Vampire bats and their legendary taste for blood are the perfect stuff for nightmares. “They are essentially living Dracula,” explains Michael Hiller, a genomics expert at the LOEWE Center for Translational Biodiversity Genomics in Frankfurt, Germany. These tiny bats, found in forests and caves throughout Central and South America and often prey on livestock, are the only mammals that feed exclusively on blood. New research on the bat genome by Hiller and his colleagues helps explain how these animals manage to live on such a nutrient-poor diet.
Although vampire movies treat blood like an elixir, this watery liquid is nearly free of carbohydrates and fat, and low in calories. Because of these deficiencies, vampire bats have lower insulin levels than other mammals, and to get enough nutrients they need to drink up to 1.4 times their body weight of blood at each meal. However, gulping down a lot of blood is dangerous, as it results in a high iron intake, which can cause damage to the digestive tract and liver. Despite weighing little more than a stylus battery, it is estimated that a vampire bat consumes 800 times more iron in its diet than the average human.
Scientists have long wondered how these animals can survive on such a poor diet. To try to answer this question, Hiller and his colleagues recently thoroughly investigated the genetics of these legendary bloodsuckers using state-of-the-art sequencing techniques. They therefore sequenced and analyzed the genome of the common vampire bat (Desmodus rotundus) and compared it to the genomes of 26 other bat species, hoping to pinpoint the specific genes that help vampire bats digest blood.
Their results, published in the journal “Science Advances”, show that, as regards the genes that allow them to feed on blood, the saying “less is more” applies: in fact, instead of developing new genes to help them metabolize blood, vampire bats have lost 13 key genes in evolution compared to other species; and 10 of these losses were so far unknown. “Generally, when we hear about mutations that destroy genes, we think it’s a bad thing,” Hiller explains. “In our study, however, we found that losing certain genes can be beneficial to adapt to this very particular diet.”
The fallout from the loss of these genes is evident everywhere, from the brain to the gut. Some deletions have led to less insulin secretion, which is less important in these animals due to their low-sugar diet. Others have reduced the amount of sweet and bitter taste receptors, making bats less sensitive to the bad taste of the blood they suck.
One of the deletions is related to the shape of the vampire bats’ strange stomach, which looks like a floppy windsock and is specialized for a single task, says Melissa Ingala, a bat biologist at Fairleigh Dickinson University who was not involved in the study. “That shape has evolved to fill with liquid like a balloon and draw as much water out of the blood as possible, so that all that’s left to digest is the solid cellular component of the blood,” she adds. This means that vampire bats must start urinating immediately after eating, to expel any excess water that fills their stomachs and weighs them down.
Another lost gene, called REP15, was once responsible for keeping iron in the blood of bats and out of their intestines. Without this mechanism, iron is able to enter the cells of the intestinal wall. But the researchers speculate that this infiltration is actually good for bats – intestinal cells are short-lived and easily replaceable, meaning bats can shed them and excrete them with droppings, thus eliminating excess iron instead. to keep it circulating in the blood.
The vampire bat brain may also have benefited from a fortuitous loss of genes. CYP39A1 it is a gene needed primarily to degrade a byproduct of cholesterol digestion. Without it, the levels of this metabolite in the bats’ brains skyrocket. Past studies have established that higher levels of the metabolite were responsible for improving memory, learning and sociability in rodents. This may help explain why vampire bats appear to be smarter and more sociable than other bats.
This possible cognitive and sociability enhancement helps bats survive a lifestyle based on blood consumption. With such a nutrient-poor diet, these animals have low energy reserves, which makes them particularly vulnerable to starvation. Going several nights without drinking blood is often fatal. So vampire bats are ready to help a hungry companion by regurgitating blood into his mouth. And what’s more noteworthy, they often return the favor by providing blood to those who have helped them in the past. To do this, it is crucial to have a good memory. “Vampire bats build long-lasting friendships based on this mutual sharing of food,” concludes Ingala. In the compassionate world of vampire bats, blood is a dish to share with those you care about.
(The original of this article was published in “Scientific American” on March 25, 2022. Translation and editing by Le Scienze. Reproduction authorized, all rights reserved.)