Effects of dispersal plasticity on population divergence and speciation.

Phenotypic plasticity is thought to have a role in driving population establishment, local adaptation and speciation. However, dispersal plasticity has been underappreciated in this literature. Plasticity in the decision to disperse is taxonomically widespread and I provide examples for insects, molluscs, polychaetes, vertebrates and flowering plants. Theoretical work is limited but indicates an interaction between dispersal distance and plasticity in the decision to disperse. When dispersal is confined to adjacent patches, dispersal plasticity may enhance local adaptation over unconditional (non-plastic) dispersal. However, when dispersal distances are greater, plasticity in dispersal decisions strongly reduces the potential for local adaptation and population divergence. Upon dispersal, settlement may be random, biased but genetically determined, or biased but plastically determined. Theory shows that biased settlement of either type increases population divergence over random settlement. One model suggests that plasticity further enhances chances of speciation. However, there are many strategies for deciding on where to settle such as a best-of-N strategy, sequential sampling with a threshold for acceptance or matching with natal habitat. To date, these strategies do not seem to have been compared within a single model. Although we are just beginning to explore evolutionary effects of dispersal plasticity, it clearly has the potential to enhance as well as inhibit population divergence. Additional work should pay particular attention to dispersal distance and the strategy used to decide on where to settle.

Why get big in the cold? Size-fecundity relationships explain the temperature-size rule in a pulmonate snail (Physa).

Most ectotherms follow a pattern of size plasticity known as the temperature-size rule where individuals reared in cold environments are larger at maturation than those reared in warm environments. This pattern seems maladaptive because growth is slower in the cold so it takes longer to reach a large size. However, it may be adaptive if reaching a large size has a greater benefit in a cold than in a warm environment such as when size-dependent mortality or size-dependent fecundity depends on temperature. I present a theoretical model showing how a correlation between temperature and the size-fecundity relationship affects optimal size at maturation. I parameterize the model using data from a freshwater pulmonate snail from the genus Physa. Nine families were reared from hatching in one of three temperature regimes (daytime temperature of 22, 25 or 28 °C, night-time temperature of 22 °C, under a 12L:12D light cycle). Eight of the nine families followed the temperature-size rule indicating genetic variation for this plasticity. As predicted, the size-fecundity relationship depended upon temperature; fecundity increases steeply with size in the coldest treatment, less steeply in the intermediate treatment, and shows no relationship with size in the warmest treatment. Thus, following the temperature-size rule is adaptive for this species. Although rarely measured under multiple conditions, size-fecundity relationships seem to be sensitive to a number of environmental conditions in addition to temperature including local productivity, competition and predation. If this form of plasticity is as widespread as it appears to be, this model shows that such plasticity has the potential to greatly modify current life-history theory.

[A few reflections and definitions on the subject of embryonic research]. / Quelques réflexions et définitions au sujet de la Recherche sur l'Embryon.

Tissue regeneration by embryonic stem cells (ESC) opens new applications for cellular therapy. ECS are used in endocrinology, rheumatology, cardiology, orthopaedics, dermatology and neurology. They come from supernumerary embryos given by their progenitors to science. The moral embryo status is the conflicting point and a hotly debated question. No ethical committee has given any valuable definition. Some countries have set time limits governing research with embryos, while others consider ECS as more akin to things or living beings such as animals.

Pharmacokinetics of melatonin in preterm infants.

AIMS: Preterm infants are deprived of the normal intra-uterine exposure to maternal melatonin and may benefit from replacement therapy. We conducted a pharmacokinetic study to guide potential therapeutic trials. METHODS: Melatonin was administered to 18 preterm infants in doses ranging from 0.04-0.6 µg kg(-1) over 0.5-6 h. Pharmacokinetic profiles were analyzed individually and by population methods. RESULTS: Baseline melatonin was largely undetectable. Infants receiving melatonin at 0.1 µg kg(-1) h(-1) for 2 h showed a median half-life of 15.82 h and median maximum plasma concentration of 203.3 pg ml(-1) . On population pharmacokinetics, clearance was 0.045 l h(-1) , volume of distribution 1.098 l and elimination half-life 16.91 h with gender (P = 0.047) and race (P < 0.0001) as significant covariates. CONCLUSIONS: A 2 h infusion of 0.1 µg kg(-1) h(-1) increased blood melatonin from undetectable to approximately peak adult concentrations. Slow clearance makes replacement of a typical maternal circadian rhythm problematic. The pharmacokinetic profile of melatonin in preterm infants differs from that of adults so dosage of melatonin for preterm infants cannot be extrapolated from adult studies. Data from this study can be used to guide therapeutic clinical trials of melatonin in preterm infants.

