Chapter 9. Hearing, Vestibular Perception, Taste, and Smell
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By JAN HOFFMAN Our daily tug of leash war goes like this. I tell Chico we’re taking a left. He yanks right, wet black nostrils burrowing in loamy leaf piles. Me versus a 15-pound Havanese, incensed by scent. Today, I let him win. That’s because I have fresh appreciation for his sniffing behavior, after reading a new book, “Being a Dog: Following the Dog into a World of Smell,” by Alexandra Horowitz, a professor of cognitive science who runs the Dog Cognition Lab at Barnard College. In it, she explains the elegant engineering of the dog’s olfactory system and how familiar canine behaviors — licking, sneezing, tail-wagging — have associations with smell. Dr. Horowitz also describes how she trained herself to enhance her inferior human sniffing ability. On a recent afternoon at Riverside Park in Manhattan, I met Dr. Horowitz and Finn (short for Finnegan), her affable, glossy black 9-year-old mixed breed. There she — and he — shared some sniffing insights that have since made my walks with Chico more intriguing and fun. “There are many ways to sniff, and the human method is not the best,” Dr. Horowitz said. Sniff researchers (yes, you read that correctly) have found we have about six million olfactory receptors; dogs have 300 million. Humans sniff once per second-and-a-half; dogs, five to 10 times a second. “They even exhale better than we do,” Dr. Horowitz continued, describing a sort of doggy yoga breath. Dogs exhale through the side slits of their nostrils, so they keep a continuous flow of inhaled air in their snout for smelling. “This gives them a continuous olfactory view of the world.” © 2016 The New York Times Company
Keyword: Chemical Senses (Smell & Taste)
Link ID: 22742 - Posted: 10.11.2016
Annette Heist Nisha Pradhan is worried. The recent college graduate just turned 21 and plans to live on her own. But she's afraid she won't be able to stay safe. That's because Pradhan is anosmic — she isn't able to smell. She can't tell if milk is sour, or if she's burning something on the stove, or if there's a gas leak, and that worries her. "It actually didn't even strike me as being a big deal until I got to college," Pradhan says. Back home in Pennington, N.J., her family did her smelling for her, she says. She's moved in with them for now, but she's looking for a place of her own. "Now that I'm searching for ways or places to live as an independent person, I find more and more that the sense of smell is crucial to how we live our lives," Pradhan says. There's no good estimate for how many people live with smell loss. Congenital anosmia, being born without a sense of smell, is a rare condition. Acquired smell loss is more common. That loss can be total, or what's known as hyposmia, a diminished sense of smell. Pradhan doesn't know how she lost her sense of smell. She thinks she was born with it because as a child, she says she liked to eat and ate a lot. But there came a point where she lost interest in food. "That's actually one of the first things that people notice whenever they have a smell problem, is food doesn't taste right anymore," says Beverly Cowart, a researcher at the Monell Chemical Senses Center in Philadelphia. That's because eating and smell go hand in hand. How food tastes often relies on what we smell. © 2016 npr
By Michelle Roberts Some people are genetically wired to prefer the taste of fatty foods, putting them at increased risk of obesity, according to UK researchers. The University of Cambridge team offered 54 volunteers unlimited portions of chicken korma, followed by an Eton mess-style dessert. Some of the meals were packed with fat while others were low-fat versions. Those with a gene already linked to obesity showed a preference for the high-fat food and ate more of it. Fat genes The gene in question is called MC4R. It is thought about one in every 1,000 people carries a defective version of this gene which controls hunger and appetite as well as how well we burn off calories. Mutations in MC4R are the most common genetic cause of severe obesity within families that has so far been identified. Humans probably evolved hunger genes to cope in times of famine, say experts. When food is scarce it makes sense to eat and store more fat to fend off starvation. But having a defect in the MC4R gene means hunger can become insatiable. In the study, published in the journal Nature Communications, the researchers created a test menu that varied only in fat or sugar content. The three versions of the main meal on offer - chicken korma - were identical in appearance, and as far as possible, taste, but ranged in fat from low to medium and high. The volunteers were offered a small sample of each and then left to eat as much as they liked of the three dishes. The same was then done for a pudding of strawberries, meringue and cream, but this time varying the sugar content rather than the fat. © 2016 BBC.
