Antennae Detect Odors

a dozen small white dampwood termites on a dark, damp piece of wood

Biological Strategy

Nevada termite

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Capture, Absorb, or Filter Chemical Entities

Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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Modify Solubility (Dissolving, Emulsifying, Precipitating, Crystallizing)

Increasing or decreasing the solubility of chemical constituents is one way of managing a host of metabolic processes including material synthesis. For example, organisms that produce calciferous shells utilize dissolved calcium and carbonate ions, but when the time is right, they raise the pH to create alkaline conditions that trigger calcium carbonate to precipitate out of solution as an insoluble solid.

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Sense Chemicals (Odor, Taste, etc.) From the Environment

Chemicals are important for signaling and communication among living systems, either intentionally (such as when two living systems try to find one another) or unintentionally (such as when a plant emits a chemical signal that an herbivore can use to find a tasty bite). They are also important for other uses, such as navigating or finding sources for minerals. But chemical signals are often relatively weak and disperse when moving through water or gases. Therefore, detecting them requires specialized abilities, including a way to determine where they are coming from. A well known example of sensing chemicals can be seen in ants following a pheromone trail laid down by others in their colony to locate a quality and abundant food source.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Odor-binding proteins on the antennae of dampwood termites mediate the transport of odoriferous chemicals to the olfactory nerves by encapsulating the hydrophobic scent chemicals in a water soluble coating.

For human beings, sight, hearing, and touch are the primary means of perceiving the world. However, many animals rely heavily on the sense of smell to detect food sources, predators, nesting sites, etc. Animals can smell a scent chemical emanating from a source only when that chemical comes in contact with receptors associated with its nervous system (hence the term chemoreception). In dampwood termites, there is a water-based fluid layer between the surface of antennae sensors and the olfactory nerve beneath. Chemical signals, however, are almost invariably insoluble in water and therefore unable to cross the thin aqueous layer unaided. That help comes from odor-binding proteins that encapsulate the scent chemicals in a water-soluble coating giving them a free pass through the layer. Negatively charged receptors on the surface of the olfactory nerves cause a structural change in the surface coating which causes the encapsulated scent chemical to be ejected onto the nerve receptor.

Last Updated August 18, 2016

References

Journal article

Pheromone Reception

The Chemistry of Pheromones and Other Semiochemicals II | 23/11/2004 | Walter S. Leal

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Reference

Journal article

Odorant-binding proteins from a primitive termite

Ishida, Y.; Chiang, V. P.; Haverty, M. I.; Leal, W. S.

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