Morningness propensity in young adults born prematurely: the Helsinki study of very low birth weight adults

The authors explored morningness-eveningness propensity in adults born prematurely at very low birth weight (VLBW; 相似文献   

Season of Birth and Morningness: Comparison Between the Northern and Southern Hemispheres

The present study explored the possible role of the photoperiod at birth on morningness by collecting data in the northern (Italy) and southern (Australia) hemispheres. To assess circadian typology, the Composite Scale of Morningness (CS) was administered to a sample of 1734 university students (977 Italian and 757 Australian; 1099 females and 635 males; age 24.79?±?7.45 yrs [mean?±?SD]). Consistent with the literature, females reported higher CS scores (morningness) than males, and Australian participants reported higher CS scores than Italian participants. Allowing for the fact the seasons are reversed between the hemispheres, the results are in line with previous studies. The authors found more evening types were born during the seasons associated with longer photoperiod (spring and summer), and more morning types were born during the seasons associated with shorter photoperiod (autumn and winter), indirectly supporting an imprinting-like phenomenon played by the photoperiod at birth. (Author correspondence: vincenzo.natale@.unibo.it)     

Effect of Birth Season on Circadian Typology Appearing in Japanese Young Children Aged 2 to 12 Years Disappears in Older Students Aged 18 to 25 Years

Several studies suggest that season of birth differentially affects the physiological characteristics of humans. Those living at relatively high latitude, such as Canada, Spain, and Italy (44°N–45°N), and born in the fall tended to be “morning-type” persons in comparison to those born in other seasons. There are relatively little data on the affect of season of birth on people residing at low latitude. Here the authors show that at low latitude, Kochi, Japan (33°N), the effect of season of birth on the morningness chronotype is confined to young children aged 1–12 yrs, disappearing in elderly persons. Only female participants aged 2–12 yrs born in the fall, especially in November, were significantly morning-typed (p < .001) in comparison to those born in the other seasons, whereas there were no such significant season-of-birth differences in morningness-eveningness preference among male participants. Moreover, both female and male participants aged 13–25 yrs showed no significant seasonal differences in morningness-eveningness preference. The small effects detected in this study might be due to smaller seasonal change in day length at the relatively lower latitude of Kochi. (Author correspondence: haratets@kochi-u.ac.jp)     

Resting energy expenditure in young adults born preterm--the Helsinki study of very low birth weight adults

Background

Adults born preterm with very low birth weight (VLBW; <1500g) have higher levels of cardiovascular and metabolic risk factors than their counterparts born at term. Resting energy expenditure (REE) could be one factor contributing to, or protecting from, these risks. We studied the effects of premature birth with VLBW on REE.

Methodology/Principal Findings

We used indirect calorimetry to measure REE and dual x-ray absorptiometry (DXA) to measure lean body mass (LBM) in 116 VLBW and in 118 term-born control individuals (mean age: 22.5 years, SD 2.2) participating in a cohort study. Compared with controls VLBW adults had 6.3% lower REE (95% CI 3.2, 9.3) adjusted for age and sex, but 6.1% higher REE/LBM ratio (95% CI 3.4, 8.6). These differences remained similar when further adjusted for parental education, daily smoking, body fat percentage and self-reported leisure time exercise intensity, duration and frequency.

Conclusions/Significance

Adults born prematurely with very low birth weight have higher resting energy expenditure per unit lean body mass than their peers born at term. This is not explained by differences in childhood socio-economic status, current fat percentage, smoking or leisure time physical activity. Presence of metabolically more active tissue could protect people with very low birth weight from obesity and subsequent risk of chronic disease.     

