Energy expenditure and testosterone in free‐living male yellow‐pine chipmunks

Abstract

The onset of mating in yellow-pine chipmunks (Tamias amoenus) follows emergence from a prolonged period of energy conservation during hibernation. Energy expenditures are greatly accelerated to meet the demands of the reproductive season. When emerging from hibernation, typical male chipmunks (breeders) have enlarged testes and a high level of plasma testosterone (T). However, certain males that do not participate in reproduction (nonbreeders) maintain small testes and low plasma T levels and emerge several weeks later than the breeders. The timing of the terminal arousal from hibernation and onset of mating are associated with increased plasma T levels. Experimental elevation of T levels in T. amoenus outside the mating season has been associated with a decrease in body mass, further suggesting an effect of T on energy balance. To test this hypothesis, we measured daily energy expenditure (DEE) in free-living, nonbreeding male chipmunks in the presence and absence of a T-implant. We also measured DEE in breeding males when endogenous T levels were high. DEE of the nonbreeders was not affected by our manipulation of plasma T, and the DEE of breeding males did not differ from that of nonbreeders. We conclude that energy expenditure on a daily basis in male yellow-pine chipmunks is not influenced by levels of T. However, on a seasonal basis, the earlier emergence from hibernation by breeding males, which appears to be influenced by T, represents an overall seasonal energy expenditure that exceeds that of nonbreeding males.

DETECTION OF SEASONAL WEIGHT LOSS AND A SEROLOGIC SURVEY OF POTENTIAL PATHOGENS IN WILD PALLAS' CATS (FELIS[OTOCOLOBUS]MANUL) OF THE DAURIAN STEPPE, RUSSIA

“…For some species of mammals, variation in body mass throughout the year is an adaptation to seasonal changes of climate and food availability (Kenagy et al 1999;Boonstra et al 2001). In these species, the increased fat stores facilitate successful hibernation, which may contribute to successful reproduction in the next year (Place et al 2002). The deep snow, strong winds, and low temperatures likely hamper effective hunting by both Pallas' cats and far-east wildcats.…”

Linking summer foraging to winter survival in yellow pine chipmunks (Tamias amoenus)

“…The number of days chipmunks were torpid or euthermic within their winter dens was estimated by multiplying duration of winter by the proportion of time that chipmunks are torpid or euthermic. Assuming that the average length of torpor bouts is 8.5 days (Geiser et al 1990), and euthermic bouts are half a day long (Place et al 2002) in a 9-day period a chipmunk spends *94% of its time torpid and *6% euthermic.…”

“…We calculated the diversity of seed species in each larder using the When chipmunks enter dormancy they alternate between long bouts of torpor and short bouts of euthermy (Geiser et al 1990). To account for different energetic requirements of torpid and euthermic metabolic states, we used estimates of energy expenditure (includes torpor, arousal and euthermy) for hibernating male yellow pine chipmunks to approximate the number of days that winter larders would provision chipmunks (328 kJ for a 22-day period of hibernation; Place et al 2002). Because these data are the only known estimates of the energetic expenditure of torpid yellow pine chipmunks, we applied them to both male and female chipmunks.…”

“…where d is days, assuming that chipmunks have a digestive assimilation efficiency of 80.8% (Humphries et al 2001), and that yellow pine chipmunks expend 0.87 kJ/day when they are torpid and 124.4 kJ/day when they are euthermic during inter-torpor bouts (Place et al 2002). The number of days chipmunks were torpid or euthermic within their winter dens was estimated by multiplying duration of winter by the proportion of time that chipmunks are torpid or euthermic.…”

“…The size and composition of the larder can serve as a quantitative measure of how well an animal is prepared to pass the lean season. Individuals with inadequate stored food might not survive the winter or could have lower reproductive success in spring (Barnes 1984(Barnes , 1986Neuhaus et al 1999;Place et al 2002).…”