Posts tagged pheromones
Articles and news from the latest research reports.
The human body produces chemical cues that communicate gender to members of the opposite sex, according to researchers who report their findings in the Cell Press journal Current Biology on May 1. Whiffs of the active steroid ingredients (androstadienone in males and estratetraenol in females) influence our perceptions of movement as being either more masculine or more feminine. The effect, which occurs completely without awareness, depends on both our biological sex and our sexual orientations.
"Our findings argue for the existence of human sex pheromones," says Wen Zhou of the Chinese Academy of Sciences. "They show that the nose can sniff out gender from body secretions even when we don’t think we smell anything on the conscious level."
Earlier studies showed that androstadienone, found in male semen and armpits, can promote positive mood in females as opposed to males. Estratetraenol, first identified in female urine, has similar effects on males. But it wasn’t clear whether those chemicals were truly acting as sexual cues.
In the new study, Zhou and her colleagues asked males and females, both heterosexual and homosexual, to watch what are known as point-light walkers (PLWs) move in place on a screen. PLWs consist of 15 dots representing the 12 major joints in the human body, plus the pelvis, thorax, and head. The task was to decide whether those digitally morphed gaits were more masculine or feminine.
Individuals completed that task over a series of days while being exposed to androstadienone, estratetraenol, or a control solution, all of which smelled like cloves. The results revealed that smelling androstadienone systematically biased heterosexual females, but not males, toward perceiving walkers as more masculine. By contrast, the researchers report, smelling estratetraenol systematically biased heterosexual males, but not females, toward perceiving walkers as more feminine.
Interestingly, the researchers found that homosexual males responded to gender pheromones more like heterosexual females did. Bisexual or homosexual female responses to the same scents fell somewhere in between those of heterosexual males and females.
"When the visual gender cues were extremely ambiguous, smelling androstadienone versus estratetraenol produced about an eight percent change in gender perception," Zhou says, a statistically very significant effect.
"The results provide the first direct evidence that the two human steroids communicate opposite gender information that is differentially effective to the two sex groups based on their sexual orientation," the researchers write. "Moreover, they demonstrate that human visual gender perception draws on subconscious chemosensory biological cues, an effect that has been hitherto unsuspected."
The scent of a man
Scientists’ inability to replicate research findings using mice and rats has contributed to mounting concern over the reliability of such studies.
Now, an international team of pain researchers led by scientists at McGill University in Montreal may have uncovered one important factor behind this vexing problem: the gender of the experimenters has a big impact on the stress levels of rodents, which are widely used in preclinical studies.
In research published online April 28 in Nature Methods, the scientists report that the presence of male experimenters produced a stress response in mice and rats equivalent to that caused by restraining the rodents for 15 minutes in a tube or forcing them to swim for three minutes. This stress-induced reaction made mice and rats of both sexes less sensitive to pain.
Female experimenters produced no such effects.
“Scientists whisper to each other at conferences that their rodent research subjects appear to be aware of their presence, and that this might affect the results of experiments, but this has never been directly demonstrated until now,” says Jeffrey Mogil, a psychology professor at McGill and senior author of the paper.
The research team, which included pain experts from Haverford College and the Karolinska Institutet in Sweden and a chemosensory expert from Université de Montreal, found that the effect of male experimenters on the rodents’ stress levels was due to smell. This was shown by placing cotton T shirts, worn the previous night by male or female experimenters, alongside the mice; the effects were identical to those caused by the presence of the experimenters, themselves.
Further experiments proved that the effects were caused by chemosignals, or pheromones, that men secrete from the armpit at higher concentrations than women. These chemosignals signal to rodents the presence of nearby male animals. (All mammals share the same chemosignals).
These effects are not limited to pain. The researchers found that other behavioural assays sensitive to stress were affected by male but not female experimenters or T-shirts.
“Our findings suggest that one major reason for lack of replication of animal studies is the gender of the experimenter – a factor that’s not currently stated in the methods sections of published papers,” says Robert Sorge, a psychology professor at the University of Alabama, Birmingham. Sorge led the study as a postdoctoral fellow at McGill.
The good news, Mogil says, is that “the problem is easily solved by simple changes to experimental procedures. For example, since the effect of males’ presence diminishes over time, the male experimenter can stay in the room with the animals before starting testing. At the very least, published papers should state the gender of the experimenter who performed the behavioral testing.”
(Source: mcgill.ca)
Uncovering maternal to paternal communications in mice
Researchers at Japan’s Kanazawa University have proven the existence of communicative signalling from female mice that induces male parental behaviour.
