Scientists have found another piece in the puzzle of how echolocation evolved in bats, moving closer to solving a decades-long evolutionary mystery.
An international study led by us, published today in Current Biology, has shown how the capability for sophisticated echolocation not only evolved multiple times in groups of bats, but also that it never evolved in fruit bats.
To navigate using echolocation, bats produce high-frequency calls in their larynx (voice box) and emit these through their nose or mouth. These calls, usually made at higher frequencies than humans can hear, echo off objects and bounce back.
From this feedback, bats can extract information about the spatial and textural properties of their surroundings.
For three decades, scientists have tried to understand how echolocation evolved in bats and why this adaptation didn’t extend to fruit bats. So far, they’ve struggled to reach a consensus.
Some evolutionary biologists think fruit bats could once echolocate like their modern counterparts, but at some point lost this capability. Others propose fruit bats never acquired this trait in the first place and that it evolved several times in different bat groups.
Uncovering the history of bat echolocation was always going to be a hard task. There are more than 1,400 species of bat, making up about a quarter of all mammal species on Earth. As such, they come in a remarkable range.
However, bat fossils are notably scarce and fragmented. Scientists lack the specimens needed to reconstruct the 65-million-year evolutionary history of bats.
Also, the genetic information of today’s echolocating bat species has done little to help us understand how the sonar-like system actually works.
We took a different approach. Rather than focusing on bat genes or fossils, we examined the very early development of their ear and throat bones.
Evolutionary studies have shown that if a group of species ends up losing a trait its ancestors possessed, not all aspects of the trait are completely lost. Instead, the trait often starts to develop in the very early stages of life, but doesn’t progress.
So if echolocation was present in the common ancestor of all bats, we would expect modern fruit bats to show some developmental trace of this in their ear and throat development.
Our research group, which included biologists from City University of Hong Kong, University of Tokyo and the Vietnam Academy of Science and Technology, studied hundreds of bat embryo specimens from all around the world.
We used a modern imaging method to digitally reconstruct the soft tissue structure of the embryos in microscopic detail. We compared fruit bats to echolocating bats and also non-echolocating mammals, such as mice.
Our analysis revealed fruit bats were indistinguishable from non-echolocating mammals in all aspects of their early ear bone development.
There were also no features which were similar to those observed in bats that do have sophisticated echolocation capability. In other words, there was no evidence to suggest fruit bats would ever have been able to echolocate.
This raised several questions for us. Does this mean the common ancestor of all bats didn’t have the echolocation skills afforded to future bats? This is a possibility.
Alternatively, this common ancestor might have only had a very primitive version of echolocation. If so, it may have looked and sounded strikingly different to what we see in today’s sophisticated echolocators.
Unfortunately, we can’t know for sure which is correct. Pteropodids have the most incomplete fossil record of all bat lineages, so we can’t study how their ear bones changed over time.
Our team also discovered the two major groups of sophisticated bat echolocators, Rhinolophoidea and Yangochiroptera, have different patterns of ear and throat development to one another. This suggests they evolved their sonar independently.
This conclusion also fits in with the latest insights from bat genome sequencing, which indicate that if the ancestor of all bats did echolocate, this was likely some kind of primitive echolocation — not the deft laryngeal echolocation found in modern bats.
The next step will be to combine insights from developmental analysis with bat genomic data.
By studying how the hearing-related genes of bats are expressed during early development, we could find out whether fruit bats completely erased a primitive echolocation system present in an ancestor, or whether it was ever there at all.
One of the first questions scientists ask when a new disease appears is, “Where did this come from?”
Many viruses jump from animals to humans, a phenomenon known as “zoonotic spillover.” Although it remains unclear which animal was the source of the current coronavirus pandemic, all the attention is on bats.
The transmission of viruses from bats to humans is not just a matter of a bat biting someone or licking their blood. (Bats do not suck blood as they do in vampire stories.) It is often a much more complex scenario that may involve an intermediary host.
Many other animals are also known to be repositories for human diseases. Rodents carry the plague, pigs transmit influenza and birds transport the West Nile virus. So, why are bats so often blamed for transmitting disease?
As a scientist who has spent years studying the evolution of bats in several countries in South America, North America and the Caribbean, I think that these night creatures are often the victims of misinformation. Most people are afraid of bats, and there is a tendency to connect them to bad things.
One reason bats are blamed for disease has nothing to do with science. Bats are associated with vampires and horror stories, which causes fear and misunderstanding towards these flying creatures.
The other reasons are grounded in evidence. Bats are the second-most species-rich order of mammals. There are more than 1,400 species distributed worldwide, except in Antarctica. They live in urban and natural areas, and they all have the potential to carry viruses. Bats are also mammals, and this relatedness to humans makes them more likely to be hosts of zoonoses than birds and reptiles, for example.
