Emma Teeling: Bats and why I love them
Emma Teeling, Photo courtesy of Emma Teeling
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Emma Teeling: Bats and why I love them
First up, one of the world’s leading bat geneticists, Professor Emma Teeling from University College Dublin. She’s Director of the Centre for Irish Bat Research and co-founding Director of Bat1K, a global consortium sequencing the genomes of every single one of the world’s living bat species. So, what makes bats so special?
Emma: Bats are probably the most extraordinary of all mammals. If you think about it, they're the only mammals that have achieved true self powered flight. Anything else just falls with style, but bats can fly. One in five of every living mammal on this planet today is actually a bat and there's about 1400 bats give or take another 200 different species. They're found throughout the entire world, they're missing only from the extreme polar regions, but also they can use extraordinary sensory perception. So bats are able to orient in complete darkness by using sound alone. And if you were ever in tropical rainforest at night out catching bats in the likes of Panama and what you'll see these great, big, huge spiderwebs and giant spiders in the middle of the web, and you see these small bats flying in total darkness, we can hear them with your bat detectors and they're able to use sound to pinpoint the spider and to avoid the web using sound alone in complete darkness.
Emma: The other unique thing that bats have is that they seem to have evolved mechanisms to slow down ageing. So typically in nature as a law small live fast and die young - think of a mouse, think of a shrew - but bats are the smallest of all mammals. The smallest mammal in the world is actually the Bumblebee Bat - shrew biologists will argue with me, but we're right they're wrong. But bats seemed to live for an extraordinarily long time. So they have booked the trend. So they're small. They have a really high metabolic rate because they fly, but they also live for an extraordinarily long time. And indeed they have the lowest rates of cancer ever recorded in any order. Bats have evolved mechanisms to somehow fight this metabolic and size constraints that drive the ageing process. So they're able to not get cancer and live for extraordinarily long time.
Emma: Indeed, the bat that holds a record for living the longest is myotis brandtii. It's this Brandt's bat in a population in Siberia and a male was caught as an adult, and then he was ringed. But what was extraordinary about this was this bat was then caught 41 years later. And now I believe the record is 43, if not more, with no signs of ageing.
Georgia: They have so many superpowers!
Emma: We haven't even talked about their other one. And their other one is their ability to live with viruses. Bats, because of their unique immune response, potentially are reservoirs for many, many pathogens because the virus doesn't kill them. They've evolved mechanisms, their unique immune system allows them to tolerate and live with different pathogens. So indeed if you study the genome of bats, all of these very unique mammalian adaptations that we could use for our benefits will be found within the bat genome. So that's why I study them.
Georgia: Wow.
Emma: I didn't even talk about their use in ecosystems. We can talk about that now if you want?
Georgia: I mean this podcast, we've only got half an hour.
Emma: We'll have to have about 10 of them
Georgia: So how are you looking into bats and all their super powers? So you examine their genes. So tell me about your project.
Emma: So the project you're talking about is the Bat1K project. This is a project whereby we want to sequence the genome of every single living bat species to chromosome error-free assembly. And to do this we want to promote bat diversity, we want to uncover their unique adaptations and we want to bring people all around the world who are interested in understanding bats, together. So we published our pilot project, which as you can see behind me there, you've got the cover of Nature in July. We're very proud of that.
Georgia: So you got your study done, you got your cover of Nature. Congratulations. Tell me what kind of things you found.
Emma: So, first of all, we wanted to know, as a phylogeneticist, I wanted to try and uncover where do they fall in the tree of life. Trying to place bats within the tree of life is difficult because they fall in this super-order group called Laurasiatheria. So I hoped that when we had full genomes, when we could go and pull out all the orthologous regions, when we could use new, very different methods to account for all the appropriate rates of change, would we be able to find unambiguously where the bats fell and we did. So what you find is a bat group in Laurasiatheria and you have, at the base, you'll have the true insectivores Eulipotyphla. Next branch down you have bats and then you'll have all of the other Laurasiatherian orders that group together such as carnivores and horses, pangolins and so forth in different groups.
