Endogenous rhythms in the succession of Sleep-wake stages inMicrocebus murinus

Sleep-wake stages were studied by means of EEG recordings in three female Microcebusmaintained under dim red light for 2 to 12 months and in a female maintained in constant bright light first for 1 month, then for 4 months. A circadian rhythm was apparent in all cases. In addition, the reduction of the alert-wake state in winter and its large increase in summer hints at a circannual rhythm.     

Taxonomic Revision of Mouse Lemurs (Microcebus) in the Western Portions of Madagascar

The genus Microcebus (mouse lemurs) are the smallest extant primates. Until recently, they were considered to comprise two different species: Microcebus murinus, confined largely to dry forests on the western portion of Madagascar, and M. rufus, occurring in humid forest formations of eastern Madagascar. Specimens and recent field observations document rufous individuals in the west. However, the current taxonomy is entangled due to a lack of comparative material to quantify intrapopulation and intraspecific morphological variation. On the basis of recently collected specimens of Microcebus from 12 localities in portions of western Madagascar, from Ankarana in the north to Beza Mahafaly in the south, we present a revision using external, cranial, and dental characters. We recognize seven species of Microcebus from western Madagascar. We name and describe 3 spp., resurrect a previously synonymized species, and amend diagnoses for Microcebus murinus (J. F. Miller, 1777), M. myoxinus Peters, 1852, and M. ravelobensis Zimmermann et al., 1998.     

Explaining geographical variation in the isotope composition of mouse lemurs (Microcebus)

Aim We sought to quantify geographical variation in the stable isotope values of mouse lemurs (Microcebus) and to determine whether this variation reflects trophic differences among populations or baseline isotopic differences among habitats. If the latter pattern is demonstrated, then Microcebus can become a proxy for tracking baseline habitat isotopic variability. Establishing such a baseline is crucial for identifying niche partitioning in modern and ancient communities. Location We studied five species of Microcebus from eight distinct habitats across Madagascar. Methods We compared isotopic variation in C₃ plants and Microcebus fur within and among localities. We predicted that carbon and nitrogen isotope values of Microcebus should: (1) vary as a function of abiotic variables such as rainfall and temperature, and (2) covary with isotopic values in plants. We checked for trophic differences among Microcebus populations by comparing the average difference between mouse lemur and plant isotope values for each locality. We then used multiple regression models to explain spatial isotope variation in mouse lemurs, testing a suite of explanatory abiotic variables. Results We found substantial isotopic variation geographically. Ranges for mean isotope values were similar for both Microcebus and plants across localities (carbon 3.5–4.0‰; nitrogen 10.5–11.0‰). Mean mouse lemur and plant isotope values were lowest in cool, moist localities and highest in hot, dry localities. Rainfall explained 58% of the variation in Microcebus carbon isotope values, and mean plant nitrogen isotope values explained 99.7% of the variation in Microcebus nitrogen isotope values. Average differences between mouse lemur and plant isotope values (carbon 5.0‰; nitrogen 5.9‰) were similar across localities. Main conclusions Isotopic data suggest that trophic differences among Microcebus populations were small. Carbon isotope values in mouse lemurs were negatively correlated with rainfall. Nitrogen isotope values in Microcebus and plants covaried. Such findings suggest that nitrogen isotope values for Microcebus are a particularly good proxy for tracking baseline isotopic differences among habitats. Our results will facilitate future comparative research on modern mouse lemur communities, and ecological interpretations of extinct Holocene communities.     

