Daylight Period Research Articles

Potency of myopic defocus in spectacle lens compensation.

Previous studies have shown that chick eyes compensate for positive or negative lenses worn for brief periods if the chicks are in darkness the remainder of the time. This study was undertaken to determine whether chicks can compensate for brief periods of lens wear if given unrestricted vision the remainder of the time. Previous studies have also shown that chick eyes alternately wearing positive and negative lenses for brief periods compensate for the positive lenses. The current study sought to determine whether brief periods of positive lens wear can outweigh daylong wearing of negative lenses. Chicks wore +6 D or +10 D lenses for between 8 and 60 min/d, in two to six periods and wore either no lenses or negative lenses for the remainder of the 12-hour daylight period. Refraction and ultrasound biometry were performed before and after the 3-day-long experiments. Wearing positive lenses for as little as 12 min/d (six periods of 2 minutes) with unrestricted vision the remainder of the time caused eyes to become hyperopic and reduced the rate of ocular elongation. These effects also occurred when the scene viewed was beyond the far point of the lens-wearing eye and thus was myopically blurred. Even when chicks wore negative lenses for the entire day except for 8 minutes of wearing positive lenses, the eyes compensated for the positive lenses, as though the negative lenses had not been worn. When chicks wore binocular negative lenses for the entire day except for 8 minutes of wearing a positive lens on one eye and a plano lens on the other, the eye wearing the positive lens became less myopic than the eye wearing the plano lens. Brief periods of myopic defocus imposed by positive lenses prevent myopia caused by daylong wearing of negative lenses. This implies that periods of myopic and hyperopic defocus do not add linearly. If children are like chicks and if the hyperopic defocus of long daily periods of reading predisposes a child to myopia, regular, brief interruptions of reading might have use as a prophylaxis against progression of myopia.

Analysis of strategies for reducing calcium deficiencies in glasshouse grown tomatoes: model functions and simulations

Energy saving measures can result in high levels of humidity in greenhouses which reduces transpiration resulting in calcium deficiency symptoms on tomato leaves with subsequent loss of yield and quality. Transpiration can be increased by lowering the saturation deficit. Control strategies need to be cost-effective so that the benefits are in excess of the costs of carrying out the dehumidification. The HORTITRANS model [Journal of Agricultural Engineering Research, 57 (1994) 23], which predicts the conditions inside a greenhouse, was modified to enable simulations to be carried out for a developing crop and to quantify the effects of high humidity on yield and quality. Saturation deficit set-points were determined so that the transpiration rate was equal to a minimum of 0.65 kg m −2 day −1, a value derived to be satisfactory from experiments. Simulations were carried out for sample single and double glazed greenhouses with dehumidification by ventilation and heating. The cost of dehumidification was high when the ventilators were widely opened and so ventilation rates were constrained by restricting the maximum angle of opening. For a double glazed house additional profit was greater when the saturation deficit was controlled during the period of daylight compared to continuous control. For the single glazed house, a maximum angle of opening of 3° produced an additional profit of 6 p m −2. One year in eight there was a loss. For the double glazed house, a maximum ventilator opening of 10° produced an average additional profit of 90 p m −2. The models can be used to study control strategies for other types of greenhouse structures in different climatic regions where short-term (hourly) meteorological data exists using local information on prices and costs.

Ritmo luz/oscuridad de las citocinas proinflamatorias en el infarto agudo de miocardio

The concentration of certain proinflammatory cytokines has been found to be elevated in patients with acute coronary syndrome. Many studies have shown that coronary ischemic accidents do not show a uniform distribution throughout the day, but instead exhibit rhythmic variations. The objective of this study is to determine whether there is a circadian pattern of variation in the concentrations of proinflammatory cytokines in patients with acute myocardial infarction. The sample included 40 patients with acute myocardial infarction and 40 controls. Levels of interleukin 6 and 1 beta were determined in the first 24 hours after the acute coronary ischemic episode. Blood samples were extracted at 3:00 a.m. (period of darkness) and at 10:00 a.m. (period of daylight). Both groups were similar in age, sex distribution, and coronary risk factors. Interleukin 6 levels showed a significant variation between daylight and nighttime concentrations in patients with acute myocardial infarction and controls (41.93 5.90/100.39 13.60 vs 25.76 4.45/52.67 7.73 pg/ml). However, interleukin 6 concentrations were higher in the acute myocardial infarction group than in the control group. Interleukin 1 beta concentrations did not vary between daylight and darkness. In both the control group and acute myocardial infarction group, interleukin 6 concentrations varied between daylight and darkness. Patients with acute myocardial infarction shown a higher concentration of interleukin 6 secondary to the physiological response to tissue damage. Circadian variations can affect the measurements obtained for different physiological and biochemical parameters.

