Natural Light-dark Cycle Research Articles

The hydrogen metabolism of sulfur deprived Chlamydomonas reinhardtii cells involves hydrogen uptake activities

Several species of unicellular microalgae such as the model species Chlamydomonas reinhardtii possess plastid-localized [FeFe]-hydrogenases which, via ferredoxin, can accept electrons from photosynthetic electron transport. Thereby, under specific conditions, these algae light-dependently produce molecular hydrogen (H2), which offers a sustainable way to generate a “green” and efficient fuel. Until today, the most common way to induce sustained H2 production is to deprive Chlamydomonas of macronutrients such as sulfur (S) which results in a downregulation of photosynthetic production of molecular oxygen (O2) and of assimilatory processes. These acclimation responses allow the O2 sensitive algal [FeFe]-hydrogenases to become active and serve as an alternative electron sink of photosynthesis. Despite much progress in the field and a general understanding of the underlying mechanisms, many basic and applied aspects of the photosynthetic H2 metabolism of eukaryotic algae remain to be elucidated. One rarely investigated factor is that microalgae have also been reported to consume H2, especially as a response to high H2 concentrations. Here, we analyzed the H2 uptake activities of S-deprived Chlamydomonas cells incubated in different PBRs providing different gas phase volumes, either in continuous light or in the dark. We show that H2 uptake occurs after prolonged incubation in the light as well as in sudden darkness. Dark-induced H2 uptake can be delayed adding the phosphoribulose kinase inhibitor glycolaldehyde, suggesting a connection to carbohydrate metabolism. The results indicate that PBR setups as well as envisioned outdoor cultivation systems with natural light-dark cycles have to be carefully designed to prevent efficiency losses.

Daily Rhythms of Blood Parameters in Broiler Chickens Reared under Tropical Climate Conditions.

Several studies carried out on humans and other mammals show that the temporal organisation of haematological parameters in the blood exhibit daily rhythms; however, such studies have been rare in poultry reared under a natural photoperiod. The present study investigated the occurrence of daily rhythms in blood parameters of broiler chickens kept under tropical climatic conditions. Ten 6–7-week-old broiler chickens served as subjects of the study. They were kept in standard individual cages under natural light-dark cycle and given access to feed and water ad libitum. Two milliliters of blood was collected from each bird via intravenous cannulae inserted into the wing vein. The blood samples were collected every 4 h over a 24-h period, starting from 09:00 h on the first day and completed at 09:00 h on the second day. The blood samples were analysed for erythrocyte, total and differential leucocyte counts. A trigonometric statistical model according to the single cosinor procedure was used to describe the periodic parameters and their acrophases, and ANOVA was used to determine significant differences. The results demonstrated the existence of daily rhythms in packed cell volume, haemoglobin, white blood cell, red blood cell, heterophil, lymphocyte, eosinophil and monocyte counts, while total protein displayed no rhythm. The characteristics of the haematological parameters showed that the acrophases were restricted to the light phase of the light/dark cycle, precisely at 09:00 h, except for eosinophil and heterophil counts, which had acrophases at 21:00 h. The amplitudes of the blood parameters varied, with packed cell volume having the greatest amplitude of 4.2 ± 0.5, closely followed by lymphocyte (3.4 ± 0.5) and heterophil (2.3 ± 0.2) counts. In conclusion, the results of the study demonstrated the existence of daily rhythms with diurnal acrophases in blood parameters of broiler chickens kept under natural photoperiods and tropical conditions.

Effects of light and microhabitat on activity pattern and behaviour of wild and hatchery-reared juveniles ofStichopuscf.horrens

