Vampire bats get energy from an unusual source

Vampire bats are the only mammals that live solely off blood. Their feeding habits may be the stuff of horror stories, but they have an interesting form of metabolism that sets them apart from other vertbrates.

Most vertebrates, including humans, use carbohydrates and fats for a source of energy. But these nutrients are in short supply in blood, the only food eaten by vampire bats.

Researchers Ken Welch, from the University of Toronto, and Giulia Rossi who is now at McMaster University in Hamilton, Canada, wondered how vampire bats actually get the energy they need for survival, when they have such a simple diet.

Eating habits of the night stalker

Vampire bats can fly from place to place, like other bats, but they also do a lot of walking. In particular, they are known to creep silently up to a sleeping animal, like a cow, in the dark of night. For this, they walk along the ground on all four limbs.

They have razor-sharp teeth that cut into the sleeping host without causing any pain. The incision, along with the bat’s anticoagulant saliva, cause blood to ooze out. This is lapped up by the bat.

Rossi and Welch wondered how vampire bats can survive on such a simple diet that is apparently deficient in carbohydrates and fats. To investigate, they caught 24 vampire bats while on location in Belize, Central America.

Innovative approach to studying metabolism

Revealing how vampire bats manage their metabolism comes with significant challenges, as traditional equipment for tracking metabolism in flying animals is cumbersome and awkward. This can interfere with natural movement and skew the results.

To overcome this, Rossi and Welch capitalized on the fact that vampire bats stalk their prey by walking or running along the ground. The researchers set the bats on a specially-designed bat treadmill that was placed inside a small enclosure.

The speed of the treadmill was increased gradually, until the bats were running along at around 30 meters per minute. With this method, the researchers could accurately measure metabolism without influencing the bats’ behavior.

Source of energy for vampire bats

Sensors monitored oxygen intake and carbon dioxide released in the bat’s breath, while the source of the energy for respiration was determined using isotopically labeled cow blood.

The results revealed that the vampire bats were using amino acids for energy, rather than metabolizing carbohydrates or fats. Amino acids derive from the digestion of proteins and are a common component in blood.

This discovery indicates that the bats get their energy from their recent blood meal, similar to the way that blood-feeding tsetse flies or mosquitoes do. 

Metabolic miracles of vampire bats

Most mammals can use amino acids as a source of energy if they are short on carbohydrates and fats, so the basic bat chemistry isn’t that unusual.

“In most of us mammals, some kind of biochemical pathways can break down amino acids for fuel or some other use, but they’re built to slowly churn along in the background,” explained Ken Welch.

Unlike fats that can be stored and used when needed, amino acids cannot be stored as an energy reserve. These bats must therefore feed daily to avoid starvation – a characteristic that gives them the reputation for being voracious blood-suckers.

Yet, they manage to navigate this challenge, surviving each night with precision and resilience one drop of blood at a time.

Bat adaptations beyond metabolism

While this unique metabolic activity of vampire bats is fascinating, their survival relies on more than just physiology. These creatures have evolved impressive adaptations to ensure their nightly success. One of the key adaptations is their highly developed sensory system.

Vampire bats possess specialized heat sensors, located on their noses, that allow them to detect the blood vessels of their prey with pinpoint accuracy.

This enables them to make precise incisions, ensuring minimal disturbance to the host and a steady food supply.

Moreover, their sharp teeth and anticoagulant saliva play crucial roles in their feeding process. The bat’s teeth are so fine and sharp that their bite is virtually painless, while their saliva contains a compound called draculin that prevents blood from clotting, ensuring a continuous flow while they feed.

These adaptations highlight that vampire bats are highly specialized creatures that rely on a suite of traits extending beyond their metabolic feats to master their environment and thrive against the odds.

The study is published in the journal Biology Letters.

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