How mammals' brains evolved to distinguish odors is nothing to sniff at

JULY 18, 2019

by Salk Institute

The world is filled with millions upon millions of distinct smells, but how mammals' brains evolved to tell them apart is something of a mystery.

Now, two neuroscientists from the Salk Institute and UC San Diego have discovered that at least six types of mammals—from mice to cats—distinguish odors in roughly the same way, using circuitry in the brain that's evolutionarily preserved across species.

"The study yields insights into organizational principles underpinning brain circuitry for olfaction in mammals that may be applied to other parts of the brain and other species," says Charles Stevens, distinguished professor emeritus in Salk's Neurobiology Laboratory and coauthor of the research published in the July 18, 2019 issue of Current Biology.

In brief, the study reveals that the size of each of the three components of the neural network for olfaction scales about the same for each species, starting with receptors in the nose that transmit signals to a cluster of neurons in the front of the brain called the olfactory bulb which, in turn, relays the signals to a "higher functioning" region for odor identification called the piriform cortex.

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Salmon may lose the ability to smell danger as carbon emissions rise

December 18, 2018, University of Washington

The ability to smell is critical for salmon. They depend on scent to avoid predators, sniff out prey and find their way home at the end of their lives when they return to the streams where they hatched to spawn and die.

New research from the University of Washington and NOAA Fisheries' Northwest Fisheries Science Center shows this powerful sense of smell might be in trouble as carbon emissions continue to be absorbed by our ocean. Ocean acidification is changing the water's chemistry and lowering its pH. Specifically, higher levels of carbon dioxide, or CO2, in the water can affect the ways in which coho salmon process and respond to smells.

"Salmon famously use their nose for so many important aspects of their life, from navigation and finding food to detecting predators and reproducing. So it was important for us to know if salmon would be impacted by future carbon dioxide conditions in the marine environment," said lead author Chase Williams, a postdoctoral researcher in Evan Gallagher's lab at the UW Department of Environmental and Occupational Health Sciences.

The study, appearing online Dec. 18 in the journal Global Change Biology, is the first to show that ocean acidification affects coho salmons' sense of smell. The study also takes a more comprehensive approach than earlier work with marine fish by looking at where in the sensory-neural system the ability to smell erodes for fish, and how that loss of smell changes their behavior.

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Researchers study animals' unique sense of smell to develop improved chemical sensors

Move over Rover: There's a new sniffing powerhouse in the neighborhood

Date:  November 19, 2018

Source:  American Physical Society

Some animals have a superpower in their sense of smell. They explore, interpret and understand their world with such sensitivity that people have enlisted canines to help solve crime and detect cancer on the breath. Scientists at the Georgia Institute of Technology are now homing in on the secrets behind animals' super sniffers to develop an artificial chemical sensor that could be used for a variety of tasks, from food safety to national security.

"We turned to animals to understand what nature has already figured out," said Thomas Spencer, a doctoral candidate in David Hu's lab at Georgia Tech. "We are applying the underlying principles that we learned about these mechanisms to design a better sensor."

Spencer will present the group's latest design for an electronic nose that concentrates odors for improved chemical sensing at the American Physical Society's Division of Fluid Dynamics 71st Annual Meeting, which will take place Nov. 18-20 at the Georgia World Congress Center in Atlanta, Georgia.

Their work began inauspiciously at a competition to develop a sensor that could identify different varieties of cheese. Turning to nature to guide their work, they traveled to the Atlanta Zoo to compare the way different animals sniff, from mice to elephants.

"We wanted to measure the sniffing frequency of animals when they are trying to identify a new source of food or something that interests them," Spencer said.

After reviewing the data, they found that sniffing speed decreases as body size increases; put another way, mice sniff faster than elephants. Using their findings, they designed a customized pump that oscillates back and forth at the same frequency that animals sniff. The design of their device moves airflow around the chemical sensor in a more controlled fashion.

