ICYMI
American woman saves hundreds of bats from freezing to death
Cathy Free13:13, Dec 31 2022

Mary Warwick's heart sank when she realised temperatures were plunging below freezing in Houston in the days before Christmas.

She raced over to downtown Houston before sunset on December 21 to check under the Waugh Drive Bridge, where a colony of 250,000 bats has lived for almost 30 years and is a popular attraction.

Her fears were confirmed: There were dozens of tiny bats on the ground suffering from hypothermia, too weak to hold on to the narrow crevices in the concrete beneath the bridge. They had dropped four to nine metres onto the cold cement below and looked lifeless.

"They're only three inches long at the most, they don't have much body fat and they get cold very quickly," said Warwick, executive director of the Houston Humane Society TWRC Wildlife Centre. "When they shut down from hypothermia, they release from the bridge and some of them will die."

Warwick, 60, put on a pair of gloves and gently collected the unresponsive bats one by one. She picked up 138 bats and placed them in a box lined with a soft blanket.

"I put the box on my heated car seat, and as the bats warmed up, they started moving around," she said.

Warwick said she was horrified to see the small animals in distress, but glad she had taken a break from her holiday shopping to check on them. They are part of a colony of Mexican free-tailed bats that thrive in temperatures above 10C. While most Texas bat populations head south for the winter, she knew that a sizeable number remained behind.

She was determined not to have a repeat of the time in February 2021 when Texas endured arctic temperatures for nine days, and more than 5000 bats dropped from the bridge and died in the cold.

ROBERT WARWICK/ROBERT WARWICK
Warwick with one of the Mexican free-tailed bats she rehabilitated in Houston over the holidays.

Warwick decided to take them home to warm them up in an incubator. She injected fluids beneath the bats' skin with a needle and syringe and hand-fed them a gruel made of mealworms, she said.

For the next several nights, she returned to the Waugh Drive Bridge with extra boxes and a flashlight to rescue more bats, and she stopped at another bridge south of Houston to rescue bats from a second colony.

"By the time I was up to 900 bats, I decided it was time to slow down their metabolism so they wouldn't need to eat as much," she said. "It was becoming pretty time-consuming to care for them all."

The solution, Warwick decided, was to put the recovered bats in large dog kennels in her attic where the temperature was cooler, until it had warmed up enough outside to return them to the bridge.

MARY WARWICK/MARY WARWICK
Warwick kept the most critically injured bats in a warm incubator inside her Houston home.

"When it's cold, but not freezing, their metabolism will slow down," she said.

The Houston Humane Society posted on social media that Warwick was single-handedly rescuing the creatures. People quickly offered to help.

"I adore sky puppies - not just for their adorable faces and gentle natures, but for everything they do for us in Texas, mosquito wise," one person commented on Facebook. "Happy to donate and thank you for helping these beautiful, so misunderstood little guys."

Chris Cruz, a sign-language interpreter who often drives past the bat colony and enjoys watching them in warmer weather, said he immediately felt compelled to spend his Christmas Eve looking for cold and injured bats.


Warwick rescued hundreds of bats.

"I was scrolling through Instagram when I came across a local TV story about what Mary was doing," said Cruz, 31. "I thought that was something I could help with, so I grabbed a foam cooler and poked some holes in it."

Cruz found 14 bats on the ground and carefully swept them into the cooler with a handheld broom, he said. He then took them home to warm them up and arranged to turn the bats over to Warwick on Christmas Day.

"I was worried that one or two might not make it through the night, so I was happy when they all started scurrying around in the box," he said, noting that he didn't dare take the lid off.

"It was a fun way to spend Christmas," Cruz said. "Bats don't really ask for anything, and I was happy to help them. Besides, they're pretty cute."

MARY WARWICK/MARY WARWICK
Some of the bats rescued by Warwick and volunteers during a cold snap in Houston.

By Christmas night, Warwick said she had more than 1500 bats hanging inside dog kennels in her attic. She kept bats from the two colonies in separate containers and made sure to keep them hydrated.

"What she did for these bats is incredible," said Beverly Brannan, board chairperson for the Houston Humane Society.

"Mary is really the only bat expert in our area - she's a one-woman show," she said. "When she saw that those bats needed help, she didn't sleep for several days so she could save them."