Most mammalian parents use communicative signals between the sexes, but it is uncertain whether such signals affect the levels of parental care in fathers. Scientists have long suspected that female mice play a definite role in encouraging paternal relationships between male mice and their pups.
Now, a research team at Kanazawa University led by Haruhiro Higashida in collaboration with scientists across Japan, Russia and the UK, have proven the existence of auditory and olfactory (smell) signals produced by females which actively trigger paternal activity in males.
Higashida and his team conducted a series of experiments with females and males living in established family groups. Pups were removed from the cage for a short time, while one or both parents remained in the nest. The pups were then returned to the cage, away from the nest. Lone females nearly always brought the pups back to the nest, but lone males were less likely to do so.
Most interestingly, the researchers showed that males were much more likely to retrieve pups when they remained with their mate. This behaviour may be related to ultra-sonic noises emitted by females under stress. These sounds are not emitted by males, pups or non-parental females, and they encouraged the males into parental behaviours. The females also released olfactory signals in the form of pheromones, which triggered the same reaction in the males.
Higashida and his team are keen to expand on their results by analyzing neural signalling in the male brain in response to these female communications.
Finding “Mr. Right,” How Insects Sniff Out the Perfect Mate
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 Persistence of Memory in Mice
It’s frequently said that scent is the sense most powerfully tied to memory. For mice, it turns out, that’s especially true—at least when it comes to a sniff of the urine of potential mates.
According to a study published in Science by researchers from the University of Liverpool, female mice exposed to the potent pheromone darcin (found in male mouse urine) just a single time will repeatedly return to the exact site of exposure up to 14 days later, even after the pheromone is taken away.
“We have shown that a male sex pheromone in mice makes females …remember exactly where they encountered the pheromone and show a preference for this site for up to two weeks afterwards,” said lead author Sarah Roberts in a statement. “Given the opportunity, they will find that same place again, even if they encountered the scent only once and the scent is no longer there.”
“This attraction to the place they remember is just as strong as attraction to the scent itself,” said co-author Jane Hurst. “Darcin, therefore, induces mice to learn a spatial map of the location of attractive males and their scents, to which they can easily return.”
The researchers determined that the important factor was the pheromone darcin because the same results occurred when a synthetic version of the chemical was put into a petri dish on its own. Additionally, when the female mice were exposed to female urine instead, there was no indication of a preference, because darcin isn’t present in the females’ urine.
Interestingly, the pheromone also produced a powerful effect on another group of mice: competitor males. When they were used in the same experiment, they also demonstrated a preference for the place where they remembered smelling other males’ urine, but they didn’t show this type of spatial memory when the urine used was their own. The researchers speculate that this is because of a motivation to linger near the site and mark the territory with their own pheromone scent, to advertise their availability to female mates.
The scientists speculate that this lingering affinity for the memory of urine is used by the mice as a mental shortcut for finding mates. In a natural setting (instead of cages), rather than having to smell the pheromones from a distance and then track them to the source, they can simply camp out by urine deposited by a potential mate and wait for their likely return.
Babies Learn the Smell of Mum
Researchers show for the first time that a mammal begins to suckle its mother’s milk through a learned response built on learning her unique combination of smells. When it is born, the newborn is exposed to the smell of its mother’s amniotic fluid and the baby then responds to those smells to feed.
Prevailing thought has been that pheromones –chemicals that trigger an innate behavior – drove the suckling response as an automatic behavior. The new work determines that, in mice, the smells must be learned before the behavior can occur.
Suckling is a critical step for survival in mammals, which are defined by giving birth to offspring that need to feed from their mother’s milk. The newborn must begin to feed soon after birth or it will die. It is a crucial, defining behavior in mammals and offers researchers an opportunity to investigate the biology of instinct.
The scent of love: Decomposition and male sex pheromones
A team of researchers, led by Christian von Hoermann from Ulm University, Germany, filled olfactometers with different volatile scents and recorded which scents female hide beetles were attracted to. The scents used were pig cadaver, collected at different stages of decay, male pheromone gland extract, synthetic pheromones, and a control, pentane (an organic solvent which was used to extract the other odours).
The females ignored both the control and synthetic pheromone. In fact they pretty much ignored everything apart from the odour of piglet in the dry remains stage, as long as it was enhanced by male pheromones.
Christian von Hoermann explained, “Although cadaver odour alone is not sufficient to attract two to three week-old virgin female hide beetles, it is enough to attract newly emerged males.” Release of pheromones by these males appears to signal the cadaver as an appropriate site for feeding, mating and egg laying. Evolution seems to have ensured that hide beetle females only respond to a mate (or a food source for their larvae) when the other is also present, so that they can optimise the chances of their offspring’s survival.