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Acidic oceans cause fish to lose their sense of smell

July 23, 2018, University of Exeter

When carbon dioxide is absorbed by seawater carbonic acid is formed, making the water more acidic. Since the Industrial Revolution, oceanic CO2 has risen by 43% and is predicted to be two and a half times current levels by the end of this century.

Fish use their sense of smell (olfaction) to find food, safe habitats, avoid predators, recognize each other and find suitable spawning grounds. A reduction in their ability to smell therefore can compromise these essential functions for their survival.

The new study provides evidence that economically important species will be affected by elevated CO2, leaving fish vulnerable because it affects their ability to detect odours.

University of Exeter researcher Dr. Cosima Porteus, who led the study, said: "Our study is the first to examine the impact of rising carbon dioxidein the ocean on the olfactory system of fish. First we compared the behaviour of juvenile sea bass at CO2 levels typical of today's ocean conditions, and those predicted for the end of the century. Sea bass in acidic waters swam less and were less likely to respond when they encountered the smell of a predator. These fish were also more likely to "freeze" indicating anxiety."

Experts at the University of Exeter, in collaboration with scientists from the Centre of Marine Sciences (CCMar, Faro, Portugal) and the Centre for Environment, Fisheries and Aquaculture Science (Cefas), also tested the ability of the sea bass' nose to detect different smells. They did this by recording the activity in the nervous system while their nose was exposed to water with different levels of CO2 and acidity.

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Decoding ants' coat of many odors

Date:  July 10, 2017

Source:  Vanderbilt University

Summary:  Biologists report a major advance in deciphering the molecular genetics underlying the ant's high-definition sense of smell, an ability that has allowed them to create the most complicated social organization on earth next to humans.

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Scans show Pawpawsaurus depended on sense of smell

MAY 24, 2016

by Brett Smith

A cousin of the tank-like Ankylosaurus, Pawpawsaurus didn’t have the club-like tail of its more famous relative.

However, the lesser-known dinosaur did have a strong sense of smell it likely depended on, according to a new study in the journal PLOS ONE.

The new study is based on the first-ever CT scans of Pawpawsaurus's fossilized skull.

"CT imaging has allowed us to delve into the intricacies of the brains of extinct animals, especially dinosaurs, to unlock secrets of their ways of life," study author Louis Jacobs, a professor of archeology at Southern Methodist University, said in a news release.

Although Pawpawsaurus’s olfaction was inferior to Ankylosaurus, the study team said, it was still better than some predatory dinosaurs like Ceratosaurus.

"Pawpawsaurus in particular, and the group it belonged to—Nodosauridae—had no flocculus, a structure of the brain involved with motor skills, no club tail, and a reduced nasal cavity and portion of the inner ear when compared with the other family of ankylosaurs," said Ariana Paulina-Carabajal, researcher for the Biodiversity and Environment Research Institute, San Carlos de Bariloche in Argentina. "But its sense of smell was very important, as it probably relied on that to look for food, find mates and avoid or flee predators.

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From land mines to cancer, animals' incredible sense of smell is saving lives

In Tanzania, they use giant pouched rats to smell for TB and landmines. In Britain, they're researching why dogs are able to sniff out some sorts of cancer. Emma Young reports on how mammals' olfactory gifts are being harnessed

Emma Young 

Thursday 18 February 2016

In a small, hot room within a compound in Tanzania's southern highlands are three white-clad technicians, a glass-and-metal chamber and a rat named Charles. After being gently dropped into the chamber, Charles aims his snout at the first of a series of 10 sliding metal plates in the base. A technician swiftly opens it, revealing a small hole. Charles sniffs… and moves on. The hole is closed, and the next one opened. This time, he sniffs hard, scratching at the metal. The technician calls out: "Two!" Over by the window, a colleague holding a chart inserts a tick. It's highly possible that Charles has just saved someone's life.

Charles is an African giant pouched rat, a species endemic to sub-Saharan Africa. He's also a pioneer, one of 30 of his species that live and work in Morogoro, a few hundred miles west of Tanzania's largest city, Dar es Salaam, on a programme to sniff out tuberculosis (TB).