An hour of bright white light in the early morning improves performance and advances sleep and circadian phase during the Antarctic winter.

Previous work has demonstrated that exposure to an hour of bright light in the morning and the evening during the Polar winter has beneficial effects on circadian phase. This study investigated the effect of a single hour of bright white morning light on circadian phase, sleep, alertness and cognitive performance. Nine individuals (eight male, one female, median age 30 years), wintering at Halley Research Station (75°S), Antarctica from 7th May until 6th August 2007, were exposed to bright white light for a fortnight from 08:30 to 09:30 h, with two fortnight control periods on either side. This sequence was performed twice, before and following Midwinter. Light exposure, sleep and alertness were assessed daily by actigraphy, sleep diaries and subjective visual analogue scales. Circadian phase (assessed by urinary 6-sulphatoxymelatonin rhythm) and cognitive performance were evaluated at the end of each fortnight. During light exposure circadian phase was advanced from 4.97 ± 0.96 decimal hours (dh) (mean ± SD) to 4.08 ± 0.68 dh (p = 0.003). Wake-up time was shifted by a similar margin from 8.45 ± 1.83 dh to 7.59 ± 0.78 dh (p < 0.001). Sleep start time was also advanced (p = 0.047) but by a lesser amount, consequently, actual sleep time was slightly reduced. There was no change in objective or subjective measures of sleep quality or subjective measures of alertness. An improvement in cognitive performance was found with both the Single Letter Cancellation Test (p < 0.001) and the Digit Symbol Substitution Test (p = 0.026) with preserved circadian variation. These beneficial effects of a single short duration light treatment may have implications not only for the Antarctic but other remote environments where access to natural light and delayed circadian phase, is problematic. These results require validation in larger studies at varying locations.

[Can one authorize oocyte donation in the Grand Duchy of Luxembourg?]. / Peut -on autoriser le don d'ovocytes au GDL?

In the case of early ovary extinction, the only way to have a child is either adoption or egg/embryo reception by donation. To day, egg donation is prohibited in Luxembourg by ministerial decision in 2003. Germ cell donation is part of artificial reproductive therapy. Oocyte donation, in particular, needs to be done by IVF treatment, which makes it more complicated then sperm donation What makes it more difficult is the fact that there are no oocyte bank yet. Today, prohibition encourages procreative tourism what only wealthy people can afford. Although donation programs are well established many questions arise about egg donation such as refunds, divulging information, women's age limit, health insurance participation.

[Retrospective study--pregnancy after assisted medical reproduction from 2001 to 2009 at the Central Hospital of Luxembourg (first section)]. / Etude retrospective--suivis de grossesses après Procréation Médicalement Assistée (PMA) de 2001 à 2009 au Centre Hospitalier de Luxembourg (1re partie).

Retrospective study on a nine year ART practice focusing on pregnancy outcomes and multiple pregnancies, their complications, the gestational duration, delivery options, the new born weights and health statements til the age of two. Post ART pregnancies seem to have an increased complication rate; multiple births are more frequent than with spontaneous conception. The first chapter deals with the entire group. The second chapter analyses several sub-groups according to the ART method employed. The results are compared to publications in PubMed and Medline.

[Retrospective studies of pregnancies after assisted medical reproduction from 2001-2009 and Central Hospital in Luxembourg (part 2)]. / Etude rétrospective--suivis de grossesses après Procréation Médicalement Assistée (PMA) de 2001 à 2009 au Centre Hospitalier de Luxembourg (2e partie).