Time allocation in migrating Northern Wheatears (Oenanthe oenanthe) during stopover: Is refuelling limited by food availability or metabolically?

According to full-day observations (scan sampling), Northern Wheatears (Oenanthe oenanthe) stopping over on the island of Helgoland (SE North Sea) during spring and autumn migration spent 51–67 % of the daylight period foraging. Large parts of the day were used for resting or being vigilant, whereas flying, preening and aggressive behaviour were of minor importance. The density of Wheatears did not influence the time devoted to foraging and aggressive behaviour, and the time spent resting/vigilant was not correlated to predation risk (measured as the rate of raptor flying over). Several observations showed that refuelling on the beach, which presented the most favourable feeding conditions and allowed high rates of body mass gain, was metabolically limited. The total time devoted to foraging was independent of day length, and additional food (mealworms) offered in bowls was completely ignored, an indication that reduced foraging effort would not improve net energy gain within the physiological capacity. In contrast, Wheatears responded strongly to additional food supplied in the poorer grassland habitat. Although this strongly suggests that refuelling is limited by the amount of food available and the costs of obtaining it, foraging times were the same as on the beach. In grassland, the behaviour pattern of birds refuelling was probably distorted by a high proportion of transient and exploring individuals. Therefore, knowledge about foraging ecology and the response to additional food improves the value of the foraging time parameter in considerations of refuelling limitations.

A Modelling Exploration of Vertical Migration by Phytoplankton

The behaviour of phytoplankton having different abilities to assimilate N in darkness was considered in simulations of vertical migrations. Such behaviour is especially important for the competitive advantage of flagellates, including harmful algal species. Three phases of biomass development were apparent. (1) Cells remained at a subsurface location with migration down to avoid photoinhibitory light at midday; as the attenuation of light increased with biomass growth, the mean depth became shallower. (2) On exhaustion of nutrients in surface waters, cells migrated down through the nutricline in the latter half of the daylight period, with a subsurface maximum in the photic zone as long as light penetration matched requirements. When that condition was no longer met (3), cells migrated between the very surface (forming dense aggregations) and the nutricline. While the ability to perform dark N-assimilation is not critical when N-sources are available at low concentrations, it is important when (as encountered following migration down to a nutricline), nutrients are available at higher concentration in darkness. The most advantageous configuration tested, where nitrate assimilation (as well as that of ammonium) continued at a high rate in darkness as long as C-reserves remained, is not actually used in migratory species but in non-migratory diatoms. The use of the outwardly inferior configurations typical of migratory species, in which dark nitrate-assimilation is notably poorer than assimilation in the light, reflects a deficient metabolism or indicates that N-sources other than nitrate are more important. It is unfortunate then that most attention has been paid to nitrate nutrition in experiments on migrating species. While an ability to continue N-assimilation in darkness as well as during daylight is advantageous, there is no evidence for phytoplankton to be able to grow at high growth rates when decoupling photosynthesis at the surface and N-assimilation at depth.

