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Pheromones : - Chemical communication has been recognized in animals, particularly in insects, fishes and mammals and this forms a part of animal communication system. According to Regnier the substances or chemicals which are employed in conveying messages between animals are called as “Semiochemicals”. The chemicals or Semiochemicals which are released in the environments for the intraspecific communication are called as “Pheromones”.

The word pheromone originates from Greek word “Pherein” meaning “to carry” and “Harman” meaning “to excite”. This term was proposed by Karlson and Luscher. Karlson defined Pheromones as “ chemical signals exchanged between individuals of same species which produces a specific reaction in form of behavioral response or in particular development process ” .

Such chemicals are released in minute quantities bringing about major effect functioning as chemical messengers. They are known as chemical regulators produced by exocrine glands causing change in the behavioral and developmental physiology of animals.

Pheromones are generally secreted by specialized glands distributed in different parts of body and are conveyed to recipient by smell, taste or by absorption.

“Allelochemics” is the term used for Semiochemicals which are utilized in interspecific communications . These are further classified into two categories: - “Allomones” and “kairomones”.

Allomones are those chemicals “which induce effect adaptively favorable to the emitter, e.g. repellents of certain insects, spray of skunk.

Kairomones are the chemicals “which induce effect adaptively favor the receiver, e.g. the signals that enable the predator to locate the pray.

Norlund and Lewis have added two more categories to these called, “Synomones” and “Apomones”. When both the categories i.e.

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emitter and receiver get beneficial response from chemical or substance, they are called as synomones, e.g. flower scent comes under this category. Whereas apomones are such substances which are emitted by non-living material and is favorable to recipient, but detrimental or harmful to an organism of another species that is located in or on that non-living material like decaying meat, food grains, the attractant emitted by meat or food grain rather than the pray(Dominic 1978). The substances which act by sense are called “Tellomones”.

Types of Pheromones: - Mainly pheromones are categorized into the following: -

1) Releaser pheromone2) Primer pheromone 3) Imprinting pheromone

1) Releaser pheromones: -

Releaser pheromones are pheromones that cause an alteration in the behavior of the recipient, by affecting the CNS of the organism. Releaser pheromone acts through central nervous system. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. This type of pheromone generally elicits a rapid response but is quickly degraded. E.g. sex attractant or sex pheromone, aggregation pheromone, territory pheromone, trial pheromone, etc. In contrast, a primer pheromone has a slower onset and a longer duration. Ex. Rabbit (mothers) release mammary pheromones that trigger immediate nursing behavior by their babies.

Sex pheromones In animals, sex pheromones indicate the availability of the female for breeding. Male animals may also emit

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pheromones that convey information about their species and genotype. Many insect species release sex pheromones to attract a mate, and many lepidopterans (moths and butterflies) can detect a potential mate from as far away as 10 kilometers (6.25 mi). Traps containing pheromones are used by farmers to detect and monitor insect population in orchards. At the microscopic level, a gamete pheromone may provide a trail leading the opposite sex's gametes towards it to accomplish 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. 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.

Aggregation pheromones: - Aggregation pheromones function in defense against predators, mate selection, and overcoming host resistance by mass attack. A group of individuals at one location are referred as aggregation, whether consisting of one sex or both sexes. Male-produced sex attractant have been called aggregation pheromones, because they usually result in the arrival of both sexes at a calling site and increase in density of conspecifics surrounding of the pheromone source. Most sex pheromones are produced by the females and small percentage of sex attractants are produced by males. Aggregation pheromones have been found in members of the Coleoptera, Hemiptera, Dictyoptera and Orthoptera. In recent decades, the importance of applying aggregation pheromones in the management of the boll weevil (Anthonomus grandis), stored product weevils (Sitophilus zeamais ), Sitophilus granarius, Sitophilus oryzae and pea and bean weevil (Sitona lineatus) has been demonstrated. Aggregation pheromones are among the most ecologically selective pest suppression methods. They are not toxic and they are effective at very low concentrations

Alarm pheromones: - Some species release a volatile substance when attacked by a predator that can trigger flight (in  aphids) or aggression (in ants, bees, termites) in members of the same species. Pheromones also exist

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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.

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.

Epideictic pheromones: - 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."

Information pheromones: - Information pheromones are indicative of an animal's identity or territory. For example, dogs and cats deposit chemicals in and around their territory, which then serve as an indicator for other members of the species about the presence of the occupant in that territory. So that the species will know of who owns that area or who that territory is being occupied by.

Signal pheromones: - Signal pheromones cause short term changes; such as, the neurotransmitter release which activates a response. For instance, GnRH molecule functions as a neurotransmitter in rats to elicit lordosis behavior

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Trail pheromones: - Trail pheromones are common in social insects. For example, ants mark their paths with these pheromones, which are 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 trail making ceases. In at least one species of ant, trails that no longer lead to food are also marked with a repellent pheromone.

2) Primer pheromones

Primer pheromones trigger a change of developmental events (in which they differ from all the other pheromones, which trigger a change in behavior). A primer pheromone has a slower onset and a longer duration. Ex. 1) Rabbit (mothers) release mammary pheromones that trigger immediate nursing behavior by their babies. 2) Queen bee substance of honey bee. Primer pheromone mediates through the nervous and endocrine system.

Primer pheromones and oestrous suppression in mammals: - The unisexual grouping of regularly cycling female mice results in the mutual disruption of oestrous cycle in small unisexual groups of the female which shows an increased incidence of pseudo pregnancies. According to Whitten in large unisexual groups, the females exhibit decrease in ovarian and uterine weights.

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Primer pheromone and oestrous induction in mammals: -

Whitten found that a male mouse produces an olfactory acting urinary pheromone which is androgen dependent and acts in a very little concentration to initiate oestrous cycle via olfactory simulation. The oestrous inducing pheromone present in the bladder and in urine of male laboratory mice free of any accessory gland secretion, rules out pre-putial gland being involved in its production. The influence of male is to stimulate the gonadotrophic secretion in female (Dominic 1978).

Primer pheromone and pregnancy block: -

Bruce in 1960 found that pregnancy block occurs if male mouse is merely caged inside the female’s cage to prevent physical contact. The pheromone responsible for pregnancy block is present in the urine of intact males.

Primer pheromone and sexual maturity: -

Sexual maturity in female mice is accelerated by the presence of adult male mouse while presence of female adult mouse retards it. Drickamer suggests that the acceleration of sexual maturity observed by presence of an adult male may be mediated by at least to cases of sensory stimuli i.e. odours and tactile stimulation.

3) IMPRINTING PHEROMONE: -

In certain laboratory rodents, particularly in mice, olfactory influence of preweaning environment has been shown to affect their adult reproductive behavior. E.g. female of Mus musculus domesticus reared their parents generally mate with the males of different strains from their own (Dominic 1978). They however show sexual

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preferences for males of their sub species Mus musculus bactrianus. Such a sexual preference and aversion of males of two subspecies are not exerted in females which are raised by their mothers alone in absence of fathers, thus no exposing to the odour of male parents.

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