Seasonal changes in acute stressor-mediated plasma glucocorticoid regulation in New World flying squirrels.

Southern flying squirrels have higher circulating cortisol levels than most vertebrates. However, regulation of tissue exposure to cortisol by the hormone's carrier protein, corticosteroid-binding globulin (CBG), appears to be altered due to lower-than-expected CBG expression levels, and a reduced affinity for cortisol. To assess the capacity of flying squirrels to regulate acute stress-mediated cortisol levels, we used the dexamethasone (DEX) suppression test followed by the adrenocorticotropic hormone (ACTH) stimulation test in both the breeding and non-breeding seasons, and quantified resultant changes in plasma cortisol and relative CBG levels.

Cyclic bouts of extreme bradycardia counteract the high metabolism of frugivorous bats.

Active flight requires the ability to efficiently fuel bursts of costly locomotion while maximizing energy conservation during non-flying times. We took a multi-faceted approach to estimate how fruit-eating bats () manage a high-energy lifestyle fueled primarily by fig juice. Miniaturized heart rate telemetry shows that they use a novel, cyclic, bradycardic state that reduces daily energetic expenditure by 10% and counteracts heart rates as high as 900 bpm during flight.

Plasma DHEA levels in wild, territorial red squirrels: seasonal variation and effect of ACTH.

In many species, territorial behavior is limited to the breeding season and is tightly coupled to circulating gonadal steroid levels. In contrast, both male and female red squirrels (Tamiasciurus hudsonicus) are highly aggressive in both the breeding and non-breeding seasons in defense of food stores on their individual territories throughout the boreal and northern forests of North America. Dehydroepiandrosterone (DHEA), an androgen precursor, is secreted from the adrenal cortex in some mammals, and DHEA has been linked to aggression in non-breeding songbirds.