume by up to 73.3% during regular contractions. Each contraction cycle follows a characteristic pattern of four phases, permitting analysis of the kinetics of contraction and expansion. Long-term observations (for >7 days) reveal that the sponge contractions display a day-night periodicity in which contraction cycles are significantly longer during the dark hours. The contractions seem to be mediated by the pinacoderm; they are triggered locally and spread over the sponge surface at 12.5 microm s(-1). If two individuals of a clone are fused, the individual contraction rhythm of both sponges persists for several days, until a single new individual sponge is formed with a synchronized rhythm. The reported results and techniques establish T. wilhelma as a model organism for research on the development of aneural signal transduction and integration during early Metazoan evolution.

Photosynthesis controls of CO2efflux from maize rhizosphere

The effects of different shading periods of maize plants on rhizosphere respiration and soil organic matter decomposition were investigated by using a 13 C natural abundance and 14 C pulse labeling simultaneously. 13 C was a tracer for total C assimilated by maize during the whole growth period, and 14 C was a tracer for recently assimilated C. CO2 efflux from bare soil was 4 times less than the total CO2 efflux from planted soil under normal lighting. Comparing to the normal lighting control (12/12 h day/night), eight days with reduced photosynthesis (12/36 h day/night period) and strongly reduced photosynthesis (12/84 h day/night period) resulted in 39% and 68% decrease of the total CO2 efflux from soil, respectively. The analysis of 13 C natural abundance showed that root-derived CO2 efflux accounted for 82%, 68% and 56% of total CO2 efflux from the planted soil with normal, prolonged and strongly prolonged night periods, respectively. Clear diurnal dynamics of the total CO2 efflux from soil with normal day-night period as well as its strong reduction by prolonged night period indicated tight coupling with plant photosynthetic activity. The light-on events after prolonged dark periods led to increases of root-derived and therefore of total CO2 efflux from soil. Any factor affecting photosynthesis, or substrate supply to roots and rhizosphere microorganisms, is an important determinant of root-derived CO2 efflux, and thereby, total CO2 efflux from soils. 14 C labeling of plants before the first light treatment did not show any significant differences in the 14 CO2 respired in the rhizosphere between different dark periods because the assimilate level in the plants was high. Second labeling, conducted after prolonged night phases, showed higher contribution of recently assimilated C ( 14 C) to the root-derived CO2 efflux by shaded plants. Results from 13 C natural abundance showed that the cultivation of maize on Chromic Luvisol decreased soil organic matter (SOM) mineralization compared to unplanted soil (negative priming effect). A more important finding is the observed tight coupling of the negative rhizosphere effect on SOM decomposition with photosynthesis.

Spatial Distribution and Temporal Variance of Fish Communities in the Channelized and Regulated Vltava River (Central Europe)

Spatial distribution and temporal variations of fish communities in a channelized portion of the Vltava River (Central Europe) were investigated from May to October 1992. Fish abundance and species number were collected monthly during diel samples in the main channel and a large oxbow. To determine differences in fish communities we chose the low-flow period when maximal differences in physical environment between habitats are expected. Fish community patterns from the main channel and oxbow differed only in abundance of ecological groups; the main channel had higher abundance of rheophilic species, whereas eurytopic species were more abundant in the oxbow. However, our analysis revealed significant differences in temporal variations between habitats. Fish abundance usually varied unpredictably over day-night periods in the main channel, whereas in the oxbow we observed a pronounced peak in fish abundance from morning to mid-afternoon. Diel changes in fish abundance in the oxbow corresponded to occurrence of low dissolved oxygen during afternoon and night-time periods. The effect of oxygen depletion induced by strong organic pollution limited the oxbow suitability for fishes. Similar habitats are usually occupied by limnophilic and phytophilic species that were absent in our samples. Our results suggested that man-induced high variability of physical environment decreased variability in fish community.