Flehmen response
That peculiar grimace many animals make—curling their upper lip and baring their teeth—isn't a sign of disgust or amusement. It's called the Flehmen response, and it's a sophisticated biological mechanism. This seemingly strange expression is a key to unlocking a hidden world of chemical communication, allowing creatures to 'read' their environment and each other in ways we're only beginning to fully appreciate. The Flehmen response allows many mammals to 'taste' or 'smell' scents, particularly non-volatile chemical cues like pheromones, which convey vital information. This distinctive facial expression creates a direct pathway to the vomeronasal organ, a specialized sensory structure dedicated to chemical communication. Animals use the Flehmen response primarily for crucial intra-species communication, from detecting reproductive signals to understanding social hierarchies, and sometimes even for inter-species interaction.
AI Summary
That peculiar grimace many animals make—curling their upper lip and baring their teeth—isn't a sign of disgust or amusement. It's called the Flehmen response, and it's a sophisticated biological mechanism. This seemingly strange expression is a key to unlocking a hidden world of chemical communication, allowing creatures to 'read' their environment and each other in ways we're only beginning to fully appreciate.
- The Flehmen response allows many mammals to 'taste' or 'smell' scents, particularly non-volatile chemical cues like pheromones, which convey vital information.
- This distinctive facial expression creates a direct pathway to the vomeronasal organ, a specialized sensory structure dedicated to chemical communication.
- Animals use the Flehmen response primarily for crucial intra-species communication, from detecting reproductive signals to understanding social hierarchies, and sometimes even for inter-species interaction.
The Enigmatic Grimace
Imagine seeing a horse or a big cat pull back its upper lip, exposing its front teeth and gums, then holding that pose for a few seconds. It might look like a snarl, a smirk, or even a laugh—but this striking facial expression is far more than just a passing grimace. It's a deliberate act with a profound purpose.
This fascinating behavior is known as the Flehmen response. Animals performing it aren't just making a funny face; they're actively inhaling, often with their nostrils closed, to draw specific airborne molecules into a special sensory organ. It's a key to unlocking a secret world of information.
The target of this peculiar maneuver is the vomeronasal organ, also called Jacobson's organ, located in the roof of the mouth. This specialized organ allows animals to detect chemical cues—particularly pheromones—which carry hidden messages about their environment and other creatures around them.
A Name from an Expression
The term 'Flehmen' comes from the German verb 'flehmen,' meaning 'to bare the upper teeth.' It's also linked to the Upper Saxon German word 'flemmen,' which means 'to look spiteful.' This accurately reflects the 'grimacing' appearance of the animal.
The word was officially introduced into scientific literature in 1930 by Karl Max Schneider, who was the director of the Leipzig Zoo and a renowned authority on big cats. While Schneider popularized the term, the response itself was first described much earlier—by Frederik Ruysch in 1732 and later by Ludwig Jacobson in 1813, for whom the vomeronasal organ is sometimes named.
The Science Behind the Scrutiny
So, how exactly does this 'grimace' work its magic? When an animal performs the Flehmen response, curling its upper lip often closes off the nostrils, creating a kind of vacuum. This action then draws air, laden with chemical signals, through small ducts located just behind the front teeth and directly into the vomeronasal organ.
Think of the vomeronasal organ as a kind of 'second nose'—an auxiliary olfactory sense organ. It sits within a bony or cartilaginous capsule in the roof of the mouth, close to the vomer and nasal bones. While the main olfactory system detects volatile smells, the VNO is finely tuned for non-volatile compounds.
Most animals exhibiting Flehmen have a small papilla behind their incisors, which contains ducts connecting the oral cavity to the VNO. Horses, however, are an interesting exception. Since they don't breathe through their mouths, their VNOs connect directly to the nasal passages via the nasopalatine duct, a slightly different anatomical pathway to achieve the same result.
The chemical cues targeted by the Flehmen response are typically non-volatile organic compounds. Unlike volatile compounds, which readily evaporate and are detected by our regular sense of smell, non-volatile compounds don't easily become airborne. They require closer, more direct contact—or, in this case, a specialized 'sniff'—to be detected.