Disorders of Orcadian Body Temperature Rhythm in Severely Brain-Damaged Patients

Twenty-four hour patterns of body temperature (BT) were recorded during consecutive 3-10 day spans from 14 severely brain-damaged patients. Seven patients exhibited a normal circadian BT rhythm with an amplitude of more than 1°C and a normal phase position of the minimum BT being observed during the latter half of the nocturnal sleep. One patient with a dispersed type of sleep exhibited an extremely low amplitude of the BT rhythm with mean average 0.69°C. In this patient, an 24-hr observation span was insufficient to detect the existence of a BT rhythm. Two patients manifested disturbance of period. As acrophase of the BT rhythm varied from day to day, the standard deviation (S.D.) of mean acrophase wasextremely large. For these patients the light-dark cycle did not act as an entrainer because both had visual disturbance. A phase advance of the minimum BT was observed in four patients. The minimum BT appeared in the first half of nocturnal sleep. These three disturbances (amplitude, period and phase), were revealed only by longitudinal observation of the BT rhythm, indicating the importance of long-term observations over a sufficient period to make the nature of the rhythm disturbances clear. These disturbances were not related to that of the sleep-wake cycle, as two patients showed normal circadian BT rhythm in spite of their dispersed-type sleep.     

Midpoint of sleep on school days is associated with depression among adolescents

Depression is a serious and prevalent disease among adolescents. Identifying possible factors involved with its genesis and presentation is an important task for researchers and clinical practitioners. The individual’s chronotype and social jetlag have been associated with depression in different populations. However, information on this is lacking among adolescents. The objective of this cross-sectional study was to examine the relationship between chronotype (midpoint of sleep) and social jetlag with the presence of depression symptoms in young students. We assessed 351 students aged 12–21?years old. They answered a questionnaire on demographic characteristics, the Munich Chronotype Questionnaire (MCTQ) and the Beck Depression Inventory (BDI). Demographic characteristics (age, sex and classes’ schedule) and circadian rhythmic variables for school and free days (sunlight exposure, sleep duration, midpoint of sleep and social jetlag) were taken as factors and the presence of at least mild depression symptoms as outcome. In univariate analysis, girls (χ²?=?5.01, p?≤?0.05) and evening students (χ²?=?6.63, p?≤?0.05) were more frequently present among the depressed. Also, the depression group was significantly delayed for both midpoints of sleep during school (t?=?2.84, p?≤?0.01) and free days (t?=?2.20, p?≤?0.05). The two groups did not differ in relation to their social jetlag hours (t?=??0.68, p?=?0.501) neither subjects with two or more hours of social jetlag were more frequent among the depressed (χ²?=?1.00, p?=?0.317). In multivariate analysis, the model that best explained our outcome (R²?=?0.058, F?=?2.318, p?≤?0.05) included sex (β?=??0.12, p?≤?0.05) and the midpoint of sleep on school days (β?=??0.21, p?≤?0.001) as significant predictor variables. A sleep phase delay (later midpoints of sleep for school and free days) was associated with higher levels of depression. However, we were not able to detect similar relationship with the social jetlag hours. This could be attributed to the fact that our sample showed a smaller amount of social jetlag, possibly because even during free days a social routine, this time parents’ rules, limited the observation from what could be a natural tendency to sleep later and over. Yet, even when considering the group with more social jetlag, we did not find an association. Perhaps, this variable will only manifest its effect if it is maintained for longer periods throughout life. Additionally, when considering all the variables together, the midpoint of sleep on school days was pointed as the predictor of greatest weight for depression, together with the factor sex. Young girls, possibly earlier types, who are required to study in the evening have more chances of presenting depression symptoms. This study explicit some peculiar characteristics of the assessment of chronobiological variables in the young, such as the presence of an imposed social routine also during free days. Therefore, the expression of chronotype under the influence of the weekly social schedule (midpoint of sleep on school days) could be a more useful marker to measure the stress produced from the mismatch between external and inner rhythms rather than social jetlag. This also reinforces the importance of reconsidering the weekly routine imposed on young people.     