A Modelling Exploration of Vertical Migration by Phytoplankton

The behaviour of phytoplankton having different abilities to assimilate N in darkness was considered in simulations of vertical migrations. Such behaviour is especially important for the competitive advantage of flagellates, including harmful algal species. Three phases of biomass development were apparent. (1) Cells remained at a subsurface location with migration down to avoid photoinhibitory light at midday; as the attenuation of light increased with biomass growth, the mean depth became shallower. (2) On exhaustion of nutrients in surface waters, cells migrated down through the nutricline in the latter half of the daylight period, with a subsurface maximum in the photic zone as long as light penetration matched requirements. When that condition was no longer met (3), cells migrated between the very surface (forming dense aggregations) and the nutricline. While the ability to perform dark N-assimilation is not critical when N-sources are available at low concentrations, it is important when (as encountered following migration down to a nutricline), nutrients are available at higher concentration in darkness. The most advantageous configuration tested, where nitrate assimilation (as well as that of ammonium) continued at a high rate in darkness as long as C-reserves remained, is not actually used in migratory species but in non-migratory diatoms. The use of the outwardly inferior configurations typical of migratory species, in which dark nitrate-assimilation is notably poorer than assimilation in the light, reflects a deficient metabolism or indicates that N-sources other than nitrate are more important. It is unfortunate then that most attention has been paid to nitrate nutrition in experiments on migrating species. While an ability to continue N-assimilation in darkness as well as during daylight is advantageous, there is no evidence for phytoplankton to be able to grow at high growth rates when decoupling photosynthesis at the surface and N-assimilation at depth.

Pyrophosphate-dependent fructose-6-phosphate 1-phosphotransferase overexpression in transgenic tobacco: physiological and biochemical analysis of source and sink tissues

Transgenic Nicotiana tabacum L. (tobacco) plants expressing an unregulated gene for pyrophosphate-dependent fructose-6-phosphate 1-phosphotransferase (PFP) from the fermentor protist Giardia lamblia were produced. Independently transformed lines revealed a high level of Giardia PFP activity but unaltered activities of native plant PFP, phosphofructokinase, and fructose-1,6-bisphosphatase. Transgenic plants exhibited a decrease in total biomass but no dramatic physiological or morphological alterations or significant reduction of seed yield. Both source and sink tissues demonstrated altered partitioning: leaf starch was significantly lower at the beginning and end of the daily light period and young seeds had lower starch but higher lipid levels, and these changes were correlated with PFP activity. Transgenic seeds had significantly higher percentages of germination, and microscopic examination of these seeds showed a temporal enhancement in growth of the young embryo. The significance of these results as they relate to our current understanding of PFP is discussed.Key words: pyrophosphate-dependent fructose-6-phosphate 1-phosphotransferase (PFP), transgenic, Nicotiana tabacum, glycolysis, photosynthate partitioning.

Foraging Decisions of Sandwich Terns in the Presence of Kleptoparasitising Gulls

AbstractWe studied prey selection of Sandwich Terns (Sterna sandvicensis) in the presence of kleptoparasitising Black-headed Gulls (Larus ridibundus) on Griend, Dutch Wadden Sea, from 1992 to 1998. Most often, gulls robbed larger sandeels rather than herring from terns. Provided that one parent attends the chick, energy intake would be too low for the chicks' survival if exclusively fed on sandeel. By provisioning an increasing proportion of herring, parent terns could theoretically overcome a potential food shortage when the chicks grow older. However, the proportion of herring did not increase with age of chicks in most years. Instead, parents increased their foraging effort with the growth of their offspring. In years with high proportions of food loss, parents left their chicks unattended at the nest more often. In that way, parents were largely able to counterbalance food shortage of offspring. In 1992 and 1996, when diet composition was unfavorable and food losses to gulls were high, parents left their chicks unattended at the nest for ∼80% of the daylight period. It is argued that the present working level of parents might be higher than in the 1960s.

Seasonal and diurnal variations of near-surface atmospheric CO 2 concentration within a residential sector of the urban CO 2 dome of Phoenix, AZ, USA

Over most of an entire year (315 days), we obtained 1-min averages of near-surface (2-m height) atmospheric CO 2 concentration, temperature and wind speed in a residential area of a suburb of Phoenix, AZ. Daily minimum CO 2 concentrations, which occurred during the afternoon, were nearly invariant over the year, averaging 390.2±0.2 ppm. Daily maximum CO 2 concentrations, however, which occurred at night, varied seasonally with the air temperature, exhibiting a mean peak of 490.6 ppm about 2 h before midnight during the coldest part of the year (December–January) and 424.3 ppm just before sunrise during the warmest part of the year (July–August). Reevaluating prior assessments of the strength of the urban CO 2 dome at the center of Phoenix, our results suggest a mean cold-season maximum there of 619.3 ppm, which is 67.4% greater than the rural background value. At our residential site, however, the mean cold-season maximum was only 32.6% greater than the surrounding rural mean. Averaged over the entire night, this enhancement dropped to 25.4% in the cold season and 10.9% in the warm season, while over the daylight period it averaged 10.5% and 10.1% in the cold and warm seasons, respectively. CO 2 concentrations were greater on weekdays than on weekends from 0415 to 0830 in the warm season and from 0445 to 1045 in the cold season. During peak morning traffic, the maximum weekday–weekend CO 2 differential was 35.9 ppm in the cold season and 22.0 ppm in the warm season.

