Circadian Rhythm Variation Research Articles

Sex-Related Variation in Circadian Rhythms in the Bumble Bee Bombus terrestris.

Mating success depends on many factors, but first of all, a male and a female need to meet at the same place and time. The circadian clock is an endogenous system regulating activity and sex-related behaviors in animals. We studied bumble bees (Bombus terrestris) in which the influence of circadian rhythms on sexual behavior has been little explored. We characterized circadian rhythms in adult emergence and locomotor activity under different illumination regimes for males and gynes (unmated queens). We developed a method to monitor adult emergence from the pupal cocoon and found no circadian rhythms in this behavior for either males or gynes. These results are not consistent with the hypothesis that the circadian clock regulates emergence from the pupa in this species. Consistent with this premise, we found that both gynes and males do not show circadian rhythms in locomotor activity during the first 3 days after pupal emergence, but shortly after developed robust circadian rhythms that are readily shifted by a phase delay in illumination regime. We conclude that the bumble bees do not need strong rhythms in adult emergence and during early adult life in their protected and regulated nest environment, but do need strong activity rhythms for timing flights and mating-related behaviors. Next, we tested the hypothesis that the locomotor activity of males and gynes have a similar phase, which may improve mating success. We found that both males and gynes have strong endogenous circadian rhythms that are entrained by the illumination regime, but males show rhythms at an earlier age, their rhythms are stronger, and their phase is slightly advanced relative to that of gynes. An earlier phase may be advantageous to males competing to mate a receptive gyne. Our results are consistent with the hypothesis that sex-related variations in circadian rhythms is shaped by sexual selection.

Deciphering a Beetle Clock: Individual and Sex-Dependent Variation in Daily Activity Patterns.

Circadian clocks are inherent to most organisms, including cryptozoic animals that seldom encounter direct light, and regulate their daily activity cycles. A conserved suite of clock genes underpins these rhythms. In this study, we explore the circadian behaviors of the red flour beetle Tribolium castaneum, a significant pest impacting stored grain globally. We report on how daily light and temperature cues synchronize distinct activity patterns in these beetles, characterized by reduced morning activity and increased evening activity, anticipating the respective environmental transitions. Although less robust, rhythmicity in locomotor activity is maintained in constant dark and constant light conditions. Notably, we observed more robust rhythmic behaviors in males than females with individual variation exceeding those previously reported for other insect species. RNA interference targeting the Clock gene weakened locomotor activity rhythms. Our findings demonstrate the existence of a circadian clock and of clock-controlled behaviors in T. castaneum. Furthermore, they highlight substantial individual differences in circadian activity, laying the groundwork for future research on the relevance of individual variation in circadian rhythms in an ecological and evolutionary context.

A Path to Better Sleep and Circadian Health: Optimizing and Personalizing Indoor Lighting

Circadian rhythms play a crucial role in the regulation of sleep, metabolism, and cognitive function. However, they are highly sensitive to disturbances caused by irregular indoor lighting, especially exposure to blue light at night. This review explored the impact of indoor lighting on circadian and sleep health by analyzing trends in light exposure, socioeconomic disparities, and the prioritization of economic efficiency over health in modern lighting design. Significant variations in individual circadian rhythms present a challenge in creating standardized lighting environments. To address this issue, a review suggested the development of personalized lighting systems that use advanced sensors to monitor and respond to the circadian phase of each individual. By dynamically adjusting light intensity, wavelength, and timing, these systems can better align with personal biological clocks, promote optimal sleep and overall health, and advance the concept of truly human-centric lighting environments.