Synergy between the light-induced acute response and the circadian cycle: a new mechanism for the synchronization of the Phaseolus vulgaris clock to light

PvLHY and Lhcb expression has been studied in primary bean leaves after exposure of etiolated leaves to two or three white light-pulses and under different photoperiods. Under the tested photoperiods, the steady-state mRNA levels exhibit diurnal oscillations with zenith in the morning between ZT21 and 4 for PvLHY and between ZT4 and 6 for Lhcb. Nadir is in the evening between ZT12 and 18 for PvLHY and ZT18 and 24 for Lhcb. Light-pulses to etiolated seedlings induce a differentiated acute response that is reciprocally correlated with the amplitude of the following circadian cycle. In addition, the clock modulates the duration of the acute response (descending part of the curve included), which according to the phase of the rhythm at light application extends from 7 to 18 h. This constitutes the response dynamics of the Phaseolus clock to light. Similarly, the waveform of PvLHY and Lhcb expression during the day of different photoperiods resembles in induction capability (accomplishment of peak after lights-on) and duration (from lights-on phase to trough) the phase-dependent progression of acute response in etiolated seedlings. Consequently, the peak of Lhcb (all tested photoperiods) and PvLHY (in LD 18:6) attained in the photophase corresponds to the acute response peak, while the peak of PvLHY during the scotophase (in LD 12:12 and 6:18) corresponds to the circadian peak. Thus, the effect of the response dynamics in the photoperiod determines the coincidence of the peak with the photo- or scotophase, respectively. This represents a new model mechanism for the adaptation of the Phaseolus clock to light.     

PHOTIC ENTRAINMENT OF CIRCADIAN ACTIVITY PATTERNS IN THE TROPICAL LABRID FISH HALICHOERES CHRYSUS

Yellow wrasses (Halichoeres chrysus) show clear daily activity patterns. The fish hide in the substrate at (subjective) night, during the distinct rest phase. Initial entrainment in a 12h:12h light-dark (12:12 LD) cycle (mean period 24.02h, SD 0.27h, n = 16 was followed by a free run (mean period 24.42h, SD 1.33h) after transition into constant dim light conditions. Light pulses of a comparable intensity as used in the light part of the LD cycles did not result in significant phase shifts of the free-running rhythm in constant darkness. Application of much brighter 3h light pulses resulted in a phase-response curve (PRC) for a fish species, with pronounced phase advances during late subjective night. The PRCs differed from those mainly obtained in other vertebrate taxa by the absence of significant phase delays in the early subjective night. At that circadian phase, significant tonic effects of the light pulses caused a shortening of the circadian period length. Entrainment to skeleton photoperiods of 1:11 LD was observed in five of six wrasses exposed, also after a 3h phase advance of this LD cycle. Subsequently, a 1:11.25 LD cycle resulted in entrainment in four of the six fish. It is suggested that the expression of the circadian system in fish can be interpreted as a functional response to a weak natural zeitgeber, as present in the marine environment. This response allows photic entrainment as described here in the yellow wrasse. (Chronobiology International, 17(5), 613–622, 2000)     

Molecular Evidence of Reproductive Isolation in Sympatric Sibling Species of Mouse Lemurs

Recent morphological and molecular phylogenetic studies of mouse lemurs (Microcebus) living in the western and southern regions of Madagascar have shown that specific diversity had been considerably underestimated. In large part, this underestimate was due to the lack of sufficient specimens from given localities to assess properly the level of phenotypic variation within and between populations. The accurate delineation of specific boundaries has no doubt been confounded by the diminutive size, nocturnal habits, and subtle morphological variation characteristic of mouse lemurs, which can make field identification of individuals problematic. We illustrate the use of molecular phylogenetic analysis to reveal reproductive isolation in two sympatric mouse lemur species, Microcebus murinus and M. griseorufus. Their documentation in the Berenty Private Reserve in the extreme south of Madagascar verifies the historically-broad distribution of Microcebus griseorufus, a species recently resurrected from synonomy.     

Seasonal effects on the sleep–wake cycle,the rest–activity rhythm and quality of life for Japanese and Thai older people

Background: The sleep-wake cycle and the rest–activity rhythm are known to change with aging, and such changes have been implicated in higher levels of depression as well as an increased incidence of dementia. However, information supporting seasonal changes in the sleep–wake cycle, the rest–activity rhythm and quality of life in older community-dwelling people remains insufficient. The aim of the present study was to prospectively investigate seasonal effects on the sleep–wake cycle, the rest–activity rhythm and quality of life among older people living in areas of Japan or Thailand with different climate classifications.