Morningness/Eveningness and Satisfaction With Life in a Polish Sample

Previous studies have provided evidence that eveningness could be related to disadvantageous individual characteristics. The hypothesis that more evening-oriented individuals exhibit lower satisfaction with life has been tested by Randler using a sample of 164 German university students, and this showed that eveningness is associated with lower satisfaction with life (r?=?.177). The aim of the present study was to answer the question of whether or not this relationship is culturally independent, and would exist if a sample from another geographical location and culture had been studied. A sample of 349 residents (149 men) aged between 13 and 59 yrs from two Polish cities completed the Morningness-Eveningness Questionnaire and the Satisfaction with Life Scale. Analysis revealed that morningness was related to greater life satisfaction (r?=?.105), regardless of age and sex. The magnitude of this relationship did not differ significantly between the Polish and the German sample, which suggests that the magnitude and direction of association between morningness/eveningness and satisfaction with life could be independent of culture or geographical location. (Author correspondence: E-mail: konrad.jankowski@psych.uw.edu.pl)     

Further Evidence for the Influence of Photoperiod at Birth on Chronotype in a Sample of German Adolescents

Individuals differ in their circadian preferences (chronotype). There is evidence in the literature to support a season-of-birth effect on chronotype but the evidence is not convincing. In part, the relationship is obscured by a number of methodological differences between studies, including the measures used to define morningness, the way in which the seasons were categorized, and the sample size. This study adds to the literature in several ways. First, we adopt a new approach to categorizing the photoperiod rather than the calendar season; thus we prefer to use the term photoperiod at birth. Second, we used two measures of morningness. Third, we used a large and homogeneous German sample. The results show that adolescents (n?=?2905) born during the increasing photoperiod (Feb–Apr) had a significantly later midpoint of sleep (MSFsc) than those born during the decreasing photoperiod (Aug–Oct). A similar pattern was found for the Composite Scale of Morningness (CSM). Furthermore, both measures of chronotype demonstrated a significant quadratic function over a 1-yr cycle. When looking at each of six consecutive years separately, the Composite Scale of Morningness suggests a cosine rhythm linked to increasing and decreasing photoperiods that becomes weaker in amplitude with increasing age. Despite the strengths in our study, the effect of photoperiod at birth on chronotype remains small. Future studies may require larger sample sizes, may need to explore how neonatal light exposure modulates chronotype, and may need to track how puberty and adolescent lifestyle habits mask the photoperiod effect. (Author correspondence: vollmer@ph-heidelberg.de)     

Lower conditioning leisure-time physical activity in young adults born preterm at very low birth weight

Background

Adults born preterm at very low birth weight (VLBW, <1500 g) have elevated levels of risk factors for cardiovascular diseases and type 2 diabetes. Preliminary observations suggest that this could partly be explained by lower rates of physical activity. The aim of this study was to assess physical activity in healthy young adults born preterm at very low birth weight compared with term-born controls.

Methodology/Principal Findings

We studied 94 unimpaired young adults, aged 21–29 years, born at VLBW and 101 age-, sex-, and birth hospital-matched term-born controls from one regional center in Southern Finland. The participants completed a validated 30-item 12-month physical activity questionnaire and the NEO-Personality Inventory based on the Big Five taxonomy, the most commonly used classification of personality traits. Yearly frequency, total time, total volume and energy expenditure of conditioning and non-conditioning leisure-time physical activity (LTPA) and commuting physical activity were compared between VLBW and term-born subjects. A subset of participants underwent dual-energy x-ray absorptiometry for body composition measurement. Data were analyzed by multiple linear regression. Compared with controls, VLBW participants had lower frequency [−38.5% (95% CI; −58.9, −7.7)], total time [−47.4% (95% CI; −71.2, −4.1)], total volume [−44.3% (95% CI; −65.8, −9.2)] and energy expenditure [−55.9% (95% CI; −78.6, −9.4)] of conditioning LTPA when adjusted for age, sex, body mass index, smoking, parental education and personality traits. Adjusting for lean body mass instead of body mass index attenuated the difference. There were no differences in non-conditioning LTPA or commuting physical activity.

