C - Michigan Technological University

mice [227], and domestic sheep [230]. In contrast, in small overwintering animals thatgain weight in the fall and fast during the winter, serum leptin becomes seasonallydissociated from body weight and basal metabolic rate [231-233]. For instance, inRaccoon Dogs (Nyctereutes procyonoides) [232, 234], blue foxes (Alopex lagopus)[232], and yellow-bellied marmots (Marmota flaiventris) [233], serum leptin increases infall as body mass rises, but declines dramatically after the animals begin the winter fast,preceding the gradual drop in body mass.Although the bears in the current study experienced an average weight gain of28% from October to January (when hibernation began), serum leptin did notsignificantly increase over this period. In contrast, in small hibernators such as thewoodchuck (Marmota monax) [235], raccoon dog [232, 234], or yellow-bellied marmot[233] serum leptin significantly increases during the months leading up to hibernation. Itis possible that the black bears in the current study began increasing serum leptin in themonths prior to the first data collection date in October, though other studies in bears donot support this idea of earlier rises in leptin. In a study of one European brown bear(Ursus arctos arctos), serum leptin began to rise in early October, for a total increase of41% during prehibernation [236]. A study in Japanese black bears (Ursus thibetanusjaponicus) reported a 170% increase in serum leptin which began in October andpeaked in November (when hibernation began) [237]. The sharper increase in serumleptin in Japanese bears was likely due to the sharper increase in weight during thesemonths (70%). Between the beginning of January and the end of April, the current studyobserved a 37% decrease in serum leptin in black bears (Figure 3.1). Unlike in smallhibernators such as the raccoon dog [232] and the yellow-bellied marmot [233], thedecrease in serum leptin of black bears was gradual. It took place over the entire fastingperiod and continued through the first month of arousal. In contrast, in a study withyellow-bellied marmots that hibernated from October through April, serum leptindecreased 59% between November and February, thus preceding changes in weight(which began between January and February) [233].There are many notable differences between a bear’s hibernation state and thatof a small hibernator. Most small hibernators can drop to ambient temperatures duringperiods of torpor, and some periodically arouse to eat and excrete wastes [115, 117,52