THE EFFECT OF FLIGHT DURATION ON ß-HYDROXYBUTYRATE CONCENTRATION IN BLOOD PLASMA OF EPTESICUS FUSCUS

Abstract

Insectivorous bats alter relative use of metabolic substrates to match requirements of their activities, including energetically expensive flight. The “fasting while foraging” hypothesis states that the metabolic demands of flight often exceed energy intake while foraging, hence bats may metabolize fat stores (especially early in the night) to power flight with ketones, a byproduct of the normal oxidation of fatty acids. Previous studies in bats have found increases in the plasma ketone ß-hydroxybutyrate following food consumption paired with or without flight. However, no study has explored whether increases in plasma ß-hydroxybutyrate occur following flight without food consumption. We used metabolite analysis to examine changes in plasma ß-hydroxybutyrate as a function of flight duration in 2 groups (fall and spring) of captive big brown bats (Eptesicus fuscus). We fasted bats for 12 hours prior to flight (exercise treatment) or rest (control), and then collected interfemoral vein blood. Exercise activity was quantified as flight time. For the Fall group, we collected three rest samples and one flight sample. Results for the Fall group were variable; interpretation of data patterns for this group may be complicated by changes in metabolism that occur in the fall when bats physiologically prepare for hibernation. To control for seasonal effects, we tested a second group of bats in the spring, collecting two rest and three flight samples. We found a positive correlation between flight duration and levels of plasma ß-hydroxybutyrate in the Spring group, which supports the fasting while foraging hypothesis.