Daily stress protein (hsp70) cycle in chitons ( Acanthopleura granulata Gmelin, 1791) which inhabit the rocky intertidal shoreline in a tropical ecosystem

Stress protein (heat shock protein, hsp70) response is involved in protecting organisms from the detrimental effects of environmental stressors, such as radiation and high temperatures. Tropical chitons can briefly tolerate high temperatures. However, they minimize the effects of elevated temperature during daylight hours and periods of tidal air exposure by remaining in rocky intertidal microhabitats along the shoreline of tropical waters. To study the natural variability of the hsp70 level, individuals of the polyplacophoran species Acanthopleura granulata Gmelin, 1791 were sampled every 4 h on two days in spring of 1999. Hsp70 levels were separately measured in the supernatant of the intestinal tract and foot muscle homogenates with a standardized immunoassay. The hsp70 level in the intestinal tract was highest in the early morning, decreased during the mid-morning hours and dropped to a comparatively low level in the afternoon, before increasing again during the night. The stress protein level in the foot muscle followed the daily air temperature curve with a time delay of a few hours, reaching the highest level in the afternoon and the lowest level in the early morning. The stress protein response can be interpreted as a sign of heat tolerance development and may play a role in allowing A. granulata to tolerate the temperature variability typical of its intertidal habitat.

Modeling cloud effects on hydrogen peroxide and methylhydroperoxide in the marine atmosphere

Hydrogen peroxide (H2O2) and methylhydroperoxide (CH3OOH) are studied with a coupled gas phase and aqueous phase chemical model representing a remote nonprecipitating cloudy boundary layer. Cloud interactions may deplete or enhance H2O2 but have a minor effect on CH3OOH. Therefore two primary questions are addressed: (1) do nonprecipitating clouds perturb the ratio of H2O2/CH3OOH, and if so, (2) what is the rate of reestablishment of this ratio to clear‐sky levels following cloud contact. The results show that the rate of recovery of the ratio of H2O2 to Ch3OOH after perturbation by cloud interactions depends on NOx (=NO + NO2) mixing ratios and on the time of day that cloud is encountered. When cloud contact is followed by a significant period of daylight, recovery to precloud values is rapid; however, when cloud contact occurs during the late afternoon or night, recovery can take up to 24 hours under high NOx conditions. Sensitivity tests show that in‐cloud heterogeneous conversion of HNO3 to aerosol has a small but detectable effect (∼10%) on the recovery of the ratio. Neglecting dry deposition of H2O2 and HNO3 increases the predicted ratio H2O2/CH3OOH in clear air prior to cloud contact, and has a small effect on the relative recovery rate of the ratio. In‐cloud consumption of H2O2 by SO2 suppresses the postcloud ratio by ∼40% relative to that in the base case for low levels of SO2 (∼200 ppt), with a more pronounced effect on the ratio and its rate of recovery for [SO2] ∼1 ppb. Because of the uncertainties associated with measurement of peroxides, and the dependence of the recovery of the ratio on the time of cloud contact, it is suggested that measurements of the ratio be considered judiciously and that they may not be of broad utility in predicting recent cloud contact.

