Snoozing Bats Tune Out Traffic Noise

For an easily crushed animal that rests during the day, a highway seems like maybe the worst possible home. Yet some bats pick roosts that are under bridges, or in other spots booming with human noise. Why subject themselves to that? For bats of at least one species, the sound of traffic is easy to doze through. And the more they hear it, the more they ignore it.

The greater mouse-eared bat, Myotis myotis, often turns up under bridges in Europe. Jinhong Luo, a PhD student at the Max Planck Institute for Ornithology, wanted to know how they can tolerate the noise. He and his colleagues trapped male bats from a cave in Bulgaria and brought them back to the laboratory for a hearing test, which was really a sleeping test.

Well, not sleeping exactly. Like many other bat species, the greater mouse-eared bat goes into "torpor" during the day, which is like a mini-hibernation. Its metabolism and body temperature drop sharply, letting the animal conserve energy. In the evening, the bats start to stir. After waking up gradually, they head out from their caves (or under-bridge roosts) to hunt.

The researchers created several different sound recordings that they would play to roosting bats to try to wake them up. There was a recording of the bats' own colony, another of local bird sounds, and one of trees rustling in the wind. The authors also created recordings that mimicked highway traffic passing 25 meters, 50 meters, and 100 meters away.

Each bat was housed by itself for the sound tests. Over the course of two roosting days, the bats heard each recording twice for five minutes. By monitoring temperature sensors on the animals' skin, the scientists could see whether bats started to wake up—that is, warm themselves—after hearing each sound.

Luo and the others tested a dozen bats. (They started with 15, but two weren't snoozing deeply enough to run all the tests, and one somehow pulled the temperature logger off the middle of its back.) The bats were most likely to wake up after hearing the recording of their colony, or the sound of rustling trees. But traffic sounds were least likely to wake them. Bats responded more strongly to all sounds later in the day, as it got closer to their normal waking time.

It's not too surprising that bats respond to the squeaks and shuffles of their own colony, which might hold useful information. But why the windblown trees? A likely answer is that Myotis myotis doesn't hunt by echolocation. Instead, it listens for the sounds of beetles walking through the grass. Since the bats are already attuned to the noise of swishing vegetation, it may make a good alarm clock.

As for the sound of cars passing, Luo points out that most rumbling traffic is at a lower frequency than the sounds of a bat colony or rustling leaves. Since bats hear better at higher frequencies, this means traffic noise is "basically out of the best hearing frequencies for nearly all bat species."

However, Luo is quick to add, "We would never claim that traffic noise is not disturbing to roosting bats or even to torpid bats." The bats in his study did respond slightly to traffic noise, raising their body temperatures compared to when there was silence. And bats might react differently to highway sounds when they're awake, or when they're roosting but not in a state of torpor.

Whatever sound they heard, bats responded less on the second playback, or when it was played continuously for an hour. They were especially quick to adjust to traffic sounds. Like a teenager sleeping through an alarm clock, bats can tune out a familiar noise more easily. But that doesn't mean they're immune to harm from their noisy human neighbors. We just don't know all the ways that living with our roads and other rackets might influence them.

"To be honest, we are in the very beginning of understanding the potential effects," Luo says. "Answers are not always straightforward."


Image: USFWS/Ann Froschauer

Luo J, Clarin BM, Borissov IM, & Siemers BM (2013). Are torpid bats immune to anthropogenic noise? The Journal of experimental biology PMID: 24311817

Squid's Daily Rhythms Are Controlled by Glowing Symbiotic Bacteria

At nightfall, the Hawaiian bobtail squid digs itself out of the sand and rises into the ocean water like a spaceship taking off. It switches on its cloaking device: glowing bacteria inside its body light up, disguising the squid's silhouette against the moonlight for any predators swimming below. As sleek a vehicle as it appears, though, the bobtail may not totally outrank its microscopic crewmembers. The bacteria seem to power a clock inside the squid's body that can't function without them.

Hiding during the day and hunting at night in shallow Pacific waters, Euprymna scolopes clearly has a working circadian clock. Researchers had noticed, though, that the squid's light organ—the specialized pocket inside its body that houses its bacterial helpers—seemed to have a rhythm of its own. The Vibrio fischeri bacteria give off fluctuating amounts of light throughout the day, for one thing. And the bacteria have their own daily rhythm of gene expression (when various genes are turned on or off), explains Margaret McFall-Ngai, a microbiologist at the University of Wisconsin, Madison.