Some bat species prefer to live in colonies, close to one another, creating a perfect setting for pathogens to spread between each other — and to other species who might also share the space. Bats are also the only mammals capable of true flight, making it easier for them to spread diseases through their guano (bat feces).
But what is particularly interesting is their tolerance to viruses, which exceeds that of other mammals. When bats fly, they release a great amount of energy, which increases their body temperature to 38–41 C. The pathogens that have evolved in bats are able to withstand these high temperatures. This poses a problem for humans because our immune system has evolved to use high temperatures — in the form of fevers — as a way to disable pathogens.
Despite all the negative press bats receive, they make positive contributions to the environment and to our lives.
The majority of species feed on insects, helping protect crops from infestations. They are involved in seed dispersal, such as those from fig trees and silver palms, and the pollination of many plants, including several commercial ones, such as the eucalyptus and agave, which provide natural fibres and beverages, such as tequila and mescal.
Bats have also been used in scientific research to understand adaptive evolution (how beneficial mutations become common in a population) and how ecosystems function. They have also be used in studies on aging, cancer, immunity and biomimetic engineering.
And most importantly, bats might actually help to provide the solution for COVID-19 and other viruses. Bats do not get sick from many viruses that might kill humans, and research on how bats achieve this could hold the key to help us fight this and future outbreaks.
It is clear that researchers around the world are doing whatever they can to report the origin of SARS-CoV-2. So far, the most accepted hypothesis is that the novel coronavirus originated in bats. The genome of the virus found in humans is 96 per cent identical to one found in bats. But are these findings being reported the way they should?
Not always, from the bat’s perspective, at least.
Complex scientific studies are being published very fast, which is understandable considering the urgency of this new disease. However, this hastiness is leading to mistrust, confusion and sometimes even fear and hatred towards these flying mammals.
In some places, this growing “bad reputation” has led to the intentional and needless killing of bats in the name of protecting public health. But this could have negative consequences: disturbing hibernating bats causes abnormal arousal and stress, which could lead to the spread of new diseases.
But even if bats are proven to be the source of this virus, they are not to blame for the transfer of SARS-CoV-2 — humans are. We destroy natural habitats at a frenetic speed; we kill threatened species, changing entire food chains; we pollute the air, the water and the soil.
It is expected that new pathogens that were previously locked away in nature will come in contact with people and spread fast as people move around the world. The people who blame bats for COVID-19 should look in the mirror to see if the real vampire resides within.
In this pandemic it’s tempting to look for someone, or something, to blame. Bats are a common scapegoat and the community is misled to believe getting rid of them could be a quick fix. But are bats really the problem?
Australian bats have been in the news recently for two main reasons: the misplaced fear they might carry COVID-19, and overblown reports they carry a koala-killing virus.
This recent bad press has seen increased incidences of disturbing cruelty against Australia’s bats, as well as calls to cull or “move on” bats that live close to people. Because fewer bats would mean less disease, right? Wrong. Here’s why.
COVID-19 is caused by the SARS-CoV-2 virus. This virus is one of thousands of coronaviruses found in mammals all over the world, most with no impact on people.
A closely related virus has previously been identified in a species of horseshoe bat in China, so it’s probable the ancestor of the SARS-CoV-2 virus originated in bats.
While several coronaviruses have been detected in various Australian bat species, none are closely related to those viruses associated with zoonotic (animal-borne) diseases like COVID-19, SARS and MERS. And none have been recorded to infect people.
Australian bats also recently appeared in the news because of the discovery of a retrovirus in black flying-foxes related to koala immune deficiency syndrome. Some news outlets have falsely suggested bats pose a risk to koala populations.
But the original scientific paper clearly stated the proposed transmission from bats to koalas happened long ago, on evolutionary time scales. What we see in these species today are two separate viruses – there’s no evidence the virus detected in today’s bats can infect koalas, let alone cause disease.
There are about 1,400 species of bats worldwide, including 81 in Australia.
All of our bat species are native and unique. Most are small, nocturnal, and call outside of the human hearing range, so the average Australian would be lucky to see more than a couple of species in their lifetime.
This is important to remember when it comes to thinking about how often they actually interact with people.
Most Australians tend to think of “bats” as the two species of flying-foxes (or “fruit bats”) we commonly see in our cities: grey-headed flying-foxes (in the south) and black flying-foxes (in the north).
Flying-foxes have had a tough few months. Many Eucalypts failed to flower, so food shortages saw thousands of flying-foxes perish from starvation, and then many more died en masse in this summer’s extreme heat.
They were also heavily affected by the summer bushfires that burnt large tracts of the bats’ winter feeding areas.
