Search

This study aims to measure the daily melatonin secretory rhythms of people living in high-, mid-, and low-latitude regions characterised by different day lengths and global solar-radiation conditions. In Poland, a high-latitude region, the amount of melatonin secretion is greater, with secretion occurring earlier (exemplifying phase advance). On the other hand, in Vietnam, a low-latitude region, the level is lower and occurs later (phase delay). Japan, a mid-latitude region, shows behaviour intermediate between these two. Melatonin secretory rhythm in Vietnam is closely related to Day length and Global Solar Radiation, though no such relationship is observed in Poland or Japan, making it necessary for other factors to be considered. The results of this study have important implications considering the impacts of light pollution and lighting-related conditions of modern life. [ABSTRACT FROM AUTHOR]

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]