Method: The survey was conducted from March 2016 to May 2017, and 109 participants were recruited from Japan and Thailand: 47 older people living in Akita prefecture, Japan, and 62 older people living in Chiang Mai or Nakhon Ratchasima, Thailand. According to the Köppen–Geiger classification of Asian climates comprising tropical, desert, steppe, temperate and subarctic climates, Akita prefecture, which is located in northern Japan, is classified as a humid subarctic climate, while the Thai study areas are classified as tropical savanna. To monitor parameters of the sleep–wake cycle during nighttime (e.g. total sleep time, sleep latency, sleep efficiency, awaking time and frequency of sleep interruptions) and to calculate parameters of the rest–activity rhythm over the 24 h profile (e.g., interdaily stability, intradaily variability, relative amplitude, mean of least active 5 h period and mean of most active 10 h period), all the participants from both countries wore an Actiwatch 2 device on their nondominant wrist continuously for 7 days during each local season. The World Health Organization Quality of Life Questionnaire-BREF (WHOQOL-BREF) was also assessed during each local season.

Results: The final sample size was 37 older people living in Akita prefecture, Japan, and 44 older people living in Thailand; these subjects completed the data collections during each local season. The dropout rates were 21% in Japan and 29% in Thailand. The results for the Japanese subjects showed a significantly shorter sleep time with higher levels of activity during the nighttime on summer (p < 0.001) and a fragmented rest–activity rhythm over the 24 h profile on winter (p < 0.001). The older Thai participants exhibited a poor state of night sleeping year-round, and a significant relationship was observed between seasonal variations in motor activity and the social domain of WHOQOL-BREF for each Thai season (|r| = 0.4, p < 0.01).

Conclusion: These findings provide new and important information regarding seasonal effects on the sleep–wake cycle, the rest–activity rhythm and quality of life in older community-dwelling people living in two different Asian climates. Consequently, clinical preventions targeting such seasonal variations might be useful for improving the quality of life of older Japanese and Thai individuals.     

The influence of the sleep-wake cycle on primary monosymptomatic nocturnal enuresis: a non-randomized comparative study

Backround: Enuresis implies severe stress in affected children, and impairs quality of life and sleep. Children with enuresis experience difficulties in their arousal from sleep, possibly associated with disturbances of the circadian rhythm. In this study, we aimed to evaluate the sleep–wake cycle and sleep disturbances in children with monosymptomatic enuresis nocturna (MEN). Method: The study comprised 70 children with MEN who were admitted to the pediatrics and urology outpatients department and 94 age-matched healthy controls. Parents completed “Strengths and Difficulties Questionnaire,” Children’s Sleep Habits Questionnaire (CSHQ), Children’s Chronotype Questionnaire scale. Results: Children with enuresis had significantly more sleep and psychological problem. Enuresis group reported higher bedtime resistance, parasomnias, breathing-related problems, and daytime sleepiness in CHSQ (p < 0.05). Although circadian preference did not differ statistically between the groups (p > 0.05), sleep duration on school days and awakening and mid-sleep points, both on scheduled and free days, were found to be significantly different in the enuretic group (p < 0.05). In logistic regression analysis, age, sleep period on scheduled days, sleep inertia on scheduled and free days were significant predictor for enuresis. Discussion: Children with enuresis were more likely to experience problematic sleep. This may reflect that enuretic children have impaired sleep–wake cycles, leading to dysregulation of daily functional changes of bladder capacity and related hormones such as ADH. These findings might imply a sleep–wake disturbance in enuresis.     