Sucrose-Phosphate Synthase, Sucrose Synthase, and Invertase in Sugar Beet Leaves

The activity of sucrose-phosphate synthase (SPS) in sugar beet (Beta vulgaris L.) leaves was shown to exceed considerably the synthesizing activity of sucrose synthase (SS). The rise in SPS activity was related to the daylight period; i.e., it was associated with the rate of photosynthesis. The highest SPS activity was characteristic of fully expanded source leaves. In young developing leaves (leaves expanded to less than half of their final size), which represent the sink organs, the SPS activity was 2.5 times lower. At all stages of leaf development, the synthesizing SS activity was rather low. The diurnal change of SS activity was independent of photosynthesis and showed a slight rise from 6:00–8:00 p.m. Under field conditions, the highest SPS activity was found in leaves in the terminal stage of their development (105-day-old plants); the synthesizing activity of SS showed little changes during this period. The activity of soluble acid invertase was characteristic of young leaves. In mature leaves, the activity of this enzyme correlated with the daylight period. These changes occurred on the background of low sucrose content in leaves. The regulation of SPS, SS, and invertase activity is discussed. It is supposed that compartmentation of these enzymes in the photosynthesizing cell is important for transport, metabolism, and the osmotic function of sucrose in leaves.

Impact of the wasting disease pathogen, Labyrinthula zosterae, on the photobiology of eelgrass Zostera marina

Labyrinthula zosterae is clearly shown to be a primary pathogen of eelgrass Zostera marina L., not merely a secondary infection of senescent leaves or an indication of decomposition. The results of this investigation using a Diving-PAM fluorometer indicate that the regions of tissue photosynthetically compromised by Labyrinthula are substantially larger than previously thought. Labyrinthula moves through Zostera marina tissue at a rate of up to 0.8 mm h -1 during daylight periods. The photosynthetic efficiency of apparently healthy green leaf tissue can be reduced by almost 50% in areas up to 3 mm from a necrotic region infected with Labyrinthula. Once a necrotic spot expands to bisect the eelgrass leaf, the condition of all acropetal tissue is diminished; leaf tissue up to 5 cm away has severely reduced photosynthetic activity.

Diurnal variations in depth profiles of UV-induced DNA damage and inhibition of bacterioplankton production in tropical coastal waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 228:25-33 (2002) - doi:10.3354/meps228025 Diurnal variations in depth profiles of UV-induced DNA damage and inhibition of bacterioplankton production in tropical coastal waters Petra M. Visser1,2,*, Jan Jaap Poos1, Bonnie B. Scheper1, Peter Boelen3, Fleur C. van Duyl1 1Department of Biological Oceanography, Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands 2Carmabi Foundation Ecological Institute, PO Box 2090, Curaçao, Netherlands Antilles 3Department of Marine Biology, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands *Present address: IBED/Aquatic Microbiology, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands. E-mail: petra.visser@science.uva.nl ABSTRACT: In this study, diurnal changes in bacterial production and DNA damage in bacterioplankton (measured as cyclobutane pyrimidine dimers, CPDs) incubated in bags at different depths in tropical coastal waters were investigated. The DNA damage and inhibition of the bacterial production was highest at the surface and decreased with depth. Inhibition of both leucine (Leu) and thymidine (TdR) incorporation was detectable to a depth of 10 m, while DNA damage was measurable only until 5 m. In addition, the decrease of the inhibition of Leu and TdR incorporation with depth was less than the decrease in DNA damage. Variations in DNA damage in bacteria and in biodosimeters were mostly explained by UV radiation (UVR) dose received over time and depth. UVB radiation (UVBR) contributed more than UVA radiation (UVAR) to the damage. The attenuation coefficient of DNA damage with depth was comparable to the attenuation coefficients of UVBR suggesting that DNA damage was induced mainly by UVBR. For incubations at the surface, there was a trend of increasing DNA damage at a constant rate during the entire period of daylight, while the inhibition of leucine incorporation showed a trend of a less rapid increase in the afternoon than in the morning. This might have been due to photorepair, which would also explain the lack of correlation between the inhibition of leucine incorporation and UV dose. It was concluded that CPD damage in DNA is not necessarily the predominant factor in the inhibition of bacterial production. It cannot explain the large impact of sunlight on bacterioplankton productivity in tropical waters. KEY WORDS: DNA damage · Bacterial production · UV radiation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 228. Online publication date: March 06, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