Conclusions/Significance

Compared with term-born controls, unimpaired VLBW adults undertake less frequent LTPA with lower total time and volume of exercise resulting in lower energy expenditure. Differences in personality that exist between the VLBW and term-born groups do not seem to explain this association.     

Premature birth and circadian preference in young adulthood: evidence from two birth cohorts

A preference for eveningness (being a “night owl”) and preterm birth (<37 weeks of gestation) are associated with similar adversities, such as elevated blood pressure, impaired glucose regulation, poorer physical fitness, and lower mood. Yet, it remains unclear if and how preterm birth is associated with circadian preference. The aim of this study was to assess this association across the whole gestation range, using both objective and subjective measurements of circadian preference.

Circadian preference was measured among 594 young adults (mean age 24.3 years, SD 1.3) from two cohorts: the ESTER study and the Arvo Ylppö Longitudinal Study. We compared 83 participants born early preterm (<34 weeks) and 165 late preterm (34 to <37 weeks) with those born at term (≥37 weeks, n = 346). We also compared very low birth weight (VLBW, <1500 g) participants with term-born controls. We obtained objective sleep data with actigraphs that were worn for a mean period of 6.8 (SD 1.4) nights. Our primary outcome was sleep midpoint during weekdays and weekend. The sleep midpoint is the half-way time between falling asleep and waking up, and it represents sleep timing. We also investigated subjective chronotype with the Morningness–Eveningness Questionnaire (MEQ) in 688 (n = 138/221/329) ESTER participants. The MEQ consists of 19 questions, which estimates the respondent to be of a “morning”, “evening,” or “intermediate” chronotype, based on the Morningness–Eveningness Score (MES). We analyzed the data from the actigraphs and the MES with three linear regression models, and analyzed distribution of the chronotype class with Pearson χ2.

There were no consistent differences across the study groups in sleep midpoint. As compared with those born at term, the mean differences in minutes:seconds and 95% confidence intervals for the sleep midpoint were: early preterm weekdays 11:47 (?8:34 to 32:08), early preterm weekend 4:14 (?19:45 to 28:13), late preterm weekdays ?10:28 (?26:16 to 5:21), and late preterm weekend ?1:29 (?20:36 to 17:37). There was no difference in sleep timing between VLBW-participants and controls either. The distribution of chronotype in the MEQ among all participants was 12.4% morningness, 65.4% intermediate, and 22.2% eveningness. The distribution of the subjective chronotype class did not differ between the three gestational age groups (p = 0.98). The linear regression models did not show any influence of gestational age group or VLBW status on the MES (all p > 0.5).

We found no consistent differences between adults born early or late preterm and those born at term in circadian preference. The earlier circadian preference previously observed in those born smallest is unlikely to extend across the whole range of preterm birth.     

Chronotype in very low birth weight adults – a sibling study

ABSTRACT

Chronotype is the temporal preference for activity and sleep during the 24 h day and is linked to mental and physical health, quality of life, and mortality. Later chronotypes, so-called “night owls”, consistently display poorer health outcomes than “larks”. Previous studies have suggested that preterm birth (<37 weeks of gestation) is associated with an earlier chronotype in children, adolescents, and young adults, but studies beyond this age are absent. Our aim was to determine if adults born preterm at very low birth weight (VLBW, ≤1500 g) display different chronotypes than their siblings. We studied VLBW adults, aged 29.9 years (SD 2.8), matched with same-sex term-born siblings as controls. A total of 123 participants, consisting of 53 sibling pairs and 17 unmatched participants, provided actigraphy-derived data on the timing, duration, and quality of sleep from 1640 nights (mean 13.3 per participant, SD 2.7). Mixed effects models provided estimates and significance tests. Compared to their siblings, VLBW adults displayed 27 min earlier sleep midpoint during free days (95% CI: 3 to 51 min, p =.029). This was also reflected in the timing of falling asleep, waking up, and sleep-debt corrected sleep midpoint. The findings were emphasized in VLBW participants born small for gestational age. VLBW adults displayed an earlier chronotype than their siblings still at age 30, which suggests that the earlier chronotype is an enduring individual trait not explained by shared family factors. This preference could provide protection from risks associated with preterm birth.     