The first chapter analyses the ART methods of the Centre Hospitalier of Luxembourg, in the department of reproductive medicine between 2001 and 2009. The second chapter examines the techniques individually, their influence on pregnancy outcomes, the complications on offsprings and their health. The results coincide with literature in that risks are acceptable as long as good medical and biological conditions are maintained. Multiple pregnancies remain the most frequent complication, particularly once out of IVF. These are analysed separately as well as the pregnancies after egg and semen donation.

[Biological parameters for evaluation of ovarian reserve and resultant antimullerian hormone]. / Paramètres biologiques d'evaluation de la réserve ovarienne et résultats en PMA.

No biological parameter allows a predictive result in ART for ovary stimulation. We studied the interest of dosing AMH in ovary stimulation in balance with the the clinical context.

[Ethical preoccupations in the daily practice of medically assisted reproduction in the Grand Duchy of Luxembourg]. / Préoccupations ethiques dans la pratique quotidienne de la Procréation Médicalement Assistée au Grand-Duché de Luxembourg.

Ethical questions are daily in usual ART practice. The answers differ from the existence or not of legal resolutions. In Grand Duchy of Luxembourg, there is no law on ART practice, by now. Practice is based human sense, ethical commission guide lines and partly on French bioethical law July, 1994. We discuss several topics encountered in daily practice.

Antibacterial effect of autologous platelet gel enriched with growth factors and other active substances: an in vitro study.

Platelet-rich plasma is a new inductive therapy which is being increasingly used for the treatment of the complications of bone healing, such as infection and nonunion. The activator for platelet-rich plasma is a mixture of thrombin and calcium chloride which produces a platelet-rich gel. We analysed the antibacterial effect of platelet-rich gel in vitro by using the platelet-rich plasma samples of 20 volunteers. In vitro laboratory susceptibility to platelet-rich gel was determined by the Kirby-Bauer disc-diffusion method. Baseline antimicrobial activity was assessed by measuring the zones of inhibition on agar plates coated with selected bacterial strains. Zones of inhibition produced by platelet-rich gel ranged between 6 mm and 24 mm (mean 9.83 mm) in diameter. Platelet-rich gel inhibited the growth of Staphylococcus aureus and was also active against Escherichia coli. There was no activity against Klebsiella pneumoniae, Enterococcus faecalis, and Pseudomonas aeruginosa. Moreover, platelet-rich gel seemed to induce the in vitro growth of Ps. aeruginosa, suggesting that it may cause an exacerbation of infections with this organism. We believe that a combination of the inductive and antimicrobial properties of platelet-rich gel can improve the treatment of infected delayed healing and nonunion.

Circadian neuroendocrine physiology and electromagnetic field studies: precautions and complexities.

The suppression of melatonin by exposure to low frequency electromagnetic fields (EMFs) 'the melatonin hypothesis'. has been invoked as a possible mechanism through which exposure to these fields may result in an increased incidence of cancer. While the effect of light on melatonin is well established, data showing a similar effect due to EMF exposure are sparse and, where present, are often poorly controlled. The current review focuses on the complexities associated with using melatonin as a marker and the dynamic nature of normal melatonin regulation by the circadian neuroendocrine axis. These are issues which the authors believe contribute significantly to the lack of consistency of results in the current literature. Recommendations on protocol design are also made which, if followed, should enable researchers to eliminate or control for many of the confounding factors associated with melatonin being an output from the circadian clock.

Acute exposure to circularly polarized 50-Hz magnetic fields of 200-300 microT does not affect the pattern of melatonin secretion in young men.

Environmental exposure to time-varying (alternating current) magnetic fields (MFs) produced by electrical current flow is a perceived public health risk. Several epidemiological studies report correlations between MF exposure and carcinogenesis. It has been hypothesized that MF-induced suppression of melatonin could provide the mechanism by which this effect is mediated. Here, we describe results from a controlled laboratory-based study designed to detect changes in human melatonin secretion after a 2-h exposure to 200-300 microTesla, 50 Hz circularly polarized MF. Exposure was timed to occur before or during the nightly melatonin rise, and levels administered were some 4-6 times higher than the commonly encountered maximum levels. Results from 19 male subjects aged between 18 and 35 yr indicate that acute exposure to 50 Hz MFs of this nature does not result in significant suppression, alteration of peak levels, or a change in timing of the nighttime melatonin rise. We conclude that acute exposure to 50 Hz MFs does not have a significant effect on the normal nighttime production of melatonin in young men.

