In most mammals, the act of running is fueled primarily by the oxidization of carbohydrates and lipids, which are stored in the body as fuel. Amino acids, on the other hand, generally contribute very little when mammals go out for a jog. But recent research into common vampire bats, which subsist on a protein-rich diet of blood, suggests that they metabolize their food differently, breaking down amino acids for fuel in a unique way. The study, published in The Royal Society’s Biology Letters in November 2024, incorporated one highly specialized piece of equipment: a tiny treadmill designed specifically for bats. Read on to find out more about the study, which sheds light on the unique ways these fascinating animals power their lives.
The Strange Truth About Vampire Bat Metabolisms
Vampire bats are known as flying bloodsuckers, but they’re also quite mobile on land. These unique mammals are known to run along the ground, tracking prey and stealing blood from animals like cattle and horses. The research team involved with the study cited above tapped into this unique running ability to explore how these bats use protein during exercise.
To evaluate the bats as the animals ran, the team used a specially designed treadmill. “Rather than flying the bats, we can capitalize on respiratory treadmill equipment that is otherwise used for studying rodents,” the researchers write in the study abstract.
Vampire Bats Exhibit Unusual Fuel Reliance
The team worked to ethically capture 24 adult vampire bats in the tropical forests at the Lamanai Archeological Reserve in Belize. The bats were then fed enriched cow’s blood, with an additional group of bats fed unenriched cow’s blood to serve as a control group. After feeding, the bats were placed on a custom-built respiratory treadmill to evaluate their oxygen use during running.
As the researchers slowly pushed the treadmill pace from walking to running, it became clear that the bats weren’t fueling their running the way one might expect. Their respiratory gas output suggested that their primary fuel source — amino acids, as the researchers later discovered — remained the same, even as the exercise became more strenuous. Conversely, other mammals typically exhibit changing gas ratios as exercise gets more strenuous, shifting from burning mostly lipids to relying more on carbs. The researchers write: “If lipids and carbohydrates were the major metabolic substrates fueling exercise, we would have expected the respiratory exchange ratio (RER) to increase with increasing treadmill speed, reflecting the characteristic shift from lipid to carbohydrate oxidation at higher exercise intensities.”
Understanding Vampire Bat Fuel Sources
Ultimately, the team found the bats primarily metabolized fuel other than the carbs or fats that typically power running mammals. Instead, the bats relied heavily on energy from their recent high-protein meal of cow blood. The gases expelled during exercise showed traces of amino acids, which are the building blocks of proteins. This means that vampire bats powered their jog largely by metabolizing blood. This is common in bloodsucking creatures like mosquitoes, but the researchers believe that this is an important first for mammals.
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While further research is needed to fully comprehend vampire bats’ fueling mechanisms, findings like these help broaden the scientific community’s understanding of these fascinating creatures.
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