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Pheromones are chemicals released by an organism into its environment enabling it to communicate with other members of its own species.
The Word pheromoneis the mixture of two words phero + hormones.Phero means "to bear" and hormonemeans "impetus". Means it is a chemical signal that triggers a natural response in other member of the species.
Pheromones are the molecules used for communication between animals. A broader term for chemicals involved in animal communication is semiochemical from the (Greek semeion sign) (Law & Regnier 1971). Strictly Speaking, pheromones are a subclass of semiochemical, used for communicationwithin the species (intraspecific chemical signals). Pheromoneswere originally defined as ‘substances secreted to the outside by an Individual and received by a second individual of the same species in which they release a specific reaction, for instance a definite behaviour [releaser pheromone] or developmental process [primer pheromone] (Karlson & Lüscher 1959); the division into primer and releaser. The word pheromone comes from the Greek pherein, to carry or transfer, and hormone, to excite or stimulate. The action of pheromones between individuals is contrasted with the action of hormones as internal signals within an individual organism. Pheromones are often divided by function, for example into sex Pheromones and aggregation pheromones. This functional division underlies the structure of the book, which has an emphasis on the ways evolved by different kinds of animals to solve the same communication needs.
The Asian elephant Elephas maximus, shares its female sex pheromone, (Z)-7-dodecen-1-yl acetate (top), with some 140 species of moth (Rasmussen et al. 1996).
Pheromones are found throughout the living world and are probably the most ancient form of animal communication. The complex but primitive single-celled amoeba Dictyostelium, for example, uses a pheromone to attract others of its kind for reproduction. Insects regularly use pheromones for the same purpose; thus, female gypsy moths and Japanese beetles each emit a species-specific sexual pheromone to attract males. The males simply fly upwind when they encounter the appropriate odor. Traps baited with synthetic pheromones are now used to capture many such pest species.
Insects also use pheromones in more complex ways. Female Douglas fir beetles locate a host tree by its odour (a piny scent peculiar to Douglas firs), bore a hole, and then broadcast their sexual pheromone. Males fly upwind, find the females, shut off their production of pheromone with an acoustic signal, and then themselves produce an odour that blocks the receptors for Douglas fir odour in other beetles. When a tree has collected a critical number of mated females, this inhibition odour makes the tree “invisible” to the beetles' sense of smell and prevents the tree from being overly parasitized.
Pheromones are also common in vertebrates. Mammals regularly mark their territorial boundaries with pheromones from specialized glands. These odours can be detected by males at enormous distances and can alter male behaviour dramatically. Owners of unsprayed female dogs, for example, regularly find their pets attracting unaltered males from more than a kilometre away. Vertebrates also have additional odours of variable chemistry that serve to identify animals individually. Neighbouring mammals of many species come to recognize one another by the odours they each leave along mutual boundaries or at traditional “scenting posts,” and intruders are detected almost immediately. Even mates and offspring often recognize one another by odour.
Pheromones have been shown to play a major part in the lives of primates as well, and the observation that human sweat takes on an odour only at puberty suggests that pheromones may also have once affected the behaviour of humans. The existence of human pheromones was also suggested by a 1998 experiment intended to explain why women who live together tend to have synchronized menstrual cycles—that is, to experience the various stages of this cycle at the same time. The results of the experiment suggest that women's sweat carries an odor that may, under certain circumstances, act as a pheromone, affecting the timing of ovulation and menstruation among other women.
For example, queen bees emit a pheromone that affects the development of worker bees, and ants use pheromones to recruit nest mates to a food source (which explains trails of ants at a picnic or in a kitchen). When laying their eggs, some flies, moths, and beetles use certain pheromones to repel insects of the same and competing species, thereby protecting their progeny from competition for resources. Others insects, such as aphids, give off alarm pheromones that urge neighbouring aphids to flee from nearby predators. Honey bees use alarm pheromones to recruit nest mates to sting and pursue intruders. Some male moths use aphrodisiac pheromones to entice females to mate with them.
SOME IMPORTANT DEFINATIONS OF PHEROMONES
- Pheromones are naturally occurring substances the fertile body excretes externally, conveying an airborne message to trigger a response from the opposite sex of the same species.
- Pheromones are chemicals produced in very small amounts by a member of a species from exocrine glands and released into the external environment where they influence the behavior of the other members of the same species.
