On the trail of the code of vampirism

“Dracula” carries signatures of his bloodthirsty way of life in the genome. © Marco AR Mello

They feed solely on blood and the vampire bats are also known for their highly developed social behavior. Researchers have now discovered peculiarities in the genome of the bizarre bats that are apparently related to their unusual diet and lifestyle. Accordingly, genetic defects reflect their adaptation to the meager supply of nutrients and the problematically high iron content in the blood food. The scientists also discovered a genetic quirk that could be linked to vampires’ complex social intelligence.

Diet with scary factor: While other bats hunt insects, eat fruit or drink nectar, vampire bats exclusively slurp up blood. The three American vampire bat species have specialized in different victims: Two tap into birds – the best-known representative, on the other hand, specializes in larger mammals: The common vampire bat (Desmodus rotundus) lands on its victims at night and scratches them with its sharp teeth Skin and then lick the leaking blood. In this way, the vampires even occasionally bleed humans. When day breaks, the real-life models of Count Dracula retire to their sleeping quarters in hollow trees, where they live in colonies of up to several hundred animals.

Are diet and lifestyle reflected in the genome?

Contrary to their diet, vampires’ social life appears extremely friendly: Studies have shown that each animal has its own personal social network within the colony. The befriended individuals even form a kind of social security system: They feed needy friends with regurgitated blood. The emergency supply has to do with the low nutrient content, which hardly allows any reserves: Although blood contains a lot of protein, it has very few carbohydrates – instead it is “burdened” with enormous amounts of iron. How do the animals cope with this difficult and one-sided diet? In order to gain information about the special adaptations of vampire bats, the researchers led by Michael Hiller from the LOEWE Center for Translational Biodiversity Genomics in Frankfurt am Main have now taken a look at the genome of vampires.

For their study, they sequenced the genome of the common vampire bat. In this way, the scientists were able to compare the genome of the bloodsuckers with known genetic information from 26 “normal” bat species. In addition, a newly developed analysis method was used that specializes in recognizing an important aspect of adaptations to special lifestyles: defective genes. This is because certain characteristics are often not based on additional gene functions, but on the modulation or blockage of certain hereditary factors.

As Hiller and his colleagues report, they identified thirteen genes that were switched off in the course of the evolution of vampire bats: These hereditary factors carry mutations that render them inoperable. It turned out that two of these defective genes are involved in the release of the blood sugar-regulating hormone insulin in other animals. As the researchers explain, vampire bats have lost gene functions because their bloody food is low in sugar and therefore requires little insulin.

Vampire specific genetic defects

According to the researchers, another genetic peculiarity has to do with the problematically high iron content in the blood. Because the vampire bats consume on average about 800 times more iron than a human, which requires a regulation of the intake. Paradoxically at first, they discovered a defective gene in vampires that normally inhibits the transport of iron from the bloodstream into the cells of the inner intestinal wall. However, the loss probably contributes to the fact that excess iron can accumulate more in the intestinal cells. Because these short-lived cells are constantly being shed from the body, the vampire bats can probably use them to get rid of the enormous amounts of iron, the researchers explain.

Among the identified genetic defects, they also put a hereditary disposition in the foreground that could be connected to the vampire-typical friendship systems: the genetic peculiarity could have influenced the evolution of certain cognitive abilities in vampire bats, the scientists suspect. According to them, it leads to a certain metabolic product accumulating in the brain, which is known to have a function in cognitive performance and social behavior. Higher concentrations of this substance can promote memory, learning and social behavior, studies in mammals including humans suggest. Perhaps the genetic peculiarity of vampires is therefore linked to their long-term social memory: Specifically, it may help them remember which colony members have previously helped them by donating blood.

As the researchers emphasize in conclusion, looking at the genetic defects is only the beginning of their search for the signatures of vampirism in the genome: “Of course, adaptations to this unique way of life are not only due to the loss of genes,” says Hiller . In the further investigations, they now want to include the other two species of vampire bats, whose genomes they are also currently sequencing. “Our goal is to get a complete picture of the genomic changes in all three vampire bat species. And there is still a lot to learn!” says the scientist.

Source: Senckenberg Research Institute and Natural History Museums, specialist article: Science Advances, doi: 10.1126/sciadv.abm6494

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