Decreased Bone Mineral Density in Adults Born with Very Low Birth Weight: A Cohort Study

Background

Very-low-birth-weight (VLBW, <1,500 g) infants have compromised bone mass accrual during childhood, but it is unclear whether this results in subnormal peak bone mass and increased risk of impaired skeletal health in adulthood. We hypothesized that VLBW is associated with reduced bone mineral density (BMD) in adulthood.

Methods and Findings

The Helsinki Study of Very Low Birth Weight Adults is a multidisciplinary cohort study representative of all VLBW births within the larger Helsinki area from 1978 to 1985. This study evaluated skeletal health in 144 such participants (all born preterm, mean gestational age 29.3 wk, birth weight 1,127 g, birth weight Z score 1.3), and in 139 comparison participants born at term, matched for sex, age, and birth hospital. BMD was measured by dual energy X-ray absorptiometry at age 18.5 to 27.1 y. Adults born with VLBW had, in comparison to participants born at term, a 0.51-unit (95% confidence interval [CI] 0.28–0.75) lower lumbar spine Z score and a 0.56-unit (95% CI 0.34–0.78) lower femoral neck Z score for areal BMD. These differences remained statistically significant after adjustment for the VLBW adults'' shorter height and lower self-reported exercise intensity.

Conclusions

Young adults born with VLBW, when studied close to the age of peak bone mass, have significantly lower BMD than do their term-born peers. This suggests that compromised childhood bone mass accrual in preterm VLBW children translates into increased risk for osteoporosis in adulthood, warranting vigilance in osteoporosis prevention. Please see later in the article for the Editors'' Summary     

Season of Birth and Sleep-Timing Preferences in Adolescents

The aim of the present study was to explore the relationship between season of birth and sleep-timing preferences in adolescence. To this end, the Morningness-Eveningness Questionnaire for Children and Adolescents (MEQ-CA) was administered to 1912 adolescents (1058 females and 854 males), ranging in age between 10 and 17 yrs. To assess preferred sleep habits, the authors considered the answers to the open-ended questions of the MEQ-CA (items 1 and 2), regarding the preferred arising time and the preferred going to bed time. Combining the answers to these two questions, the authors also indirectly computed the preferred sleep duration and preferred midpoint of sleep. Season of birth did not significantly modulate the overall MEQ-CA score; however, spring-born participants preferred to go to bed and reached the preferred midpoint of sleep later than those born in autumn. Agreeing with a previous study on young adults, the present data point to a significant season-of-birth effect on the two parameters of the sleep-timing preferences in adolescents. (Author correspondence: lorenzo.tonetti2@unibo.it)     

Infant Growth after Preterm Birth and Mental Health in Young Adulthood

Objectives

Faster growth after preterm birth benefits long-term cognitive functioning. Whether these benefits extend to mental health remains largely unknown. We examined if faster growth in infancy is associated with better self-reported mental health in young adults born preterm at very low birth weight (VLBW) (<1500g).

Study Design

As young adults, participants of the Helsinki Study of Very Low Birth Weight Adults self-reported symptoms of depression and attention deficit/hyperactivity disorder (ADHD) (n = 157) and other psychiatric problems (n = 104). As main predictors of mental health outcomes in linear regression models, we used infant weight, length, and head circumference at birth, term, and 12 months of corrected age, and growth between these time points. Growth data were collected from records and measures at term and at 12 months of corrected age were interpolated. Additionally, we examined the moderating effects of intrauterine growth restriction.

Results

Size at birth, term, or 12 months of corrected age, or growth between these time points were not associated with mental health outcomes (p-values >0.05). Intrauterine growth restriction did not systematically moderate any associations.

