Pheromone(redirected from Sex pheromone)
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A substance that acts as a molecular messenger, transmitting information from one member of a species to another member of the same species. A distinction is made between releaser pheromones, which elicit a rapid, behavioral response, and primer pheromones, which elicit a slower, developmental response and may pave the way for a future behavior.
Communication via pheromones is common throughout nature, including some eukaryotic microorganisms such as fungi that exchange vital chemical signals. The cellular slime molds form large aggregations of amebas which unite to form a sorocarp made up of a long, slender stalk that supports a spore-containing fruiting body. A pheromone is responsible for the aggregation. In several species of algae, relatively simple hydrocarbons act as sperm attractants.
By far the largest number of characterized pheromones come from insect species. In social insects, such as termites and ants, there may be as many as a dozen different types of messages that are used to coordinate the complex activities which must be carried out to maintain a healthy colony. These activities might require specialized pheromones such as trail pheromones (to lead to a food source), alarm pheromones (recruiting soldiers to the site of an enemy attack), or pheromones connected with reproductive behavior. Much less is known about mammalian pheromones because mammalian behavior is more difficult to study. There are, however, a small number of well-characterized mammalian pheromones from pigs, dogs, hamsters, mice, and marmosets.
There is great potential for controlling the behavior of a given species by manipulating its natural chemical signals. For example, pheromones have been used to disrupt the reproduction of certain insect pests. This approach can lead to reduced use of pesticides as well as advances in the control of both agricultural pests and disease vectors. See Chemical ecology, Chemoreception, Social insects
a biologically active substance that is secreted by an individual animal into the environment and that has a specific effect on the behavior, physiological and emotional state, or metabolism of another individual of the same species. Pheromones are usually produced by specialized glands.
The biological function of pheromones is generally effected through chemoreceptors and particularly, in many animals, by means of the olfactory organs. A special category is that of pheromones that are produced by external secretion and that directly regulate the metabolism and development of other individuals by their hormone-like action; for example, among common honeybees, certain components of the “queen substance,” which is produced by the queen, inhibit the development of ovaries in worker bees. Pheromones do not belong to any one class of chemical compounds; their structure, which varies, is not known for all pheromones whose existence has been theoretically proven. (See Figure 1 for the chemical composition of certain pheromones.) While pheromones may act as individual chemical compounds, more often the biological agent is a combination of several components. As a rule, the biological activity of pheromones is species-specific—that is, the chemical substances or combinations of substances acting as pheromones are different for different animal species; the same substances, however, may act as pheromones for species that are territorially separated, for example, or that differ in their daily or seasonal periods of activity. The basic function of pheromones is communication by chemical signals between the individuals of one species. An additional function, in some cases, is that of communication between species, for example, parasites may be attracted to a host by the host’s pheromones.
Pheromones have been most thoroughly studied in insects. Sex pheromones, in addition to stimulating sexual behavior, ensure that an individual insect is brought together with and “recognizes” one of the opposite sex. The chemical structure of the attracting substance, or sex attractant, in the female of the Asiatic silkworm was identified by A. Butenandt in 1959. This pheromone, named bombykol, induces a behavioral reaction in males when it is present in the air in concentrations of approximately 10–19g/cm3. The sex pheromone of the gypsy moth—gyplure—is equally effective. The chemical structure of sex pheromones has been identified in many species of insects, primarily among the Lepidoptera. The known pheromones of female moths are mainly in the category of unsaturated aliphatic esters or alcohols. In certain male butterflies the sex pheromones, which have been called aphrodisiacs, have an excitatory effect on the female, thus preparing her for mating.
The aggregation of a large number of individuals in a limited area is a characteristic trait in many insects, such as true bugs, flies, cockroaches, and certain beetles; such behavior is effected by the action of “clustering” pheromones, which have been chiefly studied in the bark beetle—a forest pest. “Anxiety” pheromones may cause an individual to flee or hide—or, on the contrary, they may evoke aggressive reactions, as observed in social insects that collectively attack an enemy. The substances involved here are, as a rule, relatively simple and more volatile than sex pheromones; for example, isoamyl acetate is a component of the anxiety pheromones in the common honeybee.
Less is known about the pheromones of vertebrates. Sex pheromones have been found in fish, tailed amphibians, and reptiles. The skin in many species of fish contains an anxiety pheromone that is released when the skin is injured and that elicits a fear reaction in other individuals. A similar process of secretion of the anxiety pheromone has been observed in tadpoles. Pheromones are not known to be present in birds.
In the case of mammals, it is difficult to define precisely the nature and operation of pheromones in view of the particular complexity of their behavior and inadequate knowledge of the chemical communication mechanisms. A considerable number of observations have been collected, demonstrating the influence of various olfactory secretions on physiological and emotional states in mammals—specifically, sexual, maternal, territorial, and aggressive behavior. In mammals’ sexual behavior, these secretions not only can serve as agents of simple attraction but can also control the more complex processes of reproduction. In certain rodents, for example, the course of the ovarian cycle is influenced by specific components of male and female odor that delay or accelerate the onset of estrus. In mice, pregnancy may be blocked by the effect of the smell of a “strange” male. Olfactory markers are very common among mammals. Such markers presumably serve as signals indicating a territorial claim, and they may also carry information about the individual animal that has left a mark.
Pheromones are potentially effective means of controlling animal behavior. Particularly promising is the use of pheromones to combat farm and forest pests. Traps equipped with synthetic pheromones are used to determine the number of harmful insects and in many cases to destroy entire insect populations.
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