Brannan, 82, said she picked up several boxes filled with bats from volunteer rescuers and delivered them to Warwick's house.

ANIAH HERNANDEZ/ANIAH HERNANDEZ
Chris Cruz with a cooler full of bats he rescued.

"When I got there, she was triaging bats, doctoring them and feeding them, one bat at a time," she said. "Her dedication to the bats was next level."

Warwick said her instincts as a wildlife expert kicked in and she felt an obligation to see the rescue through to the end.

All creatures - no matter how small - have value on the planet, she said.

Over the years, she has also rehabilitated squirrels, raccoons, hawks, ducks and owls, Warwick noted.

"Mexican free-tailed bats are common in Texas, and I'd received some training on caring for them," she said. "These bats are important to our ecosystem and they eat lots of mosquitoes. The bridge is also a popular tourist attraction, so the bats deserve our help."

Although 115 of the bats couldn't be saved, the rest perked up after five or six days. Most of the Waugh Drive Bridge bats were released back to their colony after sunset on December 28, and the others will be released in the coming days, Warwick said.

"I'm excited to get them out of my attic and send them back into the wild," she said. "I hope they'll stay warm and happy, but if they need help, we're here."

READ MORE:

* 100-year-old trees that are home to little owls face chop for new housing

* Taranaki forest frequented by endangered long-tailed bats bought by conservation trust

* Breakthrough in bat recovery project at Pelorus Bridge

* Focus on protecting NZ's long tailed bat

Bats: Out of Our Nightmares and Into Our

Hearts

October 29, 2022 by Jennifer Harbster

LIBRARY OF CONGRESS

Bats in a Texas evening sky. Paul Cryan, USGS photographer, 2009.

This post was written by Science Reference Specialist Ashley Cuffia.

Bats get a bad reputation in popular culture, and at no time of year is it more prevalent than Halloween. The image of a furry, flying nightmare with fangs, red eyes and leathery wings swooping down on unsuspecting innocents may play well in the movies; these notions could not be farther from the truth. In all sincerity, these small creatures are largely harmless and perform a wide array of beneficial services such as pest control and pollination. Let’s take a look at the bat with an open mind, and allow them to fly out of our nightmares and into our hearts.

Here are five amazing facts about bats:

• Over 300 species of plants depend on bats for their pollination needs. Some of these include avocados, cacao and agave. So without bats, there would be a lot less chocolate, guacamole and tequila in the world!
• Each night bats can eat their body weight in insects. This not only helps crops from being destroyed, but also lowers the number of bug bites we will get in the summer.
• The average bat in the wild can live up to 20 years with some reaching their 30s. The oddity of this is that normally the smaller the animal the shorter the lifespan, however bats break that mold and spend their long life zipping around the sky.
• Baby bats are called pups, and most bats give birth to a single pup. Mother bats will gather all their pups up into a nursing colony in the spring and watch over their young as they grow. Like all other mammals bats feed milk to their young until they are old enough to eat solid food.
• As the only true flying mammal on the planet, they are not only unique but incredibly fast. Their rate of flight speed depends on the species, but some can reach up to 100mph.

Color lithograph of red and brown bats in various poses. L. Prang and Co, 1874

So what can we do to help these furry little flying animals continue doing the hard work that they do? Think about planting a bat garden or building a bat house!

Just as planting a pollinator garden for bees and butterflies as mentioned in our blog “Butterflies, Beetles and Bees, Oh My! National Pollinator Week” there are a variety of things you can plant to encourage bats.

• Bats love to eat moths, so planting flowers that host moths such as evening primrose and honeysuckle would increase the odds of these furry friends stopping by for a snack.
• Trees not only give bats a place to snuggle up, but also provide a buffet of bugs for their diet.
• Insects are attracted to very fragrant plants, so not only do you get to enjoy your sweet scented flowers, but also attract more insects for the bats to eat.
• Artificial light in your yard will attract bugs, but it will negatively impact bat behavior, so keep that yard nice and dark.
• Providing water is also very important, however it is not as simple as putting out a bird bath or bucket. Bats scoop up water as they fly so a pond or water trough 7 to 10 feet in length is ideal for them. Just remember to add in a little ramp out of the water in case one crash lands or another creature happens to fall in.
• Finally think about building a bat house, this will give them somewhere warm and dark to spend the day catching some zzz’s.

