Any chemical compound secreted by an organism in minute amounts to elicit a particular reaction from other organisms of the same species. Pheromones are widespread among insects and vertebrates (except birds) and are present in some fungi, slime molds, and algae. The chemicals may be secreted by special glands or incorporated into other substances (e.g., urine), shed freely, or deposited in selected locations. Pheromones are used to bring creatures together (e.g., in termite, bee, and ant colonies), lead them to food (e.g., in scent trails laid by ants), signal danger (e.g., when released by wounded fish to alert others), attract a mate and elicit sexual behaviour (numerous examples, possibly including humans), and influence sexual development (in many mammals and certain insects). Alarm pheromones often last a shorter time and travel a shorter distance than other types. In vertebrates, chemical stimuli often influence parent-young responses. Sex-attractant pheromones are used in certain products to lure and trap unwanted or harmful insects.

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A pheromone (from Greek φέρω phero "to bear" + ‘ορμόνη "hormone") is a chemical that triggers a natural behavioral response in another member of the same species. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology. Their use among insects has been particularly well documented, although many vertebrates and plants also communicate using pheromones.

Background

The term "pheromone" was introduced by Peter Karlson and Martin Lüscher in 1959, based on the Greek pherein (to transport) and hormone (to stimulate). They proposed the term to describe chemical signals from conspecifics which elicit innate behaviours soon after Butenandt characterized the first such chemical, Bombykol (a chemically well-characterized pheromone released by the female silkworm to attract mates).

Types

Aggregation pheromones

Produced by one or the other sex, aggregation pheromones attract individuals of both sexes.

Alarm pheromones

Some species release a volatile substance when attacked by a predator that can trigger flight (in aphids) or aggression (in bees) in members of the same species. Pheromones also exist in plants: certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants. These tannins make the plants less appetizing for the herbivore.. Examples are:

• 2-Heptanone as a putative alarm pheromone in rats

Epideictic pheromones

Recognized in insects, epideictic pheromones are different from territory pheromones. According to Fabre (translated from French), "Females who lay their eggs in these fruits deposit these mysterious substances in the vicinity of their clutch to signal to other females of the same species so that they will clutch elsewhere."

Releaser pheromones

Releaser pheromones are powerful attractant molecules that some organisms may use to attract mates from a distance of two miles or more. This type of pheromone generally elicits a rapid response but is quickly degraded. In contrast, a primer pheromone has a slower onset and a longer duration.

Primer pheromones

Primer pheromones trigger a change of developmental events.

Territorial pheromones

Laid down in the environment, territorial pheromones mark the boundaries of an organism's territory. In dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory.

Trail pheromones

Trail pheromones are common in social insects. For example, ants mark their paths with these pheromones, which are non-volatile hydrocarbons.

Certain ants lay down an initial trail of pheromones as they return to the nest with food. This trail attracts other ants and serves as a guide. As long as the food source remains, the pheromone trail will be continually renewed. The pheromone must be continually renewed because it evaporates quickly. When the supply begins to dwindle, the trailmaking ceases. In at least one species of ant, trails that no longer lead to food are also marked with a repellent pheromone.

Sex pheromones

In animals, sex pheromones indicate the availability of the female for breeding. Male animals may also emit pheromones that convey information about their species and genotype. Many insect species release sex pheromones to attract a mate, and many lepidopterans (e.g., moths and butterflies) can detect a potential mate from as far away as 10 kilometers (6 mi). Pheromones can be used in gametes to trail the opposite sex's gametes for fertilization. Pheromones are also used in the detection of oestrus in sows. Boar pheromones are sprayed into the sty, and those sows which exhibit sexual arousal are known to be currently available for breeding.

Other pheromones

This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.

• Nasonov pheromones (worker bees)
• Royal pheromones (bees)
• Calming (appeasement) pheromones (mammals)

Uses

Animals

Pheromones of the pest insect species, such as the Japanese beetle and the gypsy moth, can be used to induce many behaviors. This facilitates trapping for monitoring purposes and population control by creating confusion, disrupting mating and preventing them from laying eggs.

