Ask a runner what they eat before a long race and you’ll probably get a variety of answers. Some will suggest a light meal of fruit or lean protein an hour before a race, while others will advise loading up on pasta the night before. For vampire bats, however, it turns out that a bowl full of amino acid-rich blood is enough.
Researchers from the University of Toronto captured some vampire bats and taught them to run on a treadmill. By analyzing their breath, the researchers determined that the bats primarily used amino acids found in recent blood meals as the main source of energy to power their running. These findings, published this week in Biology Letterssuggests that vampire bats may have evolved to develop a unique metabolism typically seen in blood-sucking insects.
No carbs, no problem
Bats are unique among mammals and vampires are unique among bats. The creatures that inspire the horror novel survive entirely on the blood of their victims. Vampire bats typically fly close to prey and then sprint or run with their thumbs and wrists to close. They then grab their target, usually a peccary or capybara, and use their teeth to make a small cut to draw out the blood. If necessary, vampire bats can gulp and consume four times their body weight in liquid.
But relying solely on blood severely limits what vampires can use for energy. Most mammals, including humans, typically fuel exercise by burning carbohydrates and lipids, which are not available in the blood. Blood is an abundant source of protein-building amino acids, but they typically make up only about 10% of the fuel used by mammals during exercise. Vampire bats, over generations of evolution, have flipped that script and somehow manage to sustain themselves in the first place out of amino acids. Bats lack the genes needed to secrete insulin, so they have no choice but to make do with what’s available.
“In most animals, amino acids are a fuel of last resort,” University of Toronto Scarborough professor and study co-author Ken Welch said in a statement. “It’s what the body burns when there’s not much left, but these bats burn it right away.”
The researchers trained rats to run on a treadmill
To measure that observation scientifically, the researchers captured two dozen Belizean vampire bats and trained them to use a small treadmill commonly used to measure the metabolic rates of rats. The aim of the experiment was to first feed the bats cow’s blood enriched with two isotopically labeled amino acids and then measure their respiration while running. The researchers obtained blood from a local slaughterhouse and fed it to the bats using a pipette. It took some time, but eventually, the researchers were able to train the bats to stop jumping off the side of the treadmill and to walk, then run, at a steady pace. Some of the bats were able to run at speeds of 100 feet per second and could maintain that speed for more than 90 minutes.
When the researchers took measurements of the CO2 emitted by the bat’s breath, they were able to find trace amounts of the same amino acids involved in the blood feast. The breakdown of glycine and leucine, the two amino acids added to the blood, was thought to be responsible for up to 60% of bats’ total energy production during running. In the end, the experiment showed that vampire bats can convert amino acids into energy in less than 10 minutes and use it to fuel a long endurance run.
This process makes vampires unique among mammals. These findings suggest that the metabolism of vampires is actually closer to that of blood-sucking tsetse flies than to other bat species. And while flying requires much more energy than running, researchers believe that vampires and similarly burn amino acids for flight as well.
“What’s even more impressive is that they can sustain this really high level of exertion for a long time just by burning the proteins that they have stored in their muscles,” Welch added. It’s something we can only dream of doing.”