McFall-Ngai and her coauthors looked for genes linked to circadian rhythms within the squid. They found two types of "cry" genes, which are known to control internal clocks throughout the animal and plant kingdoms. One gene had a daily cycle of activity in the squid's head—which is what you'd expect, since animals' main circadian clocks are in our brains. Other clocks can be elsewhere in the body, though, and this is what researchers found with the second cry gene. It was cycling only within the light organ.

Baby squid, which hadn't yet collected bacterial friends in their light organs, didn't show the same cycling. So it seemed that the bacteria themselves were driving the daily rhythms in the light organ. When the researchers let squid fill their light organs with defective, non-glowing bacteria, the cry gene still didn't cycle properly. This suggested that the glow of the bacteria was the crucial ingredient.

To test this idea, the scientists shone a blue light on the squid holding defective bacteria. Now they expressed just as much cry as the original squid.

McFall-Ngai explains that cryptochromes, the proteins made by cry genes, respond to blue light. Based on the light signals the cryptochromes receive, they turn other genes on or off. Cryptochromes in the squid's head respond to light from the sun to drive its daily rhythms, as in other animals and plants. Those in its light organ, though, respond to the light of its glowing bacterial companions.

The role of the bacterial clock isn't clear yet. "We don't know if the light organ rhythms control any other rhythms in the body," says McFall-Ngai. "But they certainly seem to be involved in controlling the rhythms of the organ itself." The squid controls the daily schedule of the bacteria, too: it jettisons most of its bacteria in the morning, and seems to keep them dimmed during the day by restricting their oxygen supply. At night, it gives the bacteria enough resources to glow at full strength—and that glow drives the clock within the light organ. "There seems to be a tit for tat," McFall-Ngai says. "The host and symbiont 'talk' to one another, controlling one another's biology."

The idea that bacteria can drive circadian rhythms inside their hosts is exciting to humans because we, too, are animals packed full of bacteria. Ours don't glow, but they do line our guts and participate in digesting our food. McFall-Ngai points out that scientists have found "profound circadian rhythms" within our gut tissues, both in their activity and in what genes they express.

Even though we're land-bound, non-glowing vertebrates, our bacteria could be powering circadian rhythms within our bodies just like the squid's. "We think it might be a very general phenomenon," McFall-Ngai says. Our microscopic passengers, that is, might be helping to steer the spaceship.


Heath-Heckman, E., Peyer, S., Whistler, C., Apicella, M., Goldman, W., & McFall-Ngai, M. (2013). Bacterial Bioluminescence Regulates Expression of a Host Cryptochrome Gene in the Squid-Vibrio Symbiosis mBio, 4 (2) DOI: 10.1128/mBio.00167-13

Image: Margaret McFall-Ngai

Need the Time? Ask a Rooster

"The connection with the sun coming up is a misconception," asserts an article in the rural lifestyle magazine Grit. "Roosters crow all the time." Some roosters in Japan would like to loudly disagree. They've shown scientists that their crowing has everything to do with what time of day it is—something they don't even need the sun to know.

Tsuyoshi Shimmura and Takashi Yoshimura, both of Nagoya University in Japan, investigated whether a rooster's crowing is tied to its circadian clock. That is, does the bird's internal sense of night and day determine when it's noisiest? Or do roosters crow at random hours—"morning, noon and night, not to mention afternoon, evening and the parts of the day that don’t have names," according to a disgruntled neighbor-to-roosters quoted in the Grit story?

Like any scientists studying how animals follow the sun's rhythms, the researchers began by shutting their subjects indoors. In a controlled environment, they kept the roosters on a strict schedule of 12 hours in the light and 12 hours in the dark.

Recordings showed that the roosters did not crow at random. A sudden burst of crowing came two hours before the artificial dawn, and the birds gave another "cock-a-doodle-doo" immediately after the lights came on. (Though in their country, the authors point out, it's "ko-ke-kok-koh.")

Then the scientists turned the lights out entirely, keeping the birds in a permanent night. The roosters at first continued to follow crowing cycles of roughly 24 hours, with only their internal clocks keeping them on schedule. Over the course of two lightless weeks, this rhythm gradually wound down.

