Seasonal changes in plasma glucocorticosteroids of free-living female yellow-pine chipmunks: Effects of reproduction and capture and handling

We measured plasma levels of cortisol and corticosterone in female yellow-p ine chipmunks (Tamias amoenus) while observing seasonal reproductive and li fe-history events by live-trapping a natural population during the active ( nonhibernating) season. Both glucocorticosteroids (GCs) varied significantl y from March through September, starting with minimal values at the time of mating (cortisol similar to 900 ng/ml, corticosterone similar to 50 ng/ml) , rising to a peak by late lactation (cortisol similar to 1600 ng/ml, corti costerone similar to 175 ng/ml), and then declining prior to hibernation. F ollowing their emergence from natal burrows, young of the year had GC level s indistinguishable from those of adults. Body mass also varied significant ly over the season, increasing after mating and again after parturition to a peak in lactation, after which it declined steadily until hibernation. In addition to the use of standard trapping to describe seasonal hormonal pat terns, we also trapped chipmunks using a special protocol to examine the ef fects of capture and handling on GCs; we obtained an initial (basal) blood sample immediately, within 1-3 min of observing a capture, and then a secon d sample 30 min after holding the animal in the trap. Chipmunks consistentl y increased GCs above the initial (basal) level during the 30 min after cap ture and initial handling; these significant increases in GCs ranged approx imately 70-130% for cortisol and 50-190% for corticosterone, depending on s eason and reproductive state. GC levels at 30 min after capture and handing were similar to those obtained from samples drawn from our standard trappi ng and blood sampling. We conclude that although capture and handling incre ase the absolute level of plasma GC hormones, that effect does not obscure natural patterns of seasonal variation in GCs. Overall, our observations su ggest an important role of adrenocortical activity in the energy balance of these free-living rodents in two different contexts: (1) the seasonal regu lation of physiological state, including body mass, energy reserves, and re productive function, and (2) an acute response to stimulatory events, encom passing physiological stress, as represented here by capture and handling. (C) 2000 Academic Press.