Fiber type population in limb muscles ofMicrocebus murinus

Populations and distributions of fiber types were studied in 19 limb muscles ofMicrocebus murinus. Proportions and cross-sectional areas of muscles fiber types were compared with data from the literature for other prosimians (Galago, Lemur, andNycticebus), another primate (Macaca cynomolgus), and the rat. Most muscles are heterogenous, with type I fibers (slow oxidative) localized in the deeper part, near the bone. Type IIA fibers (fast oxidative glycolytic) are more evenly distributed than type I and type IIB (fast glycolytic). The combination of large number and large size of type I fibers results in enhanced slow-twitch and oxidative properties as required for antigravity function of postural muscles. Compared with other primates,Microcebus shows relatively small cross-sectional areas of fibers and less numerous type I fibers, in every muscle, which is probably related to small body mass. The fiber type population of the different components of the quadriceps femoris is also related to the particular mode of locomotion of the mouse-lemur: running and leaping, climbing and hopping. M. vastus medialis and m. vastus lateralis are made up only of fast twitch fibers, IIA and IIB. A possible repercussion of hypothyroidism during the rest season and a decrease in locomotor activity was the subject of investigation of the fiber type proportion and section areas. No difference were found between individuals euthanized during the active period and those at rest period. Either a very low level of thyroxine associated with reduced activity is sufficient to maintain the processes controlling myosin expression, or the effects on muscles fibers of natural hypothyroidism and hypokinesia neutralize each other during the rest season.     

PHASE RELATIONSHIP BETWEEN SKIN TEMPERATURE AND SLEEP-WAKE RHYTHMS IN WOMEN WITH VASCULAR DYSREGULATION AND CONTROLS UNDER REAL-LIFE CONDITIONS

The aim of the study was to investigate whether women with primary vascular dysregulation (VD; main symptoms of thermal discomfort with cold extremities) and difficulties initiating sleep (DIS) exhibit a disturbed phase of entrainment (Ψ) under everyday life conditions. The authors predicted a phase delay of the distal-proximal skin temperature gradient and salivary melatonin rhythms with respect to the sleep-wake cycle in women with VD and DIS (WVD) compared to controls (CON), similar to that found in their previous constant-routine laboratory data. A total of 41 young healthy women, 20 with WVD and 21 matched CON without VD and normal sleep onset latency (SOL), were investigated under ambulatory conditions (following their habitual bedtimes) during 7 days of continuous recording of skin temperatures, sleep-wake cycles monitored by actimetry and sleep-wake diaries, and single evening saliva collections for determining the circadian marker of dim light melatonin onset (DLMO). Compared to CON, WVD showed increased distal vasoconstriction at midday and in the evening, as indicated by lower distal (DIST; hands and feet) and foot-calf skin temperatures, and distal-proximal skin temperature gradients (p?<?.05). WVD manifested distal vasoconstriction before lights-off that also lasted longer after lights-off than in CON. In parallel, WVD exhibited a longer SOL (p?<?.05). To define internal phase-relationships, cross-correlation analyses were performed using diurnal rhythms of wrist activity and foot skin temperature. WVD showed a phase delay in foot skin temperature (CON versus WVD: 3.57?±?17.28?min versus 38.50?±?16.65?min; p?<?.05) but not in wrist activity. This finding was validated by additional within-subject cross-correlation analyses using the diurnal wrist activity pattern as reference. DLMO and habitual sleep times did not differ between CON and WVD. The authors conclude that WVD exhibit a phase delay of distal vasodilatation with respect to their habitual sleep-wake cycle and other circadian phase markers, such as DLMO. A full factorial design will have to show whether the finding is specific to primary vascular dysregualtion, to DIS, or to their interaction. (Author correspondence: Kurt.kraeuchi@upkbs.ch)     

A contribution to the explanation of the larch bud moth cycle,the polymorphic fitness hypothesis

Studies of fluctuating insect populations generally discuss the regulating processes at high insect numbers, but very rarely why a cycling population at low densities switches immediately from the declining phase to the increasing phase of the cycle. A long-term study of the larch bud moth (Zeiraphera diniana Gn) has suggested that the key to recovery is assortative mating of specific phenotypes. Z. diniana exhibits distinct host races living either on the deciduous larch or evergreen pines and spruces. As an adaptation to its hosts Z. diniana is necessarily rather polymorphic in its life history parameters, i.e. developmental rate, fertility and survival. Apart from the direct association of the larva with the host tree, the colouration of the mature larva provides the only readily apparent trait by which the host race can be recognised; the larch form is black and the pine or spruce form has a light orange head capsule, anal plate and body colour. Evidence that frequencies of the colour morphs on larch regularly change from an intermediate colour type to black during the increasing phase of the cycle suggests that the combination of traits, such as earliest larval emergence, largest body size and homozygosity, characteristic of the black morph, constitutes the inherent driving force of population increase.     