Scientific illustration of bats. Lithograph by Adolph Giltsch and drawing by Ernst Haeckel. Published in Kunstformen der Natur, 1904

Read more on how bats have captured the hearts of our other  LC bloggers:

• Bats: Spooky Superheroes?  Stephanie Hall, former specialist at The American Folklife Centers discusses the folklore of bats along with conservation efforts
• Creatures of the Night : The bat (Order Chiroptera) is a real-life creature of the night which may have made its appearance on this planet 65 million years ago.
• Fostering Close Observations: Exploring Bat Anatomy through Scientific Illustrations” Lesley Anderson, 2021-2022 Albert Einstein Distinguished Educator Fellow at the Library of Congress, highlights early 20th c. bat drawings by Ernst Haeckel and Adolf Giltsch and encourages students to create their own scientific illustrations.

Learn more about bats from these online resources:

• Bats Conservation International 
• Bat Week is an international, annual celebration designed to raise awareness about the need for bat conservation.
• Everyday Mystery Why do Bats Live in Caves? Why don’t they Fly into Objects at Night?
• National Park Service:  Discover the Secret Lives of Bats
• U.S. Department of Interior: 13 Awesome Facts about Bats
• U.S. Fish and Wildlife Service: Bats are one of the Most Important Misunderstood Animals

 

Do artificial roosts help bats? Illinois experts say more research needed

Peer-Reviewed Publication

UNIVERSITY OF ILLINOIS COLLEGE OF AGRICULTURAL, CONSUMER AND ENVIRONMENTAL SCIENCES

 

IMAGE: JOY O'KEEFE (LEFT) AND REED CRAWFORD (RIGHT) WITH BAT BOXES INSTALLED FOR A PREVIOUS STUDY. THE RESEARCHERS POINT OUT A NUMBER OF UNKNOWNS RELATED TO ARTIFICIAL ROOSTS AS CONSERVATION TOOLS FOR BATS AND CALL FOR MORE RESEARCH. view more 

CREDIT: LAUREN D. QUINN, UNIVERSITY OF ILLINOIS.

URBANA, Ill. — Artificial roosts for bats come in many forms — bat boxes, condos, bark mimics, clay roosts, and cinder block structures, to name a few — but a new conservation practice and policy article from researchers at the University of Illinois Urbana-Champaign suggests the structures haven’t been studied rigorously enough and may harm bats in some scenarios. The article, published in Conservation Biology, lays out potential dangers and encourages more research on the popular conservation practice.

“The major emphasis among conservation managers using artificial roosts is how to attract bats, typically by modifying design or landscape placement,” said Reed Crawford, doctoral student in the Program in Ecology, Evolution, and Conservation Biology at Illinois and lead author on the article. “Their measure of success is roost occupancy or bat abundance in roosts, but we really have no idea whether artificial roosts positively or negatively affect bats compared with natural roosts. What we do know is there are multiple significant perils associated with these artificial structures that need additional research.”

The dangers associated with artificial roosts mean they could act as ecological traps in some cases, according to Crawford and co-author Joy O’Keefe, assistant professor and wildlife Extension specialist in the Department of Natural Resources and Environmental Sciences and Illinois Extension, both part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at Illinois.

“An ecological trap occurs when animal populations preferentially select sub-optimal habitat when higher-quality alternatives are available,” Crawford explained. “Basically, bats could inadvertently lower their chances of survival and reduce their reproductive success by choosing poorly designed or placed bat boxes.”

The best-documented concern is overheating. People installing artificial roosts often follow scientifically unsubstantiated advice to choose dark-colored structures and place them in sunny locations. The small structures rarely offer any insulation and can quickly reach temperatures beyond what bats can withstand. Unfortunately, there are all too many reports of mass bat deaths, with tiny bodies piled beneath roosts on the hottest days. 

Crawford, O’Keefe, and others have documented thermal gradients inside bat boxes of various shapes, sizes, colors, and materials. Most designs reach dangerous temperatures, at least for short periods. But artificial roosts can also be too cold for healthy pup development. The authors share multiple reports of freezing deaths in bats during cold snaps in Florida and elsewhere. To improve outcomes for bats, the authors suggest assessing the conditions inside new designs before offering them to bats, aiming to strike a balance between reducing overheating risk and offering bats a microclimate suitable for raising their young. 