Alva Noë Eaters and cooks know that flavor, in the jargon of neuroscientists, is multi-modal. Taste is all important, to be sure. But so is the look of food and its feel in the mouth — not to mention its odor and the noisy crunch, or juicy squelch, that it may or may not make as we bite into it. The perception of flavor demands that we exercise a suite of not only gustatory, but also visual, olfactory, tactile and auditory sensitivities. Neuroscientists are now beginning to grasp some of the ways the brain enables our impressive perceptual power when it comes to food. Traditionally, scientists represent the brain's sensory function in a map where distinct cortical areas are thought of as serving the different senses. But it is increasingly appreciated that brain activity can't quite be segregated in this way. Cells in visual cortex may be activated by tactile stimuli. This is the case, for example, when Braille readers use their fingers to read. These blind readers aren't seeing with their fingers, rather, they are deploying their visual brains to perceive with their hands. And, in a famous series of studies that had a great influence on my thinking on these matters, Miriganka Sur at MIT showed that animals whose retinas were re-wired surgically to feed directly into auditory cortex do not hear lights and other visible objects presented to the eyes, rather, they see with their auditory brains. The brain is plastic, and different sensory modalities compete continuously for control over populations of cells. An exciting new paper on the gustatory cortex from the laboratory of Alfredo Fontanini at Stony Brook University shows that there are visual-, auditory-, olfactory- and touch-sensitive cells in the gustatory cortex of rats. There are even some cells that respond to stimuli in more than one modality. But what is more remarkable is that when rats learn to associate non-taste qualities — tones, flashes of lights, etc. — with food (sucrose in their study), there is a marked transformation in the gustatory cortex. © 2016 npr
Dean Burnett You remember that time a children’s TV presenter, one who has been working in children’s television for decades and is now employed on a channel aimed at under-8-year-olds, decided to risk it all and say one of the worst possible swear words on a show for pre-schoolers that he is famous for co-hosting? Remember how he took a huge risk for no appreciable gain and uttered a context-free profanity to an audience of toddlers? How he must have wanted to swear on children’s TV but paradoxically didn’t want anyone to notice so “snuck it in” as part of a song, where it would be more ambiguous? How all the editors and regulators at the BBC happened to completely miss it and allow it to be aired? Remember this happening? Well you shouldn’t, because it clearly didn’t. No presenter and/or channel would risk their whole livelihood in such a pointless, meaningless way, especially not the ever-pressured BBC. And, yet, an alarming number of people do think it happened. Apparently, there have been some “outraged parents” who are aghast at the whole thing. This seems reasonable in some respects; if your toddler was subjected to extreme cursing then as a parent you probably would object. On the other hand, if your very small child is able to recognise strong expletives, then perhaps misheard lyrics on cheerful TV shows aren’t the most pressing issue in their life. Regardless, a surprising number of people report that they did genuinely “hear” the c-word. This is less likely to be due to a TV presenter having some sort of extremely-fleeting breakdown, and more likely due to the quirks and questionable processing of our senses by our powerful yet imperfect brains. © 2016 Guardian News and Media Limited
By Jessica Hamzelou As any weight-watcher knows, carb cravings can be hard to resist. Now there’s evidence that carbohydrate-rich foods may elicit a unique taste too, suggesting that “starchy” could be a flavour in its own right. It has long been thought that our tongues register a small number of primary tastes: salty, sweet, sour and bitter. Umami – the savoury taste often associated with monosodium glutamate – was added to this list seven years ago, but there’s been no change since then. However, this list misses a major component of our diets, says Juyun Lim at Oregon State University in Corvallis. “Every culture has a major source of complex carbohydrate. The idea that we can’t taste what we’re eating doesn’t make sense,” she says. Complex carbohydrates such as starch are made of chains of sugar molecules and are an important source of energy in our diets. However, food scientists have tended to ignore the idea that we might be able to specifically taste them, says Lim. Because enzymes in our saliva break starch down into shorter chains and simple sugars, many have assumed we detect starch by tasting these sweet molecules. Her team tested this by giving a range of different carbohydrate solutions to volunteers – who it turned out were able to detect a starch-like taste in solutions that contained long or shorter carbohydrate chains. “They called the taste ‘starchy’,” says Lim. “Asians would say it was rice-like, while Caucasians described it as bread-like or pasta-like. It’s like eating flour.” © Copyright Reed Business Information Ltd.