TB is a disease that can destroy the lungs. About nine million new cases are diagnosed worldwide every year, one-quarter of them in Africa. Antibiotics can cure TB, but it's fatal if untreated, and many patients are never diagnosed. This is partly because the 125-year-old microscope-based test used across Tanzania (and in many other cash-strapped countries) picks up only about 60 per cent of cases, a figure that drops as low as 20 per cent for people also infected with HIV.

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How The Fruit Fly Could Help Us Sniff Out Drugs And Bombs

October 17, 2014

Provided by Jacqui Bealing, University of Sussex

A fly’s sense of smell could be used in new technology to detect drugs and bombs, new University of Sussex research has found.

Brain scientist Professor Thomas Nowotny was surprised to find that the ‘nose’ of fruit flies can identify odors from illicit drugs and explosive substances almost as accurately as wine odor, which the insects are naturally attracted to because it smells like their favorite food, fermenting fruit.

Published October 15 in the journal Bioinspiration and Biomimetics, the study brings scientists closer to developing electronic noses (e-noses) that closely replicate the sensitive olfactory sense of animals.

The hope is that such e-noses will be much more sensitive and much faster than the currently commercially available e-noses that are typically based on metal-oxide sensors and are very slow, compared to a biological nose.

Professor Nowotny, Professor of Informatics at the University of Sussex, led the study alongside researchers from Monash University and CSIRO in Australia. He said: “Dogs can smell drugs and people have trained bees to detect explosives. Here we are looking more for what it is in the nose – which receptors – that allows animals to do this.

“In looking at fruit flies, we have found that, contrary to our expectation, unfamiliar odors, such as from explosives, were not only recognized but broadly recognized with the same accuracy as odors more relevant to a fly’s behavior.”

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Coral and fish can 'smell' bad reefs

22 August 2014 Last updated at 00:44

By Jonathan WebbScience reporter, BBC News

Baby corals and fish can smell the difference between good and bad reefs, according to a study based in Fiji.

When offered a choice of two water samples in the lab, the animals turned away from the stench of seaweed that invades depleted reefs, but were drawn to the smell of healthy coral.

It is the first time that corals have been shown to react over long distances to chemical "smells" in the water.

The findings suggest that controlling seaweed is key to repopulating reefs.

Once a coral reef has decayed and seaweed takes over, stopping fishing in the area may not be enough to bring the coral back.

"If you're setting up a marine protected area to seed recruitment into a degraded habitat, that recruitment may not happen if young fish and coral are not recognizing the degraded area as habitat," said Dr Danielle Dixson from the Georgia Institute of Technology, the study's first author.

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Parasitic worms sniff out their victims as 'cruisers' or 'ambushers'

Date:

August 14, 2014

Source:

PLOS

Summary:

It has been speculated that soil-dwelling parasitic worms use their sense of smell to find suitable hosts for infection. New research comparing odor-driven behaviors in different roundworm species reveals that olfactory preferences reflect host specificity rather than species relatedness, suggesting that olfaction indeed plays an important role in host location.

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African elephant genome suggests they are superior smellers

Date:

July 22, 2014

Source:

Cold Spring Harbor Laboratory

Summary:

Sense of smell is critical for survival in many mammals. In a new study, researchers examined the olfactory receptor repertoire encoded in 13 mammalian species and found that African elephants have the largest number of OR genes ever characterized; more than twice that found in dogs, and five times more than in humans.

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Sense Of Smell Was An Adaptation That Appeared When Insects Developed Ability To Fly

March 30, 2014

Odorant receptors of recent insects evolved long after insects migrated from water to land.

An insect’s sense of smell is vital to its survival. Only if it can trace even tiny amounts of odor molecules is it is able to find food sources, communicate with conspecifics, or avoid enemies. According to scientists at the Max Planck Institute for Chemical Ecology, many proteins involved in the highly sensitive odor perception of insects emerged rather late in the evolutionary process. The very complex olfactory system of modern insects is therefore not an adaptation to a terrestrial environment when ancient insects migrated from water to land, but rather an adaptation that appeared when insects developed the ability to fly. The results were published in the Open Access Journal eLife. (eLife, March 26, 2014, doi: 10.7554/elife.02115)

Many insect species employ three families of receptor proteins in order to perceive thousands of different environmental odors. Among them are the olfactory receptors. They form a functional complex with another protein, the so-called olfactory receptor co-receptor, which enables insects to smell the tiniest amounts of odor molecules in their environment very rapidly.

