Scientists might have finally figured out how vampire bats thrive on an all-blood diet

Vampire bats feed exclusively on blood, as many people know, but less is known about how or why they adapted to thrive on such a strict diet.

There are three species of vampire bats. Together, they make up the only blood-drinking mammals. It’s estimated that these species evolved about 26 million years ago from other bats, which primarily feed on insects and fruit.

Researchers in Germany at the Max Planck Institute of Molecular Cell Biology and Genetics sequenced the common vampire bat genome (Desmodus rotundus) and compared it to the genomes of 27 other bat species, looking for genes that may have gotten lost in the evolutionary fray. Their findings, published this week in the journal Science Advances, are necessary to understanding how vampire bats became the cute little furry bloodsuckers we know today.

What’s new — After generating a high-quality genome of D. rotundus, researchers homed in on 10 genes struck from the common vampire bat genome, all of which likely contribute to the creature’s unique physiology, behavior, and most importantly, sanguine diet.

“Losing genes can sometimes be beneficial and contribute to adaptations and to, for example, very specialized diets,” Michael Hiller, the paper’s supervising author and a developmental biologist at the Max Planck Institute tells Inverse. Some of the lost genes are related to reduced insulin secretion and enhanced iron excretion.

“This is a major step forward in comparing the evolution of vampires to the other bats,” behavioral ecologist Gerald Carter told Inverse in an email. Carter is a professor at The Ohio State University and was not involved in the study.

Why it matters — Genetically, knowing what’s been lost helps us understand why things are the way they are now. After all, vampire bats comprise just three of about 1,000 bat species but are the only mammals to feed on blood. This anomaly is worth studying to understand not only the exception to the rule but the rule itself.

These findings benefit all sorts of bat experts. “In learning what genes vampire bats have lost over evolutionary time, we are also learning about the role of these genes in many other organisms,” Carter writes. “When we understand more about genetic evolution and gene [function,] that does have clear implications for understanding life in general.”

While this evolution shaped the vampire bats’ macabre diet, changes rippled throughout the genome, altering its physiology, morphology, and behavior. Vampire bats are singular across the board: They can run, jump, sense heat, and share food. Carter has a special affection for this species, calling them “super bats.”

Digging into the details — In genetic evolution, there are two main paths by which genes get filtered out of a species’ genome, Hiller says. One method he calls “use it or lose it,” applies to genes where the function of the encoded protein is no longer necessary. Then, there’s no selection to preserve the gene sequence.

The other category is “less is more,” which Hiller describes as “more interesting and surprising.” He says it describes instances when inactivating a gene is actually beneficial. It may seem counterintuitive to inactivate a gene for survival, considering mutations in humans are responsible for diseases such as cancer. But with these vampire bats, inactivating these specific genes actually benefits the species’ longevity, and optimizes its sanguivorous body. Blood isn’t the healthiest diet staple, so some of these gene losses serve to alter how the vampire bat processes nutrients so that it can thrive on blood alone.

For instance, blood is only 1 percent sugar and 1 percent fat, according to Hiller. In losing the ERN2 gene, which protects the body from absorbing too much fat, bats could cope with a fat-poor diet. Since vampire bats consume very little fat, they had no need for this gene, relegating it to the “use it or lose it” category.

Blood is also extremely rich in iron. Hiller says that bats consume 800 times as much iron as humans do. In the “less is more” category, vampire bats lost inhibitory gene REP15, which regulated how much iron their cells absorbed. Hiller and his team hypothesize that in losing this gene, bats dealt with the excess iron found in blood by packing their cells full of it and then excreting it.

Another adaptation may have impacted their social intelligence. One of the lost genes was expressed in the brain, producing the only enzyme that could degrade a cholesterol metabolite. This metabolite stimulates receptors in the brain, thereby supercharging the bats’ memory, learning, and social behavior. Without the gene that produces a cholesterol-degrading enzyme, it’s expected that the metabolite builds up, juicing the brain.

Indeed, Hiller says that vampire bats express more sophisticated social behaviors, such as recognizing other bats they bonded with in captivity out in the wild. Studies have demonstrated these bats’ social side, including one of Carter’s that demonstrates bats can form bonds in captivity and then find their friends for a shared meal in the wild. These evolutionary behaviors can be attributed to this gene loss.

These changes came about, Hiller’s team believes, through a genetic mutation at the basic level at one point. For bats that lose, for example, the ERN2 gene, they may not be any weaker than bats who possess that gene, so they propagate. This mutation continued to be passed down throughout future bat generations. Sometimes “Selection will influence the fate of this mutation,” he tells Inverse.

What’s next — This finding can open up pragmatic research in areas like agriculture. Carter points out that one newfound gene loss suggests changes in vampire bats’ immune function, so comparing viruses and bacteria found in vampire bats as opposed to bat species in the same place could be useful. Carter wants to see this research with an eye toward agriculture and public health, considering vampire bats scout every night for blood, often using livestock as lunch.

There are still depths of the bat genome to be plumbed. Hiller is part of a larger project called Bat1K which aims to sequence the genome of every bat species. He’s interested in expanding his view to a broader bat family called Phyllostomidae, which includes vampire bats. This unusual group contains many other anomalous winged mammals. “We find all sorts of other diets that you could imagine,” Hiller says. The group contains insectivores, omnivores, pescatarians, and fruit- and nectar-feeding bats. “Something special’s going on in this group.”