A natural compound melatonin enhances the effects of Nimotuzumab via inhibiting EGFR in glioblastoma

Sleep disorders are prevalent and debilitating symptoms in primary brain tumor patients, notably those receiving radiation therapy. Nevertheless, the relationship between sleep disorders, melatonin - a circadian rhythm regulatory hormone, and gliomas is underexplored. Melatonin exhibits various biological functions, one of them being anti-tumor activity. In the context of gliomas, often overexpressing EGFR, the humanized monoclonal antibody Nimotuzumab targets this marker. Our research discovered that variations in circadian rhythm significantly influence tumor growth in mice through impacting melatonin secretion. Harnessing proteogenomic, we identified that melatonin could inhibit the phosphorylation of EGFR and its downstream effectors, key elements in angiogenesis and tumor progression. Building on structural simulations, we propose that melatonin may amplify Nimotuzumab's anti-glioma efficacy by inhibiting EGFR TK dimerization. This proposition was validated in our in vitro and in vivo studies where melatonin synergistically augmented cytotoxicity and apoptosis in Nimotuzumab-treated glioma cells. Thus, melatonin shows promise as a beneficial addition to Nimotuzumab treatment in glioma patients.

The Circadian Rhythm of the Behavior and Gut Microbiota in Dybowski's Frogs (Rana dybowskii) during the Autumn Migration Period.

Many amphibian behaviors and physiological functions adapt to daily environmental changes through variations in circadian rhythms. However, these adaptations have yet to be reported in Dybowski's frog (Rana dybowskii). We aimed to elucidate the dynamic changes in the behavior and gut microbiota of R. dybowskii within a 24 h cycle during their migration to hibernation sites. Thus, we monitored their behavior at 4 h intervals and collected samples for microbiome analysis. We found that the juvenile frogs arrived at hibernation sites earlier than the adults. Among the adults, the male frogs arrived earlier. The richness and diversity of the gut microbiota in the adult R. dybowskii were lowest at 14:00. At 6:00, the differences between the males and females were most significant. At 18:00, there was an increase in the activity of Bacteroides, Coprobacillus, Ruminococcus, and Dorea in the intestinal tracts of the male frogs, whereas in the intestinal tract of the female frogs, there was an increase in the activity of Pseudoramibacter_Eubacterium, Desulfovibrio, Anaerotruncus, and PW3. This indicated diurnal rhythmic variations in the gut microbiota and significant sex-based differences in the microbial activity at different time points. Our findings contribute to the understanding of the circadian rhythm of R. dybowskii and provide crucial insights into improving breeding strategies.

981-P: Transition from Standard Time to Daylight Saving Time and Vice Versa—Effects on FGM Metrics in Patients with Autoimmune Diabetes

Circadian rhythm variations, including transition from standard time (ST) to daylight saving time (DST), are associated with measurable effects on health. It is not known whether the transition from ST to DST and vice versa could affect glucose control in patients with autoimmune diabetes on intensive insulin treatment. This was a single center observational study. All FGM users sharing their glucose readings on the LibreView platform were evaluated for eligibility. Pittsburgh Sleep Quality Index (PSQI) questionnaire was administered to all patients on the day before and one week after the transition to DST. In addition, FGM metrics from two weeks before and two weeks after DST transition were acquired. Seven months later, the same evaluation was performed for the transition from DST to ST. Thirty-six patients with autoimmune diabetes were included for transition from ST to DST; sixty-five patients for transition from DST to ST. After DST transition, 16 patients reported worsening of PSQI, along with significant increase of GMI, mean glucose and TAR level 1, and reduction of TIR and CV. Conversely, FGM metrics were unchanged in the 20 patients who reported no variation or amelioration of PSQI. On the contrary, after returning to ST, no variation in FGM metrics was recorded neither for the 16 patients who reported worsening of PSQI, nor for the 49 patients with no variation or amelioration of PSQI. Consistently, after transition to DST, at linear regression analyses PSQI variation was found to be significantly related with variation of mean glucose, GMI, TIR, TAR level 2 and TBR level 1. On the other hand, after returning to ST, no relation between variations of PSQI and FGM metrics was detected. These results were confirmed for 22 patients whose data were collected for both transitions. In conclusion, transition from ST to DST, but not vice versa, is associated with glucose control derangement and could require a more intensive diabetes management. Disclosure L.Di gioia: None. S.Di molfetta: Consultant; Roche Diabetes Care, Ascensia Diabetes Care, Lilly Diabetes, Movi SpA. F.Giordano: None. M.Caporusso: None. G.Sorice: None. A.Cignarelli: Speaker's Bureau; Eli Lilly and Company, Novo Nordisk, Sanofi. A.Natalicchio: Other Relationship; AstraZeneca, Novo Nordisk, Sanofi, Boehringer-Ingelheim, Lilly. L.Laviola: Advisory Panel; A. Menarini Diagnostics, Boehringer Ingelheim Inc., Eli Lilly and Company, Novo Nordisk, Roche Diabetes Care, Sanofi, Other Relationship; Medtronic, Speaker's Bureau; Abbott, Terumo Corporation. F.Giorgino: Advisory Panel; Boehringer-Ingelheim, Amarin Corporation, Medtronic, Roche Diabetes Care, Sanofi, Bayer Inc., Novo Nordisk, Consultant; Novo Nordisk, Lilly, Research Support; Lilly, Roche Diabetes Care, AlfaSigma, Speaker's Bureau; Abbott, Boehringer-Ingelheim, Lilly, Sanofi, Medscape.