In the barnyard, though roosters need their circadian alarm clocks for any pre-dawn crows, they can rely on other cues to trigger their crowing at sunrise—say, the sun. So Shimmura and Yoshimura next checked whether light itself causes crowing.

Starting with roosters that were living in permanent night, they tried exposing the birds to a little bit of light at the dawn hour. A few of the roosters crowed. When the researchers used brighter and brighter light, more and more of the birds crowed in response, as if recognizing the sun. A sound recording of other roosters crowing also worked to set their birds off.

Yet just flipping on the lights wasn't enough to make a benighted bird start crowing. When the light and sound signals came at "dawn," the roosters readily responded. When researchers used the same signals later in the "day," their birds didn't respond as strongly. And when they tried the signals at "night," the roosters didn't crow at all.

Even though they were living in permanent dark, roosters weren't fooled by seeing a fake sun at any old time. To get them crowing in earnest, the signals of sunrise had to come at the same time that the birds' bodily alarm clocks rang.

Roosters seem to be expert timekeepers. This knowledge, though, may not make come as much consolation to their neighbors.


Shimmura, T., & Yoshimura, T. (2013). Circadian clock determines the timing of rooster crowing Current Biology, 23 (6) DOI: 10.1016/j.cub.2013.02.015

Image: by -JvL- (Flickr)

Blood Test Reveals the Time Inside You

Like flowers opening and closing with the sun, our bodies have a rhythm that follows the daily turning of the earth. Processes speed up and slow down; hormones rise and fall; we feel wakeful or tired. But our internal clocks aren't always in sync with the day. By finding out what time our bodies think it is, doctors can time their treatments to work better. And now, there might be a simple way to check the time on our inner clocks.

The idea of coordinating medical treatments with the ticking of patients' internal watch hands is called "chronotherapy." Hiroki Ueda, a researcher at the RIKEN Center for Developmental Biology in Kobe, Japan, says that some doctors are already using chronotherapy in treatments such as chemo for colon cancer. Checking a patient's internal schedule before delivering medicine can make a treatment both more effective and less toxic.

But doctors don't have an easy way to check the body clock. "It was labor-intensive and time-consuming for clinical researchers to measure body time using classical methods," Ueda says. One method involves keeping subjects under controlled conditions for more than a day while constantly sampling their blood to check levels of cortisol or melatonin (two hormones with a strong daily cycle). Methods like this aren't exactly practical, which has been an obstacle to chronotherapy. So Ueda and his colleagues have been working on a better technique.

The researchers took inspiration from a hypothetical garden described by 18th-century Swedish botanist Carolus Linnaeus. The Horologium Florae (Latin for "clock of flowers"), as Linnaeus imagined it, would hold a few dozen varieties of flowers that he'd chosen for the precise timing with which they opened and closed each day. By simply looking around the garden, a knowledgeable gardener could tell the time of day.

Instead of flowers, the Japanese researchers used molecules circulating in the bloodstream that wax and wane over the course of the day. They'd previously built this kind of molecular flower clock for mice; now they tried it with humans.

They recruited six healthy volunteers who were willing to pretty seriously jet-lag themselves inside a lab. First, subjects stayed awake and sitting in a chair for a day and a half while researchers fed them and took their blood every two hours.

In these blood samples, the researchers found 58 molecules that cycled over the course of the day. (Since subjects weren't sleeping, moving around, or eating normal meals, they knew these molecular rhythms were intrinsic to their bodies and not a reaction to their environment.) They created a timetable  that would predict the time of day based on the levels of all these molecules in the blood.

Next came the jet-lagging. For a week, subjects were put on a 28-hour cycle of sleeping and waking instead of the usual 24. This was to knock their internal rhythms out of alignment with the true time of day. Then subjects sat through the same day and a half of blood sampling as before.

The frequent blood samples let researchers find their subjects' internal body time the old-fashioned way, by closely plotting the rise and fall of one hormone (cortisol). This gave them a cheat sheet against which they could check the answers from their molecular flower clock.

Using the timetable they'd created in the first part of the experiment, Ueda and his team found that any pair of blood samples taken 12 hours apart could accurately tell their subjects' body time to within 2 or 3 hours. If a person's body thought it was 4:00 PM when it was really noon outside, the molecular timetable could detect the difference.

