Fruit flies use evolved antennae to detect wind direction

Washington, March 13 (ANI): Scientists at Caltech University, US, have discovered that fruit flies have evolved a specialized population of neurons in their antennae that let them know not only when the wind is blowing, but also the direction from which it is coming.

The behavior of fruit flies in the face of a stiff breeze is remarkable in and of itself, according to David J. Anderson, the Roger W. Sperry Professor of Biology at Caltech, and a Howard Hughes Medical Institute (HHMI) Investigator.

"We discovered that you can stop a fly dead in its tracks by blowing a gentle stream of air over it," he explained.

Once the wind stops blowing, however, the flies immediately start walking around again.

"We quickly realized that it would be interesting to ask just how the wind acts on the flies to make them stop walking. How do they sense the wind? How do they transfer that message to their brain so they know to stop moving while the wind is blowing?" said Anderson.

As it turns out, fruit flies are unusual in how they sense wind.

Other insects have sensory hairs that stand up from the cuticle, or outer body wall, and, when blown about by a passing wind, trigger a neural response.

The fruit flies, on the other hand, use their antennae to detect a breeze and its general direction, based on how the antenna moves in the breeze.

The flies' antennae also detects nearby sounds, like the male's courtship song, which cause vibrations in the air. Those vibrations twist the antennae slightly, exciting the neurons within.

"What we wanted to understand was, how can flies tell the difference between sound and wind using the same sensory organ?" said Anderson.

According to Anderson, a fly's antennae contain two distinctly different populations of neurons - one that responds to oscillating air to detect sound, and another that responds to flowing air particles to detect wind.

By selectively knocking out subsets of neurons, Anderson's graduate student Suzuko Yorozu was able to show that Johnston's organ - an area in a fruit fly antenna where sound detection is known to occur - does indeed contain at least two entirely separate groups of neurons.

"The sound-sensitive neurons are preferentially activated by small movements of the antenna that are oscillatory in nature, firing only when the antenna twists, and turn off quickly," said Anderson.

"The neurons that respond to wind, on the other hand, turn on when the antenna is pushed by air flow, and they stay on until the wind stops blowing," he added. (ANI)