These precious non-volatile compounds are often pheromones or hormones. They are typically found in substances like urine or secretions from genital regions, acting as chemical 'messages' that can reveal crucial information about another animal's presence, identity, and even its physiological state.
What Messages Are They Reading?
The primary function of the Flehmen response is intra-species communication—that is, communication within the same species. It's vital for detecting reproductive readiness; for example, a stallion might Flehmen after sniffing a mare's urine to determine if she is in estrus and ready to breed.
It's not just about mating, though. Animals can glean a wealth of information about other members of their species: identifying individuals, assessing social status, or even detecting territorial markers. It's like reading a complex chemical newspaper, filled with important social updates.
Intriguingly, the Flehmen response isn't exclusively for communicating within one's own kind. Studies on goats, for instance, showed them responding to urine from over 20 different species—even some non-mammalian ones! This suggests there might be common, interspecific pheromones, like modified forms of androgen, that trigger this behavior across species lines.
A Widespread Phenomenon
While perhaps most easily observed in domestic animals like cats and horses, the Flehmen response is performed by a remarkably diverse range of mammals. You might see a male giraffe tasting a female's urine, or even an elephant using the 'finger' at the tip of its trunk to transfer chemosensory stimuli to the vomeronasal opening in its mouth.
The list of animals exhibiting this behavior is quite extensive, showcasing its evolutionary importance. From the wild plains to our homes, this subtle grimace is a universal signal.
Common Exhibitors Sheep American Bison Tigers Tapirs Lions Giraffes Goats Llamas Kobs Hedgehogs Rhinoceros Giant Pandas Antelope Hippopotamuses
Beyond communication, the Flehmen response can sometimes signal other things. In horses, a spontaneous Flehmen response that occurs outside its usual context, especially without any obvious odor source, can actually be an indicator of discomfort or pain. It's a versatile behavior with multiple layers of meaning.
Article
Flehmen response
The flehmen response (; from German flehmen 'to bare the upper teeth', and Upper Saxon German flemmen 'to look spiteful'), also called the flehmen position, flehmen reaction, flehmen grimace, flehming, or flehmening, is a behavior in which an animal curls back its upper lip exposing its front teeth, inhales with the nostrils usually closed, and then often holds this position for several seconds. The behavior occurs as a response to relevant external stimuli, typically pheromones, which may have been produced by animals of the same or different species. It may be performed with the neck stretched and the head held high in the air.
Flehmen is performed by a wide range of mammals, including ungulates and felids. The behavior facilitates the transfer of pheromones and other scents into the vomeronasal organ (VNO, or Jacobson's organ) located above the roof of the mouth via a duct which exits just behind the front teeth of the animal.
Etymology
Flehmen response
The word originates from the German verb flehmen 'to bare the upper teeth'. It comes from the Upper Saxon German flemmen 'to look spiteful'. The word was introduced in 1930 by Karl Max Schneider, director of the Leipzig zoo and an authority on big cats in captivity.
Discovery
Flehmen response
The flehmen response was first described by Frederik Ruysch in 1732 and described later by Ludwig Jacobson in 1813.
Description
Flehmen response
This response is characterized by the animal curling back its top lip exposing the front teeth and gums, then inhaling and holding the posture for several seconds. The behavior may be performed over particular locations, in which case the animal may also lick the site of interest, or may perform the flehmen with the neck stretched and head held high in the air for a more general gustatory or taste-related investigation. The flehmen response can give the appearance that the animal is looking spiteful, grimacing, smirking, disgusted, or laughing. The relationship between emotions and expressions across species is debated.