Ueda's subjects for this study were all young adult males. But he says the cycling molecules in the timetable—including steroid hormones, amino acids, and lipids—should apply to females and other age groups as well. One of the researchers' next steps will be to start testing their molecular clock in these other populations. They'd also like to hone the technique so it works with a single blood sample, rather than two.

Even when we're not trapped inside a sleep lab with manipulative researchers, our circadian rhythms can get misaligned. Jet lag or night shifts at work can push people's bodies out of sync with the sun. Genetic mutations can create whole families of extra-early risers who wake up before dawn.

If a simple blood test allows doctors to peek at patients' internal clocks, they could more easily diagnose these disorders. They could also better tailor chemotherapy and other treatments to patients' bodies. And recent research in mice suggested that high-fat foods consumed during the usual sleeping hours contribute more to obesity than the same foods eaten during waking hours. Understanding our individual clocks might keep us not just sleeping and waking well, but blooming with health.


Takeya Kasukawa, Masahiro Sugimoto, Akiko Hida, Yoichi Minami, Masayo Mori, Sato Honma, Ken-ichi Honma, Kazuo Mishima, Tomoyoshi Soga, & Hiroki R. Ueda (2012). Human blood metabolite timetable indicates internal body time. PNAS : 10.1073/pnas.1207768109

Image: Josh Greenberg/Flickr

Why Good Time Estimators Are Better at Math

Since most of us were never called on in class to answer a tough time-estimation question, or quizzed on the lengths of tones in milliseconds, we don't have a good grasp of our skill in this area. It's kind of exciting. You could be a prodigy and not know it! But a cold dose of reality comes from new research saying skill in time estimation is tied to mathematical intelligence. If you're not amazing at math, your temporal abilities probably aren't A-plus either.

Writing in PLos ONE, a group of Italian researchers describe a study done on 202 adults. The subjects listened to a series of tones through headphones, and estimated the length of each tone in milliseconds. ("We first made sure that participants knew that one millisecond is a thousandth of a second.") Tones ranged from 100 to 3000 milliseconds long. That's a tenth of a second to three seconds, for those of you who are non-amazing at math.

Everyone became more accurate as tones got longer. Unsurprisingly, it's easier to guess that a sound lasts for one second or three seconds than 100 or 200 milliseconds.

Subjects were also tested on their arithmetic skills, general intelligence, and working memory. All these tests came from a standard set of IQ questions. Arithmetic problems ranged from very simple ("What's 5 apples plus 4 apples?") to more difficult ("If 8 machines can finish a job in 6 days, how many machines are needed to finish it in half a day?"). To gauge non-mathematical intelligence, researchers gave subjects a verbal comprehension test (for example, "How are an orange and a banana similar?"). A challenge to remember strings of digits and recite them forward or backward tested subjects' "working memory," which is the ability to hold things in the mind and process them.

People's accuracy at guessing the length of tones was closely tied to their mathematical IQ. Less accurate estimators had lower math scores, and better estimators were better at math. But this connection didn't extend to general intelligence, or at least not to verbal intelligence: there was no relationship between subjects' estimation skills and their performance on the verbal comprehension test.

The researchers also found no relationship between time estimation and working memory. This is a little unexpected, since judging how long something took seems like a task for the short-term memory. And a previous study of time estimation did find a connection to working memory. But in that study, subjects did arithmetic problems while estimating times. The authors argue that making subjects do two things at once was a test of their working memory to begin with; subjects who excelled at estimating times while doing math problems would necessarily have a good working memory. In the new study, tasks were taken one at a time, and skill at time estimation seemed to be separate from working memory.

Subjects were also asked to rate their own mathematical ability on a scale of 0 to 10. These ratings followed the same pattern as math IQ scores: people who considered themselves as better at math were also better at estimating tone lengths. (Interestingly, out of the 202 Italian subjects, not one person rated himself or herself a 10. Does this indicate a general trepidation toward math? Some sort of cultural modesty? Surely in the U.S. someone would have claimed to be the best.)

Your sense of time, then, seems to be tied not to your intelligence or memory, but to your sense of numbers. The authors believe the connection lies in lines--the timeline and the number line. Previous research has shown that people use a mental number line to do math, sensing smaller numbers to the left and larger numbers to the right. People estimate lengths of time using another left-to-right mental path: small intervals are on the left, and larger intervals are on the right. (How would these experiments play out in a culture that reads right-to-left, or vertically?)