Another concern is that artificial roosts could provide easier access by predators, such as snakes or raccoons, with little room for bats to retreat or escape. 

When bats roost in trees, they tend to use multiple openings, be higher off the ground, and split up into smaller groups, which might disperse guano and make it harder for predators to see them or to sniff them out. According to O’Keefe, “We need to look at predation rates in natural and artificial roosts and develop effective guards and designs that keep roosting bats safe from predators.”

In their article, the researchers highlight ectoparasite accumulation as another understudied threat associated with artificial roosts.  

“We found more than a thousand bat bugs inside some of the bat boxes we had installed for a previous study. We don't know if that’s normal or if it’s just something that's happening in these artificial roosts,” Crawford said. “It could be a really big deal when you potentially have 10 bat bugs for every one bat. To a bat, those would be like a golfball-sized parasite. They could lose a lot of blood. And we know the bugs preferentially target young bats and pups that can't groom themselves as effectively.”

The researchers note bat boxes may lure bats into low-quality habitat. Urban homeowners or farmers wanting bats for mosquito or crop pest control may inadvertently reduce bats’ diet choices to just a few insect species while likely increasing their exposure to environmental pollutants and novel predators, like prowling cats. Or a well-intended land owner might put up a bat box across a busy road from a forest, increasing the odds of vehicle collisions as bats head for the trees each night.

“There’s a lot more we need to know about bat health in urban and human-altered landscapes to inform decisions about where to place artificial roosts,” Crawford said.

Despite their potential pitfalls, many artificial roosts are “successful” in attracting large colonies of bats, sometimes hundreds of individuals. But Crawford and O’Keefe say those numbers could exacerbate the dangers of artificial roosts. 

“Again, that's deemed a measure of success: if you see 500 bats in one box, that's fantastic. But there's a rare tree that could support that many individuals. In my experience tracking tree-dwelling bats, a colony is often spread across multiple tree roosts in a forest,” O’Keefe said. “And so, in bat boxes, you have this concentration of bats that's potentially more vulnerable — because there's so many of them — to predators, weather extremes, and ectoparasites. Having so many bats together could compound the risks to the population.”

Given that forest habitat is shrinking and bats most definitely need help, what’s a conservation manager or a homeowner to do?

“First, we need much more research on the effects of all of these factors on bats in artificial roosts. But I’d also encourage folks to look more holistically at their landscape and provide additional resources for bats,” Crawford said. “For example, adding clean water sources or maybe putting in pollinator gardens to attract different types of insects for greater dietary diversity. Looking at the artificial roost itself, make sure it’s high enough off the ground and not so small as to heighten exposure to overheating or predators.” 

O’Keefe added, “I encourage people to look beyond their own backyards and think about whether there's a better place to install a roost nearby, like a park, that also offers foraging habitat for bats. Think at the neighborhood or village scale, as bats cover a lot of ground across their roosting and foraging areas. And no one should be putting up artificial roosts and walking away. You should be paying attention to them, keeping an eye on the bats and what's going on in and around the structure, including predators and ectoparasites, to know how bats using that structure might be affected.”

O’Keefe’s laboratory maintains a website with tips for making bat boxes safer for bats.

The article, “Improving the science and practice of using artificial roosts for bats,” is published in Conservation Biology [DOI: 10.1111/cobi.14170].

---

JOURNAL

Conservation Biology

DOI

10.1111/cobi.14170 

ARTICLE TITLE

Improving the science and practice of using artificial roosts for bats

 

Same species, different sizes: Rare evolution in action spotted in island bats

UNIVERSITY OF MELBOURNE

 

IMAGE: 

A COMPARISON OF THE BODY SIZES OF THE SMALLER HIPPOSIDEROS DIADEMA BAT AND THE LARGER H. DINOPS.

view more 

CREDIT: TYRONE LAVERY

A University of Melbourne researcher has spotted a rare evolutionary phenomenon happening rapidly in real time in bats living in the Solomon Islands.

Dr Tyrone Lavery reports in a paper published in Evolution that two groups of leaf-nosed bats with vastly different body sizes that were thought to be separate species are an example of a rare type of parallel evolution. Parallel evolution is when different populations living in similar environments evolve similar features independently.