Flying-foxes show up in urban areas in search of food. Many residents equate seeing more flying-foxes to the species increasing in numbers, and are frustrated that the bats are classified as threatened.
In fact, grey-headed flying-foxes have experienced substantial population declines in recent years. While there are currently hundreds of thousands, historical data indicate that there were once millions.
Nonetheless, bats are not always easy to live close to. Their fly-outs make for spectacular shows, but colonies can also create a lot of noise, smell and mess.
Managing bats in urban environments is no straightforward matter. Flying-foxes have complex movement dynamics, which makes “dispersing” them from urban areas extremely difficult.
Those who advocate for dispersals to be carried out often cite the Sydney and Melbourne Botanic Gardens as examples of successes. But these took place over months and years, large areas, and cost more than A$2 million each. Relatively cheaper dispersals have also been attempted, but ultimately failed.
Culling is an equally impractical and extremely controversial suggestion. Most Australians accept that needless killing and harming of native wildlife is unacceptable, and our laws reflect this.
There are the obvious animal ethics issues, but from a practical perspective, proposing we could cull (by shooting) flying-foxes in densely-populated urban areas to effectively reduce populations is also completely unrealistic.
What’s more, attempts at both dispersals and culling are known to have the undesirable effect of splintering colonies, and driving stressed bats into surrounding areas (parks, residential backyards, school grounds). Essentially, increasing people’s exposure to bats.
Physiological stress could also promote viral shedding. Flying-fox populations are already struggling to recover from severe food shortages, extreme heat events and bushfires. So advocating such actions is misguided, with the potential to amplify, rather than alleviate disease risk.
No, bats are our friends – we rely on them more than most people realise.
Many bats are voracious predators of insects and their service to the global agricultural industry is worth billions of dollars each year.
Flying-foxes also help maintain the integrity of forests by providing long-distance pollination and seed-dispersal services. That makes them integral to the recovery of Australia’s forests from last summer’s fires.
The fundamental issue is not the viruses in bats. SARS-CoV-2 is now a human virus, and we are responsible, knowingly or not, for its global spread.
The “epidemiological bridges” that we’ve inadvertently created – which increase our contact with wildlife through encroachment into natural areas, habitat destruction, and unregulated wildlife trade – are what’s really to blame.
Pia Lentini, Research Fellow, School of BioSciences, University of Melbourne; Alison Peel, Senior Research Fellow in Wildlife Disease Ecology, Griffith University; Hume Field, Science and Policy Advisor for China & Southeast Asia, EcoHealth Alliance | Honorary Professor, School of Veterinary Science, The University of Queensland, and Justin Welbergen, President of the Australasian Bat Society | Associate Professor of Animal Ecology, Western Sydney University
Genomic research showing that the COVID-19 coronavirus likely originated in bats has produced heavy media coverage and widespread concern. There is now danger that frightened people and misguided officials will try to curb the epidemic by culling these remarkable creatures, even though this strategy has failed in the past.
As an environmental historian focusing on endangered species and biological diversity, I know that bats provide valuable services to humans and need protection. Instead of blaming bats for the coronavirus epidemic, I believe it’s important to know more about them. Here’s some background explaining why they carry so many viruses, and why these viruses only jump infrequently to humans – typically, when people hunt bats or intrude into places where bats live.
It’s not easy being the world’s only flying mammal. Flying requires a lot of energy, so bats need to consume nutritious foods, such as fruits and insects.
As they forage, bats pollinate around 500 plant species, including mangoes, bananas, guavas and agaves (the source of tequila). Insect-eating bats may consume the equivalent of their body weight in bugs each night – including mosquitoes that carry diseases like Zika, dengue and malaria.
Since fruits and insects tend to follow seasonal boom-and-bust cycles, most bats hibernate for long periods, during which their core body temperatures may fall as low as 43 degrees Fahrenheit (6 degrees Celsius). To conserve warmth, they gather in insulated places like caves, use their wings as blankets and huddle together in colonies.
When fruits ripen and insects hatch, bats wake up and flutter out of their roosts to forage. But now they have a different problem: Flying requires so much energy that their metabolic rates may spike as high as 34 times their resting levels, and their core body temperatures can exceed 104 degrees F.
To stay cool, bats have wings filled with blood vessels that radiate heat. They also lick their fur to simulate sweat and pant like dogs. And they rest during the heat of the day and forage in the cool of night, which makes their ability to navigate by echolocation, or reflected sound, handy.
Humans are more closely related to bats than we are to dogs, cows or whales. But bats seem more alien, which can make it harder for people to relate to them.
Bats are the most unusual of the world’s 26 mammal orders, or large groups, such as rodents and carnivores. They are the only land mammals that navigate by echolocation, and the only mammals capable of true flight.
