Ask a runner what they eat before a lengthy race and you’ll probably receive a variety of answers. Some will suggest a light meal of fruits or lean protein an hour ahead of a race while others will advise loading up on pasta the night before. For vampire bats, however, it turns out a heaping bowl of amino acid-rich blood will suffice.
Researchers from the University of Toronto captured several vampire bats and taught them to run on a treadmill. By analyzing their breath, the researchers determined the bats primarily used amino acids found in recent blood meals as the primary energy source to power their run. Those findings, published this week in Biology Letters, suggest vampire bats may have evolved to develop a unique metabolism typically observed in blood-sucking insects.
No carbs, no problem
Bats are unique amongst mammals and vampires are unique among bats. The horror-novel-inspiring creatures survive entirely on the blood of their victims. Vampire bats typically fly near prey and then quickly walk or run on their thumbs and wrists to close in. They then latch onto their target, typically a peccary or capybara, and use their teeth to make a small incision to draw out blood. If necessary, vampire bats can gorge and consume four times their body weight in liquid.
But that sole reliance on blood severely limits what the vampires can use for energy. Most mammals, humans included, typically fuel exercise by burning carbohydrates and lipids, neither or which are available in the blood. Blood is a plentiful source of protein-building amino acids, but those typically only account for around 10% of the fuel used by mammals during exercise. Vampire bats, through generations of evolution, have flipped that script and somehow manage to sustain themselves primarily off of amino acids. The bats lack genes needed for insulin secretion 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.”
Researchers trained rats to jog on a treadmill
To scientifically measure that observation, researchers captured two dozen vampire bats from Belize and trained them to use a small treadmill typically used to measure the metabolic rates of rats. The goal of the experiment was to first feed the bats with cow blood enriched with two isotopically labeled amino acids and then measure their breath while running. Researchers sourced the 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 walk, then run, at a steady pace. Some of the bats were able to run at speeds of 100 feet per second and could sustain that speed for over 90 minutes.
When the researchers took measurements of CO2 emitted from the bat’s breath, they were able to find trace amounts of the same amino acids included in the blood feast. The breakdown of glycine and leucine, the two amino acids added to the blood, were deemed responsible for as much as 60% of the bat’s total energy production during the run. In the end, the experiment demonstrated vampire bats can convert amino acids into energy in less than 10 minutes and use it to fuel a lengthy endurance run.
That process makes vampires unique among mammals. These findings suggest the metabolism of vampires is actually closer to that of blood-drinking tsetse flies than it is to other bat species. And while flying requires substantially more energy than running, the researchers believe the vampires and similarly burning amino acids for flight as well.
“What’s even more impressive is they can sustain this really high rate of exertion for a long time by only burning the proteins they’ve stored in their muscles,” Welch added. It’s something we can only dream of doing.”