Animals develop behavioural strategies throughout life to improve their survival in nature. Juvenile activity and behaviour of the commercial tropical sea cucumberStichopuscf.horrenswere examined considering factors that may influence survival at this critical developmental stage. Wild juveniles were observedin situto describe diel activity and movement. Wild and hatchery-reared juveniles were observed in the laboratory to evaluate the influence of different light-dark cycles and microhabitats on feeding and sheltering behaviour. All juveniles (4–54 g) displayed a distinct nocturnal activity pattern both in the field and laboratory. Nocturnal activity was strongly associated with feeding and locomotion. Wild and hatchery-reared juveniles were most active at night, displayed intermediate activity during twilight, and minimal to no activity during daytime. Movement rates of wild juvenilesin situwere significantly influenced by time and size to a lesser extent. Under constant light and constant dark for 48 h, juvenile feeding rhythm was endogenously controlled and strongly entrained to natural light-dark cycles. Sheltering was directly affected by light and linked to strong phototactic and thigmotactic reflexes. Juveniles preferred vegetation as shelter compared to coral, sand or open space, and showed equal preference for seagrass and macroalgae. Deviations in behaviour of hatchery-reared juveniles under laboratory conditions indicate some degree of acclimation to an artificial environment with minimal threats and a decreased sensitivity to light. The implications of nocturnal feeding, light-induced sheltering, shelter preferences and acclimation to artificial conditions are discussed in relation to juvenile survival in nature and potential restocking of the species.

Entrainment range of the suprachiasmatic nucleus affected by the difference in the neuronal amplitudes between the light-sensitive and light-insensitive regions.

Mammals not only can be synchronized to the natural 24-h light-dark cycle, but also to a cycle with a non-24-h period. The range of the period of the external cycle, for which the animals can be entrained to, is called the entrainment range, which differs among species. The entrainment range as a characteristic of the animal is determined by the main circadian clock, i.e., the suprachiasmatic nucleus (SCN) in the brain. The SCN is composed of ∼10000 heterogeneous neurons, which can be divided into two subgroups, i.e., the ventrolateral subgroup (VL) directly receiving the light information from the retina and relaying the information to the dorsomedial subgroup (DM). Among the SCN neurons, the amplitudes are different; however, it is unclear that the amplitude is related to the location of the neurons in experiments. In the present study, we examined the effect of the difference in the neuronal amplitude between the VL and the DM on the entrainment range of the SCN, based on a mathematical model, i.e., the Poincaré model, which is used to describe the circadian clock. We find that the maximal entrainment range is obtained when the difference is equal to a critical point. If the difference of the amplitudes of the VL neurons to the amplitudes of the DM neurons is smaller than a critical point, with the increase of the difference, the entrainment range of the SCN increases, while if the difference is larger than the critical point, the entrainment range decreases with the increase of the difference. Our finding may give a potential explanation for the diversity of the entrainment range among species.

Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend

Reduced exposure to daytime sunlight and increased exposure to electrical lighting at night leads to late circadian and sleep timing [1-3]. We have previously shown that exposure to a natural summer 14hr 40min:9hr 20min light-dark cycle entrains the human circadian clock to solar time, such that the internal biological night begins near sunset and ends near sunrise [1]. Here we show that the beginning of the biological night and sleep occur earlier after a week's exposure to a natural winter 9hr 20min:14hr 40min light-dark cycle as compared to the modern electrical lighting environment. Further, we find that the human circadian clock is sensitive to seasonal changes in the natural light-dark cycle, showing an expansion of the biological night in winter compared to summer, akin to that seen in non-humans [4-8]. We also show that circadian and sleep timing occur earlier after spending a weekend camping in a summer 14hr 39min:9hr 21min natural light-dark cycle compared to a typical weekend in the modern environment. Weekend exposure to natural light was sufficient to achieve ∼69% of the shift in circadian timing we previously reported after a week's exposure to natural light [1]. These findings provide evidence that the human circadian clock adapts to seasonal changes in the natural light-dark cycle and is timed later in the modern environment in both winter and summer. Further, we demonstrate that earlier circadian timing can be rapidly achieved through natural light exposure during a weekend spent camping.

Effects of Cold-Dry (Harmattan) and Hot-Dry Seasons on Daily Rhythms of Rectal and Body Surface Temperatures in Sheep and Goats in a Natural Tropical Environment.