Importance and relevance of melatonin to human biological rhythms.

The pineal hormone melatonin is a remarkable molecule, with a conserved time-keeping function across species. It is extensively used as a self-administered remedy for sleep disturbance in countries where it is freely available, and to some extent when it is available on prescription, as in the UK. In some circumstances, notably free-running sleep disorder of the blind, it is the treatment of choice. It is also the marker rhythm of choice for the determination of circadian phase and period. This review outlines the current state of knowledge within a physiological perspective with emphasis on human biological rhythms.

Circularly polarised MF (500 micro T 50 Hz) does not acutely suppress melatonin secretion from cultured Wistar rat pineal glands.

Magnetic fields (MF, 50 Hz) have been proposed to affect melatonin production in mammals; however, there is very little data about the mechanism by which this possible interaction may occur. Here we describe results from the first study in which circularly polarised 50 Hz MF have been administered to isolated pineals in highly controlled conditions. Melatonin release from isolated Wistar rat pineal glands, dissected 2 h after light onset ZT 2, was measured in a flow through culture system, during and after exposure to a 4 h MF similar in nature and magnitude to that produced in extremely close proximity to a high voltage power line (500 micro T 50 Hz circularly polarised). Melatonin release from isolated pineals was comparable to that observed in previous studies, plateauing to approximately 100 pg/ml/30 min. No significant alterations in pineal melatonin release were caused by exposure to the MF when compared to sham exposure (< 1 micro T). These results suggest that if the circadian system is acutely responsive to MF exposure of this nature, an intact circadian axis may be necessary in order to observe an effect on the production on melatonin from the pineal gland

Adaptation of the circadian rhythm of 6-sulphatoxymelatonin to a shift schedule of seven nights followed by seven days in offshore oil installation workers.

This study evaluated circadian adaptation in a 'swing shift' schedule (seven nights, 18:00-06:00 h; then 7 days, 06:00-18:00 h) on North Sea oil installations. Eleven healthy men provided sequential urine collections for the study period offshore. The urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was used as an index of circadian phase. A significant difference (P=0.0004) was found between the mean aMT6s acrophase (calculated peak time) at the start (+/-SD: 05:34+/-2.42 h) and end (+/-SD: 10.95+/-3.34 h) of the night shift week, but not between the start (+/-SD: 11:04+/-4.03 h) and end (+/-SD: 12:59+/-8.83 h) of the day shift week. As a group, the subjects adapted to the night shift but very large individual variations were seen during the day shift. These individual differences clearly require further study.

[The treatment of assisted reproduction--clinical and preclinical aspects, functioning of the Unit of Human Reproduction at the Central Hospital of Luxembourg]. / Les traitements en PMA--prise en charge--aspects cliniques et paracliniques, fonctionnement de l'unité de reproduction humaine au CHL.

Since a few years the OBGYN department at the Centre Hospitalier in Luxembourg has intensified its practice of ART with the introduction of a multidisciplinary team and a decentralized IVF program. While clinical investigations, cycle-monitoring and surgery, oocyte pick-up are commonly performed at the CHL, the biological supplement is transferred to next situated Belgian laboratories. As Luxembourg has no national bio-ethical law, we apply partly the French law of 1994.

Postprandial hormone and metabolic responses amongst shift workers in Antarctica.