Impact of circadian rhythm and daytime variation on outcome after heart transplantation.

Recently, the impact of circadian rhythm and daytime variation on surgical outcomes has attracted interest. Although studies for coronary artery and aortic valve surgery report contrary results, effects on heart transplantation have not been studied. Between 2010 and February 2022, 235 patients underwent HTx in our department. The recipients were reviewed and categorized according to the start of the HTx procedure - between 04:00 am and 11:59 am (morning, n=79), 12:00 pm and 07:59 pm (afternoon, n=68) or 08:00 pm and 03:59 am (night, n=88). The incidence of high urgency status was slightly but not significantly increased (p=.08) in the morning (55.7%), compared to the afternoon (41.2%) or night (39.8%). The most important donor and recipient characteristics were comparable among the three groups. The incidence of severe primary graft dysfunction (PGD) requiring extracorporeal life support (morning: 36.7%, afternoon: 27.3%, night: 23.0%, p=.15) was also similarly distributed. In addition, there were no significant differences for kidney failure, infections, and acute graft rejection. However, the incidence of bleeding that required rethoracotomy showed an increased trend in the afternoon (morning: 29.1%, afternoon: 40.9%, night: 23.0%, p=.06). 30-day survival (morning: 88.6%, afternoon: 90.8%, night: 92.0%, p=.82) and 1-year survival (morning: 77.5%, afternoon: 76.0%, night: 84.4%, p=.41) were comparable between all groups. Circadian rhythm and daytime variation did not affect the outcome after HTx. Postoperative adverse events as well as survival were comparable throughout day- and night-time. As the timing of the HTx procedure is rarely possible and depends on the timing of organ recovery, these results are encouraging, as they allow for the continuation of the prevalent practice.

Cortisol: Analytical and clinical determinants.

Cortisol, the main human glucocorticoid, is synthesized from cholesterol in the adrenal cortex and predominantly metabolized by the liver. Interpretation of quantitative results from the analysis of serum, urine and saliva is complicated by variation in circadian rhythm, response to stress as well as the presence of protein-bound and free forms. Interestingly, cortisol is the only hormone routinely measured in serum, urine, and saliva. Preanalytical and analytical challenges arise in each matrix and are further compounded by the use of various stimulation and suppression tests commonly employed in clinical practice. Although not yet included in clinical guidelines, measurement of cortisol in hair may be of interest in specific situations. Immunoassays are the most widely used methods in clinical laboratories to measure cortisol, but they are susceptible to interference from synthetic and endogenous steroids, generally producing a variable overestimation of true cortisol results, especially in urine. Analysis by mass spectrometry provides higher specificity and allows simultaneous measurement of multiple steroids including synthetic steroids, thus reducing diagnostic uncertainty. An integrated review of cortisol in various disease states is also addressed.

Unravelling the Complexity of Irregular Shiftwork, Fatigue and Sleep Health for Commercial Drivers and the Associated Implications for Roadway Safety.

