What makes bats so special?
“The nitty-gritty law of nature is that small things live fast and die young,” says bat expert Emma Teeling, Professor of Zoology at University College Dublin. “Bats buck that trend.”
We do too, in a way. It’s not that we’re small, but, when you adjust for body size, there are only 19 species of mammal that live longer than humans. 18 of those are bats.
“The longest-lived bat we know about lived in the wild for over 41 years, with no signs of ageing,” says Teeling, “which is like a human living to 250.”
That bat was still flying – not just old: healthy.
That’s important. If we want to understand all of bats’ unique adaptations, flight’s the best place to start.
When Teeling says small things live fast, she means they burn energy quickly: that they have a high metabolic rate. One of the main theories of ageing connects this to lifespan, which helps explain why animals like mice usually die within a couple of years.
But bats live faster than any other mammal. Flying is the hardest way to get around, and it means bats use 3 to 5 times more energy moving than mice do. If anything, then, bats’ lives should be shorter.
“Flying causes a whole bunch of these byproducts of metabolism that break up DNA,” explains Teeling. “Broken DNA can drive cancer; it overexcites your immune system, which can make you ill; it drives all ageing. Our hypothesis is that bats must have evolved special mechanisms to allow them to deal with the damage of flight.”
Perhaps, once you’ve worked out a safe way of swimming through the sky, the rest of living comes a little bit easier.
Just look at us. People only started flying 120 years ago, but average life expectancy around the world has more than doubled since then. That’s thanks to our unique adaptations: our big brains and ability to think, which have given us vaccines and cancer immunotherapies alongside air travel. Now we can use them to learn from other animals too.
“When you look to nature, you can find solutions,” explains Teeling. “After billions of years of evolution on this planet, every species alive today has a signature of survival, so the answers we need are already here. But to really understand evolution, you’ve got to look at the raw material evolution acts on. That’s the genome.”
The genome is the complete set of DNA instructions for every living thing. It appears in full in the nucleus of every cell, where it’s wound tightly into structures called chromosomes. The fact we can now look at it is down to another one of humanity’s greatest technological achievements: whole genome sequencing (WGS).
Although we don’t yet know what all the information in our genome means, we can learn more by comparing it to other animals.
Teeling runs a project called Bat1K, which aims to record the genome of every species of bat in the world. That’s a long-term goal, but the number of bat genomes sequenced is climbing, and smaller studies of single bat genomes have already taught us a lot about where their superpowers come from.
How do bats resist cancer?
For more than a decade, Teeling’s team has been following a colony of long-lived mouse-eared bats (which have been recorded at 37 years old) in France. With the help of the local community and a conservation charity, they microchipped the whole colony, which means they can keep track of different individuals over time.
Now, every year, the team come back to the old churches where the bats roost, to take a few drops of their blood.
“It’s quite vampire-esque,” says Teeling, though she stresses that the process doesn’t hurt the bats. “We take blood from bats in Gothic churches back to our lab in Ireland and sequence it to see if it shows any of the changes that underlie ageing and can cause cancer in humans.”
They’ve found the opposite.
At the end of chromosomes are protective caps called telomeres, which, like the plastic tips on shoelaces, keep our genes from tangling or unravelling. These wear down as our cells divide, until, eventually, there’s so little telomere left the process can’t continue. The cell either retires from the copying life, or it dies.
In 2018, Teeling’s team showed that the telomeres in mouse-eared bat cells don’t degrade. The telomeres in most cancer cells don’t either, which is how they can keep growing and dividing when they shouldn’t. They’re like zombies, relentlessly moving forward even as their bones snap and their limbs fall off.
Or, if you prefer, cancer cells are vampires. Like Dracula, they can seem normal to the rest of the body even as they put it in danger. As cancers get bigger, they can encourage the growth of new blood vessels. And they’re only vulnerable to special weapons like chemotherapy, radiotherapy or – for vampires specifically – a stake in the heart.
But mouse-eared bat cells know how to look after themselves. In 2019, Teeling and her colleagues showed how they stay young, strong and under control.
“These bats have extra checkpoints to help maintain control of how their cells divide,” she explains. “Then the genes responsible for repairing DNA get more active as they age; and their ability to remove other damage from their cells also increases. They clean up messes that could lead to cancer, rather than allowing damage to build up.”
The Batman immune response
Different bats seem to have their own approaches. Horseshoe bats – which can also live for more than 30 years – regrow their telomeres while they’re hibernating. That might be even more impressive. These bats can reverse the effects of ageing on their cells.
They do it with an enzyme called telomerase, which hasn’t been found in mouse-eared bats, but is also how cancer cells keep themselves going. The big difference is that bats always have both on-switches and off-switches. It’s part of the balance that keeps them in the air.