The smaller bat, Hipposideros diadema, is found across its six main islands and many smaller islands. It is also common in South East Asia, Papua New Guinea and parts of northern Australia. The much larger bats were named in 1905 as H. dinops, or Fierce Leaf-Nosed Bat, and are found only in the Solomon Islands. The two sizes live together on most islands, which all have similar forested habitat.

“Although they are very different sizes, the bats’ DNA is very similar. They use very different sonar frequencies, they probably eat different food, and even when they live in the same cave together they don’t interbreed. That is why no one has ever really questioned whether they were different species,” Dr Lavery said.

Dr Lavery said despite their independent origins, each group of larger bats has evolved to look the same, averaging more than double the weight of the small bat. “Our research suggests the rapid and repeated evolution of larger bodied bats from smaller bats, each happening independently on separate islands,” he said.

“When we created family trees using the bats’ DNA, we found that what we thought was just one species of large bat in the Solomon Islands was actually a case where bigger bats had evolved from the smaller species multiple times across different islands,” he said.

This type of parallel evolution arising from separated populations of the same species has only been observed in action a few times before and is believed to be the first time it has been documented in real time in mammals.

Parallel evolution has been found in parts of the world when populations are geographically separated but live in similar environments – such as different islands or lakes. One common type of parallel evolution is convergent evolution. For example thylacines and wolves are two separate species with different origins that evolved separately to look similar. But Dr Lavery said it was rare to see two isolated populations of the same species go through the same evolutionary process.

“Something very strong is pushing or selecting for these big bats, and it is strong enough for it to happen multiple times on different islands. We think these larger bats might be evolving to take advantage of prey that the smaller bats aren’t eating. Although they could probably interbreed, they don’t for some reason,” he said.

Across the islands, the sonar frequencies of larger bats are lower and suited to hunting bigger prey, while the smaller bats use a higher frequency. This probably means the larger bats are eating larger insects, or even frogs, Dr Lavery said.

Measuring 103 bat specimens from the Australian Museum, Queensland Museum, University of Kansas Natural History Museum, and the Bernice Pauahi Bishop Museum in Hawaii, Dr Lavery also found no overlap in body size between the two groups – the smaller “species” was always easily identified from the larger bats.

“Over time larger body size may have been part of behavioural and physical adaptations needed to hunt larger prey. This might mean the bigger and smaller bats no longer recognise each other as mates, and so they live separate lives.”

Dr Lavery said this parallel evolution pattern in leaf-nosed bats had been observed in Solomon Islands on Guadalcanal and in the Western Province, and more research was needed to see if the same pattern was repeated on other islands.

“We may think of evolution as very slow process, but it can happen rapidly when the conditions are right and two groups are separated and stop interbreeding. They can begin to evolve on different pathways,” he said.

“Islands are famous for helping us to observe and understand the processes for how species evolve in real time. They’re also places that are very vulnerable to the types of disturbance created by humans create. It’s important that we look after these incredible landscapes in Solomon Islands before we lose these stories even before we find them.”

A University of Melbourne researcher has spotted a rare evolutionary phenomenon happening rapidly in real time in bats living in the Solomon Islands.

Dr Tyrone Lavery reports in a paper published in Evolution that two groups of leaf-nosed bats with vastly different body sizes that were thought to be separate species are an example of a rare type of parallel evolution. Parallel evolution is when different populations living in similar environments evolve similar features independently.

The smaller bat, Hipposideros diadema, is found across its six main islands and many smaller islands. It is also common in South East Asia, Papua New Guinea and parts of northern Australia. The much larger bats were named in 1905 as H. dinops, or Fierce Leaf-Nosed Bat, and are found only in the Solomon Islands. The two sizes live together on most islands, which all have similar forested habitat.

“Although they are very different sizes, the bats’ DNA is very similar. They use very different sonar frequencies, they probably eat different food, and even when they live in the same cave together they don’t interbreed. That is why no one has ever really questioned whether they were different species,” Dr Lavery said.

Dr Lavery said despite their independent origins, each group of larger bats has evolved to look the same, averaging more than double the weight of the small bat. “Our research suggests the rapid and repeated evolution of larger bodied bats from smaller bats, each happening independently on separate islands,” he said.