Fatigue can be a significant problem for commercial motor vehicle (CMV) drivers. The lifestyle of a long-haul CMV driver may include long and irregular work hours, inconsistent sleep schedules, poor eating and exercise habits, and mental and physical stress, all contributors to fatigue. Shiftwork is associated with lacking, restricted, and poor-quality sleep and variations in circadian rhythms, all shown to negatively affect driving performance through impaired in judgment and coordination, longer reaction times, and cognitive impairment. Overweight and obesity may be as high as 90% in CMV drivers, and are associated with prevalent comorbidities, including obstructive sleep apnea, hypertension, and cardiovascular and metabolic disorders. As cognitive and motor processing declines with fatigue, driver performance decreases, and the risk of errors, near crashes, and crashes increases. Tools and assessments to determine and quantify the nature, severity, and impact of fatigue and sleep disorders across a variety of environments and populations have been developed and should be critically examined before being employed with CMV drivers. Strategies to mitigate fatigue in CMV operations include addressing the numerous personal, health, and work factors contributing to fatigue and sleepiness. Further research is needed across these areas to better understand implications for roadway safety.

Interaction between photoperiod and variation in circadian rhythms in tomato

BackgroundMany biological processes follow circadian rhythmicity and are controlled by the circadian clock. Predictable environmental changes such as seasonal variation in photoperiod can modulate circadian rhythms, allowing organisms to adjust the timing of their biological processes to the time of the year. In some crops such as rice, barley or soybean, mutations in circadian clock genes have altered photoperiod sensitivity, enhancing their cultivability in specific seasons and latitudes. However, how changes in circadian rhythms interact with the perception of photoperiod in crops remain poorly studied. In tomato, the appearance during domestication of mutations in EMPFINDLICHER IM DUNKELROTEN LICHT 1 (EID1, Solyc09g075080) and NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED GENE 2 (LNK2, Solyc01g068560) delayed both the phase and period of its circadian rhythms. The fact that variation in period and phase are separated in tomato provides an optimal tool to study how these factors affect the perception of photoperiod.ResultsHere we develop tomato near isogenic lines carrying combinations of wild alleles of EID1 and LNK2 and show that they recreate the changes in phase and period that occurred during its domestication. We perform transcriptomic profiling of these near isogenic lines under two different photoperiods, and observe that EID1, but not LNK2, has a large effect on how the tomato transcriptome responds to photoperiod. This large effect of EID1 is likely a consequence of the global phase shift elicited by this gene in tomato's circadian rhythms.ConclusionsOur study shows that changes in phase that occurred during tomato domestication determine photoperiod perception in this species, while changes in period have little effect.

Stress System Activation in Children and Adolescents With Autism Spectrum Disorder.

The mission of the human stress system is the maintenance of homeostasis in the presence of real or perceived, acute or chronic stressors. The hypothalamic–pituitary–adrenal (HPA) axis and the autonomic nervous system (ANS) are the stress system-related neuroendocrine pathways. There is abundant evidence that children and adolescents with autism spectrum disorder (ASD) may exhibit atypical function within the HPA axis and the ANS both at the resting state and during the presence of social and/or non-social stressors. The aim of this review is to provide an up-to-date summary of the findings regarding stress system alterations in children and adolescents with ASD. We focus on the variations of stress hormones circadian rhythms, specifically cortisol and alpha-amylase (i.e., a surrogate index of epinephrine/norepinephrine secretion), and on the alterations of stress system responsivity to different stressors. Also, we present imaging and immunological findings that have been associated with stress system dysregulation in children and adolescents with ASD. Finally, we review the pivotal role of HPA axis-ANS coordination, the developmental trajectory of the stress system in ASD, and the possible role of early life stress in the dysregulation of the stress system demonstrated in children and adolescents with ASD. This synthesis will hopefully provide researchers with a foundation for an integrated approach to future research into stress system variations in children and adolescents with ASD.

