Low ambient temperature reduces the time for fuel switching in the ruby-throated hummingbird (Archilochus colubris)

Publication date: Available online 22 August 2019Source: Comparative Biochemistry and Physiology Part A: Molecular & Integrative PhysiologyAuthor(s): Derrick J.E. Groom, Nadia Bayram, Mary Shehata, L. Gerardo Herrera M., Kenneth C. WelchAbstractPhysiological adaptations that enhance flux through the sugar oxidation cascade permit hummingbirds to rapidly switch between burning lipids when fasted to burning ingested sugars when fed. Hummingbirds may be able to exert control over the timing and extent of use of ingested sugars by varying digestive rates when under pressure to accumulate energy stores or acquire energy in response to heightened energy demands. We hypothesized that hummingbirds would modulate the timing of a switch to reliance on ingested sugars differently when facing distinct energetic demands (cool versus warm ambient temperatures). The timing of the oxidation of a single nectar meal to fuel metabolism was assessed by open-flow respirometry, while the time to first excretion following the meal was used as a proxy for digestive throughput time. As predicted, birds showed a more rapid switch in respiratory exchange ratio (RER = rate of O2 consumption/CO2 production) and excreted earlier when held at cool temperatures compared to warm. In both cases, RER peaked barely above 1.0 indicating ingested sugar fueled ≈100% of resting metabolism. Our findings suggest that energetic demands modulate the rate of fuel switching through shifts of the sugar oxidation cas...
Source: Comparative Biochemistry and Physiology Part A: Molecular and Integrative Physiology - Category: Biochemistry Source Type: research