Studies on daily rhythmicity in livestock under natural conditions are limited, and there is mounting evidence that rhythm patterns differ between chronobiological studies conducted in the laboratory and studies conducted under pronounced natural seasonality. Here, we investigated the influence of cold-dry (harmattan) and hot-dry seasons on daily rhythmicity of rectal (RT) and body surface temperatures (BST) in indigenous sheep and goats under natural light-dark cycles. The RT and BST of the animals, and the ambient temperature (AT) and relative humidity (RH) inside the pen, were measured every three hours for a period of two days, twice on separate days during the hot-dry and the harmattan seasons, respectively. The AT and RH had minimum values of 16°C and 15% recorded during the harmattan and maximum values of 32°C and 46% recorded during the hot-dry season, respectively. A trigonometric statistical model was applied to characterize the main rhythmic parameters according to the single cosinor procedure. The result showed that RT and BST exhibited different degrees of daily rhythmicity, and their oscillatory patterns differed with the seasons (larger amplitude during the harmattan season than during the hot-dry season). The goats displayed greater (p < 0.05) amplitude of BST than the sheep in all seasons. The acrophases were restricted to the light phase of the light-dark cycle. The mesor of RT in goats was not affected by the season, but mesors of BST in both species were significantly higher (p < 0.05) during the hot-dry than the harmattan season. The goats had a more robust RT rhythm (70%) as compared to the sheep (56%). Overall, the results demonstrated that seasonal changes influenced considerably the daily rhythmicity of RT and BST in sheep and goats under natural light-dark cycle. Awareness of these changes may be useful in the improvement of diagnosis, treatment and prevention of diseases, and welfare and productivity of sheep and goats under cold-dry and hot-dry conditions.

Transformation of plastids in soil-shaded lowermost hypocotyl segments of bean (Phaseolus vulgaris) during a 60-day cultivation period.

The maintenance but substantial transformation of plastids was found in lowermost hypocotyl segments of soil-grown bean plants (Phaseolus vulgaris cv. Magnum) during a 60-day cultivation period. Although the plants were grown under natural light-dark cycles, this hypocotyl segment was under full coverage of the soil in 5-7 cm depth, thus it was never exposed to light. The 4-day-old plants were fully etiolated: amyloplasts, occasionally prolamellar bodies, protochlorophyllide (Pchlide) and protochlorophyll (Pchl) were found in the hypocotyls of these young seedlings. The 633 and 654 nm bands in the 77 K fluorescence emission spectra indicated the presence of Pchlide and Pchl pigments. During aging, both the Pchlide and Pchl contents increased, however, the Pchl to Pchlide ratio gradually increased. In parallel, the contribution of the 654 nm form decreased and in the spectra of the 60-day-old samples, the main band shifted to 631 nm, and a new form appeared with an emission maximum at 641 nm. The photoactivity had been lost; bleaching took place at continuous illumination. The inner membranes of the plastids disappeared, the amount of starch storing amyloplasts decreased. These data may indicate the general importance of plastids for plant cell metabolism, which can be the reason for their maintenance. Also the general heterogeneity of plastid forms can be concluded: in tissues not exposed to light, Pchl accumulating plastids develop and are maintained even for a long period.

Light pollution reduces activity, food consumption and growth rates in a sandy beach invertebrate

The continued growth of human activity and infrastructure has translated into a widespread increase in light pollution. Natural daylight and moonlight cycles play a fundamental role for many organisms and ecological processes, so an increase in light pollution may have profound effects on communities and ecosystem services. Studies assessing ecological light pollution (ELP) effects on sandy beach organisms have lagged behind the study of other sources of disturbance. Hence, we assessed the influence of this stressor on locomotor activity, foraging behavior, absorption efficiency and growth rate of adults of the talitrid amphipod Orchestoidea tuberculata. In the field, an artificial light system was assembled to assess the local influence of artificial light conditions on the amphipod's locomotor activity and use of food patches in comparison to natural (ambient) conditions. Meanwhile in the laboratory, two experimental chambers were set to assess amphipod locomotor activity, consumption rates, absorption efficiency and growth under artificial light in comparison to natural light-dark cycles. Our results indicate that artificial light have significantly adverse effects on the activity patterns and foraging behavior of the amphipods, resulting on reduced consumption and growth rates. Given the steady increase in artificial light pollution here and elsewhere, sandy beach communities could be negatively affected, with unexpected consequences for the whole ecosystem.