Conclusions

Despite the high variability in early growth of VLBW infants, the previously described association between slow growth in infancy and poorer cognitive functioning in later life is not reflected in symptoms of depression, ADHD, and other psychiatric problems. This suggests that the development of cognitive and psychiatric problems may have dissimilar critical periods in VLBW infants.     

Impact of Perinatal Photoperiod on the Chronotype of 11- to 18-Year-Olds in Northern European Russia

The study investigates the effect of the month of birth and ambient light conditions at birth on sleep length and chronotype among residents of high latitudes. The authors surveyed 1172 persons (609 girls, 563 boys) age 11 to 18 yrs living in five villages and four towns located between 59.5°N and 67.6°N latitude. Survey participation was voluntary and anonymous. Sleep length and chronotype were assessed using the Munich chronotype questionnaire (MCTQ). The study showed the sleep length and chronotype of the children and adolescents depended on sex, age, type of settlement (town/village), and latitude of residence. Latitude exerted a stronger impact on sleep length and chronotype of children and adolescents living in villages than on those of their urban counterparts. Month of birth had no effect on sleep length and chronotype. There was a significant effect of the time of sunrise, sunset, and day length at birth on the chronotype of children and adolescents. A later chronotype was observed in the sample of young persons living above the Arctic Circle who were born during the polar day and polar night. (Author correspondence: borisenkov@physiol.komisc.ru)     

Morningness: Protective Factor for Sleep-Related and Emotional Problems in Childhood and Adolescence?

The relationship between morningness/eveningness, sleep, and psychological problems is well documented in adults as well as in adolescents. However, research on the circadian orientation and its concomitants in younger children is scarce. The authors investigated the distribution of morningness/eveningness and its connection to sleeping and psychological problems in 91 children and 151 adolescents in Austria. The authors found that morning (M) types had less sleep-related and psychological problems than intermediate (I) and evening (E) types, respectively. Among children, M-types suffered less from daytime sleepiness (females: χ²₍₂₎?=?8.1, p?=?.017; males: χ²₍₂₎?=?14.8, p?=?.001). Among adolescents, M-types showed fewer sleep-wake problems (females: χ²₍₂₎?=?17.5, p?<?.001; males: χ²₍₂₎?=?19.8, p?<?.001), and female M-types showed less externalizing (χ²₍₂₎?=?8.7, p?=?.013) as well as internalizing problem behavior (χ²₍₂₎?=?9.0, p?=?.011). In conclusion, these findings indicate that morningness may act as a protective factor against the development of sleep-related problems in childhood and sleep-related and psychological problems in adolescence, especially in females. (Author correspondence: gloriagelbmann@gmx.at)     

Seasonality in the Incidence of Cervical Carcinoma in Teenagers and Young Adults in Northern England, 1968–2005

Infection with human papillomavirus is an established risk factor for cervical carcinoma. However, the role of other environmental factors is less well established. To further investigate whether other agents may be involved, the authors have analyzed seasonal variation in cervical cancer with respect to month of birth and separately month of diagnosis. All 85 cases diagnosed in 15–24-yr-olds during the period 1968–2005 were extracted from the specialist population-based Northern Region Young Persons' Malignant Disease Registry. The chi-square heterogeneity test was used to assess overall nonuniform variation in month of birth and separately month of diagnosis. Poisson regression analysis was used to fit sinusoidal (harmonic) models to the data using month of birth and month of diagnosis in separate models. Based on month of birth, there was statistically significant heterogeneity (p?=?.03) and a significant sinusoidal pattern, with an incidence peak involving births in the autumn months (p?=?.03). Based on month of diagnosis, there was marginally significant heterogeneity (p?=?.06). The evidence of seasonal variation around time of birth for cervical carcinoma is highly novel and suggests possible early etiological involvement of environmental factors. (Author correspondence: Richard.McNally@ncl.ac.uk)     