“When we created family trees using the bats’ DNA, we found that what we thought was just one species of large bat in the Solomon Islands was actually a case where bigger bats had evolved from the smaller species multiple times across different islands,” he said.

This type of parallel evolution arising from separated populations of the same species has only been observed in action a few times before and is believed to be the first time it has been documented in real time in mammals.

Parallel evolution has been found in parts of the world when populations are geographically separated but live in similar environments – such as different islands or lakes. One common type of parallel evolution is convergent evolution. For example thylacines and wolves are two separate species with different origins that evolved separately to look similar. But Dr Lavery said it was rare to see two isolated populations of the same species go through the same evolutionary process.

“Something very strong is pushing or selecting for these big bats, and it is strong enough for it to happen multiple times on different islands. We think these larger bats might be evolving to take advantage of prey that the smaller bats aren’t eating. Although they could probably interbreed, they don’t for some reason,” he said.

Across the islands, the sonar frequencies of larger bats are lower and suited to hunting bigger prey, while the smaller bats use a higher frequency. This probably means the larger bats are eating larger insects, or even frogs, Dr Lavery said.

Measuring 103 bat specimens from the Australian Museum, Queensland Museum, University of Kansas Natural History Museum, and the Bernice Pauahi Bishop Museum in Hawaii, Dr Lavery also found no overlap in body size between the two groups – the smaller “species” was always easily identified from the larger bats.

“Over time larger body size may have been part of behavioural and physical adaptations needed to hunt larger prey. This might mean the bigger and smaller bats no longer recognise each other as mates, and so they live separate lives.”

Dr Lavery said this parallel evolution pattern in leaf-nosed bats had been observed in Solomon Islands on Guadalcanal and in the Western Province, and more research was needed to see if the same pattern was repeated on other islands.

“We may think of evolution as very slow process, but it can happen rapidly when the conditions are right and two groups are separated and stop interbreeding. They can begin to evolve on different pathways,” he said.

“Islands are famous for helping us to observe and understand the processes for how species evolve in real time. They’re also places that are very vulnerable to the types of disturbance created by humans create. It’s important that we look after these incredible landscapes in Solomon Islands before we lose these stories even before we find them.”

A photo of H.Dinops in a cave in the Solomon Islands.

H.diadama

CREDIT

Tyrone Lavery

JOURNAL

Evolution

DOI

10.1093/evolut/qpae039 

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Parallel evolution in an island archipelago revealed by genomic sequencing of Hipposideros leaf-nosed bats

 

Fruit, nectar, bugs and blood: How bat teeth and jaws evolved for a diverse dinnertime

Peer-Reviewed Publication

UNIVERSITY OF WASHINGTON

 

IMAGE: 

THIS JAMAICAN FRUIT BAT, ARTIBEUS JAMAICENSIS, HAS A SHORT JAW, LIKE MANY NOCTILIONOID FRUIT-EATING BATS.

view more 

CREDIT: ALEXA SADIER

Link to full release with images:

https://www.washington.edu/news/2023/10/26/bat-teeth/

They don’t know it, but Darwin’s finches changed the world. These closely related species — native to the Galapagos Islands — each sport a uniquely shaped beak that matches their preferred diet. Studying these birds helped Charles Darwin develop the theory of evolution by natural selection.

A group of bats has a similar — and more expansive — evolutionary story to tell. There are more than 200 species of noctilionoid bats, mostly in the American tropics. And despite being close relatives, their jaws evolved in wildly divergent shapes and sizes to exploit different food sources. A paper published Aug. 22 in Nature Communications shows those adaptations include dramatic, but also consistent, modifications to tooth number, size, shape and position. For example, bats with short snouts lack certain teeth, presumably due to a lack of space. Species with longer jaws have room for more teeth — and, like humans, their total tooth complement is closer to what the ancestor of placental mammals had.

According to the research team behind this study, comparing noctilionoid species can reveal a lot about how mammalian faces evolved and developed, particularly jaws and teeth. And as a bonus, they can also answer some outstanding questions about how our own pearly whites form and grow.