If it's all about lines, then mathematical and temporal skills may come down to a person's ability to judge increments, to arrange items in a path. Working with your mental timeline or number line, that is, may really be a spatial skill. And the best time estimators in the classroom might be the line leaders.

Kramer, P., Bressan, P., & Grassi, M. (2011). Time Estimation Predicts Mathematical Intelligence PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028621

Image: James Laing/Flickr

Clocks, Cancer, and the Best Time to Tan

If you can't bear to face your inbox before your first cup of coffee, you'll sympathize with cells in your body that are better equipped to face some challenges at certain times of day. Carcinogens, such as ultraviolet radiation, may be one such challenge. Can we lower our cancer risk by limiting our carcinogen exposure to certain hours of the day?

Circadian rhythms are day-long cycles that ebb and flow like tides within our bodies. We use the sun to keep our internal clocks calibrated. But even if left in a dark room for days on end, our bodies maintain their rhythms. Our internal temperatures, levels of circulating hormones, and activity of various genes within our cells all rise and fall throughout the day.

One of the genes that follows a daily cycle is responsible for making a DNA-repair protein called XPA. When your DNA is damaged, a molecular task force within the cell identifies the bad spot, snips it out, and fills in the gap with fresh nucleotides. XPA is a crucial member of this task force. Researchers in North Carolina wanted to know how the cycling of XPA affects skin cancer. When XPA is off-duty--when its daily cycle reaches its lowest point--are skin cells more vulnerable to cancer-causing sun damage?

To find out, the researchers used hairless mice that are bred to develop humanlike skin cancer. Mice have an internal clock that's nearly identical to that of humans, and repair their DNA in the same way. The researchers exposed one group of mice to UV radiation at 4 AM, the lowest point of their XPA cycle. Another group of mice was exposed at 4 PM, the high point, instead.

For the 12 hours following UV exposure, the researchers monitored the rate of DNA repair in mouse skin cells. They saw that in the afternoon group, repair happened quickly, thanks to the high amounts of XPA at work. But in the morning-exposure group, DNA repair was delayed significantly.

Does this delay in fixing DNA errors add up to cancer? The researchers again divided the mice into groups. One group was exposed to UV radiation at 4 AM, three days a week, for 25 weeks. The second group was again exposed to UV at 4 PM, and a third group was left alone.

Both groups of mice exposed to UV developed skin tumors. But the group that got its UV radiation in the early morning grew tumors sooner. Those mice also had twice as many tumors as the afternoon UV group, and their tumors were nearly twice as wide. (All this evidence was easily, and disgustingly, visible due to their hairlessness.)

In humans, damage and repair likely follow the same rhythm. But there's one major difference: Since mice are nocturnal, their clock is opposite to ours. Hormones that are needed during waking hours, for instance, would peak during the night in mice and during the day in humans. In an earlier study, the researchers found that XPA follows a circadian rhythm in humans just as it does in mice--but for us, production is highest in the early morning.

Our levels of XPA peak around 7 AM. Based on this study, our ability to protect our skin from cancer-causing sun damage probably peaks at the same time. Adding to the danger is the fact that in both humans and mice, DNA replication follows a cycle opposite to XPA production. This means that when XPA is lowest, more DNA is being stitched together--making the risk of errors even higher.

The authors suggest that if we must expose ourselves to UV radiation, we do so in the morning. We should avoid the sun in afternoon and evening hours, when XPA is lowest and our skin cells are most vulnerable to carcinogenic damage. Of course, unless you live in the Arctic circle, you're not likely to get a lot of dangerous sun exposure at 7 PM. But for people who use tanning beds, sessions late in the day may be more harmful than those in the morning.

There may be other carcinogens whose danger varies throughout the day, depending on how hormones and other molecules are cycling through our affected organs. Is there an ideal time of day to smoke a cigarette? Eat a hot dog? Have an x-ray? If we can't remove risks from our lives, maybe we can at least reschedule them.


Gaddameedhi, S., Selby, C., Kaufmann, W., Smart, R., & Sancar, A. (2011). Control of skin cancer by the circadian rhythm Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1115249108