SEASON OF BIRTH AND SMOKING: FINDINGS FROM THE NORTHERN FINLAND 1966 BIRTH COHORT

A season of birth effect in addictive disorders has scarcely been studied. As smoking is known to be a highly addictive behavior, we examined whether there exists an association between season of birth and smoking habits among the general population in the Northern Finland 1966 Birth Cohort (NFBC, n?=?8,319). The birth month of each cohort member was categorized into one of the four seasons: spring (March–May), summer (June–August), autumn (September–November), or winter (December–February). Smoking habits of the cohort members were assessed by a postal questionnaire at the age of 31 yrs. Those who reported that they regularly smoked 11 or more cigarettes/day were regarded as heavy smokers. The association between season of birth and smoking was assessed with a logistic regression analysis: first, after controlling for early pregnancy-related and perinatal characteristics (Model 1) and second, after controlling for cohort members' hospital-treated psychiatric disorders, suicide attempts, adult educational level, and marital status (Model 2). Compared to males born in winter, the likelihood for heavy daily smoking was significantly increased, up to 1.3-fold, among males born in the autumn in both logistic regression models. However, among females the likelihood for heavy smoking was statistically significantly elevated among those born during any season other than winter. Season of birth may modify the development of dopaminergic or other neurotransmitter systems divergently among males and females. Altered expression of dopaminergic genes due to environmental climatic factors could explain the association between season of birth and heavy smoking. (Author correspondence: kaisa.riala@oulu.fi).     

Pregnancy complications among women born preterm

Background:

Adults who were born with low birth weights are at increased risk of cardiovascular and metabolic conditions, including pregnancy complications. Low birth weight can result from intrauterine growth restriction, preterm birth or both. We examined the relation between preterm birth and pregnancy complications later in life.

Methods:

We conducted a population-based cohort study in the province of Quebec involving 7405 women born preterm (554 < 32 weeks, 6851 at 32–36 weeks) and a matched cohort of 16 714 born at term between 1976 and 1995 who had a live birth or stillbirth between 1987 and 2008. The primary outcome measures were pregnancy complications (gestational diabetes, gestational hypertension, and preeclampsia or eclampsia).

Results:

Overall, 19.9% of women born at less than 32 weeks, 13.2% born at 32–36 weeks and 11.7% born at term had at least 1 pregnancy complication at least once during the study period (p < 0.001). Women born small for gestational age (both term and preterm) had increased odds of having at least 1 pregnancy complication compared with women born at term and at appropriate weight for gestational age. After adjustment for various factors, including birth weight for gestational age, the odds of pregnancy complications associated with preterm birth was elevated by 1.95-fold (95% confidence interval [CI] 1.54–2.47) among women born before 32 weeks’ gestation and 1.14-fold (95% CI 1.03–1.25) among those born at 32–36 weeks’ gestation relative to women born at term.

Interpretation:

Being born preterm, in addition to, and independent of, being small for gestational age, was associated with a significantly increased risk of later having pregnancy complications.Numerous studies examining cohorts born mostly in the first half of the 20th century have emphasized the inverse relation between low birth weight and incidence later in life of cardiovascular and metabolic conditions, such as hypertension and type 2 diabetes.¹ Epidemiologic studies seldom consider the effects of preterm birth and intrauterine growth restriction separately when studying the relation of these factors to low birth weight. Studies have suggested that adolescents and young adults born preterm have higher incidence of risk factors for metabolic (insulin resistance) and cardiovascular (higher blood pressure) dysfunctions.^2–4 With the increased survival of preterm newborns over the past 30 years, a substantially greater proportion of young adults are born before 37 or even 32 weeks’ gestation and thus may represent a growing population at risk for conditions related to metabolic syndrome as they get older.Pregnancy can be considered a stress test for future cardiovascular and metabolic health. Women with a history of gestational diabetes, gestational hypertension or preeclampsia are at increased risk of metabolic syndrome later in life.^5–7 Furthermore, studies have shown that women born with low birth weights are at increased risk of gestational hypertension, preeclampsia and gestational diabetes.^8–10 However, many of these studies either have not taken into account gestational age or have a number of shortcomings, such as small sample, young population (mostly teenagers), degree of prematurity not specified or study population consisting mostly of late preterm births.^6,11,12In the province of Quebec, weight and gestational age have been recorded in a registry for all births since 1976, and data on all hospital-based diagnoses have been collected since 1987. The aim of our study was to examine the relation between preterm birth and later pregnancy complications, independently of intrauterine growth restriction, among women born preterm in Quebec between 1976 and 1995 who delivered at least 1 newborn between 1987 and 2008. We also examined whether this association represents a dose–response relation, namely, whether the more prematurely born a woman is, the greater her risk of gestational diabetes, gestational hypertension, preeclampsia or eclampsia.     