By Alison F. Takemura A stationary Carolina sphinx moth (Manduca sexta) is the Cinderella of the animal kingdom. The hummingbird-size insect has dull, dark wings that are mottled like charred wood, and a plump body reminiscent of a small breakfast sausage. Casual observers of M. sexta often see little else. “They say, ‘Oh, it doesn’t look so nice. It’s just grey.’ But as soon as [the moths] start flying, they’re completely impressed,” says Danny Kessler, a pollination ecologist at the Max Planck Institute of Chemical Ecology in Germany. “They change their minds completely.” Hawkmoths, the group to which M. sexta belongs, whir their wings like hummingbirds as they flit between flowers, hovering to drink nectar. M. sexta’s proboscis, longer than its 2-inch body, stays unfurled, a straw ready to sip. Kessler studies the interaction between the Carolina sphinx moth, whose larvae are known as tobacco hornworms, and its preferred food source, the coyote tobacco plant (Nicotiana attenuata), to better understand how insect behavior affects a plant’s reproductive success. M. sexta adults drink nectar from tobacco’s skinny, white, trumpet-shape flowers, foraging from them at night and pollinating them in the process. Scientists have known for decades that the moth uses its antennae to detect the flowers’ scent—even from several miles away, Kessler says. © 1986-2016 The Scientist
Keyword: Chemical Senses (Smell & Taste)
Link ID: 22626 - Posted: 09.05.2016
By Simon Oxenham It can seem like barely a week goes by without a new study linking the stage in a woman’s monthly cycle to her preferences in a sexual partner. Reportedly, when women are ovulating they are attracted to men who are healthier, more dominant, more masculine, have higher testosterone levels– the list goes on. But do women really exhibit such behavioural changes – and why are we so fascinated by the idea that they do? A popular theory in evolutionary psychology is that women seek out men with better genes while they are ovulating to have short term affairs with, so as to produce healthier babies. These men may not necessarily stick around for the long haul, but appear particularly attractive when a woman is in the fertile stage of her cycle. During the non-fertile phase, the theory goes that women seek out men who are more likely to make reliable long-term partners and good fathers. But something smells a bit fishy here. Are women really evolutionarily hard-wired to cuckold their partners? Or might the attraction of a salacious hypothesis – with slightly sexist overtones – be shaping some of this research? Masculine all month A review of these kinds of studies is now challenging this often-told story. Wendy Wood at the University of Southern California and her team have analysed 58 studies – some of which were never published – and found that this theory is largely unsupported by evidence. © Copyright Reed Business Information Ltd.
By Virginia Morell Scientists have long worried whether animals can respond to the planet’s changing climate. Now, a new study reports that at least one species of songbird—and likely many more—already knows how to prep its chicks for a warming world. They do so by emitting special calls to the embryos inside their eggs, which can hear and learn external sounds. This is the first time scientists have found animals using sound to affect the growth, development, behavior, and reproductive success of their offspring, and adds to a growing body of research revealing that birds can “doctor” their eggs. “The study is novel, surprising, and fascinating, and is sure to lead to much more work on parent-embryo communication,” says Robert Magrath, a behavioral ecologist at the Australian National University in Canberra who was not involved in the study. The idea that the zebra finch (Taeniopygia guttata) parents were “talking to their eggs” occurred to Mylene Mariette, a behavioral ecologist at Deakin University in Waurn Ponds, Australia, while recording the birds’ sounds at an outdoor aviary. She noticed that sometimes when a parent was alone, it would make a rapid, high-pitched series of calls while sitting on the eggs. Mariette and her co-author, Katherine Buchanan, recorded the incubation calls of 61 female and 61 male finches inside the aviary. They found that parents of both sexes uttered these calls only during the end of the incubation period and when the maximum daily temperature rose above 26°C (78.8°F). © 2016 American Association for the Advancement of Scienc
Dean Burnett A lot of people, when they travel by car, ship, plane or whatever, end up feeling sick. They’re fine before they get into the vehicle, they’re typically fine when they get out. But whilst in transit, they feel sick. Particularly, it seems, in self-driving cars. Why? One theory is that it’s due to a weird glitch that means your brain gets confused and thinks it’s being poisoned. This may seem surprising; not even the shoddiest low-budget airline would get away with pumping toxins into the passengers (airline food doesn’t count, and that joke is out of date). So where does the brain get this idea that it’s being poisoned? Despite being a very “mobile” species, humans have evolved for certain types of movement. Specifically, walking, or running. Walking has a specific set of neurological processes tied into it, so we’ve had millions of years to adapt to it. Think of all the things going on in your body when you’re walking, and how the brain would pick up on these. There’s the steady thud-thud-thud and pressure on your feet and lower legs. There’s all the signals from your muscles and the movement of your body, meaning the motor cortex (which controls conscious movement of muscles) and proprioception (the sense of the arrangement of your body in space, hence you can know, for example, where your arm is behind your back without looking at it directly) are all supplying particular signals. © 2016 Guardian News and Media Limited