Light piping driven photosynthesis in the soil: Low-light adapted active photosynthetic apparatus in the under-soil hypocotyl segments of bean (Phaseolus vulgaris)

Photosynthetic activity was identified in the under-soil hypocotyl part of 14-day-old soil-grown bean plants (Phaseolus vulgaris L. cv. Magnum) cultivated in pots under natural light-dark cycles. Electron microscopic, proteomic and fluorescence kinetic and imaging methods were used to study the photosynthetic apparatus and its activity. Under-soil shoots at 0–2cm soil depth featured chloroplasts with low grana and starch grains and with pigment-protein compositions similar to those of the above-soil green shoot parts. However, the relative amounts of photosystem II (PSII) supercomplexes were higher; in addition a PIP-type aquaporin protein was identified in the under-soil thylakoids. Chlorophyll-a fluorescence induction measurements showed that the above- and under-soil hypocotyl segments had similar photochemical yields at low (10–55μmolphotonsm−2s−1) light intensities. However, at higher photon flux densities the electron transport rate decreased in the under-soil shoot parts due to inactivation of the PSII reaction centers. These properties show the development of a low-light adapted photosynthetic apparatus driven by light piping of the above-soil shoot. The results of this paper demonstrate that the classic model assigning source and sink functions to above- and under-soil tissues is to be refined, and a low-light adapted photosynthetic apparatus in under-soil bean hypocotyls is capable of contributing to its own carbon supply.

Influence of exposure in ovo to different light wavelengths on the lateralization of social response in zebrafish larvae

Exposure of the chick embryo to different wavelengths of light of the same intensity has shown that only certain wavelengths may be important in generating visual asymmetries. This study aimed to detect the possible influence of different wavelengths of light on development of asymmetry of social recognition in zebrafish larvae, tested using the fish's mirror image as the stimulus. From fertilization until day 10 post-hatching zebrafish were kept in five different lighting conditions: natural light/dark (LD) cycle, complete darkness (DD), and artificial LD cycles with 14h of monochromatic light (red, green, or violet light) and 10h of darkness (rLD 14:10, gLD 14:10, vLD 14:10, respectively). On day 10 after hatching, the zebrafish larvae were subjected to a mirror test. A preference for using the left eye to scrutinize their mirror image was apparent only in zebrafish larvae exposed to and reared under a natural LD cycle, and not following exposure to any of other lighting conditions. These results are discussed with reference to other evidence of brain lateralization.

Natural selection against a circadian clock gene mutation in mice

Circadian rhythms with an endogenous period close to or equal to the natural light-dark cycle are considered evolutionarily adaptive ("circadian resonance hypothesis"). Despite remarkable insight into the molecular mechanisms driving circadian cycles, this hypothesis has not been tested under natural conditions for any eukaryotic organism. We tested this hypothesis in mice bearing a short-period mutation in the enzyme casein kinase 1ε (tau mutation), which accelerates free-running circadian cycles. We compared daily activity (feeding) rhythms, survivorship, and reproduction in six replicate populations in outdoor experimental enclosures, established with wild-type, heterozygous, and homozygous mice in a Mendelian ratio. In the release cohort, survival was reduced in the homozygote mutant mice, revealing strong selection against short-period genotypes. Over the course of 14 mo, the relative frequency of the tau allele dropped from initial parity to 20%. Adult survival and recruitment of juveniles into the population contributed approximately equally to the selection for wild-type alleles. The expression of activity during daytime varied throughout the experiment and was significantly increased by the tau mutation. The strong selection against the short-period tau allele observed here contrasts with earlier studies showing absence of selection against a Period 2 (Per2) mutation, which disrupts internal clock function, but does not change period length. These findings are consistent with, and predicted by the theory that resonance of the circadian system plays an important role in individual fitness.

Density regulation in toad populations (Epidalea calamita, Bufotes viridis) by differential winter survival of juveniles

The size of amphibian populations varies considerably between years, so that systematic trends in dynamics are difficult to detect. Informed conservation management of presumably declining populations requires the identification of the most sensitive life stage. In temperate-zone anurans there is growing evidence that juveniles hibernating for the first time suffer from substantial winter losses. In two syntopic toads (Epidalea calamita, Bufotes viridis) we monitored survival of such juveniles during four consecutive winters in the natural habitat and in four temperature treatments (3°, 5°C, 10°/15°C or 20°C, natural light-dark cycle) in temperature-controlled chambers during winter. Specifically, we tested the hypotheses that (1) winter mortality of juvenile toads which hibernate for the first time in their life is an important component of population dynamics, and that (2) mortality rates differed between the two species. Parameters quantified were size-dependent winter mortality and body condition of pre- and post-hibernating juveniles. Field data provided evidence for the important role of winter mortality of first-hibernators in population dynamics. Choice of hibernacula differed in E. calamita between small and medium-sized individuals and also between the two species suggesting distinct mortality risks. The inability of small E. calamita to reach frost-proof hibernacula by burrowing, and the exposure of small B. viridis to predators are the most probable causes of size-assortative winter mortality. In conclusion, E. calamita juveniles may benefit from rising average winter temperatures in the future by decreased risk of freezing to death, whereas predator-caused winter mortality of B. viridis juveniles will also depend on the effects of climate warming on predator phenology.