Comparative diurnal and seasonal variations of ACTH, cortisol and aldosterone in Ouled Djellal and D’Man sheep breeds reared in arid lands

Abstract. Amokrane-Ferrah A, Annane A, Ferrouk-Boukenaoui N, Khaldoun M, Amirat Z, Mormede P, Khammar F. 2021. Comparative diurnal and seasonal variations of ACTH, cortisol and aldosterone in Ouled Djellal and D’Man sheep breeds reared in arid lands. Biodiversitas 23: 388-395. This study aimed to explore the diurnal and seasonal variations of adrenocorticotropic hormone (ACTH), cortisol and aldosterone, main hormones involved in adaptation to the harsh climate of the Sahara Desert in two breeds of sheep (Ovis aries Linnaeus, 1758), Ouled Djellal rams (seasonal breeder) and D'Man (no seasonal breeder). Blood samples were taken every hour for 24 hours during equinoxes and solstices. Plasma ACTH levels were similar in the two breeds, with higher levels in the morning and a seasonal rhythm characterized by lower levels and dampened diurnal cycle in winter. In most experimental conditions, plasma cortisol levels showed no circadian rhythm but marked ultradian variations. The seasonal cortisol rhythm was different from the ACTH rhythm and characterized by lowest levels at equinoxes and highest levels in summer. Mean cortisol levels were higher in Ouled Djellal than in the D’Man breed, which may favor better robustness of Ouled Djellal sheep. Plasma aldosterone levels were characterized by diurnal variations with an acrophase around midnight, with large differences across breeds and seasons. In contrast to cortisol, the seasonal rhythm of plasma aldosterone showed the highest levels at equinoxes and lowest at solstices. These changes can be driven by environmental conditions and exceptionally high summer temperatures.

Circadian rhythm for female entering old age: exploration on the effect of eating behavior

Unhealthy lifestyle and eating behavior are associated with circadian rhythm disruption which contributes to numerous harmful outcomes. The relationship between circadian rhythm and eating behavior remains unclear. The study aims to investigate different types of eating behavior in middle-aged women and their variation in circadian rhythm. A descriptive, cross-sectional design was used. We recruited a convenience sample of 150 female aged 45 years or over from the community in southern Taiwan. Sociodemographic status, sleep diary and eating behavior were collected by questionnaires; behavioral circadian rhythm were monitored with the wrist-worn application. Four middle-aged participants were interviewed. Preliminary data show three main findings: (1) Sleep efficiency was decrease with age, (2) First meal within 2 hours after waking up was associated with higher amplitude (2.24 vs 1.43 log count), relative amplitude (0.92 vs 0.71), middle to vigorous physical activity time (101.22 vs 58.41 minute), lower lowest active 5 hr midpoint (2.63 vs 4.34 hour) and acrophase (13.67 vs 15.75), (3) Participants with morning chronotype have less sedentary behavior and higher most active 10 hr during wake time. Age and timing of first meal after waking up seem dominating circadian rhythm. Chronotype might be a significant factor for physical activity level. More data is needed to further confirm the association.

Estimation of resting blood pressure using facial thermal images by separating acute stress variations

The increasing number of people with hypertension worldwide has become a matter of grave concern. Blood pressure monitoring using a non-contact measurement technique is expected to detect and control this medical condition. Previous studies have estimated blood pressure variations following an acute stress response based on facial thermal images obtained from infrared thermography devices. However, a non-contact resting blood pressure estimation method is required because blood pressure is generally measured in the resting state without inducing acute stress. Day-long blood pressure variations include short-term variations due to acute stress and long-term variations in circadian rhythms. The aim of this study is to estimate resting blood pressure from facial thermal images by separating and excluding short-term variations related to acute stress. To achieve this, short-term blood pressure variations components related to acute stress on facial thermal images were separated using independent component analysis. Resting blood pressure was estimated with the extracted independent components excluding the short-term components using multiple regression analysis. The results show that the proposed approach can accurately estimate resting blood pressure from facial thermal images, with a 9.90 mmHg root mean square error. In addition, features related to resting blood pressure were represented in the nose, lip, and cheek regions.