Many bats are small and have rapid metabolisms, but they reproduce slowly and live long lives. That’s more typical of large animals like sharks and elephants.
And a bat’s internal body temperatures can fluctuate by more than 60 degrees Fahrenheit in response to external conditions. This is more typical of cold-blooded animals that take on the temperature of their surroundings, like turtles and lizards.
Bats carry a range of viruses that can sicken other mammals when they jump species. These include at least 200 coronaviruses, some of which cause human respiratory diseases like SARS and MERS. Bats also host several filoviruses, including some that in humans manifest as deadly hemorrhagic fevers like Marburg and probably even Ebola.
Normally, these viruses remain hidden in bats’ bodies and ecosystems without harming humans. People raise the risk of transmission between species when they encroach on bats’ habitats or harvest bats for medicine or food. In particular, humans pack live bats into unsanitary conditions with other wild species that may serve as intermediate hosts. This is what happened at the Wuhan wet market where many experts believe COVID-19 emerged.
With a few exceptions, such as rabies, bats host their pathogens without getting sick. Recent media coverage attempting to explain this riddle has focused on a 2019 study suggesting that bats carry a gene mutation, which may enable them to remain healthy while harboring such viruses. But while the mutation may be of interest from a public health perspective, understanding where this novel coronavirus came from requires understanding what makes a bat a bat.
Why do bats carry so many diseases but seem unaffected by them? Genetic mutations that boost their immune systems may help. But a better answer is that bats are the only mammals that fly.
With thousands of bats crowded together licking, breathing and pooping on one another, bat caves are ideal environments for breeding and transmitting germs. But when bats fly, they generate so much internal heat that, according to many scientists, their bodies are able to fight off the germs they carry. This is known as the “flight as fever hypothesis.”
Bats may not always be around to eat insect pests, pollinate fruit crops and provide fertilizer. According to the International Union for the Conservation of Nature and Bat Conservation International, at least 24 bat species are critically endangered, and 104 are vulnerable to extinction. For at least 224 additional bat species, scientists lack the data to know their status.
Overharvesting, persecution and habitat loss are the greatest threats that bats face, but they also suffer from their own novel diseases. Since it was first documented in upstate New York in 2007, the fungal pathogen Pseudogymnoascus destructans (Pd), which causes white-nose syndrome, has infected 13 North American bat species, including two listed as endangered.
Nobody knows where Pd came from, but the fact that several bat species seem never to have encountered it before suggests that people probably introduced or spread it. The fungus thrives in cool, damp places like caves. It grows on bats while they’re hibernating, causing such irritation that they become restless, wasting precious energy during seasons when little food is available. White-nose syndrome has killed millions of bats, including more than 90% of the bats in some populations.
Bats are extraordinary creatures that benefit people in myriad ways, and our world would be a poorer, duller and more dangerous place without them. They need protection from the cruel treatment and wasteful exploitation that also threatens human health.
We already know how deadly this summer’s fires have been for mammals, birds, and reptiles across Australia. But beyond this bushfire season, many of those same species – including our bats, which make up around a quarter of all Australian mammal species – are facing another devastating threat to their survival.
White‐nose syndrome has recently decimated bat populations across North America. While the fungal pathogen responsible for this disease, Pseudogymnoascus destructans, currently doesn’t occur in Australia, the fungus is virtually certain to jump continents in the next decade.
Our recent research, published in the journal Austral Ecology, attempted to quantify this risk – and the results are not encouraging. Up to eight bat species occupy caves in south-eastern Australia that provide conditions suitable for the fungus to grow.
Even before this summer’s fires, seven of those types of bats were listed on state or federal legislation as threatened with extinction. This includes the critically endangered southern bent-winged bat (Miniopterus orianae bassanii), a species whose caves would all provide optimal conditions for growth of the fungus.
White-nose syndrome was first detected in the United States in 2006 at a popular tourist cave in the state of New York. Since then, the disease has spread across North America, killing millions of bats in its wake, with many local populations experiencing 90 to 100% mortality.
The novel pathogen hypothesis explains why P. destructans has such catastrophic impacts on North American bats: the immune system of these species is evolutionarily naive to this fungal attack. Accordingly, in Europe and Asia, where P. destructans is endemic and widespread, few bats exhibit white‐nose syndrome and mortalities are rare.
Australia’s unique wildlife is inherently at risk from invasive novel pathogens because of its long‐term biogeographical isolation. Thus Australian bats, like their distant North American relatives, probably lack an effective immune response to P. destructans and would be susceptible to developing white-nose syndrome.
Most fungal pathogens grow best at cool temperatures, and a high body temperature in mammals and birds provides an effective barrier against fungal diseases. The fungus causing white-nose syndrome is also cold-loving, ceasing to grow at temperatures above 20°C. The only time it can infect and kill bats is when they hibernate.
