Sensing & Navigating Naturalistic Odor Plumes

Insects find food, mates, and egg-laying sites by tracking odor plumes swept from their sources by complex wind patterns. Previous studies have shown that insects navigate odor signals to their sources by surging upwind when they detect odor and casting cross- or downwind when the signal is lost. These strategies lead to reliable odor encounters in relatively regular plumes, such as streaming odor ribbons. Much less is understood about behavioral strategies in intermittent plumes, where the location and timing of odor encounters (whiffs) are less predictable. The timing and history dependence of whiffs could provide important information to the navigator, but it has been challenging to connect behaviors to individual odor encounters because it is difficult to visualize odors and behavior simultaneously. Here, I imaged for the first time both intermittent odor plumes and the movements of freely-walking flies navigating them, allowing us to quantify behavior in response to whiffs. We found that walking flies navigate these unpredictable plumes by using whiff timing to modulate the rate of stochastic transitions between turns, stops, and walks. Turns are random, stereotyped saccades whose direction is biased upwind by whiff frequency. Stop decisions depend on the time since the most recent whiff, while walk decisions are made by accumulating evidence from whiffs over time. Drosophila and other animals precisely encode whiff timing within their olfactory circuit, and our findings reveal how they leverage this sensory precision to navigate the natural world.

Host: Steve Hagen