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Urology => Reproductive System => Pheromone
Pheromone
Pheromone, odor produced by an animal that affects the behavior of other animals. The way pheromones work is analogous to the way hormones in the body send specific chemical signals from one set of cells to another, causing them to perform a certain action.
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. The sexual pheromones of other undesirable insects are sometimes sprayed over an infested area so as to disorient males seeking females of their species.
Insects also use pheromones in more complex ways. Female Douglas fir beetles locate a host tree by its odor (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 odor that blocks the receptors for Douglas fir odor in other beetles. When a tree has collected a critical number of mated females, this inhibition odor makes the tree "invisible" to the beetles' sense of smell and prevents the tree from being overly parasitized.
Social insects-insects that live together in groups-usually have a repertoire of pheromonal messages. Ants, for example, usually have a pheromone for marking trails to food, another for eliciting attacks on enemies they have discovered, a third that signals the need to flee, and yet others that identify their larvae in the darkness of the nest. Several species of invertebrates have broken the elaborate code of ants; for example, assassin bugs lay false odor trails and eat the ants that follow them, and a variety of parasitic or symbiotic beetles, millipedes, and arachnids produce the pheromones typical of larval ants and manage thereby to live undisturbed inside ant nests, often feasting on eggs and larvae.
Such deception is by no means limited to animals. A few species of tropical orchids, for example, produce the sexual pheromones of certain wasps. The male wasps' unsuccessful attempts to mate with a succession of the wasplike flowers serve to carry the orchid pollen from one flower to another.
Pheromones are also common in vertebrates. Mammals regularly mark their territorial boundaries with pheromones from specialized glands. These odors can be detected by males at enormous distances and can alter male behavior dramatically. Owners of unspayed female dogs, for example, regularly find their pets attracting unaltered males from more than a kilometer away. Vertebrates also have additional odors of variable chemistry that serve to identify animals individually. Neighboring mammals of many species come to recognize one another by the odors 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 odor.
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 odor only at puberty suggests that pheromones may also have once affected the behavior 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.
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