FORAGING DECISIONS OF SANDWICH TERNS IN THE PRESENCE OF KLEPTOPARASITISING GULLS

We studied prey selection of Sandwich Terns (Sterna sandvicensis) in the presence of kleptoparasitising Black-headed Gulls (Larus ridibundus) on Griend, Dutch Wadden Sea, from 1992 to 1998. Most often, gulls robbed larger sandeels rather than herring from terns. Provided that one parent attends the chick, energy intake would be too low for the chicks' survival if exclusively fed on sandeel. By provisioning an increasing proportion of herring, parent terns could theoretically overcome a potential food shortage when the chicks grow older. However, the proportion of herring did not increase with age of chicks in most years. Instead, parents increased their foraging effort with the growth of their offspring. In years with high proportions of food loss, parents left their chicks unattended at the nest more often. In that way, parents were largely able to counterbalance food shortage of offspring. In 1992 and 1996, when diet composition was unfavorable and food losses to gulls were high, parents left their chicks unattended at the nest for ∼80% of the daylight period. It is argued that the present working level of parents might be higher than in the 1960s.

Comparative activity pattern during foraging of four albatross species

The activity patterns of foraging Yellow‐nosed Diomedea chlororhynchos, Sooty Phoebetria fusca, Black‐browed D. melanophris impavida and Grey‐headed Albatross D. chrysostoma were compared using loggers recording the timing of landing and take‐offs, as well as the duration of bouts in flight or on the water, and the overall time spent in flight. The four species spent a similar proportion of their foraging time in flight (56–65%). During the day they were mostly flying (77–85% of the daylight period) whereas at night they were mainly (61–71%) sitting on the water. The amount of time spent in flight during the daytime foraging period was related to the amount of time spent sitting on the water at night. Differences between species occurred in the duration of bouts in flight and on the water as well as in the frequency of landings and in the time elapsed between successive landings. Yellow‐nosed Albatrosses were more active than the other species, with more frequent short bouts in flight and more frequent successive landings at short intervals. Sooty Albatrosses landed or took‐off less often than the other species and were more active just before dusk. Black‐browed and Grey‐headed Albatrosses were more active at night, especially the first part of the night and far from the colonies. Their trips consisted of a commuting part and a foraging part. Black‐browed Albatrosses landed more often during the foraging than the commuting part, suggesting that they were not searching when travelling. The study suggests that there is no fundamental difference between the overall activity budgets of the four species although they show distinctive diet, morphology and life history traits. The differences observed between the four species were related mainly to differences in foraging technique. Comparison with the Wandering Albatross, the only species for which data were available previously, suggest that this larger species might differ completely in foraging technique from the smaller albatrosses.

The influence of nutrients on growth and photosynthesis of seedlings of two rainforest dipterocarp species.

This study aims to determine the influence of nutrient additions in the form of nitrogen (N), phosphorus (P) and potassium (K) on the photosynthetic physiology, morphology and growth of Dryobalanops lanceolata Burck and Shorea johorensis Foxw., two co-existing dipterocarp species in the understorey of secondary forest. Analysis of the light environment revealed that the total daily irradiance in the understorey was 4.57 ± 0.70 mol photons m-2 d-1, approximately 20% higher than that which could be expected to occur in the primary forest understorey. Around 50% of total irradiance occurred at fluxes over 400 μmol photons m-2 s-1, and this was received over 7% of the daylight period. Both D. lanceolata and S. johorensis grew over the 16-month study, but only S. johorensis increased growth in response to nutrient additions. Neither species altered biomass partitioning in response to additional nutrients. Both species also showed increased rates of photosynthetic induction (T0.5Asat) in response to nutrient additions, but only S. johorensis showed an increase in light-saturated rates of photosynthetic capacity (Asat), and the chlorophyll content of leaves. We argue that additional nutrients increased the capacity of S. johorensis to utilise the sporadic burst of high irradiance in sunflecks. Analysis of the nutrient composition of leaves from age cohorts up to > 16 months showed that additional nutrients increased the P and K concentration in D. lanceolata leaves, and the P and N content of S. johorensis leaves. This suggests that neither P nor K were limiting the growth of D. lanceolata in this secondary forest environment, but that P and/or N may limit growth of S. johorensis. Our data highlights differences in the ecology of two co-existing dipterocarp species. We argue that D. lanceolata shows characteristics consistent with a low resource-demanding species that may have a competitive advantage over S. johorensis in low resource environments, while S. johorensis shows traits better suited to higher resource availability. Thus, there are distinct species-specific differences in the ability to respond to nutrients that depend on the irradiance environment, and which may have a role in niche partitioning among the dipterocarps.