Mechanism
Flehmen response
The flehmen response draws air into the vomeronasal organ (VNO), an auxiliary olfactory sense organ that is found in many animals. This organ plays a role in the perception of certain scents and pheromones. The vomeronasal organ is named for its closeness to the vomer and nasal bones, and is particularly well developed in animals such as cats and horses. The VNO is found encompassed inside a bony or cartilaginous capsule which opens into the base of the nasal cavity. Animals that exhibit flehmen have a papilla located behind the incisors and ducts which connect the oral cavity to the VNO, with horses being an exception. Horses exhibit flehmen but do not have an incisive duct communication between the nasal and oral cavity because they do not breathe through their mouths; instead, the VNOs connect to the nasal passages by the nasopalatine duct.
Chemical cues
The chemical cue obtained by an animal exhibiting the flehmen response is the presence of a non-volatile organic compound. In contrast to volatile organic compounds (VOCs), non-volatile organic compounds are those carbon compounds that do not participate in atmospheric photochemical reactions or evaporate under normal atmospheric conditions. The VNO detects non-VOCs, which must have direct contact with the odor source. Sources of non-VOCs relevant to the flehmen response include pheromones and hormones excreted from the genital regions or urine of animals.
Function
Flehmen response
An animal may perform the flehmen response when investigating sites of particular interest, or perhaps (more generally) odors or tastes. In horses, spontaneous flehmen response outside of the normal context can also indicate discomfort.
Intra-species communication
The primary function of the flehmen response is intra-species communication. By transferring air containing pheromones and other scents to the VNO, animals can gather chemical "messages". These scents tell an animal about other members of their species in some of the following ways:
• Identifying reproductive status – male individuals commonly use the flehmen response as an olfactory mechanism for identifying the reproductive state of females of the same species based on pheromones in the female's urine or genitals. This is exhibited in the reproductive behavior of sheep. The ram often exhibits flehmen after sniffing ewes' external genital regions, but this occurs most frequently on the day before estrus when the ewes are sexually receptive. • Reproductive synchrony – flehmen behavior also plays a role in reproductive synchrony between females. In the sable antelope, the frequency of flehmen changes seasonally, with the highest levels just prior to conception. Female antelopes associate closely with other females in the same reproductive state. Flehmen rates between females anticipated birth synchrony. Additionally, the level of synchrony was predicted by the frequency of female urine sampling during the previous year. Flehmen is a mechanism used by female sable antelopes to manipulate the timing of both conception and birth of offspring. In the American bison, flehmen behavior in females has also been shown to stimulate the onset of estrus and copulation synchronization. • Post-parturition – in horses, mares commonly show a peak in flehmen response during the first few hours after giving birth. Smelling the newborn foal and the amniotic fluids associated with birth often produces the reaction. • Immature animals – in young horses, both colts (males) and fillies (females) exhibit flehmen behavior toward other conspecifics with neither sex performing the behavior more than the other. However, it has been reported that young colts flehmen up to five times more frequently than fillies, and fillies flehmen more frequently than mature mares. Young elephants also have a flehmen response to stimulants. The VNO of newborn elephants displays a structural maturity similar to adults, which supports the conclusion that flehmen at only six weeks of age is used to deliver chemical pheromones to a functional VNO.
Inter-species communication
The flehmen response is not limited to intra-species communication. Goats have been tested for their flehmen response to urine from 20 different species, including several non-mammalian species. This study suggests there is a common element in the urine of all animals, an interspecific pheromone, which elicits flehmen behavior. Specifically, chemical pheromone levels of a modified form of androgen, a sex hormone, were associated with the response in goats.
Mammals exhibiting
Flehmen response
A wide range of mammals exhibit flehmen including both predatory and non-predatory species.
The response is perhaps most easily observed in domestic cats and horses; both exhibit a strong flehmen response to odors. Stallions usually smell the urine of mares in estrus whereas the male giraffe's flehmen response includes tasting the female's urine. Elephants perform a flehmen response but also transfer chemosensory stimuli to the vomeronasal opening in the roof of their mouths using the prehensile structure, sometimes called a "finger", at the tips of their trunks.
Other animals which exhibit the flehmen response include sheep, American bison, tigers, tapirs, lions, giraffes, goats, llamas, kobs, hedgehogs, rhinoceros, giant pandas, antelope and hippopotamuses.