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A ‘Sixth Sense’ for Humidity Helps Insects Stay Out of Climatic Trouble

ELSEVIER SciTech Connect (May 20, 2016 )

The amount of water vapor in the air – humidity – profoundly alters our experience of the environment around us. A hot, dry morning in the desert of California feels miles apart from a hot, sticky one in the Cambodian jungle.
People generally dislike hot and humid conditions for good reasons. Our bodies dissipate heat through evaporation of sweat from the skin surface. When humidity is high, this process is less effective, and more blood needs to be pumped to the skin for cooling. This results in fatigue and can ultimately lead to hyperthermia (“heat stroke”).
Varying levels of humidity characterize all habitats on our planet. Animal species have evolved to tolerate and even to thrive in the most extreme climates, from the frozen tundras of the north to the arid deserts of the equator. It’s particularly impressive that small, cold-blooded animals such as insects can flourish in cold climates as well as in desert habitats. In part, these adaptations are made possible by sophisticated sensory systems that allow them to quickly react to potentially dangerous extremes.
When it comes to air humidity, scientists have known since the early 1900s that insects possess dedicated sensory systems that detect changes in water vapor in the air. This “sixth sense” for humidity has no direct parallels in big land mammals such as us. But it serves the small critters well as they work to avoid desiccation and to find open water : for example, a pond in which to lay eggs (crucial for many species of mosquitoes). We decided to investigate how these humidity-sensing systems work in insects.
Using our favorite fruit fly Drosophila melanogaster as an experimental subject, we set out to determine just how insects can detect water vapor in the air. Which neurons serve as the humidity sensors in this species ? Which genes and receptor mechanisms could be used to detect changes in air humidity ? How is the information about external humidity relayed and ultimately processed in the fly’s brain ?

Source  : Marco Gallio and Marcus Stensmyr

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