By Marlene Cimons Former president Jimmy Carter, 91, told the New Yorker recently that 90 percent of the arguments he has with Rosalynn, his wife of 70 years, are about hearing. “When I tell her, ‘Please speak more loudly,’ she absolutely refuses to speak more loudly, or to look at me when she talks,” he told the magazine. In response, the former first lady, 88, declared that having to repeat things “drives me up the wall.” Yet after both went to the doctor, much to her surprise, “I found out it was me!” she said. “I was the one who was deaf.” Hearing loss is like that. It comes on gradually, often without an individual’s realizing it, and it prompts a range of social and health consequences. “You don’t just wake up with a sudden hearing loss,” says Barbara Kelley, executive director of the Hearing Loss Association of America. “It can be insidious. It can creep up on you. You start coping, or your spouse starts doing things for you, like making telephone calls.” An estimated 25 percent of Americans between ages 60 and 69 have some degree of hearing loss, according to the President’s Council of Advisors on Science and Technology. That percentage grows to more than 50 percent for those age 70 to 79, and to almost 80 percent of individuals older than 80. That’s about 30 million people, a number likely to increase as our population ages. Behind these statistics are disturbing repercussions such as social isolation and the inability to work, travel or be physically active.
Link ID: 22561 - Posted: 08.16.2016
Cassie Martin Understanding sea anemones’ exceptional healing abilities may help scientists figure out how to restore hearing. Proteins that the marine invertebrates use to repair damaged cells can also repair mice’s sound-sensing cells, a new study shows. The findings provide insights into the mechanics of hearing and could lead to future treatments for traumatic hearing loss, researchers report in the Aug. 1 Journal of Experimental Biology. “This is a preliminary step, but it’s a very useful step in looking at restoring the structure and function of these damaged cells,” says Lavinia Sheets, a hearing researcher at Harvard Medical School who was not involved in the study. Tentacles of starlet sea anemones (Nematostella vectensis) are covered in tiny hairlike cells that sense vibrations in the water from prey swimming nearby.The cells are similar to sound-sensing cells found in the ears of humans and other mammals. When loud noises damage or kill these hair cells, the result can range from temporary to permanent hearing loss. Anemones’ repair proteins restore their damaged hairlike cells, but landlubbing creatures aren’t as lucky. Glen Watson, a biologist at the University of Louisiana at Lafayette, wondered if anemones’ proteins — which have previously been shown to mend similar cells in blind cave fish — might also work in mammals. |© Society for Science & the Public 2000 - 2016.
Helen Thompson A roughly 27-million-year-old fossilized skull echoes growing evidence that ancient whales could navigate using high-frequency sound. Discovered over a decade ago in a drainage ditch by an amateur fossil hunter on the South Carolina coast, the skull belongs to an early toothed whale. The fossil is so well-preserved that it includes rare inner ear bones similar to those found in modern whales and dolphins. Inspired by the Latin for “echo hunter,” scientists have now named the ancient whale Echovenator sandersi. “It suggests that the earliest toothed whales could hear high-frequency sounds,” which is essential for echolocation, says Morgan Churchill, an anatomist at the New York Institute of Technology in Old Westbury. Churchill and his colleagues describe the specimen online August 4 in Current Biology. Modern whales are divided on the sound spectrum. Toothed whales, such as orcas and porpoises, use high-frequency clicking sounds to sense predators and prey. Filter-feeding baleen whales, on the other hand, use low-frequency sound for long-distance communication. Around 35 million years ago, the two groups split, and E. sandersi emerged soon after. CT scans show that E. sandersi had a few features indicative of ultrasonic hearing in modern whales and dolphins. Most importantly, it had a spiraling inner ear bone with wide curves and a long bony support structure, both of which allow a greater sensitivity to higher-frequency sound. A small nerve canal probably transmitted sound signals to the brain. © Society for Science & the Public 2000 - 2016. All rights reserved.
