Biological Rhythms and Sleep in Reindeer ($\textit{Rangifer tarandus tarandus}$) across Arctic Seasons

• Main Author: Meier, Sara Andrea
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2024
• Subjects: Institute of Pharmacology and Toxicology; Institute of Evolutionary Biology and Environmental Studies; UZH Dissertations; 570 Life sciences; biology; 610 Medicine & health; 590 Animals (Zoology); Arctic; Rangifer; Rangifer tarandus
• Online Access: https://www.zora.uzh.ch/id/eprint/258694/

Biological rhythms synchronize organisms to their environment and accordingly orchestrate physiological process and behaviors. For example, the circadian clock anticipates 24-h rhythms of day and night and accordingly synchronizes behavior and physiological processes like sleep and wake and feeding and fasting. Additionally, it detects changes in day length (photoperiod) across seasons, entraining the circannual clock. The circannual clock controls physiology and behavior on an annual scale, such as filling-up energy deposits in summer or slowing down metabolic rate in winter to reduce energy expenditure. Throughout the day, ultradian rhythms regulate behavioral and physiological processes with periods shorter than 24 h. Sleep is an essential behavior for maintenance of brain function, reduction of energy expenditure and survival. Sleep behavior is regulated by a homeostatic process, tracking time spent awake and a circadian process, modulating sleep need across the day. Biological rhythms and sleep are found across almost all kingdoms of life and their disruption has severe consequences to health and survival. In humans, chronic sleep restriction or circadian disruption by jet lag, shift work or artificial light at night increase the risk for many metabolic diseases like obesity, metabolic syndrome and cancer. Arctic species experience the most drastic seasonal changes in environmental conditions, posing unique challenges to their biological timing systems. Daylength varies from constant darkness for several months in winter to constant light for several months in summer. Under these unusual photoperiods reindeer (Rangifer tarandus) lose 24-h patterns in behavioral activity, while they show normal 24-h rhythms in activity under the light-dark conditions of spring and fall, raising the question whether reindeer have a functional circadian clock. Additionally, reindeer are highly active during summer to maximize food intake during the short arctic growing season and drastically decrease their behavioral activity ...