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Environmental Sciences
ENVS 1030
Rebecca Hallett

GLOSSARY Semiochemical: A chemical emitted by a plant or animal that evokes a behavioral or physiological response in another organism Allelochemical: When the semiochemical affects an individual of a different species Pheromone: When the semiochemical affects an individual of the same species Allomone: An allomone is any chemical substance produced and released by an individual of one species that affects the behaviour of a member of another species to the benefit of the originator but not the receiver. Production of allomones is a common form of defense, such as by plant species against insect herbivores or prey species against predators. Kairomone: A kairomone is a semiochemical, emitted by an organism, which mediates interspecific interactions in a way that benefits an individual of another species, which receives it, without benefitting the emitter. Two main ecological cues are provided by kairomones; they generally either indicate a food source for the receiver, or give warning of the presence of a predator. Synomone: benefit both sender and receiver -- such as plant volatiles that attract insect pollinators. Hormone: a chemical released by a cell, a gland, or an organ in one part of the body that affects cells in other parts of the organism Primer pheromone: Primer pheromones trigger a change of developmental events (in which they differ from all the other pheromones, which trigger a change in behavior). Releaser pheromone: cause an alteration in the behavior of the recipient. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. In general, this type of pheromone elicits a rapid response, but is quickly degraded Chemoreception: the detection of chemical components of the environment. Gustation: Gustation is analogous to taste. Gustatory stimuli (generally non-volatile compounds), from foodstuffs or on plant surfaces, are detected in the liquid phase by chemoreceptors on the mouthparts and feet. Gustatory sensillae require the stimuli to be present in high concentrations (> 10-5 M thresholds) before chemoreception can occur. Olfaction: Olfaction is analogous to smell. Olfactory stimuli, such as pheromones and volatile plant compounds, are detected in the gas phase by chemoreceptors on the antennae. Olfactory sensillae can detect the stimulus at very low concentrations (10-10 M thresholds). Volatility is a property referring to the vapour pressure of a chemical -- that is, the affinity the chemical has for the gaseous phase at ecologically relevant temperatures. Chemicals that are highly volatile can be readily sensed in the air. 1 GLOSSARY Stability, in the context of pheromones, refers to the reactivity of a chemical. Pheromones which do not tend to react or break down are referred to as stable. Stable pheromone signals can be long-lasting or act over long distances. Persistence refers to the duration of the pheromone signal. Stable, non-volatile pheromones which are regularly released produce the most persistent signal. An arrestant causes an organism to slow down or stop its movements when in contact with the substance. An attractant is a substance which causes the receiving organism to make oriented movements towards the source of the chemical, whereas a repellent causes an organism to make movements away from the source.  A stimulant is a substance which causes an organism to make some action, or increase the frequency of the action -- such as walking, feeding, mating or oviposition -- whereas a deterrent is a substance that prevents or decreases the frequency of these actions. We’ve already introduced primer and releaser pheromones, and now we can explore these ideas in greater depth. Remember that primer pheromones are ones that alter or “prime” the receiver’s physiology for some event, such as bringing about sexual maturity in preparation for mating. Releaser pheromones are compounds that cause or “release” an immediate behavioral response in the receiver. Releaser pheromones can be further categorized into several functional groups:  Aggregation pheromones cause individuals of both sexes to move towards the source, bringing about a localized increase in population density. Aggregation pheromones are typically produced by one sex but attractive to both.  Alarm pheromones bring about defensive or escape behaviours.  Epideictic or spacing pheromones cause behaviours which result in increased spacing between individuals of a species, and are used to reduce intraspecific competition for a resource.  Recruitment or trail pheromones are most commonly observed in social insects, and are used to “recruit” nestmates to a food source.  Sex attractants are chemicals which mediate mate location, and are usually released by one sex (usually female) to “call” to the other. Note that not all sex pheromones are attractants; some sex pheromones may have a role in courtship, maturation, or mate acceptance, but the umbrella term “sex pheromone” is often used to refer to sex attractants. Seco
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