- Pheromones are chemical substances produced by a member of a species from exocrine gland and released into the external environment where they influence the behavior of the other member of the same species.
- Pheromones are chemicals emitted by living organisms to send messages to individuals of the same species. The classes most widely explored are the sex pheromones produced by female moths which are used to attract non specific males for mating.
- A pheromone (including identical or substantially similar synthetic compounds) as defined by the Agency is a compound produced by a species which, alone or in combination with other compounds produced by that species, modifies the behavior of other individuals of the same species. Straight Chain Lepidopteran Pheromones (SCLPs) are those produced by a member of the order Lepidoptera, which includes butterflies and moths.
BACKGROUND OF PHEROMONES
Pheromones were first defined in 1959 as chemical substances excreted by animals to trigger REPRODUCTIVE behavioural response from a recipient of the same species.
It was in 1986 that Dr. Winifred Cutler, founder of Athena Institute, and her colleagues conducted the first controlled scientific studies to document the existence of pheromones in humans. Prior to their landmark research there were no conclusive indications that pheromones were excreted by humans.
By 1999, from a biological perspective, the term pheromone can be defined as a chemical excreted by animals that promote behaviours which PERPETUATE THE SPECIES.
In 2005, the scientific literature recognizes four classes of pheromones; territorial markers, mother-infant, menstrual synchrony, and the fourth class that is the area of expertise for Dr. Cutler and Athena Institute; human sex-attractant pheromones.
ROLE OF PHEROMONES
Pheromones serve as a mean of communication between animals like sight and sound. They transfer information from one animal to another by smell or taste. Pheromones evoke specific behavioral response in the recipients, and these responds may be of great importance for the survival of the species. Pheromones also accelerate reproductive maturity in many species and enable members of one sex to distinguish which members of the opposite sex are in breeding condition. Pheromones may also synchronize reproduction within a group. In desert locust any sexually mature male produces a pheromone, locustrol, which speeds up sexual development in immature members of both sexes. This enables most of the locusts in the area to reproduce simultaneously, producing numerous young locusts at once so that predators can kill only a small fraction and many more survive than if they hatched over a long time, giving predator's time to eat one brood before the next appears.
An area of particular interest is the evolution of pheromone diversity. This problem is important in sex pheromones, where cross-attraction between species can have strong negative effects. The evolution of the biomechanics required to produce and sense pheromone molecules has also been examined, as has the use of pheromones to regulate recruitment. Typically, the majority of colony members choose the most profitable among multiple food sources. This can be seen as a natural byproduct of the use of pheromones—lesser-used trails will not be as heavily reinforced and will consequently be chosen less frequently. Based on observed behaviors, several models have been developed to capture recruitment behavior in the presence of multiple targets. Pheromone Use in Evolutionary Computation. The evolution of pheromone use has been studied in evolutionary computation (EC) environments since the early 1990s.These works tend to focus on harnessing pheromones to be used as navigational cues in robotics and other multi-agent systems. Ant-colony optimization has been applied successfully to several computational tasks such as network routing and the traveling salesman problem. In the Ant Farm project, an early study of EC-based pheromones, a genetic algorithm was designed to closely model the real-life capabilities of ants. Homogeneous groups of organisms were rewarded based on the amount of food brought from a source to the nest. In addition to the ability to sense and produce pheromones, organisms were given a virtual compass to aid in navigation. Experiments showed an increase in the amount of food brought back to the nest over time.
Types of pheromones and their examples: -
pheromones are of two main kinds with regard to their mode of action: releaser pheromones and primer pheromones.
1. Releaser Pheromones
These act on the central nervous system and philology of the recipient and almost immediately trigger a reversible change in its behaviour. These include trial substance, sex attractants and death substances.
a.) Trail substances:-
Foraging worker ants leave a trial substance along their path to and from the source of food. This substance enables other ants of their colony to find their way to the food and back home to the food and back home after foraging. When the food is supply is exhausted, the returning ants to not release the trial substances. The trial substance is volatile and evaporates quickly so that the ants are not misled by old trails. It has been found that the trail substances are species specifies. This specificity is biologically adaptive as it ensures that workers do not mistakenly follow trials of the other ant species which may cross their own trial. The trial substance is laid from the tip of the worker ant's stinger and evaporates to from an active space so that it is picked up by other worker ants.
