Surviving on blood alone is no picnic. Vampire bats are the only mammal known to feed exclusively on the stuff. They may have gained this ability by losing some genes, researchers now report.
Vampire bats have developed special feeding behaviors to drink their meals. Their bodies, too, have evolved to thrive on a blood-only diet. But scientists didn’t know what changes in the bats’ DNA might explain these bodily adaptations.
Michael Hiller studies how an animal’s genome — its full set of genes — drives behavior and other traits. He runs a lab at the Senckenberg Society for Nature Research in Frankfurt, Germany. Hiller is part of a team that pieced together the genome of the common vampire bat (Desmodus rotundus). The researchers compared it with the genomes of 26 other bat species, including six from the same family as vampire bats. The team then searched for genes that were now missing or inactive in D. rotundus.
“Sometimes losing genes in evolutionary time frames can actually be adaptive or beneficial,” Hiller says.
The team found 13 genes that were active in other bats but not vampires. In the blood-diners, these genes had changes — mutations — that messed up their instructions. It turned off those genes. Over time, these changes may have led to vampire bats’ unique lifestyle. Hiller’s team shared its new findings March 25 in Science Advances.
Poor taste
Three of the genes were already known to be missing in vampire bats. These genes are linked to sweet and bitter taste receptors in other animals. Without them, vampire bats likely can’t taste as well — all the better for drinking blood.
Loss of another 10 genes showed up for the first time in this study. The researchers looked at what these genes do in other animals to get ideas about how losing them might support a blood-rich diet.
Many of the genes play roles in digestion. Some help boost levels of insulin in the body. This hormone helps the body process sugar from food. But blood doesn’t contain much sugar. If vampire bats have little need for insulin, these genes probably weren’t that useful anymore. Another gene is linked in other mammals to making the stomach acid that breaks down solid food. That gene may have been lost as the vampire bat’s stomach evolved to handle mostly fluid.
Yet another lost gene controls iron absorption in the gut. For most animals, eating too much iron can be toxic. When active, this gene blocks cells in the gut from taking in too much iron. Blood is rich in iron but low in calories, so vampire bats need plenty of it. They must drink up to 1.4 times their own weight during each feed. In the process, they consume a potentially harmful amount of iron.
The researchers now think that losing this gene may help the bats get rid of that extra iron. The gut of vampire bats sheds cells frequently. Without the active gene, these cells may be able to take in huge amounts of iron — then quickly excrete it. That might allow them to avoid an iron overload. This idea is also supported by an earlier study. It found cells full of iron in vampire-bat poop.
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One more lost gene may support vampire bats’ social behaviors. In other animals, one role of this gene is to break down a compound produced by nerve cells — one that is important for learning and memory. Vampire bats lead complex social lives that rely on strong memory. And because their bodies don’t store much sugar, vampire bats are susceptible to starvation. Their friends may sometimes help out by sharing regurgitated blood. And they’re more likely to share with bats that previously shared with them. Vampire bats also form long-term bonds and even feed with their friends in the wild. So loss of this gene could help support their socializing.
“I think there are some compelling hypotheses there,” says David Liberles. He works at Temple University in Philadelphia. There he studies how genomes evolve. Liberles didn’t work on this study, but does note that there are two other species of vampire bats. Both feed more on the blood of birds. D. rotundus, in contrast, prefers to drink from mammals. It would be interesting to see if the same genes were also lost in other vampire bats, he says.
Whether dining on blood caused these changes — or the other way round — isn’t known. Either way, those changes likely occurred gradually over millions of years, Hiller says. “Maybe they started drinking more and more blood, and then you have time to better adapt to this very challenging diet.”
Power Words
More About Power Wordsadaptation: (in biology) The development of new programs, processes, policies and structures to make communities and their inhabitants better able to head off — or at least withstand — the dangerous impacts of a warming climate. Those impacts may include drought, flooding, wildfires, extreme heat and extreme storms.
bat: A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal. (in sports) The usually wooden piece of athletic equipment that a player uses to forcefully swat at a ball. (v.) Or the act of swinging a machine-tooled stick or flat bat with hopes of hitting a ball.
behavior: The way something, often a person or other organism, acts towards others, or conducts itself.
birds: Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
calorie: The amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. It is typically used as a measurement of the energy contained in some defined amount of food. The exception: when referring to the energy in food, the convention is to call a kilocalorie, or 1,000 of these calories, a "calorie." Here, a food calorie is the amount of energy needed to raise 1 kilogram of water 1 degree C.
cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells.
compound: (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
diet: (n.) The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. Sometimes this is a specific food-intake plan. (v.) To adopt a specific food-intake plan.
DNA: (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
evolve: (adj. evolutionary) To change gradually over generations, or a long period of time. In living organisms, such an evolution usually involves random changes to genes that will then be passed along to an individual’s offspring. These can lead to new traits, such as altered coloration, new susceptibility to disease or protection from it, or different shaped features (such as legs, antennae, toes or internal organs). Nonliving things may also be described as evolving if they change over time. For instance, the miniaturization of computers is sometimes described as these devices evolving to smaller, more complex devices.
excrete: To remove waste products from the body, such as in the urine.
family: A taxonomic group consisting of at least one genus of organisms.
gene: (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
genome: The complete set of genes or genetic material in a cell or an organism. The study of this genetic inheritance housed within cells is known as genomics.
gut: An informal term for the gastrointestinal tract, especially the intestines.
hormone: (in zoology and medicine) A chemical produced in a gland and then carried in the bloodstream to another part of the body. Hormones control many important body activities, such as growth. Hormones act by triggering or regulating chemical reactions in the body. (in botany) A chemical that serves as a signaling compound that tells cells of a plant when and how to develop, or when to grow old and die.
insulin: A hormone produced in the pancreas (an organ that is part of the digestive system) that helps the body use glucose as fuel.
iron: A metallic element that is common within minerals inEarth’s crust and in its hot core. This metal also is found in cosmic dustand in many meteorites.
mammal: A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
mutation: (v. mutate) Some change that occurs to a gene in an organism’s DNA. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet. A gene with this change is referred to as a mutant.
receptor: (in biology) A molecule in cells that serves as a docking station for another molecule. That second molecule can turn on some special activity by the cell.
social: (adj.) Relating to gatherings of people; a term for animals (or people) that prefer to exist in groups. (noun) A gathering of people, for instance those who belong to a club or other organization, for the purpose of enjoying each other’s company.
species: A group of similar organisms capable of producing offspring that can survive and reproduce.
strategy: A thoughtful and clever plan for achieving some difficult or challenging goal.
taste: One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).
toxic: Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.
trait: A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
unique: Something that is unlike anything else; the only one of its kind.
Citations
Journal: M. Blumer et al. Gene losses in the common vampire bat illuminate molecular adaptations to blood feeding. Science Advances. Vol. 8, March 25, 2022. doi: 10.1126/sciadv.abm6494.
Journal: W. Hong and H. Zhao. Vampire bats exhibit evolutionary reduction of bitter taste receptor genes common to other bats. Proceedings of the Royal Society B. Vol. 281, August 7, 2014. doi: 10.1098/rspb.2014.1079.