Temperature-induced phase shifting of circadian rhythms in cotton seedlings as related to variations in chilling resistance

The relationship between the degree of chilling resistance and phase shifting caused by low-temperature pulses was examined in two circadian rhythms in cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 1212 h at 33° C. The seedlings showed a circadian rhythm of chilling resistance and of cotyledon movement. A pulse of 19° C for 12 h during the chilling-sensitive phase (light period) caused a phase delay of 6 h, while a similar temperature pulse during the chilling-resistant phase (dark period) did not cause any phase shift. Exposure to 19° C, 85% RH (relative humidity) for 12 h during the dark period induced chilling resistance in the following otherwise chilling-sensitive light period. In this light period a 12-h 19° C pulse did not cause a phase shift of chilling resistance. Pulses of low temperatures (5–19° C) were more effective in causing phase delays in the rhythm of cotyledon movement when given during the chilling-sensitive phase than when given during the chilling-resistant phase. A 12-h pulse of 5° C, 100% RH during the light period caused a phase delay of cotyledon movement of 12 h. However, when that pulse had been preceded by a chill-acclimating exposure to 19° C, 85% RH for 12 h during the dark period the phase delay was shortened to 6 h. The correlation between higher degree of chilling resistance and the prevention or shortening of the phase delay caused by low temperatures indicates that the mechanism that increases chilling resistance directly or indirectly confers greater ability for prevention of phase shifting by low temperatures in circadian rhythms.Abbreviations CT circadian time - LDC light-dark cycle of 24 h - RH relative humidity     

Sleep Architecture When Sleeping at an Unusual Circadian Time and Associations with Insulin Sensitivity

Circadian misalignment affects total sleep time, but it may also affect sleep architecture. The objectives of this study were to examine intra-individual effects of circadian misalignment on sleep architecture and inter-individual relationships between sleep stages, cortisol levels and insulin sensitivity. Thirteen subjects (7 men, 6 women, age: 24.3±2.5 y; BMI: 23.6±1.7 kg/m²) stayed in a time blinded respiration chamber during three light-entrained circadian cycles (3x21h and 3x27h) resulting in a phase advance and a phase delay. Sleep was polysomnographically recorded. Blood and salivary samples were collected to determine glucose, insulin and cortisol concentrations. Intra-individually, a phase advance decreased rapid eye movement (REM) sleep and slow-wave sleep (SWS), increased time awake, decreased sleep and REM sleep latency compared to the 24h cycle. A phase delay increased REM sleep, decreased stage 2 sleep, increased time awake, decreased sleep and REM sleep latency compared to the 24h cycle. Moreover, circadian misalignment changed REM sleep distribution with a relatively shorter REM sleep during the second part of the night. Inter-individually, REM sleep was inversely associated with cortisol levels and HOMA-IR index. Circadian misalignment, both a phase advance and a phase delay, significantly changed sleep architecture and resulted in a shift in rem sleep. Inter-individually, shorter REM sleep during the second part of the night was associated with dysregulation of the HPA-axis and reduced insulin sensitivity. Trial Registration: International Clinical Trials Registry Platform NTR2926 http://apps.who.int/trialsearch/     

月经周期对女性睡眠-觉醒和静息-活动的影响

目前有关月经周期对睡眠影响的研究结果并不一致,而对月经周期中昼夜睡眠-觉醒及静息-活动节律尚缺乏系统性的研究.本研究旨在观察正常育龄期女性月经周期中睡眠-觉醒及静息-活动昼夜节律的变化.我们采用静息-活动监测仪(actigraphy)和睡眠日志,调查了12个自然生活状态下健康育龄期妇女在月经周期不同阶段,即行经期、围排卵期、黄体早期及黄体晚期中睡眠与活动节律的变化.结果显示,睡眠-觉醒节律参数在四期之间无统计学显著差异;而静息-活动节律方面,所有受试女性静息-活动节律的平均日周期长度为(24.01±0.29)h,并且四期之间无显著性差异.行经期日间稳定系数(interdaily stability,IS)比黄体早期显著增加(P＜0.05).黄体早期日间活动开始时间明显较黄体晚期提前(P＜0.05);黄体早期的活动峰值时相比围排卵期显著提前(P＜0.05).月经周期可以影响静息-活动昼夜节律时相.而总体静息-活动数量与质量未发生显著变化;健康育龄期妇女在月经周期的各阶段中睡眠-觉醒节律亦无明显变异.     