Jon Hamilton Two studies released at an international Alzheimer's meeting Tuesday suggest doctors may eventually be able to screen people for this form of dementia by testing the ability to identify familiar odors, like smoke, coffee and raspberry. In both studies, people who were in their 60s and older took a standard odor detection test. And in both cases, those who did poorly on the test were more likely to already have — or go on to develop — problems with memory and thinking. "The whole idea is to create tests that a general clinician can use in an office setting," says Dr. William Kreisl, a neurologist at Columbia University, where both studies were done. The research was presented at the Alzheimer's Association International Conference in Toronto. Currently, any tests that are able to spot people in the earliest stages of Alzheimer's are costly and difficult. They include PET scans, which can detect sticky plaques in the brain, and spinal taps that measure the levels of certain proteins in spinal fluid. The idea of an odor detection test arose, in part, from something doctors have observed for many years in patients with Alzheimer's, Kreisl says. "Patients will tell us that food does not taste as good," he says. The reason is often that these patients have lost the ability to smell what they eat. That's not surprising, Kreisl says, given that odor signals from the nose have to be processed in areas of the brain that are among the first to be affected by Alzheimer's disease. But it's been tricky to develop a reliable screening test using odor detection. © 2016 npr
By Maggie Koerth-Baker Q: I want to hear what the loudest thing in the world is! — Kara Jo, age 5 No. No, you really don’t. See, there’s this thing about sound that even we grown-ups tend to forget — it’s not some glitter rainbow floating around with no connection to the physical world. Sound is mechanical. A sound is a shove — just a little one, a tap on the tightly stretched membrane of your ear drum. The louder the sound, the heavier the knock. If a sound is loud enough, it can rip a hole in your ear drum. If a sound is loud enough, it can plow into you like a linebacker and knock you flat on your butt. When the shock wave from a bomb levels a house, that’s sound tearing apart bricks and splintering glass. Sound can kill you. Consider this piece of history: On the morning of Aug. 27, 1883, ranchers on a sheep camp outside Alice Springs, Australia, heard a sound like two shots from a rifle. At that very moment, the Indonesian volcanic island of Krakatoa was blowing itself to bits 2,233 miles away. Scientists think this is probably the loudest sound humans have ever accurately measured. Not only are there records of people hearing the sound of Krakatoa thousands of miles away, there is also physical evidence that the sound of the volcano’s explosion traveled all the way around the globe multiple times. Now, nobody heard Krakatoa in England or Toronto. There wasn’t a “boom” audible in St. Petersburg. Instead, what those places recorded were spikes in atmospheric pressure — the very air tensing up and then releasing with a sigh, as the waves of sound from Krakatoa passed through. There are two important lessons about sound in there: One, you don’t have to be able to see the loudest thing in the world in order to hear it. Second, just because you can’t hear a sound doesn’t mean it isn’t there. Sound is powerful and pervasive and it surrounds us all the time, whether we’re aware of it or not.
Link ID: 22453 - Posted: 07.19.2016
Paula Span An estimated one zillion older people have a problem like mine. First: We notice age-related hearing loss. A much-anticipated report on hearing health from the National Academies of Sciences, Engineering and Medicine last month put the prevalence at more than 45 percent of those aged 70 to 74, and more than 80 percent among those over 85. Then: We do little or nothing about it. Fewer than 20 percent of those with hearing loss use hearing aids. I’ve written before about the reasons. High prices ($2,500 and up for a decent hearing aid, and most people need two). Lack of Medicare reimbursement, because the original 1965 law creating Medicare prohibits coverage. Time and hassle. Stigma. Both the National Academies and the influential President’s Council of Advisors on Science and Technology have proposed pragmatic steps to make hearing technology more accessible and affordable. But until there’s progress on those, many of us with mild to moderate hearing loss may consider a relatively inexpensive alternative: personal sound amplification products, or P.S.A.P.s. They offer some promise — and some perils, too. Unlike for a hearing aid, you don’t need an audiologist to obtain a P.S.A.P. You see these gizmos advertised on the back pages of magazines or on sale at drugstore chains. You can buy them online. © 2016 The New York Times Company
Link ID: 22449 - Posted: 07.16.2016
Ramin Skibba Is Justin Bieber a musical genius or a talentless hack? What you 'belieb' depends on your cultural experiences. Some people like to listen to the Beatles, while others prefer Gregorian chants. When it comes to music, scientists find that nurture can trump nature. Musical preferences seem to be mainly shaped by a person’s cultural upbringing and experiences rather than biological factors, according to a study published on 13 July in Nature1. “Our results show that there is a profound cultural difference” in the way people respond to consonant and dissonant sounds, says Josh McDermott, a cognitive scientist at the Massachusetts Institute of Technology in Cambridge and lead author of the paper. This suggests that other cultures hear the world differently, he adds. The study is one of the first to put an age-old argument to the test. Some scientists believe that the way people respond to music has a biological basis, because pitches that people often like have particular interval ratios. They argue that this would trump any cultural shaping of musical preferences, effectively making them a universal phenomenon. Ethnomusicologists and music composers, by contrast, think that such preferences are more a product of one’s culture. If a person’s upbringing shapes their preferences, then they are not a universal phenomenon. © 2016 Macmillan Publishers Limited