Bats go cold (use torpor) during hibernation to prevent starvation over winter in temperate climates. Hibernating bats that are infected by P. destructans rewarm more frequently than normal. These unscheduled bursts of metabolic heat production prematurely burn up the body fat of overwintering bats. Hence, despite the damage caused by white-nose syndrome to the bat’s skin tissue, they apparently die due to starvation or dehydration.
Hibernation is key to predicting the susceptibility of bat populations to mortality from white-nose syndrome: those with less energy to spare over winter are more at risk. Consequently, white-nose syndrome has fuelled a large research program on the winter ecology and hibernation physiology of North American bats.
Bats in south-eastern Australia do enter a period of winter hibernation, but that is about the extent of what we know. This knowledge gap makes it impossible to predict how they will respond if exposed to P. destructans. Even non-lethal impacts, however, will worsen the extinction-bound trajectory of several cave-roosting species, most notably the eastern and southern bent-winged bats.
Given the impending arrival of P. destructans in Australia, and our study’s findings of widespread thermal cave suitability in south-eastern Australia, we urge immediate action. This includes tightening biosecurity measures and gaining missing information on bat biology so we are better prepared for a possible white-nose syndrome epidemic.
The importance of this threat has not been missed by Wildlife Health Australia, which has produced guidelines for reporting and response to incursion. Advice is also available from the Commonwealth. Just recently, white-nose syndrome was listed in the national priority list for exotic environmental pests and diseases, ranking in the top five of native animal diseases and their pathogens.
Cave enthusiasts have also been proactive in alerting members to white-nose syndrome and the risk of accidentally introducing P. destructans, especially when returning from overseas caving adventures. And the Australasian Bat Society – a strong advocate for bat conservation – has alerted the public and government agencies to this potential new threat.
At present, there is little that would prevent P. destructans from making it its way to Australian caves, despite two years passing since experts assessed the risk of incursion as almost certain.
We need effective measures at all levels, from requiring incoming visitors to identify contact with cave environments, to decontamination procedures at caves popular with international tourists.
Predicting the impact of white-nose syndrome on Australian bats is currently not possible because we know so little about their winter biology. We urge the Australian government to fund specific research to gain this information.
The US Fish and Wildlife Service has injected more than US$46 million since 2008 into research and fieldwork to address the threat. Australian researchers can use this work to focus on the critical data needed to inform models that predict the vulnerability of local bat populations.
Bats are incredibly valuable in their own right. But the world needs healthy bat populations: a single insectivorous bat can eat up to half its body mass in insects each night, and together colonies of bats provide a service with an estimated value to the agricultural industry alone in the billions of dollars per year.
We hope this terrible disease will not threaten Australian bats. But the precautionary principle dictates we should plan and act now, assuming the worst-case scenario. Alarm bells are ringing.
Christopher Turbill, Senior Lecturer in Animal Ecology, Western Sydney University and Justin Welbergen, President of the Australasian Bat Society | Associate Professor of Animal Ecology, Western Sydney University
Review: Bat by Tessa Laird.
Did you know that the collective noun for bats is a “cloud”, or that in the first scientific classification of mammals, bats were placed close to humans because, like us, they have two nipples? The book Bat, by Tessa Laird, is full of similar tidbits that you will want to share with others. It is also engrossing, eloquent and beautifully illustrated.
Bat contains hundreds of delightful bat facts, but they are so grounded in context that the whole is much more than the sum of its parts. One cannot help but become intrigued and eventually transformed. I know I will never look at bats the same way again.
The author moves between Chiropteran (the scientific name for the bat group) biology, conservation, history, psychology and pop culture to capture the essence of bats, not only in all their marvellous diversity, but in our collective imagination.
Because their flight is erratic, bats are used as a symbol of insanity. Because they hang upside down and are active at night, bats can imply an inversion of normality. Their triumphant daily emergence from their caves can even represent rebirth.
Bats suffer from not fitting comfortably into familiar categories. In Aesop’s Fables, the bat switched allegiance in the war between birds and beasts, so that when it was over the bat was shunned by both and forced to live at night. Their apparently hybrid nature was first noted by the Comte de Buffon in the 1780s when he wrote that the bat is an “imperfect quadruped and a still more imperfect bird”.
Early Christian iconography used bat wings for demons, to contrast with the bird wings that we see on angels. This may have something to do with the European prejudice against bats. When a sailor from Captain Cook’s Endeavour saw an Australian flying fox for the first time, he ran back to camp terrified, claiming to have met a real live devil.
Bats have been misunderstood throughout human history. It is, on reflection, extraordinary that we still use the phrase “blind as a bat”, knowing that they catch insects on the wing in the dark. Echolocation was not discovered until 1938, and because we cannot hear their calls, we did not know that bats basically spend their lives yelling at the world.