Emma: So we found where they went in the tree, which as a phylogeneticist, I was happy. There's still parts that are difficult and tricky, but we found where they fell in the tree. So with that information, we're then able to go and look at, okay, what's going on when you look at expansion of gene families, or contraction of gene families? For example, can we find any evidence of selection of different environmental and evolutionary pressures acting on bats that maybe could underlie and show us where their parts of genome had evolved that was different that maybe led to the unique adaptations. So we did a whole series of this. So what we found, which was particularly interesting to their immune response was that, you can see in the genome that there's expansions of these families, this APOBEC family, for example, which are these antiviral mechanisms and they're expanded in the bats.
Emma: So right there and then that gives, you think, okay, they have evolved antiviral mechanisms. We found evidence of selection acting on many of their different immune genes that are involved in potentially the downstream inflammatory responses. We found a whole series of genes that were knocked out that weren't there in bats. Again, this has been seen before from the first two bat genomes ever sequenced and then indeed bats are missing a cascade of genes in their inflammatory response. And then what does this mean? So what this means is bats seem to be able to mount a very aggressive antiviral response, but yet they equally respond to that by mounting an equally aggressive anti-inflammatory response. Now we could see this in the genome. That was fantastic. We found evidence of selection in certain genes that maybe underlie their echolocation capabilities. And this is just looking at six species.
Georgia: I mean, all the amazing things bats can do that have this genetic underpinning. It seems like these things would be very useful for everyone else to be able to do too. So do we know what's special about bats or is it just by chance? They just had this mutation that was super good for them.
Emma: So this is a very good question. A little controversial. I have my theories, not everybody agrees with me. So if you think, what do all bats do? They all fly. So flight happened in the ancestral bat. And so flight happened somewhere between 80 and 65 million years. There are 20 million years of evolution where the pre-bat evolved flight. And so what had to happen to evolve flight? So you had this huge morphological adaptation of the skeleton. Finger bones had to grow, you had to have flight membrane grow from an ankle, grow from a tail. Potentially, it's not that crazy to think that other pathways had to evolve to allow for flight.
Emma: Now, what I mean by this is flight is the most metabolically costly of all forms of locomotion. And typically what they've shown us that will expend three to 10 times more energy when they're flying than when they're not for example. Their oxygen consumption is huge when they fly. So the question is what is the metabolic cost of flight? It's been argued that it's very, very high. High, high metabolic cost causes the cell to have to, I suppose it's like an engine. The engine has to rev up, the engine has to consume lots of oxygen, but then there's also a by-product of metabolism, which are the free radicals. And so the idea is that free radicals break up your cells, free radicals excite your immune system. So there's deleterious effects of having too high a metabolic rate. And so potentially, I argue, that bats had to evolve mechanisms, the immune response, to deal with this. They also have to evolve the ability to repair their DNA. They have to evolve the ability to remove the damage. So they have to evolve the ability to maintain homeostasis despite this high metabolic rate. The result of this is an ability to tolerate pathogens.
Emma: So they deal with pathogens in the same way as they deal with this constant sterile inflammation they experience. So they're able to dampen their immune response, but also they then don't experience the same level of age driven inflammation. As we get older, what's the thing that really kills as you get older? Your own inflammatory response, arthritis, all these different types of old age diseases are your immune system potentially going crazy. So the bats have evolved these mechanisms. And I started this long term project in Brittany, in France, studying these long lived bats where we take a non-lethal sample from the same individual year after year after year, as they age. I want to see, well, what are the bats doing to potentially slow down the ageing process? And indeed all of those things I told you about, you can see that happening in bats as they age and it's different for us.