“Bats have all four types of teeth — incisors, canines, premolars and molars — just like we do,” said co-author Sharlene Santana, a University of Washington professor of biology and curator of mammals at the Burke Museum of Natural History & Culture. “And noctilionoid bats evolved a huge diversity of diets in as little as 25 million years, which is a very short amount of time for these adaptations to occur.”

“There are noctilionoid species that have short faces like bulldogs with powerful jaws that can bite the tough exterior of the fruits that they eat. Other species have long snouts to help them drink nectar from flowers. How did this diversity evolve so quickly? What had to change in their jaws and teeth to make this possible?” said lead author Alexa Sadier, an incoming faculty member at the Institute of Evolutionary Science of Montpellier in France, who began this project as a postdoctoral researcher at the University California, Los Angeles.

Scientists don’t know what triggered this frenzy of dietary adaptation in noctilionoid bats. But today different noctilionoid species feast on insects, fruit, nectar, fish and even blood — since this group also includes the infamous vampire bats.

The team used CT scans and other methods to analyze the shapes and sizes of jaws, premolars and molars in more than 100 noctilionoid species. The bats included both museum specimens and a limited number of wild bats captured for study purposes. The researchers compared the relative sizes of teeth and other cranial features among species with different types of diets, and used mathematical modeling to determine how those differences are generated during development.

The team found that, in noctilionoid bats, certain “developmental rules” caused them to generate the right assortment of teeth to fit in their diet-formed grins. For example, bats with long jaws — like nectar-feeders — or intermediate jaws, like many insect-eaters, tended to have the usual complement of three premolars and three molars on each side of the jaw. But bats with short jaws, including most fruit-eating bats, tended to ditch the middle premolar or the back molar, if not both.

“When you have more space, you can have more teeth,” said Sadier. “But for bats with a shorter space, even though they have a more powerful bite, you simply run out of room for all these teeth.”

Having a shorter jaw may also explain why many short-faced bats also tended to have wider front molars.

“The first teeth to appear tend to grow bigger since there is not enough space for the next ones to emerge,” said Sadier.

“This project is giving us the opportunity to actually test some of the assumptions that have been made about how tooth growth, shape and size are regulated in mammals,” said Santana. “We know surprisingly little about how these very important structures develop!”

Many studies about mammalian tooth development were done in mice, which have only molars and heavily modified incisors. Scientists are not entirely sure if the genes and developmental patterns that control tooth development in mice also operate in mammals with more “ancestral” sets of chompers — like bats and humans.

Sadier, Santana and their colleagues believe their project, which is ongoing, can start to answer these questions in bats — along with many other outstanding questions about how evolution shapes mammalian features. They’re expanding this study to include noctilionoid incisors and canines, and hope to uncover more of the genetic and developmental mechanisms that control tooth development in this diverse group of bats.

“We see such strong selective pressures in these bats: Shapes have to closely match their function,” said Santana. “I think there are many more evolutionary secrets hidden in these species.”

Co-authors are Neal Anthwal, a research associate at King’s College London; Andrew Krause, an assistant professor at the Durham University in the U.K.; Renaud Dessalles, a mathematician with Green Shield Technology; Robert Haase, a researcher at the Dresden University of Technology in Germany; UCLA research scientists Michael Lake, Laurent Bentolila and Natalie Nieves; and Karen Sears, a professor at UCLA. The research is funded by the National Science Foundation.

A side-view image of the skull of a greater spear-nosed bat, Phyllostomus hastatus, a noctilionoid species with an omnivorous diet.

An extreme case of noctilionoid bats with a fruit-based diet, the wrinkle-faced bat, Centurio senex, has a short bulldog-like snout and reduced numbers of teeth.

The orange nectar bat, Lonchophylla robusta, is a noctilionoid species that has a longer jaw and drinks nectar.

The pale-faced bat, Phylloderma stenops, is a noctilionoid bat with an omnivorous diet.

The hairy-legged vampire bat, Diphylla ecaudata, feeds primarily on the blood of birds. It is one of three living species of vampire bats — all of them noctilionoid, and all with sharply reduced numbers of teeth and short jaws, likely due to their specialized diet.

CREDIT

Sharlene Santana/University of Washington

Bats in Tamana cave, on the Caribbean island of Trinidad.

CREDIT

Alexa Sadier

For more information, contact Santana at ssantana@uw.edu and Sadier at alexa.sadier@gmail.com.