Subjective Sleep Quality Exclusively Mediates the Relationship Between Morningness-Eveningness Preference and Self-Perceived Stress Response

Eveningness preference has been associated with lower sleep quality and higher stress response compared with morningness preference. In the current study, female morning (n?=?27) and evening (n?=?28) types completed the Pittsburgh Sleep Quality Index (PSQI) and were additionally challenged with an arithmetic stress-induction task. Evening types reported lower subjective sleep quality and longer sleep latency than morning types. Furthermore, evening types reported higher self-perceived stress after the task than morning types. Subjective sleep quality fully mediated the relationship between morningness-eveningness preference and stress response. Poor sleep quality may, therefore, contribute to the elevated health risk in evening types. (Author correspondence: karolin.roeser@uni-wuerzburg.de)     

Seasonal Effect on Infants' Sleep Regulation: A Preliminary Study in a Mediterranean Climate

Infants' sleep-wake rhythms are influenced by multiple factors, including developmental and contextual aspects, as well as circadian cycles. Empirical studies that address the seasonal impact on infants' sleep are scarce. The present study examined aspects of sleep schedule and quality, comparing summer and winter months in a Mediterranean climate. This report is based on a convenience sample of 34 healthy 7-mo-olds, an age in which sleep is well consolidated and regulated compared with the first few months of life. Sleep was measured with actigraphy, in the home context. It was found that compared with winter, in the summer months, sleep onset occurred at a later hour, and more motor activity during sleep was detected. Although the overall sleep quality, as defined by sleep efficiency score, was similar in the two seasons, in the summer, more active sleep was observed. The authors discuss the finding in terms of circadian rhythms, developmental characteristics, as well as possible environmental factors and family routines, and call for more studies, in different climates and geographical zones, and in different developmental periods. (Author correspondence: cohen.dini@gmail.com or anats@edu.haifa.ac.il)     

Robustness of Circadian Timing Systems Evolves in the Fruit Fly Drosophila melanogaster as a Correlated Response to Selection for Adult Emergence in a Narrow Window of Time

Robustness is a fundamental property of biological timing systems that is likely to ensure their efficient functioning under a wide range of environmental conditions. Here we report the findings of our study aimed at examining robustness of circadian clocks in fruit fly Drosophila melanogaster populations selected to emerge as adults within a narrow window of time. Previously, we have reported that such flies display enhanced synchrony, accuracy, and precision in their adult emergence and activity/rest rhythms. Since it is expected that accurate and precise circadian clocks may confer enhanced stability in circadian time-keeping, we decided to examine robustness in circadian rhythms of flies from the selected populations by subjecting them to a variety of environmental conditions comprising of a range of photoperiods, light intensities, ambient temperatures, and constant darkness. The results revealed that adult emergence and activity/rest rhythms of flies from the selected stocks were more robust than controls, as they displayed enhanced stability under a wide variety of environmental conditions. These results suggest that selection for adult emergence within a narrow window of time results in the evolution of robustness in circadian timing systems of the fruit fly D. melanogaster. (Author correspondence: vsharma@jncasr.ac.in or vksharmas@gmail.com)