Emma: They upregulate their DNA repair mechanisms as they age, they upregulate their ability to remove protein damage as they age, they maintain their immune response when you look at the different cytokine transcripts. And their mitochondria, It's firing like crazy, they're producing all of this free radicals and so forth, but they do not show the same level of oxidative stress damage you would expect. So is it flight or is it something very unique in these long lived bats? I don't know. The question is had you really test it? Best thing to do would be to be able to look at a non-flying bat, compare it with the flying bat and see, but all bats fly, so that's not going to work. So the other thing is compared with our other flying vertebrate group, which are birds, this something that I think that we do need to do.
Emma: Does flight drive this or not? And so now people are really addressing this question. For sure something weird is going on with their inflammatory response. You can see this in the ancestral bat. Some bats you have long lived bats and you have the shorter lived bats. You have the in-between living bats. You've the bats that feed on fruit, the bats that feed on insects, the bats that feed on other bats, the bats that feed on fish, all these different ecological strategies that have different lifespans. And by looking at this phylogenic, independent contrast of long versus short accounting for ecological variation, we can see is it a signature within their genomes that underlies their longer health span and their unique immunity. And so that's why I think we should do it all.
Georgia: I mean, thinking from a very selfish point of view, is there any way we can steal this ability short of learning to fly ourselves? Can we use the genetic information to help human health?
Emma: I absolutely, completely, a hundred percent think we can. We are mammals. They are mammals. We shared the same suite of genes. And if you think about it, for example, let's look at what we know about SARS-CoV-2. What we've found that in, in a hospital, a local hospital here in Dublin, there was researchers when an individual patient comes in to them, they look at their inflammatory and anti-inflammatory cytokines. They can predict by looking at this ratio, whether this person is probably going to need to be intubated or not. So if you have an immune response that is not like a bat, you're going to be sick. If you had an immune response, much more like the bats, they don't do so badly, they do better. They can deal with this. So they're the same genes.
Emma: And what you can do is you can look at, for example, what happens when a bat gets exposed to a pathogen, what do they do to allow them to live with and tolerate that pathogen in terms of switching these genes on and off? You have to have enough of an antiviral response to neutralise the pathogen and then enough of an anti-inflammatory response to neutralise your own inflammatory response. So by studying these, we will get insight into when we give us the antiviral versus the anti-inflammatory drugs. And that is just to kind of a, quite a crude example.
Georgia: And what about the bats themselves? Because I know they've got all these super powers, but they're still, not all doing great are they? They are still a conservation concern.
Emma: They're a huge conservation concern. Think about when you're younger and you looked up in the sky in the summer, if you're out somewhere in the countryside or even in the city, you'd see bats and you'd walk through woodlands, you'd see bats, but you know what else you'd see when you're driving through the country lanes? What would your windscreen be full of? Insects! And so right now we're having this huge global crisis where we're losing our arthropods. And if you think about what feeds on arthropods, what modulates them, they're the bats. So we need them because they're of huge ecological importance. So bats are keystone predators in ecosystems, and they modulate all the different arthropods and they feed on pest insects for example. They would feed on an insect that would eat crops. It's been estimated that if you were to wipe out one particular species of bat in the United States of America, you would cost the US taxpayer 3 billion US dollars in insecticides, to do the job that the bats do.
Emma: We've got to find ways to live with bats, much more. Regardless of their superpowers. And again, part of Bat1K we want to promote bat conservation. We want to say, right, they're really important. Here's why they're important. Let's all work together to try and conserve our bats because our ecosystems function better. And we are simply another species that exists in our ecosystems. So you take out those keystone predators and the modulators of our ecosystems, and it doesn't work. I mean, the bats are like bees. We need to keep them or we aren't going to do so well as a species.
Georgia: And do you have a favourite species of bat you'd like to tell us about?
Emma: Oh, that's a very naughty question! That's like asking me, do I have a favourite child?
Kat: The wonderfully enthusiastic Emma Teeling from University College Dublin talking to Georgia Mills about bats and their fascinating genomes.