Sleep patterns in Amazon rubber tappers with and without electric light at home.

Today’s modern society is exposed to artificial electric lighting in addition to the natural light-dark cycle. Studies assessing the impact of electric light exposure on sleep and its relation to work hours are rare due to the ubiquitous presence of electricity. Here we report a unique study conducted in two phases in a homogenous group of rubber tappers living and working in a remote area of the Amazon forest, comparing those living without electric light (n = 243 in first phase; n = 25 in second phase) to those with electric light at home (n = 97 in first phase; n = 17 in second phase). Questionnaire data (Phase 1) revealed that rubber tappers with availability of electric light had significantly shorter sleep on work days (30 min/day less) than those without electric light. Analysis of the data from the Phase 2 sample showed a significant delay in the timing of melatonin onset in workers with electric light compared to those without electric light (p < 0.01). Electric lighting delayed sleep onset and reduced sleep duration during the work week and appears to interfere with alignment of the circadian timing system to the natural light/dark cycle.

Sleep Hygiene and Recovery Strategies in Elite Soccer Players.

In elite soccer, players are frequently exposed to various situations and conditions that can interfere with sleep (e.g., playing night matches interspersed with 3 days; performing activities demanding high levels of concentration close to bedtime; use of products containing caffeine or alcohol in the period preceding bedtime; regular daytime napping throughout the week; variable wake-up times or bedtime), potentially leading to sleep deprivation. We outline simple, practical, and pharmaceutical-free sleep strategies that are coordinated to the constraints of elite soccer in order to promote sleep. Sleep deprivation is best alleviated by sleep extension; however, sleep hygiene strategies (i.e., consistent sleep pattern, appropriate napping, and active daytime behaviors) can be utilized to promote restorative sleep. Light has a profound impact on sleep, and sleep hygiene strategies that support the natural environmental light-dark cycle (i.e., red-light treatment prior to sleep, dawn-simulation therapy prior to waking) and prevent cycle disruption (i.e., filtering short wavelengths prior to sleep) may be beneficial to elite soccer players. Under conditions of inordinate stress, techniques such as brainwave entrainment and meditation are promising sleep-promoting strategies, but future studies are required to ascertain the applicability of these techniques to elite soccer players. Consuming high-electrolyte fluids such as milk, high-glycemic index carbohydrates, some forms of protein immediately prior to sleep, as well as tart cherry juice concentrate and tryptophan may promote rehydration, substrate stores replenishment, muscle-damage repair and/or restorative sleep. The influence of cold water immersion performed close to bedtime on subsequent sleep is still debated. Conversely, the potential detrimental effects of sleeping medication must be recognized. Sleep initiation is influenced by numerous factors, reinforcing the need for future research to identify such factors. Efficient and individualized sleep hygiene strategies may consequently be proposed.

Continuously Changing Light-Dark Phase Decreases Milk Yield, Fat, Protein and Lactose in Dairy Cows