RNA-binding proteins and circadian rhythms in Arabidopsis thaliana.

An Arabidopsis transcript preferentially expressed at the end of the daily light period codes for the RNA-binding protein AtGRP7. A reverse genetic approach in Arabidopsis thaliana has revealed its role in the generation of circadian rhythmicity: AtGRP7 is part of a negative feedback loop through which it influences the oscillations of its own transcript. Biochemical and genetic experiments indicate a mechanism for this autoregulatory circuit: Atgrp7 gene transcription is rhythmically activated by the circadian clock during the day. The AtGPR7 protein accumulates with a certain delay and represses further accumulation of its transcript, presumably at the post-transcriptional level. In this respect, the AtGRP7 feedback loop differs from known circadian oscillators in the fruitfly Drosophila and mammals based on oscillating clock proteins that repress transcription of their own genes with a 24 h rhythm. It is proposed that the AtGRP7 feedback loop may act within an output pathway from the Arabidopsis clock.

Effects of light intensity on animal husbandry and digestive enzyme activities in sea bass Dicentrachus labrax post-larvae

A 3-week experiment was carried out to investigate the effects of light intensity on animal husbandry performances (mainly growth, survival and cannibalism rates) and their relationships with digestive enzyme activities (pepsin, trypsin, chymotrypsin and amylase) in sea bass post-larvae. Four light intensities (5, 50, 100 and 400 lx) were compared in triplicate. Fish (initial body weight: 34 mg) were automatically fed eight times a day during the daylight period. During the first experimental week, fish were progressively habituated to ingest compound diet by a progressive replacement of Artemia metanauplii by dry food (weaning phase). Survival and cannibalism rates were estimated at the end of the experiment. On Days 0, 7, 14 and 21, post-larvae were collected to monitor growth and to assay enzymatic activities and food consumption. Light intensity did not significantly affect neither survival (25.5–39.4%) nor cannibalism (0.6–1.5%) rates or growth (169–195 mg). Trypsin and chymotrypsin specific activities were affected by light intensity during the weaning period. Significantly lower specific activities rates were obtained in the 5-lx treatment, but this phenomenon was no longer observed after Day 7. Specific activity of amylase was not modulated by light intensity. On the other hand, specific activity of pepsin was extremely dependent on light intensity. In sea bass, this enzyme is functional at the end of the first developmental month and its activity increases with age. In the present experiment, only the light intensity of 50 lx induced this increase at the end of weaning. The increase was delayed to Day 14 in fish reared under 100-lx light intensity. Specific activity of pepsin decreased during the 21 experimental days for 5- and 400-lx light intensities. This induced a delay in the onset of stomach digestion, while digestive performances of sea bass post-larvae were optimized when fish were reared under medium (50–100 lx) light intensity.

Influence of diet on development and oviposition of Forficula auricularia (Dermaptera: Forficulidae)

In North America, the life cycle of the European earwig (Forficula auricularia L.) can be divided into a nesting phase (hypogean phase) and a free-foraging phase (epigean phase) (Crumb et al. 1941; Behura 1956; Lamb and Wellington 1975). Adults spend the nesting phase in the soil; females burrow into the ground at the onset of the cold weather, lay eggs, and then care for the eggs. Hatching occurs in spring; first- or second-instar nymphs move to the soil surface for the free-foraging period. The earwig, a nocturnal insect, spends the entire daylight period of hiding under trash or in dark crevices. Where two broods occur, females reenter the ground a second time (Lamb and Wellington 1975). Stomach content analyses (Crumb et al. 1941; Sunderland and Vickerman 1980) and food preference tests (McLeod and Chant 1952; Buxton and Madge 1976) revealed that the European earwig is omnivorous. Under laboratory conditions, nymphs fed freshly frozen aphids, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), survive better than those fed green algae or carrots, develop faster, and produce heavier females (Phillips 1981; Carrillo 1985).