Examination on treadmills How vampire bats use blood for locomotion
November 7, 2024, 6:37 p.m. Listen to article
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As a flying species, bats represent a special feature within the group of mammals. But a blood-sucking subspecies also seems to be different when it comes to metabolism. Researchers discovered this after they captured the animals, fed them, put them on a treadmill and examined them.
Most mammals rely on carbohydrates and fats for energy to move. On the other hand, amino acids, the building blocks of proteins, can often hardly be used as fuel. But things are different for a certain group of mammals: vampire bats. They feed exclusively on blood. One Study in the journal “Biology Letters” shows that these bats primarily use amino acids from their protein-rich blood meals to move forward.
The researchers from the University of Toronto in Canada compare this type of fuel use with that of blood-sucking insects. Tsetse flies, for example, use the amino acid proline to fly. “The optionally blood-sucking female Egyptian tiger mosquitoes, but not the exclusively nectar- or fruit-feeding male tiger mosquitoes, exhibit a similar ability,” they write.
Research work in the rainforest
For the study, Giulia Rossi and Kenneth Welch caught a total of 24 vampire bats (Desmodus round) in the tropical rainforest in Belize, Central America. These animals usually fly towards herd animals or wild animals such as tapirs and deer to make a tiny wound in their skin and lick up the blood that comes out. The animals, which weigh around 15 to 45 grams, can absorb up to 40 percent of their body weight.
The bats usually do not land on their victims, but rather close to them. To sneak up on them, they can run and jump on the ground with their flight membranes folded. The researchers took advantage of this ability: They examined the captured animals on a treadmill, which is otherwise used for rats, instead of in a wind tunnel.
Inhalation and exhalation analyzed
Before the experiments, the animals received a meal of cow blood enriched with isotopically labeled amino acids, either leucine or glycine. Then the bats were placed on the treadmill, the speed of which was increased several times. The air flowing through was examined to determine how much oxygen was consumed by the animals and how much carbon dioxide was emitted. The carbon dioxide was further analyzed for isotopes.
“The CO2 produced by the oxidation of the ingested amino acids was almost immediately present in the breathing air of the moving bats, suggesting that the most recent protein meal is immediately used as fuel for aerobic activity in this species,” says of the study. The bats utilized both amino acids equally well.
Vulnerable to starvation
The researchers conclude that the bats got most of their mileage from their most recent blood meal. The experiments confirmed that vampire bats are not good at storing and using carbohydrates or fats, Welch emphasized. “They are extremely vulnerable to starvation.” If a vampire bat doesn’t consume blood for 24 to 48 hours, it could die.
The animals probably used their amino acid reserves as fuel during their daily fasting period during the hours of sunshine, for example by breaking down proteins from certain tissues, he continued.
“But they have another trick to survive missing a meal. Vampire bats are extremely sociable animals that roost in a network of friends. If a bat goes a day without foraging or is unable to have a blood meal “A successful friend can share his blood meal with his hungry friend.” The animals remembered who had previously been friendly to them – and returned such gestures.
Wind tunnel research is still pending
Because the research was conducted in a rural part of Belize, the researchers used the easy-to-transport treadmill. “Wind tunnels, such as those needed to study the flight metabolism of birds or bats, are large, building-like devices,” explained Welch. Transport would have been logistically impossible.
But it is certainly interesting to examine the metabolism of bats in flight, according to the study: it is usually a much more energetically expensive form of locomotion than running. According to Rossi and Welch, such an experiment has not yet been carried out.