NSF grant numbers: 2017738, 201780

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JOURNAL

Nature Communications

DOI

10.5281/zenodo.8058070 

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Bat teeth illuminate the diversification of mammalian tooth classes

Evolutionary chance made this bat a specialist hunter

Peer-Reviewed Publication

UNIVERSITY OF SOUTHERN DENMARK

 

IMAGE: 

A BARBASTELLE BAT FLYING IN THE DARK

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CREDIT: SHERRI AND BROCK FENTON

Ask a biologist why predators don't exterminate all their prey, part of the answer often is that there is an ongoing arms race between predators and prey, with both parties continuously evolving new ways to cheat each other.

The hypothesis is particularly prevalent for bats and their prey; insects. 50 million years ago, the first bats evolved the ability to echolocate and thus hunt in the dark, and in response to this, some insects evolved ultrasound-sensitive ears so they could hear and evade the bats.

But if there is an ongoing arms race, bats should have responded to this, says University of Southern Denmark biologist, associate professor and bat expert Lasse Jakobsen, co-author of a new study published in Current Biology, In the study, he and colleagues question the evolutionary arms race between bats and insects.

The other authors are Daniel Lewanzik and Holger R. Goerlitz from the Max Planck Institute for Biological Intelligence and John M. Ratcliffe and Erik Etzler from the University of Toronto.

The main argument supporting the arms race hypothesis is that some bats do not call as loudly as others when hunting, and thus cannot be heard as easily by the insects. These are the barbastelles (Barbastella barbastellus), and they are approx. 20 dB quieter than other bats that hunt flying insects, which means that the sound pressure they emit is 10 times lower.

- The barbastelle is traditionally highlighted as the bat that has “struck back” at the insects, says Lasse Jakobsen.

But something puzzled him and his colleagues: If you look at the barbastelle’s close relatives, there are virtually no other members catching insects in the air. Instead, they eat insects that sit on surfaces such as leaves and branches, and those species are all quieter than the species that hunt flying insects.

In bat research circles, the bats that catch insects in the air are called hawking bats, while the bats that pick insects from a surface, so to speak, are called gleaning bats. The barbastelle is a hawking bat.

- If most of the barbastelle’s family are gleaners, then their ancestor was very likely also a gleaner, says Lasse Jakobsen.

Accordingly, it is therefore unlikely that the ancestor of the barbastelle was a loud hawker that evolved into the whispering barbastelle as a response to insect hearing.

- A species does not have free choice when it evolves in a new direction. For example, it is a condition for mammals that their ancestor did not have feathers, so their descendants will never evolve a wing with feathers. Instead, they have found another solution for flying: modified skin between the fingers, explains Lasse Jakobsen.

But if the barbastelle didn't evolve its ability to be quieter when hunting in the air, as part of the arms race between insects and bats; where does it come from?

- It is not an evolved ability. It just cannot produce louder calls than it does, because as a descendant of a gleaner it is probably morphologically limited. But it has found a niche, where it can use its low amplitude calls. It is an evolutionary coincidence; it sort of fell into this niche, where there was something to eat.

This niche is populated by flying, nocturnal insects that can hear and are thus good at avoiding nocturnal bats. But they cannot hear well enough to register the barbastelle, so they end up as their prey.

The reason for the morphological limitation must be found in how bats emit their sound. Most bats call out of their mouths, and this allows them to emit loud sounds. Many gleaners, on the other hand, emit sound with their noses, and this makes their calls 20 dB lower.

- So, the reason why the barbastelles are so quiet today is not an expression of an arms race between bats and insects, but rather simply an expression of the fact that it is descended from bats that cannot call as loudly as others, says Lasse Jakobsen.

Nocturnal flying insects: Examples of nocturnal flying insects are moths, beetles and mosquitoes. Many moths have ears and can hear if a bat is approaching. Until approx. 50 million years ago, when bats arose, nocturnal flying insects had no enemies of significance. Today, only bats hunt insects at night.

barbastelle catching insect [VIDEO] |

JOURNAL

Current Biology

DOI

10.1016/j.cub.2023.10.014 

METHOD OF RESEARCH

News article

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Stealth echolocation in aerial hawking bats reflects a substrate gleaning ancestry

ARTICLE PUBLICATION DATE

27-Oct-2023