Pheromone
A pheromone is a chemical that is secreted or excreted by an organism, which triggers a social response in members of the same species. There are alarm pheromones, food trail pheromones, sex pheromones, and many others that affect behavior or physiology. Pheromones are used by many organisms, from basic unicellular prokaryotes to complex multicellular eukaryotes. Their use among insects has been particularly well documented. In addition, some vertebrates, plants and ciliates communicate by using pheromones. The ecological functions and evolution of pheromones are a major topic of research in the field of chemical ecology.
Background
The portmanteau word "pheromone" was coined by Peter Karlson and Martin Lüscher in 1959, based on the Greek φέρω and ὁρμων . Pheromones are also sometimes classified as ecto-hormones. They were researched earlier by various scientists, including Jean-Henri Fabre, Joseph A. Lintner, Adolf Butenandt, and ethologist Karl von Frisch who called them various names, such as "alarm substances". These chemical messengers are transported outside of the body and affect neurocircuits, including the autonomous nervous system with hormone or cytokine mediated physiological changes, inflammatory signaling, immune system changes and/or behavioral change in the recipient. They proposed the term to describe chemical signals from conspecifics that elicit innate behaviors soon after the German biochemist Adolf Butenandt had characterized the first such chemical, bombykol, a chemically well-characterized pheromone released by the female silkworm to attract mates.Categorization by function
Aggregation
Aggregation pheromones function in mate choice, overcoming host resistance by mass attack, and defense against predators. A group of individuals at one location is referred to as an aggregation, whether consisting of one sex or both sexes. Male-produced sex attractants have been called aggregation pheromones, because they usually result in the arrival of both sexes at a calling site and increase the density of conspecifics surrounding the pheromone source. Most sex pheromones are produced by the females; only a small percentage of sex attractants are produced by males. Aggregation pheromones have been found in members of the Coleoptera, Collembola, Diptera, Hemiptera, Dictyoptera, and Orthoptera. In recent decades, aggregation pheromones have proven useful in the management of many pests, such as the boll weevil, the pea and bean weevil. Aggregation pheromones are among the most ecologically selective pest suppression methods. They are non-toxic and effective at very low concentrations.Alarm
Some species release a volatile substance when attacked by a predator that can trigger flight or aggression in members of the same species. For example, Vespula squamosa use alarm pheromones to alert others to a threat. In Polistes exclamans, alarm pheromones are also used as an alert to incoming predators. 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 to herbivores.An alarm pheromone has been documented in a mammalian species. Alarmed pronghorn, Antilocapra americana flair their white rump hair and exposes two highly odoriferous glands that releases a compound described having the odor "reminiscent of buttered popcorn". This sends a message to other pronghorns by both sight and smell about a present danger. This scent has been observed by humans 20 to 30 meters downwind from alarmed animals. The major odour compound identified from this gland is 2-pyrrolidinone.
Epideictic
Epideictic pheromones are different from territory pheromones, when it comes to insects. Fabre observed and noted how "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 they should clutch elsewhere." It may be helpful to note that the word epideictic, having to do with display or show, has a different but related meaning in rhetoric, the human art of persuasion by means of words.Territorial
Laid down in the environment, territorial pheromones mark the boundaries and identity of an organism's territory. Cats and dogs deposit these pheromones by urinating on landmarks that mark the perimeter of the claimed territory. In social seabirds, the preen gland is used to mark nests, nuptial gifts, and territory boundaries with behavior formerly described as 'displacement activity'.Trail
Social insects commonly use trail pheromones. For example, ants mark their paths with pheromones consisting of 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 available, visiting ants will continuously renew the pheromone trail. The pheromone requires continuous renewal because it evaporates quickly. When the food supply begins to dwindle, the trail-making ceases. Pharaoh ants mark trails that no longer lead to food with a repellent pheromone, which causes avoidance behaviour in ants.Repellent trail markers may help ants to undertake more efficient collective exploration.
The army ant Eciton burchellii provides an example of using pheromones to mark and maintain foraging paths. When species of wasps such as Polybia sericea found new nests, they use pheromones to lead the rest of the colony to the new nesting site.
Gregarious caterpillars, such as the forest tent caterpillar, lay down pheromone trails that are used to achieve group movement.
Sex
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.At the microscopic level, a number of bacterial species release specific chemicals into the surrounding media to induce the "competent" state in neighboring bacteria. Competence is a physiological state that allows bacterial cells to take up DNA from other cells and incorporate this DNA into their own genome, a sexual process called transformation.
Among eukaryotic microorganisms, pheromones promote sexual interaction in numerous species. These species include the yeast Saccharomyces cerevisiae, the filamentous fungi Neurospora crassa and Mucor mucedo, the water mold Achlya ambisexualis, the aquatic fungus Allomyces macrogynus, the slime mold Dictyostelium discoideum, the ciliate protozoan Blepharisma japonicum and the multicellular green algae Volvox carteri. In addition, male copepods can follow a three-dimensional pheromone trail left by a swimming female, and male gametes of many animals use a pheromone to help find a female gamete for fertilization.
Many well-studied insect species, such as the ant Leptothorax acervorum, the moths Helicoverpa zea and Agrotis ipsilon, the bee Xylocopa sonorina, the frog Pseudophryne bibronii, and the butterfly Edith's checkerspot release sex pheromones to attract a mate, and some lepidopterans can detect a potential mate from as far away as. Some insects, such as ghost moths, use pheromones during lek mating. Traps containing pheromones are used by farmers to detect and monitor insect populations in orchards. In addition, Colias eurytheme butterflies release pheromones, an olfactory cue important for mate selection. In mealworm beetles, Tenebrio molitor, the female preference of pheromones is dependent on the nutritional condition of the males.
The effect of Hz-2V virus infection on the reproductive physiology and behavior of female Helicoverpa zea moths is that in the absence of males they exhibited calling behavior and called as often but for shorter periods on average than control females. Even after these contacts virus-infected females made many frequent contacts with males and continued to call; they were found to produce five to seven times more pheromone and attracted twice as many males as did control females in flight tunnel experiments.
Pheromones are also utilized by bee and wasp species. Some pheromones can be used to suppress the sexual behavior of other individuals allowing for a reproductive monopoly – the wasp R. marginata uses this. With regard to the Bombus hyperboreus species, males, otherwise known as drones, patrol circuits of scent marks to find queens. In particular, pheromones for the Bombus hyperboreus, include octadecenol, 2,3-dihydro-6-transfarnesol, citronellol, and geranylcitronellol.
Sea urchins release pheromones into the surrounding water, sending a chemical message that triggers other urchins in the colony to eject their sex cells simultaneously.
In plants, some homosporous ferns release a chemical called antheridiogen, which affects sex expression. This is very similar to pheromones.
Other
This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.- Nasonov pheromones
- Royal pheromones
- Calming pheromones
- Necromones, given off by a deceased and decomposing organism; consisting of oleic and linoleic acids, they allow crustaceans and hexapods to identify the presence of dead conspecifics.
- Suckling: TAA is present in rabbit milk and seems to play a role of pheromone inducing suckling in the newborn rabbit.
Categorization by type