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Circadian rhythms, which respond to the day-night cycle on the earth, arise from the endogenous timekeeping system within organisms, called the "biological clock." For accurate circadian rhythms, daily fluctuations in light and temperature are considered one of the important time cues. In social insects, both abiotic and biotic factors (i.e., social interactions) play a significant role in activity-rest rhythm regulation. However, it is challenging to monitor individual activity-rest rhythms in a colony because of the large group size and small body size. Therefore, it is unclear whether individuals in a colony exhibit activity-rest rhythms and how social interactions regulate their activity-rest rhythms in the colony. This study developed an image-based tracking system using 2D barcodes for Diacamma cf. indicum from Japan (a monomorphic ant) and measured the locomotor activities of all colony members under laboratory colony conditions. We also investigated the effect of broods on activity-rest rhythms by removing all broods under colony conditions. Activity-rest rhythms appeared only in isolated ants, not under colony conditions. In addition, workers showed arrhythmic activities after brood removal. These results suggested that a mixture of social interactions, and not light and temperature, induces the loss of activity-rest rhythms. These results contribute to the knowledge of a diverse pattern of circadian activity rhythms in social insects. [ABSTRACT FROM AUTHOR]

Many species show rhythmicity in activity, from the timing of flowering in plants to that of foraging behavior in animals. The free-running periods and amplitude (sometimes called strength or power) of circadian rhythms are often used as indicators of biological clocks. Many reports have shown that these traits are highly geographically variable, and interestingly, they often show latitudinal or longitudinal clines. In many cases, the higher the latitude is, the longer the free-running circadian period (i.e., period of rhythm) in insects and plants. However, reports of positive correlations between latitude or longitude and circadian rhythm traits, including free-running periods, the power of the rhythm and locomotor activity, are limited to certain taxonomic groups. Therefore, we collected a cosmopolitan stored-product pest species, the red flour beetle Tribolium castaneum, in various parts of Japan and examined its rhythm traits, including the power and period of the rhythm, which were calculated from locomotor activity. The analysis revealed that the power was significantly lower for beetles collected in northern areas than southern areas in Japan. However, it is worth noting that the period of circadian rhythm did not show any clines; specifically, it did not vary among the sampling sites, despite the very large sample size (n = 1585). We discuss why these cline trends were observed in T. castaneum. [ABSTRACT FROM AUTHOR]

Background: Sleep health-related issues, such as poor subjective sleep quality during the night and nocturnal wakefulness, have been a focus of recent research on frailty. However, current trends regarding the chronotypes of older individuals with frailty have not been well documented, and information on the impact of frailty on circadian rest-activity patterns is limited. The aim of this research was to clarify the relationship among frailty, nonparametric rest-activity patterns, and chronotype in older community-dwelling subjects. Method: A survey was conducted between June and December 2018, and the participants of this study were recruited from among community-dwellers aged 60 years or older living in Akita prefecture, Japan. The frailty phenotype defined by the National Center for Geriatrics and Gerontology Study of Geriatric Syndromes (NCGG-SGS) was used to evaluate the frailty status of each participant. To evaluate nonparametric rest-activity rhythm (RAR) parameters (e.g., interdaily stability [IS], intradaily variability [IV], and relative amplitude [RA]), each participant wore an Actiwatch Spectrum Plus device on his or her non-dominant wrist for seven continuous days without removal. The Munich chronotype questionnaire-Japanese version (MCTQ-J) was also used to measure the midpoint of sleep in free days (MSF). Results: The final study cohort was composed of 105 participants (85.7% women) and was divided into 58 non-frail subjects, 45 pre-frail subjects, and 2 frail subjects. According to a binomial logistic regression analysis, the pre-frail individuals had a weaker grip strength (coefficient [beta], −0.18; odds ratio, 0.84; 95% confidence interval [CI], 0.76–0.93; p =.001) and a lower RA (beta, −8.78; odds ratio, 0.0002; 95% CI, 0.00–0.15; p =.01). In addition, correlation analyses also showed that the MSF was negatively associated with the RA in the pre-frail group (r = −0.30, p <.05) and positively correlated with the RA in the non-frail group (r = 0.26, p <.05); furthermore, the MSF of the pre-frail group occurred at a later time than that of the non-frail one (p =.03). Conclusion: The present study provides grounds for our proposal that pre-frailty is significantly associated with a low grip power and relative imbalance between rest and active statuses as indexed using nonparametric RAR parameters. Furthermore, elderly individuals with pre-frailty or frailty may have a later MSF time. However, these potential findings need to be validated in future research. [ABSTRACT FROM AUTHOR]