In mammals and reptiles, pheromones may be detected by the vomeronasal organ, or Jacobson's organ, which lies between the nose and mouth and is the first stage of the accessory olfactory system. Some pheromones in these animals are detected by regular olfactory membranes.

Humans

Few well-controlled scientific studies have ever been published suggesting the possibility of pheromones in humans. The best known case involves the reported synchronization of menstrual cycles among women based on unconscious odor cues (the McClintock effect, named after the primary investigator, Martha McClintock, of the University of Chicago). This study proposes that there are two types of pheromone involved: "One, produced prior to ovulation, shortens the ovarian cycle; and the second, produced just at ovulation, lengthens the cycle". However recent studies and reviews of the McClintock methodology have called into question the validity of her results.

Other studies have suggested that people might be using odor cues associated with the immune system to select mates who are not closely related to themselves. Using a brain imaging technique, Swedish researchers have shown that homosexual and heterosexual males' brains respond differently to two odors that may be involved in sexual arousal, and that the homosexual men respond in the same way as heterosexual women. The study was expanded to include homosexual women; the results were consistent with previous findings meaning that homosexual women were not as responsive to male identified odors, but their response to female cues was similar to heterosexual males. According to the researchers, this research suggests a possible role for human pheromones in the biological basis of sexual orientation.

Another study demonstrated that the smell of androstadienone, a chemical component of male sweat, maintains higher levels of cortisol in females. The scientists suggest that the ability of this compound to influence the endocrine balance of the opposite sex makes it a human pheromonal chemosignal. In 2002 a study published in the quarterly journal Physiology and Behavior showed an unnamed synthetic chemical in women's perfume appeared to increase intimate contact with men. The authors hypothesize, but do not demonstrate, that the observed behavioural differences are olfactory mediated.

In 2006 it was shown that a second mouse receptor sub-class is found in the olfactory epithelium. Called the trace amine-associated receptors (TAAR), some are activated by volatile amines found in mouse urine, including one putative mouse pheromone. A study in urinary odour preferences of mice (2001) concluded that the pheromones associated with urinary odor assisted in deterring them from selecting mates from a related species. Interbreeding within mammals has shown to lead to a decrease in the overall fitness of that species, thus pheromones that decrease the probability of interbreeding are selected for. Orthologous receptors exist in humans providing, the authors propose, evidence for a mechanism of human pheromone detection.

Some body spray advertisers claim that their products contain human sexual pheromones which act as an aphrodisiac. In the 1970's "copulins" were patented as products which release human pheromones, based on research on rhesus monkeys. Subsequently, androstenone, axillary sweat, and "vomodors" have been claimed to act as human pheromones. Despite these claims, no pheromonal substance has ever been demonstrated to directly influence human behavior in a peer reviewed study.

See also

References

Further reading

• Kohl, JV., Atzmueller, M., Fink, B. & Grammer, K. (2001). Human Pheromones: Integrating Neuroendocrinology and Ethology. Neuroendocrinology Letters, 22(5), 319-331. Full text
• Liberles, S.D., Buck, L.B. (2006). A second class of chemosensory receptors in the olfactory epithelium. Nature, 442, 645-50.
• McClintock, M.K. (1984). Estrous synchrony: modulation of ovarian cycle length by female pheromones. Physiological Behavior, 32, 701-705.
• Wilson, E. O., Bossert, W. H. (1963). Chemical communication among animals. Recent Progress in Hormone Research, 19, 673-716.
• Wyatt, Tristram D. (2003). Pheromones and Animal Behaviour: Communication by Smell and Taste. Cambridge: Cambridge University Press. ISBN 0-521-48526-6.

External links

• Pherobase, the database of insect pheromones
• Male Axillary Extracts Contain Pheromones that Affect Pulsatile Secretion of Luteinizing Hormone and Mood in Women Recipients
• Sexual Orientation, in the Brain
• Review of published debate about HOW insects detect pheromones over large distances, even when the wind seems unfavourable
• Male sweat boosts women's hormone levels -- from UC Berkeley, February 2007
• The Effect of Male Sweat on Women's Hormone Levels -- from Science Daily, February 2007
• Pheromones In Male Perspiration Reduce Women's Tension, Alter Hormone Response -- from Science Daily (March 2003)