Perturbations of malate accumulation and the endogenous rhythms of gas exchange in the Crassulacean acid metabolism plant<Emphasis Type="Italic"> Kalanchoë daigremontiana</Emphasis>: testing the tonoplast-as-oscillator model

In continuous light, leaves of the Crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perrier exhibit a circadian rhythm of CO₂ uptake, stomatal conductance and leaf-internal CO₂ pressure. According to a current quantitative model of CAM, the pacemaking mechanism involves periodic turgor-related tension and relaxation of the tonoplast, which determines the direction of the net flux of malate between the vacuole and the cytoplasm. Cytoplasmic malate, in turn, through its inhibitory effect on phosphoenolpyruvate carboxylase, controls the rate of CO₂ uptake. According to this mechanism, when the accumulation of malate is disrupted by removing CO₂ from the ambient air, the induction of a phase delay with respect to an unperturbed control plant is expected. First, using the mathematical model, such phase delays were observed in numerical simulations of three scenarios of CO₂ removal: (i) starting at a trough of CO₂ uptake, lasting for about half a cycle (ca. 12 h in vivo); (ii) with the identical starting phase, but lasting for 1.5 cycles (ca. 36 h); and (iii) starting while CO₂ increases, lasting for half a cycle again. Applying the same protocols to leaves of K. daigremontiana in vivo did not induce the predicted phase shifts, i.e. after the end of the CO₂ removal the perturbed rhythm adopted nearly the same phase as that of the control plant. Second, when leaves were exposed to a nitrogen atmosphere for three nights prior to onset of continuous light to prevent malate accumulation, a small, 4-h phase advance was observed instead of a delay, again contrary to the model-based expectations. Hence, vacuolar malic acid accumulation is ruled out as the central pacemaking process. This observation is in line with our earlier suggestion [T.P. Wyka, U. Lüttge (2003) J Exp Bot 54:1471–1479] that in extended continuous light, CO₂ uptake switches gradually from a CAM-like to a C3-like mechanism, with oscillations of the two CO₂ uptake systems being tightly coordinated. It appears that the circadian rhythm of gas exchange in this CAM plant emerges from one or several devices that are capable of generating temporal information in a robust manner, i.e. they are protected from even severe metabolic perturbations.Abbreviations CAM Crassulacean acid metabolism - c_ia Ratio of mesophyll CO₂ concentration to external CO₂ concentration - J_C Rate of carbon dioxide uptake - J_W Transpiration rate - g_W Stomatal conductance - LL Continuous light conditions - PEPC Phosphoenolpyruvate carboxylase - Rubisco d-Ribulose-1,5-bisphosphatecarboxylase/oxygenase - Effective quantum yield of photosystem II     

Genetic and morphological diversity of mouse lemurs (Microcebus spp.) in northern Madagascar: The discovery of a putative new species?

