Scientists put blood-pumped vampire bats on tiny treadmills. Here’s what they found

In a groundbreaking study, scientists have discovered that common vampire bats (Desmodus rotundus) possess a unique metabolic strategy, burning proteins directly for energy during exercise—a trait previously thought to be exclusive to certain blood-feeding insects. Researchers Dr. Giulia Rossi and Dr. Kenneth Welch embarked on an expedition to the Lamanai Archaeological Reserve in Belize, capturing 24 adult vampire bats to investigate how these mammals fuel their activities on an entirely blood-based diet.

Vampire bats are remarkable creatures that survive exclusively on blood, a diet rich in proteins but low in fats and sugars. This makes them exceptional among mammals, which typically rely on carbohydrates and fats for energy. Drs. Rossi and Welch aimed to uncover the metabolic mechanisms behind the bats' ability to thrive on such a diet. They hypothesized that vampire bats might utilize a metabolic trick similar to that of certain blood-sucking insects, such as tsetse flies and female mosquitoes, which burn amino acids from blood meals for fuel.

To test their hypothesis, the researchers fed the bats cow's blood containing amino acids with labeled carbon atoms. Following the meal, the bats were placed on a custom-built treadmill designed specifically for them. Studying metabolism in flying animals poses challenges due to the complexity of monitoring them in flight. However, vampire bats are surprisingly adept runners, so the treadmill allowed the researchers to measure the bats' metabolic outputs during exercise without the need for large wind tunnels.

The bats ran at speeds of up to 30 meters per minute while their oxygen intake and carbon dioxide exhalations were monitored using specialized sensors. By analyzing the carbon isotopes in the exhaled breath, the team could determine whether the bats were drawing energy from their recent meal or from stored fats and sugars. The presence of labeled carbon atoms in the exhaled carbon dioxide indicated that the bats were burning the amino acids from the blood meal.

The results were striking. During exercise, a substantial portion of the carbon dioxide the bats exhaled—up to 60 percent—came from the metabolization of amino acids from their recent meal. This finding confirmed that vampire bats are indeed using proteins directly as a primary energy source during physical activity. "What's different here is that this seems to be what this animal is going to do all year round, every day when it feeds, and that it's making use of the protein in that blood meal that it ingested just minutes before," said Dr. Kenneth Welch, according to a report in New Scientist.

This discovery positions vampire bats alongside certain blood-feeding insects in their metabolic strategies, suggesting a remarkable example of convergent evolution. Both vampire bats and these insects have independently developed similar solutions to the challenges posed by a blood-based diet. "In an extraordinary example of convergent evolution, it is likely that natural selection led both vampire bats and blood-feeding insects to develop very similar solutions to the same problem," notes the study.

However, there are significant trade-offs to this metabolic approach. Unlike fats and carbohydrates, amino acids cannot be stored in the body as energy reserves. This reliance on proteins leaves vampire bats vulnerable to starvation if they fail to feed regularly. Studies indicate that they risk starvation after only 24 hours without a meal. Dr. Welch explained, "This different strategy leaves vampire bats far more susceptible to starvation."

To counteract this vulnerability, vampire bats have evolved strong social bonds and cooperative feeding behaviors. They engage in reciprocal altruism, where individuals share food with others in their group. Vampire bats will regurgitate some of their own blood meal into the mouths of roost-mates that have failed to feed, ensuring the survival of the group. This social strategy mitigates the risks associated with their unique metabolism.

The researchers also faced challenges during the experiments due to the bats' intelligence and agility. The customized treadmill had to be modified because the bats, being exceptionally smart and clever, found ways to avoid running. "A rat likely wouldn't have noticed these. But, with their long forelimbs and large thumbs, the vampires could easily reach up and grab onto those holes in order to avoid having to spend the effort to actually walk on the treadmill belt," Dr. Welch, Associate Professor at the University of Toronto Scarborough, recounted, according to IFLScience.

This study sheds light on the flexibility of mammalian physiology and how dietary specialization can drive unique evolutionary adaptations. "How powerfully what you eat can shape what you burn, and just how flexible mammalian physiology can be in meeting unusual physiological challenges, and the opportunities that come from dietary specialization," Dr. Welch remarked. 

Moreover, the research underscores the importance of understanding vampire bats beyond common misconceptions. "Vampire bats are exceptionally smart, clever little animals," stated Dr. Welch. Their complex social structures and unique metabolic strategies make them a fascinating subject of study.

All the bats involved in the study were released back into their natural habitat at the end of the experiments, ensuring minimal impact on the wild population. 

Sources: New Scientist, Phys.org, The Economist, IFLScience, Science News

This article was written in collaboration with generative AI company Alchemiq