Read more at http://www.redorbit.com/news/science/1113107723/insect-sense-of-smell-033014/#VRYX8wuriwxPcMHK.99

Mosquito sperm have 'sense of smell,' make sperm swim harder

Date: February 3, 2014

Source: Vanderbilt University

Summary: Biologists have discovered that mosquito sperm have a “sense of smell” and that some of same chemicals that the mosquito can smell cause the sperm to swim harder.

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Genetic Engineering Alters Mosquitoes' Sense of Smell

May 29, 2013 — In one of the first successful attempts at genetically engineering mosquitoes, HHMI researchers have altered the way the insects respond to odors, including the smell of humans and the insect repellant DEET. The research not only demonstrates that mosquitoes can be genetically altered using the latest research techniques, but paves the way to understanding why the insect is so attracted to humans, and how to block that attraction. "The time has come now to do genetics in these important disease-vector insects.

I think our new work is a great example that you can do it," says Leslie Vosshall, an HHMI investigator at The Rockefeller University who led the new research, published May 29, 2013 in the journal Nature.

In 2007, scientists announced the completion of the full genome sequence of Aedes aegypti, the mosquito that transmits dengue and yellow fever. A year later, when Vosshall became an HHMI investigator, she shifted the focus of her lab from Drosophilaflies to mosquitoes with the specific goal of genetically engineering the insects. Studying mosquitoes appealed to her because of their importance as disease carriers, as well as their unique attraction to humans.

Vosshall's first target: a gene called orco, which her lab had deleted in genetically engineered flies 10 years earlier. "We knew this gene was important for flies to be able to respond to the odors they respond to," says Vosshall. "And we had some hints that mosquitoes interact with smells in their environment, so it was a good bet that something would interact with orco in mosquitoes."

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Finding 'Mr. Right,' How Insects Sniff out the Perfect Mate

Feb. 13, 2013 — You may want to ramp up your romance this year by sharing a candlelight dinner, a walk on the beach, or even the scent of a perfume, but will that help you find your perfect mate? For one wasp species, it only takes a whiff of his special love potion to know whether he's "Mr. Right."

Unlike humans, most insects rely on their sense of smell when looking for a mate. Scientists have found that sex pheromones play an important role in finding a suitable partner of the same species; yet, little is known about the evolution and genetic basis of these alluring smells.

A team of researchers from Arizona State University and Germany found that one wasp species has evolved a specific scent, or pheromone, which keeps it from mating with other species. In addition, they discovered that the genetic basis of the new scent is simple, which allows the males to change an existing scent into a new one. Over time, the females recognize and use this new scent to distinguish their own species from others.

Scientists from ASU, the University of Regensburg, the Zoological Research Museum Alexander Koenig Bonn, and the Technical University Darmstadt in Germany, present their findings in an article published Feb. 13 online in the journal Nature.

The researchers studied two species of the parasitic wasp genus Nasonia to learn about the evolution of sex pheromones. They asked, if male sex pheromones are used as unique mating signals to attract females, and if female wasps will not mate with males that have different pheromones, then how did the vast array of these scents evolve in insects?

Read on:  http://www.sciencedaily.com/releases/2013/02/130213114504.htm

Insects groom to improve sense of smell

By Ella Davies, Reporter, BBC Nature

Cockroaches groom to improve their sense of smell, scientists say.

The insects are known to manipulate their antennae, the protrusions on their head which they use to sense the smells, temperature and physical layout of their environment.

US researchers found that the cockroaches groom to wipe away secretions that would otherwise interfere with their sense of smell.

They also identified the same behaviour in carpenter ants and houseflies.