Even now, few people realise that bats are socially sophisticated; they share food, information, and maintain lifelong friendships within their colonies. They even engage in oral sex!
Yet bats are celebrated in some cultures. In China, bats are a symbol of luck, in part because the words “bat” and “luck” sound like each other in Chinese. They are also beloved in indigenous cultures from Mexico to Samoa to Papua New Guinea. Interestingly, cultures that venerate ancestors tend to love bats.
And just when you think that this book is about bats, it flips perspective and shines a light on humanity and our own foibles. Such as the second world war project to drop bats with incendiary devices strapped to them so they would crawl into the enemy’s roof cavities and explode.
Or when someone threw a live bat on stage and Ozzy Osbourne bit its head off thinking it was a toy – he was rushed to hospital for shots but apparently privately wondered if anyone would have noticed a change if he had contracted rabies.
There are pages dedicated to an analysis of the Batman superhero and his many incarnations, the Dracula story and its evolution since Bram Stoker’s publication in 1897, as well as more contemporary bat-inspired art.
For example, the 2015 installation in Federation Square in Melbourne, titled Batmania, consisted of 200 life sized flying foxes made from black plastic rubbish bags with holes burned in a filigreed pattern so that they looked like the stars of the night sky shining through. Each bat was juxtaposed with a collapsed parachute, as if to emphasise man’s inability to fly unaided. If we do not yearn for the freedom of flight, perhaps we dream of the immortality of vampires or the strength and anonymity of Batman himself.
The bad reputation bats have in the human world has not been without consequences for them. Blamed for disease outbreaks from Ebola to rabies to SARS, bats have been killed in great numbers due to fear and ignorance. Their habitats are fragile and shrinking, and it is hard to overstate the planetary implications of their demise.
Bats eat many tons of insect pests and are responsible for the pollination of some important and beautiful plants: mangoes, bananas, saguaro cactus. The conservation movement for bats has taken off in recent years, due in part to some excellent photography and a new appreciation of the cuteness of baby bats.
If you read this book you cannot fail to care more about bats, which I hope means that more people will become active in bat conservation. In the author’s own words:
As we have seen, bats have been variously associated with sexuality, diversity and sociability, combined with intuition and an ability to navigate through dark places, all of which seem like desirable qualities at the start of the twenty-first century.
Australian health authorities regularly issue public reminders not to touch bats because they can host Australian Bat Lyssavirus (ABLV). This type of health education is necessary because it reduces human exposure to bat-borne diseases. However, subsequent sensationalist media reporting risks demonising bats, which increases human-wildlife conflict and poses barriers to conservation.
Bats are remarkable native creatures of key ecological and economic importance. We urgently need more matter-of-fact style reporting around the risks of bat-borne diseases to avoid vilification and persecution of these unappreciated mammals.
Australia has 81 bat species, from nine families. They comprise the second-largest group of mammals after marsupials (159 species). They range in size from the little-known northern pipistrelle that weighs less than three grams and ranks amongst the smallest bats in the world, to the black flying-fox that can weigh more than a kilogram and is among the world’s largest.
Bats play many different roles in Australian ecosystems. The southern myotis or “fishing bat”, for example, has long toes that it uses to rake up small fish and invertebrates from rivers, lakes and ponds. The golden-tipped bat delicately plucks spiders from their webs, while the ghost bat feeds on large insects, rodents, birds, and even other bats. These are examples of “microbats” — species that use echolocation to find their way in darkness and detect prey.
Australia is also home to nine “megabats” — species that rely on large eyes and a keen sense of smell to find pollen, nectar, or fruit. The common blossom bat, for example, is a mouse-sized fruit bat with a very long tongue for feeding on nectar; the eastern tube-nosed fruit bat is a solitary bat with long tubular nostrils that are thought to prevent fruit juices from running up its nose; and the little red flying fox is adapted for long-distance flight, travelling thousands of kilometres across the Australian landscape in search of food.
Bats are largely nocturnal and inconspicuous, except for those flying-foxes that sometimes appear in large numbers in urban environments where they can be cause for much frustration and conflict.
All bats are vulnerable to a range of human threats, including the clearing of foraging areas and the loss or disturbance of roosts. Thirteen of Australia’s bat species are now listed as “threatened” under our national conservation legislation. Australia’s most recent extinction was a bat: the Christmas Island pipistrelle winked out of existence forever in 2009 following a sluggish federal government response to calls for urgent conservation action.
Bats are important in two ways. First, each species has its own value as a part of Australia’s natural and cultural heritage. They are fragile creatures, but tough enough to survive and thrive in the harsh Australian bush — if they are given the chance.
