Hibernation and Circannual Rhythms of Food Consumption in Marmots and Ground Squirrels

Abstract

In order to understand better the evolution and adaptive value of hibernation, ecological aspects and experimental studies of closely related hibernators, the Marmotini, are examined. The central hypothesis is that annual changes in the environment integrate three or, perhaps, four physiological processes: torpor, reporduction, consumption of food, and metabolism. Reproduction occurs promptly after emergence from hibernation. For most species, the breeding season is very short. Although the experimental data are rather meager, no variation in external factors has consistently altered the season of reproduction. Consumption of food and change in weight increases until July or September and then decreases. The large members of the Marmotini store their energy as fat, but small species store their energy as seeds and nuts. Experiments to test the hypothesis that some aspect of the supply, such as fat content, might vary seasonally have produced negative results. Complex experiments on the length of the photoperiod on woodchucks and several species of ground squirrels failed to alter the annual cycle of consumption of food. Animals kept in constant conditions showed a cycle of about 11 months, but woodchucks sent tto Australia changed their cycle in two years to match the seasons of the southern hemisphere. Experiments with temperature and torpor and castration did not alter the annual did not alter the rhythm...

Seasonal variations in daily rhythms of activity in athletic horses

“…While the core of the circadian molecular clock has been defined in mammals, the knowledge in the regulation of the circannual (annual) clock is very poor (Davis, 1976;Gwinner, 2003). A recent study on sheep suggests an anatomical substrate of circannual clock based in the pituitary gland in which melatonin-receptor-containing cells may operate as key calendar cells, transmitting seasonal temporal information to the endocrine system (Lincoln et al, 2006).…”

Temporal Dynamics of the Cecal Gut Microbiota of Juvenile Arctic Ground Squirrels: a Strong Litter Effect across the First Active Season

“…In the weeks prior to the onset of hibernation, obligate hibernators decrease rates of feeding and activity (28)(29)(30). Reduced feeding correlates with changes in gastrointestinal tract (GIT) physiology (29) that occur prior to hibernation in alpine marmots (Marmota marmota) and thirteen-lined ground squirrels (31,32).…”

“…In the weeks prior to the onset of hibernation, obligate hibernators decrease rates of feeding and activity (28)(29)(30). Reduced feeding correlates with changes in gastrointestinal tract (GIT) physiology (29) that occur prior to hibernation in alpine marmots (Marmota marmota) and thirteen-lined ground squirrels (31,32). It is possible that the decreased metabolic rate (33) and decreased body temperature (T b ) (34) in arctic ground squirrels are reflective of reduced feeding and changes in the gut and gut microbiota in preparation for the onset of hibernation.…”

To eat or not to eat: the effect of AICAR on food intake regulation in yellow-bellied marmots (Marmota flaviventris)

“…Hibernators, such as the yellow-bellied marmot (Marmota flaviventris), nearly double their body mass in the form of white adipose tissue (WAT) over summer, then reduce their food intake to zero prior to hibernation and continue to fast for nearly 7months (Dark, 2005;Davis, 1976;Ward and Armitage, 1981). Marmots do not store food in their burrow but resume eating in early spring when food is once again available.…”

“…During winter hibernation, WAT stored over the summer and autumn is used for endogenous energy. Marmots lose as much as 30% of their body mass during the winter while going through bouts of torpor (Davis, 1976). In spring, marmots cease to hibernate, become reproductively active, and begin the food intake cycle once again.…”