These type pheromones are common in social insects. For example certain ants, as they return to the nest with food, lay down a trail pheromone.
This trail attracts and guides other ants to the food. It is continually renewed as long as the food holds out. When the supply begins to dwindle, trail making ceases. The trail pheromone evaporates quickly so other ants stop coming to the site and are not confused by old trails when food is found elsewhere. And at least in one species of ant, trails that no longer lead to food are also marked with a repellant pheromone.
A stick treated with the trail pheromone of an ant (left) can be used to make an artificial trail with is followed closely by other ants emerging from their nest (right). The trail will not be maintained by other ants unless food is placed at its end.
b.) Sex attractants: -
Many insects produce pheromones that act as sex attractants. The female of commercial silk moth, bombyx mori, secretes a substance called bombycol which, with a gentle wind, quickly spread over a wide area. The male silk moth has extremely sensitive receptors in the antennae for detecting the attractant. If the wind is blowing, male moths sitting download can locate the female moth from an astonishing distance of several kilometers. It still air, they may fail to locate the female only a meter away. Even though each female releases less than 0.00000001 gram (0.01 microgram) of the attracting chemicals. The area within witch the attractant is dense enough to be detected by a male moth is called active space. Only just around the female is the contraction of pheromones sufficient to establish a gradient. When the male enters this region from active area, it stops flying upwind and follows the gradient instead till female is located. That the male responds to the chemical releaser and not to the visual stimuli can be easily shown. Male will be attracted to female clearly visible in a tightly sealed glass cage from which pheromones cannot escape.
Another example of a pheromone affecting the reproductive behaviour is found in dogs. A female dog in heat secretes a pheromone which not only attracts the male dogs from a considerable distance but also indicates the sexual of the female and excites the male.
c.) Alarm substances:-
When distributed, ants release alarm substances which spread through the air and warm the ants in the vicinity of danger. The alarm substances are less specific so that the ants of many species respond to the same alarm substance. Sensing danger, worker bees release an alarm substance which communicates danger to all the bees in the hive.
Alarm substances are found in fish too. An injured fish release a chemical that makes other fish to leave the place and hide.
When an ant is disturbed, it releases a pheromone that can be detected by other ants several centimeters away. They are attracted by low concentrations of the pheromone and begin to move toward the region of increasing concentration. As they get nearer to their disturbed nest mate, their response changes to one of alarm. The higher concentration causes them to run about as they work to remedy the disturbance.
Unless additional amounts of the alarm pheromone are released, it soon dissipates. This ensures that once the emergency is over, the ants return quietly to their former occupations. Honeybees also have an alarm pheromone (which is a good thing not to elicit around a colony of "Africanized" bees).
2. Primer Pheromones
These pheromones initiate more profound physiological changes but act slowly and affect the growth and differentiation of the recipient over a long time. They play an important role in regulating composition of the population in conical insects such as bees, ants and termites.
A bee colony consists of three morphologically different castes: a queen, some drones (male) and numerous workers (sterile females). The queen secretes a pheromone which, when ingested (not smelled) by workers inhibits the development of their ovaries and their ability to build royal cells meant for rearing of new queens. The pheromones also ensure that the workers feed all the female larvae to raise the worker population in the hive. When old, the queens cannot produce the “antiqueen substance” enough for all the workers. Therefore, new queen cells are built and the queen lays eggs in them. The old queen leaves the nest because only one queen can survive in a hive. As she leaves, queen secrets a swarming pheromone, which attracts many of the workers and keeps them with her to found a new colony at an appropriate site. The chemical structure of sex attractant pheromones of honeybees is CH3CO (CH2)5CH.COOH. The queen that emerges first kills the others who are still developing takes over the control of the hive. Pheromones also enable the bees to identify their own hive and serve as alarm signal too.
Terminate queens and kings secrets substances which, when ingested, prevent the workers from developing reproductive capabilities. The number of soldiers in a termite colony is regulated by similar pheromones secreted by fully developed soldiers.
Rats and mice give off pheromones that elicit mating behavior. However, the response is not immediate as it is in the releaser pheromones of mother rabbits and insects. Instead, detection of the pheromone primes the endocrine system of the recipient to make the changes, e.g., ovulation, needed for successful mating.