Second, microbats provide valuable ecosystem services because many are voracious predators of insects, including many agricultural and forestry pests. Megabats, meanwhile, provide long-distance pollination and seed-dispersal services, helping to maintain the integrity of Australia’s increasingly fragmented natural ecosystems.
Some Australian bats are hosts for Australian bat lyssavirus (ABLV) that can cause a rabies-like disease in humans and potentially pets. Since its discovery in 1996, there have been three human deaths from ABLV in Australia.
The virus is rare, and its prevalence among bats is thought to be less than 1%. But it is more common among sick, orphaned, or injured bats – that are in turn more likely to end up in hands of the public.
A rabies vaccine has been around since the time of Louis Pasteur, and when combined with proper wound management and prompt medical care, is very effective in preventing the disease. Rabies vaccine that is given after exposure to ABLV, but before a person becomes unwell, can still prevent the disease. But once a person develops the disease there is no effective treatment.
Humans are not exposed to ABLV when bats fly overhead or feed or roost in gardens. Bat urine and faeces are not considered to be infectious, and tank or surface water contaminated with these substances is also not a threat.
The primary ABLV transmission route is through bites or scratches, bringing infected bat saliva into direct contact with the eyes, nose or mouth, or with an open wound. Therefore, the best protection by far is to avoid handling bats.
If you do get scratched or bitten by a bat, the Australian Department of Health recommends that you immediately wash the wound thoroughly with soap and water for at least five minutes, apply an antiseptic with antiviral action, and seek medical attention.
Prevention is better than cure, so people should never handle bats (or other wildlife) unless they are trained, vaccinated, and wearing appropriate protective gear. If you find an injured or sick bat, the best thing to do is to contact your local wildlife agency or veterinarian.
We strongly encourage a more matter-of-fact style of reporting around the risks from bat-borne diseases. You are much more likely to be killed by lightning or by falling out of bed than by a bat.
Granted, the risks posed by bat-borne diseases are relatively new to most of the public, but more nuanced framing can effectively support both public health and wildlife conservation goals. So while you remember to slip-slop-slap, be croc-wise and snake aware, and wear gloves when gardening, you should also add “don’t touch bats” to your common-sense repertoire.
Justin Welbergen, President of the Australasian Bat Society | Senior Lecturer in Animal Ecology, Western Sydney University and Kyle Armstrong, Past president of the Australasian Bat Society | South Australian Museum, University of Adelaide
Bats are a natural host for more than 100 viruses, some of which are lethal to people. These include Middle Eastern Respiratory Syndrome (MERS), Ebola and Hendra virus. These viruses are among the most dangerous pathogens to humans and yet an infected bat does not get sick or show signs of disease from these viruses.
The recent Ebola outbreak in West Africa showed the devastating impact such diseases can have on human populations.
As treatments in the form of therapeutics or vaccines rarely exist for emerging diseases, future outbreaks of disease have the potential to result in similar outcomes.
Understanding disease emergence from wildlife and the mechanisms responsible for the control of pathogens in their natural hosts provides a chance to design new treatments for human disease.
Until recently, bats were among the least studied groups of mammals, particularly in regard to their immune responses.
But even early studies of virus-infected bats provided clues that there may be differences in the immune responses of bats. It was observed that some bats were capable of clearing viral infection in the absence of an antibody response.
Antibodies are one of the hallmarks of the immune response and allow the host to respond more rapidly to subsequent infection when the same pathogen invades the body. The absence of a detectable antibody response within the bat was striking and drew our attention to the earliest stages of the immune response, called the innate immune system.
The recent sequencing of the first bat genome provided some of the first clues that the innate immune system may be key to the ability of bats to control viral infection. There is intriguing evidence for unique changes in innate immune genes associated with the evolution of flight, and bats are the only mammal capable of sustained flight.
Flight is energetically expensive and results in the production of oxygen radicals. In the research we speculated that bats have made changes to their DNA repair pathways to deal with the toxic oxygen radicals.
A number of innate immune genes intersect with the DNA repair pathways. These genes have also undergone changes, so it appears that the evolution of flight may have had inadvertent consequences for the immune system.
In humans and other vertebrates, infection with viruses triggers the induction of special proteins called interferon.
This is one of the first lines of defence following infection. It starts the induction of a variety of genes, known as interferon-stimulated genes. These genes play specific roles in restricting viral replication in infected and neighbouring cells.
Humans and other mammals have a large family of interferons, including multiple interferon-alpha genes and a single interferon-beta gene. People have 17 type I interferons, including 13 interferon-alpha genes.
Analysis published today of the interferon region of the Australian black flying fox reveals that bats have fewer interferon genes than any other mammal sequenced to date. They have only ten interferon genes, three of which are interferon-alpha genes.
This is surprising given that bats have this unique ability to control viral infections that are lethal in people and yet they can do this with a lower number of interferons.