The circadian rhythms of many night-shift workers are maladapted to their imposed behavioural schedule, and this factor may be implicated in the increased occurrence of cardiovascular disease (CVD) reported in shift workers. One way in which CVD risk could be mediated is through inappropriate hormonal and metabolic responses to meals. This study investigated the responses to standard meals at different circadian times in a group of night-shift workers on a British Antarctic Survey station at Halley Bay (75 degrees S) in Antarctica. Twelve healthy subjects (ten men and two women) were recruited. Their postprandial hormone and metabolic responses to an identical mixed test meal of 3330 kJ were measured on three occasions: (i) during daytime on a normal working day, (ii) during night-time at the beginning of a period of night-shift work, and (iii) during the daytime on return from night working to daytime working. Venous blood was taken for 9 h after the meal for the measurement of glucose, insulin, triacylglycerol (TAG) and non-esterified fatty acids. Urine was collected 4-hourly (longer during sleep) on each test day for assessment of the circadian phase via 6-sulphatoxymelatonin (aMT6s) assay. During normal daytime working, aMT6s acrophase was delayed (7.7+/-1.0 h (s.e.m.)) compared with that previously found in temperate zones in a comparable age-group. During the night shift a further delay was evident (11.8+/-1.9 h) and subjects' acrophases remained delayed 2 days after return to daytime working (12.4+/-1.8 h). Integrated postprandial glucose, insulin and TAG responses were significantly elevated during the night shift compared with normal daytime working. Two days after their return to daytime working, subjects' postprandial glucose and insulin responses had returned to pre-shift levels; however, integrated TAG levels remained significantly elevated. These results are very similar to those previously found in simulated night-shift conditions; it is the first time such changes have been reported in real shift workers in field conditions. They provide evidence that the abnormal metabolic responses to meals taken at night during unadapted night shifts are due, at least in part, to a relative insulin resistance, which could contribute to the documented cardiovascular morbidity associated with shift work. When applied to the 20% of the UK workforce currently employed on shift work, these findings have major significance from an occupational health perspective.

Health in a 24-h society.

With increasing economic and social demands, we are rapidly evolving into a 24-h society. In any urban economy, about 20% of the population are required to work outside the regular 0800-1700 h working day and this figure is likely to increase. Although the increase in shiftwork has led to greater flexibility in work schedules, the ability to provide goods and services throughout the day and night, and possibly greater employment opportunities, the negative effects of shiftwork and chronic sleep loss on health and productivity are now being appreciated. For example, sleepiness surpasses alcohol and drugs as the greatest identifiable and preventable cause of accidents in all modes of transport. Industrial accidents associated with night work are common, perhaps the most famous being Chernobyl, Three Mile Island, and Bhopal.

An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans.

1. Non-image forming, irradiance-dependent responses mediated by the human eye include synchronisation of the circadian axis and suppression of pineal melatonin production. The retinal photopigment(s) transducing these light responses in humans have not been characterised. 2. Using the ability of light to suppress nocturnal melatonin production, we aimed to investigate its spectral sensitivity and produce an action spectrum. Melatonin suppression was quantified in 22 volunteers in 215 light exposure trials using monochromatic light (30 min pulse administered at circadian time (CT) 16-18) of different wavelengths (lambda(max) 424, 456, 472, 496, 520 and 548 nm) and irradiances (0.7-65.0 microW cm(-2)). 3. At each wavelength, suppression of plasma melatonin increased with increasing irradiance. Irradiance-response curves (IRCs) were fitted and the generated half-maximal responses (IR(50)) were corrected for lens filtering and used to construct an action spectrum. 4. The resulting action spectrum showed unique short-wavelength sensitivity very different from the classical scotopic and photopic visual systems. The lack of fit (r(2) < 0.1) of our action spectrum with the published rod and cone absorption spectra precluded these photoreceptors from having a major role. Cryptochromes 1 and 2 also had a poor fit to the data. Fitting a series of Dartnall nomograms generated for rhodopsin-based photopigments over the lambda(max) range 420-480 nm showed that rhodopsin templates between lambda(max) 457 and 462 nm fitted the data well (r(2) > or =0.73). Of these, the best fit was to the rhodopsin template with lambda(max) 459 nm (r(2) = 0.74). 5. Our data strongly support a primary role for a novel short-wavelength photopigment in light-induced melatonin suppression and provide the first direct evidence of a non-rod, non-cone photoreceptive system in humans.