Common vampire bats (Desmodus rotundus) are the only mammals that can survive while feeding exclusively on blood, and it may have to do with their genetic code.
When researchers compared the genome of vampire bats to 26 other bat species, they found 13 genes that were missing or inactive, reports Christina Larson for the Associated Press. Over the years, these changes in the genetic code have allowed the bats to survive on an iron-rich blood diet that's low in fats or carbohydrates. Details on the study were published last week in Science Advances.
Vampire bats are found in caves and forests throughout Central and South America and often prey on livestock at night for a quick bite. However, since blood is mainly made up of water and low in calories, the blood-thirsty bats need to consume 1.4 times their body weight in blood during each meal to get the energy they need, reports Alice Klein for New Scientist. For perspective, the mini bats weigh slightly more than a one AA battery, reports Jack Tamisiea for Scientific American.
Blood is also high in iron, which can disrupt the digestive tract and liver. Incredibly, the bats consume 800 times more iron in their diet than an average human.
"Blood is a terrible food source," Hannah Kim Frank, a bat expert at Tulane University who was not involved in the study, tells the Associated Press. "It's totally bizarre and amazing that vampire bats can survive on blood — they are really weird, even among bats."
To see how the bats can survive on the nutrient-poor liquid diet, Michael Hiller, a genomics expert at the LOEWE Center for Translational Biodiversity Genomics, and his team sequenced the genomes of 26 other bat species and compared them to the vampire bat genome.
The team identified 13 genes that vampire bats lost over their evolution. Three of those genes were responsible for taste receptors that distinguish foods by sweetness or bitterness, New Scientist reports. Two genes that the bats shed managed blood sugar levels. Since an all-blood diet is low in carbohydrates, some deletions for insulin secretions also were found, per Scientific American.
One of the lost genes is related to the vampire bat's stomach shape and how it digests blood. The bat's stomach is shaped like a conical tube that fills up like a water balloon. The stomach will expel as much water as it can from the consumed blood, so all there is to digest is the solids filtered out of the blood, explains Melissa Ingala, a Smithsonian National Zoo bat expert not involved with the study, explained to Scientific American. To expel all the extra water inside their stomachs, vampire bats will begin urinating as soon as they finish their bloodmeal.
Two other genes that were lost are called REP15 and CYP39A1. The loss of REP15 most likely aided vampire bats in adapting to high dietary iron levels by enhancing iron excretion, the team explains in their study. The gene keeps iron in a bat's bloodstream and out of the intestines. Without this gene, iron can seep into cells in the intestinal wall, per Scientific American. When intestinal cells are shed through their digestive systems, they are expelled in iron-rich droppings instead of having extra iron from their diets flowing through their bloodstream.
The loss of the gene CYP39A1 may have enhanced vampire bats' cognitive abilities. Losing this gene boosted a chemical called 24S-hydroxycholesterol, which has been shown to enhance learning and memory, per New Scientist. This missing gene in the genome of vampire bats may explain why vampire bats are more intelligent and social than other bats.
"Vampire bats are especially dependent on such advanced social behavior, as it helps them to cope with the negative consequences of their carbohydrate-poor blood diet," says study author Moritz Blumer, a computational genomicist at the University of Cambridge, to New Scientist.
The cognitive boost and increased social skills most likely help the bats survive their nutrient-poor diet, which makes them vulnerable to starvation. To get by, vampire bats help starving roost mates by regurgitating blood into their friend's mouth, and they often return the favor, Scientific American reports. Bats will remember bat mates who provided them with a meal in the past and help them out in the future.
"Vampire bats develop long-term friendships with each other built on this mutual food sharing," Ingala tells Scientific American.