Photoperiod impacts feeding behavior, health, growth and milk production of dairy cattle. In humans behaviors that are asynchronous with the natural light-dark cycle, such as shift work or jet lag, are strongly associated with metabolic disorders as well as impaired reproductive performance. The objective of this study was to determine the effects of exposing mid-lactation dairy cows to chronically shifting 8h light (L)-8h dark (D) cycles on feed intake, milk yield, milk composition and mammary gene expression. Six first lactation Holsteins ∼90d in milk were maintained on a 16 h L: 8 h D cycle and milked at 5AM and 4PM for 7d (control, Period 1). During Period 2, 7 d immediately following Period 1, cows were exposed to continuous cycles of 8 h L: 8 h D, but maintained on the same milking and feeding schedule. Exposure to chronic 8 h LD cycles significantly depressed milk yield (P<0.05), but did not affect daily feed intake. Percent milk fat, protein and lactose were not different, but milk urea nitrogen (MUN) significantly increased. On the last day of each period mammary gene expression was measured by Q-PCR of total RNA isolated from the cytosolic components of milk fat globules. Expression of the core clock gene BMAL1 in addition to Beta-casein, Alpha-lactalbumin, Fatty acid synthase and Acetyl CoA-carboxylase were all decreased (P < 0.05) after 7 d of chronic 8 h LD cycles. The results from this study show for the first time that exposing lactating cows to chronic light shifts decreases milk production and may alter metabolism. Further, experimental design may provide a paradigm to study the effects of changing lighting schedules on milk production and a potential model to study effects of disrupting circadian system on production efficiency.

Circadian rhythms of crawling and swimming in the nudibranch mollusc Melibe leonina.

Daily rhythms of activity driven by circadian clocks are expressed by many organisms, including molluscs. We initiated this study, with the nudibranch Melibe leonina, with four goals in mind: (1) determine which behaviors are expressed with a daily rhythm; (2) investigate which of these rhythmic behaviors are controlled by a circadian clock; (3) determine if a circadian clock is associated with the eyes or optic ganglia of Melibe, as it is in several other gastropods; and (4) test the hypothesis that Melibe can use extraocular photoreceptors to synchronize its daily rhythms to natural light-dark cycles. To address these goals, we analyzed the behavior of 55 animals exposed to either artificial or natural light-dark cycles, followed by constant darkness. We also repeated this experiment using 10 animals that had their eyes removed. Individuals did not express daily rhythms of feeding, but they swam and crawled more at night. This pattern of locomotion persisted in constant darkness, indicating the presence of a circadian clock. Eyeless animals also expressed a daily rhythm of locomotion, with more locomotion at night. The fact that eyeless animals synchronized their locomotion to the light-dark cycle suggests that they can detect light using extraocular photoreceptors. However, in constant darkness, these rhythms deteriorated, suggesting that the clock neurons that influence locomotion may be located in, or near, the eyes. Thus, locomotion in Melibe appears to be influenced by both ocular and extraocular photoreceptors, although the former appear to have a greater influence on the expression of circadian rhythms.

About the Cover.

Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverMelibe leonina (small inset on cover), is a nudibranch that is most often found in seagrass meadows and kelp beds along the West Coast of the United States and Canada. It feeds on small prey that it captures using rhythmic movements of its large oral hood. Occasionally it can also be observed floating in the water column or swimming using rhythmic lateral flexions of its entire body. Previous studies have demonstrated that it will swim, and crawl, most often at night. In this issue, the paper by James Newcomb, Winsor Watson, and their students, describes how the locomotion of this species is influenced by a circadian clock that might be associated with its eyes.M. leonina has relatively clear skin, so light can easily reach its eyes. The eyes are located on the brain, which is unusual for gastropods. The main picture shows a M. leonina brain that has been removed and pinned out in a dish of saline where it can be kept alive and will continue to express certain behaviors such as swimming. The eyes have black pigment associated with them; the two white spots lateral to the eyes are neurons with a white pigment. All the other round objects are the cell bodies of individual neurons. The clear structures leaving the brain are nerves.M. leonina has been used by a number of scientists to study the neural basis of behavior because, as is evident from the picture of its brain, its neurons are very large, and readily identifiable. The size, color, and consistent location of these neurons, such as the pair of white pigmented cells adjacent to the eyes, make it possible to insert microelectrodes into individual neurons and record their activity, both in intact animals and in isolated brains. Because the eyes are on the brain, these isolated brains, like intact animals, will express swimming activity more in the dark than in the light. In their article, the authors demonstrated that if the eyes of this species are removed, it is still able to synchronize its daily rhythms to the natural light-dark cycle, suggesting that it probably has other, extraocular, photoreceptors. However, without their eyes, individuals do not exhibit circadian rhythms of locomotion in constant darkness, suggesting that these organs may contain an element of the endogenous biological clock.In view of these facts, this nudibranch provides a good model system for investigating the connection between biological clocks and the neural circuitry underlying behaviors that are expressed with a circadian rhythm.Credits: Large image, Winsor Watson III, University of New Hampshire; inset, James N. Newcomb, New England College; layout, Beth Liles, Marine Biological Laboratory. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 227, Number 3December 2014 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/BBLv227n3cover © 2014 by Marine Biological Laboratory. All rights reserved.PDF download Crossref reports no articles citing this article.