Relationship between circadian rhythm characteristics and chronotypes with multiple sclerosis: literature review

Circadian rhythm disorder is described as discrepancy between person’s sleep habits and usual, generally accepted sleep model during 24-hour period. Circadian rhythm disorders affect not only person’s working capacity during the day but also may reduce quality of life. The term chronotype refers to a specific circadian rhythm manifestation – person’s preference to sleep and to be awake at some point of 24-hour period. Both circadian rhythm disorders and increased serum levels of proinflammatory cytokines are considered as factors negatively affecting sleep homeostasis among patients with multiple sclerosis. It is important to recognize and manage circadian rhythm variations and associated sleep disorders among patients with multiple sclerosis in order to reduce fatigue, improve cognitive functions and mood, and general quality of life. In this review article, we describe mechanism of action of circadian rhythm, its imbalances, objective and subjective evaluation methods of circadian rhythm and chronotypes, as well as relationship between circadian rhythm characteristics, chronotypes, melatonin concentration, oxidative stress, and multiple sclerosis.

Effect of Antihypertensive Drugs on Circadian Variation of Blood Pressure Measured by Ambulatory Blood Pressure Monitoring in Controlled Hypertensive Individuals

Background: Rewinding back a 100 years ago, Riva Rocci introduced the meticulous way of measuring blood pressure (BP) in clinical practice. With recent years, ambulatory BP monitoring came into existence which is still not used routinely in the management of hypertension. This thought led to the commencement of our study to analyze the variations in ambulatory BP recording over a 24-h cycle. Objectives: The objectives of the study are to determine the BP differences throughout the circadian cycle and to analyze the variations in circadian rhythm due to various antihypertensive drugs. Methods: On the first visit to the Medicine Outpatient Department, patient's medical history was recorded. Three readings of office BP were recorded using a sphygmomanometer. The patient was then provided with the ambulatory BP monitoring device, sent home and asked to follow-up after 24 h and the report was recorded. Results: On comparing the nocturnal pattern among candidates taking single versus combination drug, the dip was found to be in 31.7% in patients on single drug compared to 38.6% combination therapy. The surge in BP was seen in 56.8% of patients on single-drug therapy compared to 43.3% patients on combination drug therapy. Conclusion: Single-drug therapy for hypertension did not show a significant nocturnal pattern compared to the combination drug therapy for hypertension. The presence of the risk factors such as obesity smoking, dyslipidemia, diabetes mellitus, hypothyroidism, family history, and chronic kidney disease showed a presence of dipping and nondipping pattern in BP.

Disruption in Circadian Rhythm Increases Cardiovascular Disease Risk Factors in Shift Working Nurses

Abstract Background Shift work is associated with behavioral, psychosocial, and physiological consequences in the body that may cause cardiovascular disease (CVD) risk. Therefore, in this study we tried to demonstrate the disruption in circadian rhythm of blood pressure by ambulatory blood pressure monitor in shift working nurses. Methods A total of 50 nurses, 25 night shift working nurses (NSWN), and 25 day shift working nurses (DSWN) underwent ambulatory blood pressure monitoring (ABPM) for a period of 24 hours. Along with measurements of inflammatory markers (hs-CRP and IL-6) the risk factors for cardiovascular disease between NSWN and DSWN and their possible relationship with disrupted circadian rhythm were measured by circadian rhythm questionnaire. Results The mean systolic and diastolic pressure for a period of 24 hours and mean diastolic blood pressure analysis throughout the sleep time was found greater in the NSWN than the DSWN (118 mm Hg vs. 112 mm Hg, p < 0.05: 72 mm Hg vs. 68 mm Hg, p < 0.05: 62 mm Hg vs. 59 mm Hg, p < 0.05). High mean blood pressure readings were found to be more frequent in the NSWN (p < 0.05) than in DSWN. No significant differences were found in IL-6 and hs-CRP levels. However, a significant difference in circadian rhythm abnormality was found in NSWN than in DSWN. Conclusion The 7 day/24 hours ambulatory blood pressure monitoring (ABPM) in NSWN showed a reduced circadian rhythm variation in blood pressure along with abnormality in circadian rhythm itself as compared with DSWN. Work schedules and the consequent rest–activity schedules affect circadian rhythms, with likely long-term impact on health. Therefore, working in critical care unit during night hours leads to abnormal blood pressure in NSWN, suggesting that this type of work, in which sleep is disturbed, leading to mental stress, could be a direct risk factor in cardiovascular diseases.

Naturally occurring circadian rhythm variation associated with clock gene loci in Swedish Arabidopsis accessions.

