Vampire bats are extremely strange animals, and it really makes very little sense for a flying fruit-eater to evolve into sucking the blood from other mammals. There are lots of unanswered questions about the vampire bats, but a [recently published paper](https://www.nature.com/articles/s41559-018-0476-8) has looked at the genetics of the vampire bats to find out why they are feeding on blood. 

<center>https://upload.wikimedia.org/wikipedia/commons/3/3f/Desmodus.jpg</center>
*A common vampire bat in Sangayan Island, Paracas National Reserve, Departamento Ica, Peru. [Image by Wikimedia Commons user Acatenazzi, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license](https://commons.wikimedia.org/wiki/File:Desmodus.jpg)*.

## The biology of the vampire bats
There are currently three living species of vampire bats: the common vampire bat (*Desmodus rotundus*), which is shown in the picture above, the hairy-legged vampire bat (*Diphylla ecaudata*), and the white-winged vampire bat (*Diaemus youngi*). All three species are found in the Americas, and are found in areas in Mexico, Chile, Uruguay, Argentina and Brazil. 

The vampire bats feeds mainly on the blood of livestock and other mammals during the night, and uses razor-sharp teeth to cut open the skin of the prey and suck blood out of It by using its tongue. This is their primary food, and most vampire bats never really eat anything else than blood their entire life! 

Most vampire bats carry a lot of different diseases such as rabies, and are considered a pest in most places because of this. [While only 6 % of the vampire bats have rabies, they are known to have transmitted the disease to both pets and humans](https://www.cdc.gov/rabies/bats/education/index.html), so it is best to stay away from them, and seek medical attention if you get bitten. They don’t really feed on humans, but those infected with rabies are obviously pretty weakened, which might lead them to trying to feed on anything they can. 

<center>https://upload.wikimedia.org/wikipedia/commons/b/b0/Vampire_Bat_12.jpg</center>
*[Image by Wikimedia Commons user Ltshears, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license](https://commons.wikimedia.org/wiki/File:Vampire_Bat_12.jpg)*.

## The species have a common ancestor
Feeding only on blood is obviously a very unique trait, so not surprisingly scientists believe that this evolutionary trait only evolved once in a common ancestor of all three species. Despite this the three species are very genetically different, and are even put in three different genera, where they are all alone. They all belong to the subfamily *Desmodontinae* in the family *Phyllostomidae* that includes all leaf-nosed bats, which are all bats that are found in the Americas. 

## How come the vampire bats drink blood?
I briefly mentioned how strange it is that vampire bats do drink blood, and for a long time it has baffled scientists that they are able to live purely off this diet. There are a few problems with eating only blood, such as:
- Blood has a high protein concentration (93 % of blood is protein), and almost no carbohydrates or vitamins. This should be a harmful diet just based on the sheer lack of vitamins! [Protein poisoning is also a serious threat](https://en.wikipedia.org/wiki/Protein_poisoning). 
- There are lots of blood-borne diseases that will infect animals that come into contact with the blood, so how do the bats survive this?
- The huge amount of liquid should be dangerous for the kidneys. 
- Blood is high in iron, which should lead to iron poisoning. 

So how do they deal with all of this? I won’t lie and say that we know all the answers, but a research team from University of Copenhagen in Denmark has taken a look at the hologenome of the bats, and at least made some nice progress towards these questions. 

A **hologenome** is the entire set of genes of an organism, including all microbial genetics found within the organism. This means that the hologenome not only looks at the genes of the organism itself, but also all parasites, gut bacteria and neutral microorganisms in the body. The researchers obtained this by collecting guano (scat) from the vampire bats, and tested it against the hologenome of other non-vampire bats. 

<center>https://upload.wikimedia.org/wikipedia/commons/8/8b/Dyoungi.jpg</center>
*[Image by Wikimedia Commons users Sreejithk2000, posted with the Creative Commons Attribution-Share Alike 2.5 Generic license](https://en.wikipedia.org/wiki/File:Dyoungi.jpg)*.

## The crazy gut microbes of the vampire bats
The first thing that the research team found out was that the gut microbes of the vampire bats was a lot more crazy than the other bats, and includes many bacterial species that cause disease is most other mammals. In fact, they found over 200 disease-bearing microbes in the gut biome of the vampire bats!

This is an important discovery, because it lead to the theory that the ability to live of blood is closely related to the gut microbiome! The scientists believe that these microorganisms are helping out with some of the unique problems that arise when you only feed on blood, meaning that the same organisms that can cause disease and death in most mammals actually serve an important function for the vampire bats! 


## Other interesting discoveries about the vampire bats
The same study also obviously looked at the genome of the vampire bats themselves, and what the found is that the transposon gene called *MULE-MuDR* is found in over twice the amount in vampire bats compared to other bats. This type of gene is able to multiply and move around on the DNA on its own, and are often also called “jumping genes”. While the exact function of the gene is still unclear, it was found in areas that were responsible for immune response, viral defense and metabolism, so the researchers believe that it is playing a part in the process of controlling the problems related to the consumption of all that blood. 

## Thanks for reading
I hope you enjoyed the post, and as always, thank you very much for taking the time to check it out! If you want to learn more, then [check out the paper that was published](https://www.nature.com/articles/s41559-018-0476-8), or [check out the article by BBC that also interviews the lead author](http://www.bbc.com/news/science-environment-43112650).

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