Hydrogen production by Chlamydomonas reinhardtii under light-driven and sulfur-deprived conditions: Using biomass grown in outdoor photobioreactors at the Yucatan Peninsula

Photosynthesis is the ultimate natural process that supports all the biofuels generation. Photosyntetic production of hydrogen by microalgae is very attractive from the renewability point of view. Moreover, it faces several challenges: since the process itself has a low yield, a large number of considerations should be studied to optimize the hydrogen production at the lowest cost. In this work, wild-type Chlamydomonas reinhartii was grown outdoors in the Yucatán peninsula. Three different diameters of tubular photobioreactors (PBRs), two autotrophic culture media, as well as two seasons of the year were analyzed. From these variables, it was determined that the best biomass yield was during the winter season and with the Sueoka culture medium. Statistical significance differences were not found for the diameters of the PBRs. During growth, the biomass was exposed to natural light–dark cycles and at the end of the exponential phase of growth it was harvested with superabsorbent polymers. This biomass was able to produce hydrogen under anaerobic conditions in Tris-Acetate-Phosphate culture medium in indoor PBRs exposed to continuous artificial illumination. Experiments with different initial biomass concentrations in the anaerobic PBRs showed direct relationship with the hydrogen production profile.

Nycthemeral variation in melatonin receptor expression in the lymphoid organs of a tropical seasonal breeder Funambulus pennanti.

Seasonal variations in immune functions point toward the involvement of melatonin in its regulation. These chronobiotic effects are exerted by receptors present on the immunocompetent cells. The present study investigated daily/nycthemeral variation in expression of melatonin receptor subtypes MT1/MT2 in the lymphoid organs (spleen/thymus) of a tropical squirrel, Funambulus pennanti. The receptor expression was noted every 4 h interval over 24 h under natural light-dark cycle, during two seasons and was correlated with peripheral level of melatonin. The MT1/MT2 receptor expression displayed higher levels at the time of dusk (light-dark transition; 1800 hours), while plasma melatonin was still low compared to the preceding time point. The receptors were downregulated during the nighttime with a minimum expression at 0200 hours. Thymus, during the long day length, showed a tissue-specific pattern of receptor expression with a minimum expression at 0600 hours. Results suggest that photoperiod by modulation of melatonin level inversely regulates the receptor expression. The observations imply that there exists a temporal window of sensitivity in the target organs to the melatonin signal that is regulated by modulation of melatonin receptor expression which might be involved in mediating the photoperiodic effects of melatonin in the control of seasonal immune physiology.

Young Adults' Sleep Duration on Work Days: Differences between East and West.

Human sleep schedules vary widely across countries. We investigated whether these variations were related to differences in social factors, Morningness–Eveningness (ME) preference, or the natural light–dark cycle by contrasting the sleep duration and timing of young adults (age: 18–35 years) on work and free days in Singapore (n = 1898) and the UK (n = 837). On work days, people in Singapore had later bedtimes, but wake times were similar to the UK sample, resulting in shorter sleep duration. In contrast, sleep duration on free days did not differ between the two countries. Shorter sleep on work days, without compensatory extra long sleep hours on free days, suggest greater demands from work and study in Singapore. While the two samples differed slightly in ME preference, the associations between eveningness preference and greater extension in sleep duration as well as delays in sleep timing on free days were similar in the two countries. Thus, differences in ME preference did not account for the differences in sleep schedules between the two countries. The greater variability in the photoperiod in the UK was not associated with more prominent seasonal changes in sleep patterns compared to Singapore. Furthermore, in the UK, daylight saving time did not alter sleep schedules relative to clock time. Collectively, these findings suggest that differences in social demands, primarily from work or study, could account for the observed differences in sleep schedules between countries, and that in industrialized societies, social zeitgebers, which typically involve exposure to artificial light, are major determinants of sleep schedules.