The findings are published in the journal Proceedings of the National Academy of Sciences.

"The insect antenna is full of sensory structures, called sensilla, used by insects to gather information about their surroundings, which is essential for their survival," said Dr Katalin Boroczky from the North Carolina State University, US, who authored the study.

Continued:  http://www.bbc.co.uk/nature/21275518

Evidence Moles Can Smell in Stereo

Feb. 5, 2013 — Most mammals, including humans, see in stereo and hear in stereo. But whether they can also smell in stereo is the subject of a long-standing scientific controversy.

Now, a new study shows definitively that the common mole (Scalopus aquaticus) - the same critter that disrupts the lawns and gardens of homeowners throughout the eastern United States, Canada and Mexico -- relies on stereo sniffing to locate its prey. The paper that describes this research, "Stereo and Serial Sniffing Guide Navigation to an Odor Source in a Mammals," was published on Feb. 5 in the journal Nature Communications.

"I came at this as a skeptic. I thought the moles' nostrils were too close together to effectively detect odor gradients," said Kenneth Catania, the Stevenson Professor of Biological Sciences at Vanderbilt University, who conducted the research.

What he found turned his assumptions upside down and opened new areas for potential future research. "The fact that moles use stereo odor cues to locate food suggests other mammals that rely heavily on their sense of smell, like dogs and pigs might also have this ability,"Catania said.

Read on:  http://www.sciencedaily.com/releases/2013/02/130205123011.htm

Animals Learn to Fine-Tune Their Sniffs

ScienceDaily (Oct. 30, 2012) — Animals use their noses to focus their sense of smell, much the same way that humans focus their eyes, new research at the University of Chicago shows.

A research team studying rats found that animals adjust their sense of smell through sniffing techniques that bring scents to receptors in different parts of the nose. The sniffing patterns changed according to what kind of substance the rats were attempting to detect.

The sense of smell is particularly important for many animals, as they need it to detect predators and to search out food. "Dogs, for instance, are quite dependent on their sense of smell," said study author Leslie Kay, associate professor of psychology and director of the Institute for Mind & Biology at the University of Chicago. "But there are many chemicals in the smells they detect, so detecting the one that might be from a predator or an explosive, for instance, is a complex process."

Kay was joined in writing the paper by Daniel Rojas-Líbano, a postdoctoral scholar at the University of Chile in Santiago, who received his PhD from UChicago in 2011. Rojas-Líbano, who did the work as a doctoral scholar, was the first author on the publication. Their results are published in an article, "Interplay Between Sniffing and Odorant Properties in the Rat," in the current issue of the Journal of Neuroscience.

Read on:  http://www.sciencedaily.com/releases/2012/10/121030210035.htm

Can a whale's nose lead it to food?

Julie Hagelin remembers the day she hugged a rare New Zealand kakapo parrot to her chest. The soft, green bird emitted the scent of lavender, like dust and honey; it lingered on Hagelin's T-shirt for hours. That powerful essence inspired her question to the revered biologist for whom she was working. Was the bird's pleasant odor attractive to other birds?

"Julie, don't you know birds can't smell?"

Hagelin, now a biologist at the University of Alaska Fairbanks and then a volunteer on a once-in-a-lifetime project, nodded politely. But the thought kept bouncing around her inquiring young mind: "How do we know birds can't smell?"

Thus began a recurring theme in Hagelin's work that has taken her from St. Lawrence Island, where auklets gathered by the thousands mysteriously emit the scent of tangerines, to Creamer's Field, where she has applied peppermint oil to the nests of house sparrows to see if they return to a smell they know.


Read on:  http://www.alaskadispatch.com/article/can-whales-nose-lead-it-food

Smells May Help Birds Find Their Homes, Avoid Inbreeding; Research May Bring Help to Endangered Species

ScienceDaily (Sep. 22, 2011) — Birds may have a more highly developed sense of smell than researchers previously thought, contend scholars who have found that penguins may use smell to determine if they are related to a potential mate.The research by the University of Chicago and the Chicago Zoological Society, which manages Brookfield Zoo, shows how related birds are able to recognize each other. The study, published Sept. 21 in the journal PLoS ONE, could help conservationists design programs to help preserve endangered species.

