Seasonal changes in reindeer physiology

Abstract

Abstract:The seasonal changes in the photoperiod, temperature and availability of food need to be converted to hormonal signals in order to induce adaptations in the physiology of the reindeer. The most reliable of the seasonal changes in the environment is the photoperiod, which affects the reindeer physiology through pineal gland and its hormone, melatonin. Usually there are large diurnal changes in the concentration of melatonin, but in the reindeer the daily rhythm disappears during the arctic summer to return again in the autumn. Seasonal changes in melatonin secretion are involved in the regulation of reproduction, the growth of pelage, thermogenesis, body mass and immune function. Melatonin may exert its effects through gene activation, but the mechanisms are not completely understood. Other hormones that show seasonality are thyroid hormones, insulin and leptin. Thus the observed physiological changes are a result of actions of several hormones. Appetite, energy production and thermogenesis are all vital for survival. During winter, when energy balance is negative, the reindeer uses mainly body fat for energy production. The use of fat stores is economical as the rate of lipolysis is controlled and the use of fatty acids in tissues such as muscle decreases. Only in severe starvation the rate of lipolysis increases enough to give rise to accumulation of ketone bodies. The protein mass is maintained and only in starved individuals muscle protein is used for energy production. The winter feed of the reindeer, the lichens, is poor in nitrogen and the nitrogen balance during winter is strongly negative. Reindeer responds to limited availability of nitrogen by increasing the recycling of urea into rumen. In general the adaptation of reindeer physiology enables the reindeer to survive the winter and although several aspects are known many others require further studies.

Age estimation in bowhead whales using tympanic bulla histology and baleen isotopes

“…() proposed a different mechanism for GLG formation in the bones of the small arboreal primate Microcebus , showing conclusively that GLG formation was dependent on photoperiod during the year. Physiological variables that affect GLG formation are also known to be affected by photoperiod in arctic and subarctic artiodactyls, although these may be modulated by other environmental factors (Suttie and Webster , Pösö , Piccione et al . ).…”

Effects of winter-feeding on reindeer’s future ability to utilize natural pastures

“…In some areas, the highest proportion of lichen may be ingested in March (Mathiesen et al 2000). In winter, reindeer's energy and nitrogen (protein) balance are negative (catabolic phase; Pösö 2005). A negative energy balance and the subsequent weight loss in winter is considered a regulated process, and reindeer often lose 10-20% of their body mass (Tyler & Blix 1990;White et al 2014).…”