Primer pheromones are detected by the olfactory epithelium with which normal odors are detected and also in most mammals (but not humans) by thevomeronasal organ(VNO). The VNO is a patch of receptor tissue in the nasal cavity distinct from the olfactory epithelium. The receptors areG-protein-coupled HYPERLINK "http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/G.html"transmembraneHYPERLINK "http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/G.html" proteinssimilar to those that mediate olfaction, but encoded by entirely different genes.
3. Vertebrate pheromones: -
vertebrates release pheromones in the excrement or from glands in the feet, near the tails or around the anus, near eyes or horns. Their pheromones act as sex attractants, but may also serve as tutorial makers. When a dog urinates, a bush, it deposits a pheromone which tells the other dogs can locate a bitch from a distance of about a kilometer with the help of her sex attractant pheromone.
Some pheromones act slowly and have a long lasting effect. For instance, the odour of a pheromone passed in the urine by a strange male, may terminate the pregnancy of a newly fertilized female mouse. Odour is picked up via the female's olfactory organs and triggers the nervous activity in her hypothalamus. The later causes the release pituitary hormones that reduce progesterone output by the ovaries. This reduction inhibits preparation of uterus for implementation and pregnancy aborts. This enables the strange mouse to mate with the female. The oestrous cycles of females mice can be initiated by synchronized by the odour of a male mouse. Even if the male cannot he seen or heard.
It has been found that overcrowding of female mice results in disturbance and even blockage of oestrous cycles. Pheromones are probably involved, because removal of the olfactory bulbs restores the cycles to normal. It seems likely, therefore, that pheromones help regulate population help regulate population density in some species.
In monkeys, the sexual response of the male to the female is greater at the time of the ovolution that at other times of her cycle. At this time, her vaginal secretions contain certain fatty acids which send an olfactory “message” to the male, and, thus act as pheromones. These fatty acids are also found in increased amounts in human vaginal secretion at about midcycle.
4. Plants Pheromones: -
Some lower plant groups also produce pheromones. In these plants a chemical is secreted into water by female gametes to attract male gametes.
When used in combination with traps, sex pheromones can be used to determine what insect pests are present in a crop and what plant protection measures or further investigations might be in order to assure that there will be no excessive damage to the crop. If the synthetic attractant is exceptionally seducing and the population level is very low, some control is achieved with pheromone traps or with a technique called "attract and kill".
Importance or uses of pheromones
Different pheromones and pheromone blends can be used to attract mates, signal warnings, and mark territories, among several other behaviours. By leaving traces in their environment, organisms are able to effectively communicate without the need for other complex or long-distance mechanisms. Also, the completely decentralized nature of pheromone usage makes this method robust in the face of changing environments.
The sex attractant pheromones can be used to trap insect for use in scientific research. Efforts are being made to employee pheromones for the non-toxic and species -specific control of insect pests in place of the toxic and relatively non-specific insecticides in use at present.
Pheromones can be highly effective at low doses and great distances. Detection of just 30 pheromone molecules can prompt a response in cockroaches. In less than five days a single caged female pine sawfly attracted more than 11,000 males from the field. From a pest management standpoint, pheromones are a critical key to manipulating insect behaviors.
Pheromones are also used in mating disruption which is more effective: Synthetic pheromone is released from numerous sources placed throughout the crop to be protected; the males are then unable to locate the females and the number of mating and offspring is reduced.
Pheromone traps are used to control the insects such as the European corn borer that damages millions of dollars of crops each year. The European corn borer larvae feed on and bore into the corn plant. Cavities produced by borers reduce the strength of the corn and interfere with plant physiology, including the translocation ofwaterand nutrients.
Pheromones can be used as honest signals (Zahavi 1975) which provide reliable information
because they accurately reflect the signaler's ability or resources (Guilford 1995).For example,
female tiger moths (Utetheisa ornatrix)
Advantages and Disadvantages of Pheromones
There are many advantages to using chemical signals. Some basic ones include the fact that chemicals can transmit through darkness, around obstacles, and they are very energetically efficient. Pheromones are relatively cheap to biosynthesize and they can be released in a very simple manner, including the simple operation of opening a gland. Pheromones can also last for days and be transmitted over great potential distances. This includes millimeters for microorganisms and kilometers for other organisms, without even altering the reception or biosynthesis. Some pheromones last so long that once they are released, they are actually used by the same organism in the future if it returns. Some pheromones are not very specific and will affect other species when they are released. For example, agitated honeybee workers discharge isoamyl acetate or 2-heptanone, which alarm the other nest mates but also alarms any ants or termites that are in the vicinity. This is beneficial to the ants and termites, which are now aware of the danger that may be present.