"Smell is likely the primary mechanism for kin recognition to avoid inbreeding within the colony," said Heather Coffin, lead author of the paper.

Coffin conducted the research while a graduate student at UChicago and was joined in writing the paper by Jill Mateo, associate professor in Comparative Human Development at UChicago, and Jason Watters, director of animal behavior research for the Chicago Zoological Society.

"This is the first study to provide evidence for odor-based kin discrimination in birds," said Mateo, who is a specialist on kin recognition.

Experts said the work offers important insights into how birds use smell to guide behavior.

"The work by the research group is truly groundbreaking in that it shows for the first time ever in birds how the olfactory sense of captive penguins is both informative and functional in a behaviorally critical context: namely the recognition of friends from foes in general, and relatives from non-relatives in particular," said Mark E. Hauber, professor of psychology at Hunter College, a specialist on bird social recognition.

Penguins are ideal subjects because they typically live in colonies made up of thousands of birds. They live in monogamous pairs -- an arrangement that facilitates rearing of their young, since parents frequently take turns leaving the nest to gather food. Despite the size of the community, mates are able to find each other after traveling for days foraging for food in the ocean.

Research on other sea birds has shown that smell helps guide birds to their home territory and helps them forage for food. Other research has shown that birds could use sound and sight to recognize each other, but no other studies have shown that smell might be used in connection with kin recognition, Mateo said.

In the study conducted at Brookfield Zoo, researchers first sought to determine if the penguins were able to recognize familiar individuals by smell. They constructed an experiment using a dozen penguins, from a group that included breeding pairs, their offspring and nonbreeding individuals. The birds -- all Humboldt penguins -- endangered natives of Peru -- were from groups either on exhibit or off exhibit.

The zoo is an ideal setting for the research, as it has extensive records on which penguins are related and have been housed together, Watters said.

Researchers took odor samples from glands near the penguins' tails, where an oil that the birds use for preening is secreted. They put the oil on cotton swabs and rubbed the odor inside dog kennels, similar to the enclosures penguins at a zoo use for their nests. They also put the odor on paper coffee filters and placed them under mats inside the kennels.

When the penguins were released to the area containing the kennels, the researchers found that penguins spent more time in the kennels with familiar odors. The penguins were able to distinguish between the odors of birds they spent time with and the odors of unfamiliar penguins.

"What I found particularly notable about the study was that the authors identified the oil secreted from the penguins' preen gland, which is rubbed on the feathers to make them water repellent, as the odor source used in recognition," said Bryan D. Neff, professor and associate chair of biology, University of Western Ontario and an expert on kin recognition. "Oils are used in kin recognition by species of other animals, most notably a variety of insect species, including bees and wasps, which when considered with the penguin data provide a wonderful example of convergent evolution."

"It's important for birds that live in large groups in the wild, like penguins, to know who their neighbors are so that they can find their nesting areas and also, through experience, know how to get along with the birds nearby," Watters said.

Because offspring usually return to the same colony for nesting, siblings have the potential of becoming mates, something that can be avoided by their smell mechanism, the new research shows.
Researchers also found that when the birds were exposed to the odors of unfamiliar kin and unfamiliar non-kin, they spent more time in the kennels with odors of unfamiliar non-kin, indicating they were probably able to determine by smell which animals they were related to and were more curious about the novel odors. Being able to make the distinction may help the penguins avoid mating with kin, researchers said. The discovery also could assist zoos in managing their breeding programs.

"It could also be true that birds may be able to help zoo 'matchmakers' in determining potential mates," Watters said.

The ability of birds to be able to recognize familiar scents and thus be guided to their home territory also has potential value to naturalists, he said.

"You could imagine that if you were trying to reintroduce birds to an area, you could first treat the area with an odor the birds were familiar with. That would make them more likely to stay."
http://www.sciencedaily.com/releases/2011/09/110921172834.htm