Although interferons are essential for clearing infection, their expression is also tightly regulated. This is to avoid over-activation of the immune system, which can have negative consequences for the host.
The expression of interferon-alpha and interferon-beta proteins, which account for the majority of the antiviral response generated following viral infection, is normally undetectable in the absence of infection. It is rapidly induced following detection of a pathogen.
Yet we again see a difference in bats. The three interferon-alpha genes are continuously expressed in bat tissues and cells in the absence of any detectable pathogen. Bats appear to use fewer interferon-alpha genes to efficiently perform the functions of as many as 13 interferon-alpha genes in other species. And they have a system that is constantly ready to respond to infection.
Continual activation of the interferon response in other species can lead to over-activation of the immune response. This frequently contributes to the detrimental effects associated with viral infection, including tissue damage. In contrast, bats appear able to tolerate constant interferon activation and are continually primed for viral infection.
We are familiar with the important role bats play in the ecosystem as pollinators and insect controllers. They are now demonstrating their worth in potentially helping to protect people from infectious diseases.
The ability of bats to tolerate a constant level of interferon expression is poorly understood at the moment. But the identification of the unique expression pattern of interferons in bats is a first step in identifying new ways of controlling viruses in humans and other species.
If we can redirect other species’ immune responses to behave in a similar manner to that of bats, then the high death rate associated with diseases such as Ebola could be a thing of the past.
Peng Zhou was a co-author of this article. He’s a researcher in pathogen discovery and antiviral immunity, formerly employed at Duke–National University of Singapore Medical School and CSIRO.
As a wildlife veterinarian, I often get asked about bats. I like bats, and I am always eager to talk about how interesting they are. Unfortunately the question is often not about biology but instead “what should I do about the ones in my roof?”.
With some unique talents and remarkable sex lives, bats are actually one of the most interesting, diverse and misunderstood groups of animals. Contrary to popular belief, they are beautiful creatures. Not necessarily in the cuddly, human-like sense – although some fruit bats with doey brown eyes and button noses could be considered so – but they are beautifully designed.
This couldn’t be illustrated better than by the discovery of the oldest known complete bat fossil, more than 53 million-years-old yet with a similar wing design to those flying around today. To put it in perspective, 50m years ago our ancestors were still swinging from the trees and would certainly not be recognised as human. But even then bats already had the combination of thin, long forearms and fingers covered by an extremely thin, strong membrane, which allowed them to master the art of powered, agile flight.
Soon afterwards, fossils record another game-changing adaptation in the evolution of most bats, and that is the ability to accurately locate prey using sound (what we call echolocation). These two adaptations early in their history gave bats an evolutionary edge compared to some other mammals, and allowed them to diversify into almost all habitats, on every continent except Antarctica.
There are now more than 1,300 different species, divided among 26 different families (compared to fewer than 500 primate species). Indonesia alone has 219 different bat species.
It is not just a quantity though – the variety is astonishing. The thumb-sized bumblebee bat of Thailand is the smallest species, weighing just two grammes. And like other insectivorous bats, it can eat its own body weight in insects every night. At the other end of the scale, some large flying foxes have wingspans of well over a metre and, having lost the ability to echolocate, eat fruit and nectar.
Everyone knows that some bats feed on blood, but despite the “vampire” myth, only three species actually feed on blood. And these haematophagous bats are only found in parts of South America. They also definitely don’t get tangled in your hair. Bats are far too good at flying.
If thus far I haven’t persuaded you to like bats, you must admit that they are useful. Bats defecate while regularly flying very long distances (up to 350km in one night), making them extremely effective at dispersing seeds. Add to that the fact that some fruit bats live in colonies up to 1m strong, and you can start to imagine their impact. So much so, they have been proven key in reforestation.
Another unappreciated and major role is as pest controllers. The sheer volume of insects that some bats species can eat makes them very effective at suppressing pest insects. Bats reduce the nuisance and disease threat of mosquitoes, and it has been estimated they save the US economy at least $3.7 billion every year through increased crop productivity and reduction of pesticide usage.
Despite their ancient design, they show some remarkable talents. One of these is shared only by several select animals. Bats are vocal learners – able to learn and then imitate sounds even in adulthood. This is likely important for the development of the complex social organisation seen in many bat species. Most surprising of all is the recent revelation that they are also members of an even more exclusive and less salubrious club: animals known to partake in fellatio during copulation.
Bats have had some bad press recently due to their association with infectious diseases, from rabies to Ebola. And they appear able to tolerate some viruses fatal to other species. If anything, that illustrates again why they should be respected, especially as various bat species are also endangered and therefore protected by law in many regions.
So my response to those interested in what to do about the bats in their roof? Leave them alone.