Tropical forests harbor extremely high levels of biological diversity and are quickly disappearing. Despite the increasingly recognized high rate of habitat loss, it is expected that new species will be discovered as more effort is put to document tropical biodiversity. Exploring under‐studied regions is particularly urgent if we consider the rapid changes in habitat due to anthropogenic activities. Madagascar is known for its extraordinary biological diversity and endemicity. It is also threatened by habitat loss and fragmentation. It holds more than 100 endemic primate species (lemurs). Among these, Microcebus (mouse lemurs) is one of the more diverse genera. We sampled mouse lemurs from several sites across northern Madagascar, including forests never sampled before. We obtained morphological data from 99 Microcebus individuals; we extracted DNA from tissue samples of 42 individuals and amplified two mitochondrial loci (cytb and cox2) commonly used for species identification. Our findings update the distribution of three species (Microcebus tavaratra, Microcebus arnholdi, and Microcebus mamiratra), including a major increase in the distribution area of M. arnholdi. We also report the discovery of a new Microcebus lineage genetically related to M. arnholdi. Several complementary approaches suggest that the newly identified Microcebus lineage might correspond to a new putative species, to be confirmed or rejected with additional data. In addition, morphological analyses showed (a) clear phenotypic differences between M. tavaratra and M. arnholdi, but no clear differences between the new Microcebus lineage and the sister species M. arnholdi; and (b) a significant correlation between climatic variables and morphology, suggesting a possible relationship between species identity, morphology, and environment. By integrating morphological, climatic, genetic, and spatial data of two northern Microcebus species, we show that the spatial distribution of forest‐dwelling species may be used as a proxy to reconstruct the past spatial changes in forest cover and vegetation type.     

Melatonin accelerates reentrainment of the circadian rhythm of its own production after an 8-h advance of the light-dark cycle

Summary The rhythm in melatonin production in the rat is driven by a circadian rhythm in the pineal N-acetyltransferase (NAT) activity. Rats adapted to an artificial lighting regime of 12 h of light and 12 h of darkness per day were exposed to an 8-h advance of the light-dark regime accomplished by the shortening of one dark period; the effect of melatonin, triazolam and fluoxetine, together with 5-hydroxytryptophan, on the reentrainment of the NAT rhythm was studied.In control rats, the NAT rhythm was abolished during the first 3 cycles following the advance shift. It reappeared during the 4th cycle; however, the phase relationship between the evening rise in activity and the morning decline was still compressed.Melatonin accelerated the NAT rhythm reentrainment. In rats treated chronically with melatonin at the new dark onset, the rhythm had already reappeared during the 3rd cycle, in the middle of the advanced night, and during the 4th cycle, the phase relationship between the evening onset and the morning decline of the NAT activity was the same as before the advance shift. In rats treated chronically with melatonin at the old dark onset or in those treated with melatonin 8 h, 5 h and 2 h after the new dark onset during the 1st, 2nd and 3rd cycle, respectively, following the advance shift, the NAT rhythm reappeared during the 3rd cycle as well but in the last third of the advanced night only.Neither triazolam nor fluoxetine together with 5-hydroxytryptophan administered around the new dark onset facilitated NAT rhythm reentrainment after the 8-h advance of the light-dark cycle.Abbreviations NAT N-acetyltransferase - LD cycle light-dark cycle - CT circadian time - LD xy light dark cycle comprising x h of light and y h of darkness     

CELL DIVISION IN THE DINOFLAGELLATE GAMBIERDISCUS TOXICUS IS PHASED TO THE DIURNAL CYCLE AND ACCOMPANIED BY ACTIVATION OF THE CELL CYCLE REGULATORY PROTEIN,CDC2 KINASE1

The cell division cycle in several pelagic dinoflagellate species has been shown to be phased with the diurnal cycle, suggesting that their cell cycle may be regulated by a circadian clock. In this study, we examined the cell cycle of an epibenthic dinoflagellate, Gambierdiscus toxicus Adachi and Fukuyo (Dinophyceae), and found that cell division was similarly phased to the diurnal cycle. Cell division occurred during a 3-h window beginning 6 h after the onset of the dark phase. Cell cycle progression in higher eukaryotes is regulated by a cell cycle regulatory protein complex consisting of cyclin and the cyclin-dependent kinase CDC2. In this report, we identified a CDC2-like kinase in G. toxicus that displays activity in vitro against a known substrate of CDC2 kinase, histone H1. As in higher eukaryotes, CDC2 kinase was expressed constitutively in G. toxicus throughout the cell cycle, but it was activated only late in the dark phase, concurrent with the presence of mitotic cells. These results indicate that cell division in G. toxicus is regulated by molecular controls similar to those found in higher eukaryotes.