There is one major disadvantage of chemical communication. It is very slow. Organisms cannot quickly transmit pheromones over long distances or change from one chemical message to another. Also, there has been no evidence that organisms use amplitude and frequency modulation in the transfer of pheromones.
Although slow transfer is a major disadvantage, organisms have been able to adapt to counteract it. They do this by the multiplication of glands and other principal biosynthetic sites to allow the independent discharge of pheromones with different meanings. One example of this is the black-tailed deer. The deer produces pheromones in at least seven different sites, including urine, feces tarsal glands, metatarsal glands, pre orbital glands, forehead glands, and inter digital glands. The pheromones from each site have a different function.
With pride and satisfaction, a farmer eyes the glistening red globes of the tomatoes he has just harvested. A few years ago he had been ready to abandon tomato farming because the destructive tomato pinworm was ruining as much as two-thirds of his crop. Despite his zealous use of insecticides, these worms would tunnel into his tomatoes, leaving telltale pinholes and unsightly black blotches that destroyed the crop's marketability.
But now, spiraling around the stems of many of his tomato plants, are dispensers of a potent chemical guardian. These hollow plastic tubes emit a chemical that interferes with the ability of the pinworm moth to find mates, and breaks the cycle of infestation. Thanks to pinworm birth control, the farmer was able to bring three-quarters of his crop to market this year.
PROPERTIES OF PHEROMONES
Pheromones are largely hydrophobic compounds, whereas pheromone receptors are surrounded by an aqueous solution (the sensillar lymph) and are isolated from the external environment.
Dynamic properties of pheromone plumes are behaviorally important in some moths for inducing upwind flight, but little is known about the time-dependent properties of odor transduction or the mechanisms that limit receptor dynamic sensitivity. We stimulated male antennae of two moth species, Cadra cautella and Spodopteraexigua, with pheromone plumes in a wind tunnel while recording electroantennograms (EAG) and concentration of a surrogate plume (propylene, which mimics a pheromone plume) using a photo ionization detector (PID). Turbulent plumes were produced by mechanical baffles, creating broad frequency range dynamic concentration changes at the antennae. Dynamic structures of pheromone plumes provide important information to male moths, and neural substrates for decoding such information have been proposed in the CNS.
Nonlinear properties of pheromone responses
Coherence values below unity can indicate noise or nonlinearity in a system. To test for nonlinear behavior, we used block-structured nonlinear cascade models (NLN models) based on static nonlinear and dynamic linear components.
SUMMARY AND RESULTS
It has been found in the recent years that the behaviour of animals is influenced not only by hormones but also by certain other substances called pheromones .Whereas the hormones regulate the physiological process of an individual ,the pheromones bring about communication between the various members of a species.
What are pheromones?
Pheromones are chemical substances produced by a member of a species from exocrine glands and released into the external environment where they influence the behaviour of other members of the same species.
Pheromones generally act in two ways:-
Some pheromones act on the central nervous system of the recipient and immediately affect its behaviour. These are called Releaser pheromones. These include trail substances, sex substances and alarm substances.
Other pheromones act slowly and affect the growth and differentiation of the recipient. These are called primer pheromones. They play an important role in regulating the composition of the population in conical insects such as bees, ants and termites.
Vertebrate pheromones in the excrement or from glands in the feet, near the tail or around the anus. Some of the plant groups also produce pheromones. In these plants, a chemical is secreted into water by female gametes to attract male gametes.
the sex attractant hormones can be used to trap insects for use in scientific research. Efforts are being made to employ pheromones for the nontoxic and species-specific control of insect pests in place of the toxic and relatively nonspecific insecticides in use at present. These are generally used to attract mates and signal warning. Sex attractants are used to attract trap insect for use in scientific research. Pheromone traps are used to control the insects such as the European corn borer that damages millions of dollars of crops each year. Pheromones are also used in mating dispersions.