By Michael Price The blind comic book star Daredevil has a highly developed sense of hearing that allows him to “see” his environment with his ears. But you don’t need to be a superhero to pull a similar stunt, according to a new study. Researchers have identified the neural architecture used by the brain to turn subtle sounds into a mind’s-eye map of your surroundings. The study appears to be “very solid work,” says Lore Thaler, a psychologist at Durham University in the United Kingdom who studies echolocation, the ability of bats and other animals to use sound to locate objects. Everyone has an instinctive sense of the world around them—even if they can’t always see it, says Santani Teng, a postdoctoral researcher at the Massachusetts Institute of Technology (MIT) in Cambridge who studies auditory perception in both blind and sighted people. “We all kind of have that intuition,” says Teng over the phone. “For instance, you can tell I’m not in a gymnasium right now. I’m in a smaller space, like an office.” That office belongs to Aude Oliva, principal research scientist for MIT’s Computational Perception & Cognition laboratory. She and Teng, along with two other colleagues, wanted to quantify how well people can use sounds to judge the size of the room around them, and whether that ability could be detected in the brain. © 2016 American Association for the Advancement of Science.
Link ID: 22427 - Posted: 07.12.2016
By Michael Price Doctors and soldiers could soon place their trust in an unusual ally: the mouse. Scientists have genetically engineered mice to be ultrasensitive to specific smells, paving the way for animals that are “tuned” to sniff out land mines or chemical signatures of diseases like Parkinson’s and Alzheimer’s. Trained rats and dogs have long been used to detect the telltale smell of TNT in land mines, and research suggests that dogs can smell the trace chemical signals of low blood sugar or certain types of cancer. Mice also have powerful sniffers: They sport about 1200 genes dedicated to odorant receptors, cellular sensors that react to a scent’s chemical signature. That’s a few hundred less than rats and about the same as dogs. (Humans have a paltry 350.) Paul Feinstein wants to upgrade the mouse’s already sensitive nose. For the last decade, the neurobiologist at Hunter College in New York City has been studying how odorant receptors form on the surface of neurons within the olfactory system. During development, each olfactory neuron specializes to express a single odorant receptor, which binds to chemicals in the air to detect a specific odor. In other words, each olfactory neuron has a singular receptor that senses a particular smell. Normally, there is an even distribution of receptors throughout the system, so each receptor can be found in about 0.1% of mouse neurons. Feinstein wondered if he could make the mouse’s nose pay more attention to particular scents by making certain odorant receptors more numerous. He and colleagues developed a string of DNA that, when injected into the nucleus of a fertilized mouse egg, appears to make olfactory neurons more likely to develop one particular odorant receptor than the others. This receptor, called M71, detects acetophenone, a chemical that smells like jasmine. When the team added four or more copies of the DNA sequence to a mouse egg, a full 1% of neurons carried it—10 times more than normal. © 2016 American Association for the Advancement of Science.
Keyword: Chemical Senses (Smell & Taste)
Link ID: 22412 - Posted: 07.08.2016
By Patrick Monahan Birds are perhaps best known for their bright colors, aerial prowess, and melodic songs. But research presented in Austin last week at the Evolution Conference shows that bacteria have granted some birds another important attribute: stink. Having long taken a back seat to sight and sound, scent is becoming more and more recognized as an important sense for songbirds, and dark-eyed juncos (Junco hyemalis, pictured) are no stranger to it. When these common birds clean their feathers—or preen—they spread pungent oil from their “preen glands” all over their bodies. The act is important for enticing mates: Three of the gland’s smelly chemicals are found in very different quantities in the two sexes, and males with a more masculine musk end up with more offspring. Females with a more feminine scent profile are more successful, too. But juncos likely aren’t making their perfume alone: Lots of those preen gland chemicals are naturally made by bacteria. And new work is making the bird-bacteria link even more firm. When researchers inject antibiotics into the juncos’ preen glands, the concentrations of three smelly molecules tend to decrease—the same three molecules that juncos find sexy in the right proportions, Danielle Whittaker of Michigan State University in East Lansing told attendees. So it seems like juncos may actually be picking mates based on their bacterial—rather than self-produced—body odor, a first for birds. © 2016 American Association for the Advancement of Science.