Circadian clocks have evolved to resonate with external day and night cycles. However, these entrainment signals are not consistent everywhere and vary with latitude, climate and seasonality. This leads to divergent selection for clocks which are locally adapted. To investigate the genetic basis for this circadian variation, we used a delayed fluorescence imaging assay to screen 191 naturally occurring Swedish Arabidopsis accessions for their circadian phenotypes. We demonstrate that the period length co‐varies with both geography and population sub‐structure. Several candidate loci linked to period, phase and relative amplitude error (RAE) were revealed by genome‐wide association mapping and candidate genes were investigated using TDNA mutants. We show that natural variation in a single non‐synonymous substitution within COR28 is associated with a long‐period and late‐flowering phenotype similar to that seen in TDNA knock‐out mutants. COR28 is a known coordinator of flowering time, freezing tolerance and the circadian clock; all of which may form selective pressure gradients across Sweden. We demonstrate the effect of the COR28‐58S SNP in increasing period length through a co‐segregation analysis. Finally, we show that period phenotypic tails remain diverged under lower temperatures and follow a distinctive “arrow‐shaped” trend indicative of selection for a cold‐biased temperature compensation response.

The Athlete Specific Chronotype Index (ACTi)

The circadian variation of athletic performance has been observed to coincide with daily peaks in body temperature. Chronotypes (CT) take into account inter-individual variations in circadian rhythms, yet there is discord regarding the relationship between CT and athletic performance. This may be due to the most common chronotyping method, the Morningness-Eveningness Questionnaire (MEQ), lacking validity for athletic populations. PURPOSE: The purpose of this study was to develop and validate an athlete specific CT index (ACTi). METHODS: 297 athletes completed a CT questionnaire in MEQ (19) and newly-developed questions (15). Principle component analysis (PCA) was used to identify common themes and reduce the final number of questions. 10 respondents from each CT category, as determined by the MEQ, then participated in a 24-hour laboratory study. Participants abided by their typical sleep/wake cycle, provided hourly saliva samples (for dim light melatonin onset (DLMO) analysis) whilst awake and hourly core body temperature (CBT) readings (ingestible thermistor) for the 24-hours. Stepwise multiple linear regression analysis to predict DLMO onset and CBT was used to further refine the ACTi. RESULTS: PCA of the extended ACTi responses were performed, identifying 7 themes. Multiple regression identified 11 questions that explained DLMO (r2=0.81), forming the final ACTi. DLMO CT differences were observed between MEQ morning-type (MT) and intermittent-type (IT) (64±61.6 min, p=0.02); and MT and evening-type (ET) (114±71.2min, p=0.002). No CT differences were observed in CBT for MEQ or ACTi. Cohen’s Kappa revealed moderate CT classification changes between MEQ and ACTi (0.62). CONCLUSION: The ACTi is an 11-point index that enhances CT determination of athletes versus MEQ, based on the criterion measure DLMO. The ACTi may be used in team-sports to examine the impact of CT upon performance, monitoring of training responsiveness and athlete wellbeing.

Genetic variation and phenotypic plasticity in circadian rhythms in an armed beetle, Gnatocerus cornutus (Tenebrionidae)

Abstract Circadian rhythms, their free-running periods and the power of the rhythms are often used as indicators of biological clocks, and there is evidence that the free-running periods of circadian rhythms are not affected by environmental factors, such as temperature. However, there are few studies of environmental effects on the power of the rhythms, and it is not clear whether temperature compensation is universal. Additionally, genetic variation and phenotypic plasticity in biological clocks are important for understanding the evolution of biological rhythms, but genetic and plastic effects are rarely investigated. Here, we used 18 isofemale lines (genotypes) of Gnatocerus cornutus to assess rhythms of locomotor activity, while also testing for temperature effects. We found that total activity and the power of the circadian rhythm were affected by interactions between sex and genotype or between sex, genotype and temperature. The males tended to be more active and showed greater increases in activity, but this effect varied across both genotypes and temperatures. The period of activity varied only by genotype and was thus independent of temperature. The complicated genotype–sex–environment interactions we recorded stress the importance of investigating circadian activity in more integrated ways.