Odor Landscapes in Turbulent Environments

Abstract

International audienceThe olfactory system of male moths is exquisitely sensitive to pheromones emitted by females and transported in the environment by atmospheric turbulence. Moths respond to minute amounts of pheromones, and their behavior is sensitive to the fine-scale structure of turbulent plumes where pheromone concentration is detectible. The signal of pheromone whiffs is qualitatively known to be intermittent, yet quantitative characterization of its statistical properties is lacking. This challenging fluid dynamics problem is also relevant for entomology, neurobiology, and the technological design of olfactory stimulators aimed at reproducing physiological odor signals in well-controlled laboratory conditions. Here, we develop a Lagrangian approach to the transport of pheromones by turbulent flows and exploit it to predict the statistics of odor detection during olfactory searches. The theory yields explicit probability distributions for the intensity and the duration of pheromone detections, as well as their spacing in time. Predictions are favorably tested by using numerical simulations, laboratory experiments, and field data for the atmospheric surface layer. The resulting signal of odor detections lends itself to implementation with state-of-the-art technologies and quantifies the amount and the type of information that male moths can exploit during olfactory searches

Natural search algorithms as a bridge between organisms, evolution, and ecology

“…the physical and chemical environment that marine microbes experience in the ocean (17), the flow environment that influences search decisions of planktonic predators (33), and the physical structure and chemical composition of the odor plumes to which moths and other olfactory searchers respond (5,10,11,34,35). These studies notwithstanding, we have little quantitative information about the structure and spatiotemporal dynamics of the environments in which most organisms search, largely because of the difficulty of quantifying spatially and temporally varying cues in natural settings.…”

“…In wind-tunnel experiments with moths, odors that are pulsed in this natural frequency range cause strong firing responses in central olfactory neurons, and elicit stereotyped search behavior, whereas odors outside this range elicit weak responses at both the neural and behavioral levels. At greater distances from an odor source, pulses of odor are far more intermittent, yet moths and other insects are still able to distinguish relevant olfactory cues from noise and to use these cues to navigate (5). The neural mechanisms that underpin this long-range response to odors are still poorly understood, but quantitative characterization of odor landscapes has provided crucial clues (5,11).…”

“…At greater distances from an odor source, pulses of odor are far more intermittent, yet moths and other insects are still able to distinguish relevant olfactory cues from noise and to use these cues to navigate (5). The neural mechanisms that underpin this long-range response to odors are still poorly understood, but quantitative characterization of odor landscapes has provided crucial clues (5,11).…”

“…Mayer and his contemporaries, including Jean-Henri Fabre (2), initiated the study of what is now one of the most heavily investigated search algorithms in nature: the olfactory search strategies of insects. Over a century later, studies of how insects and other animals find odor targets have led to major discoveries about the structure and information contained within chemical plumes (3)(4)(5) and the properties of the nervous system that allow animals to extract and respond to that information in a complex and ever-changing landscape (6)(7)(8)(9)(10)(11).…”

Mice Develop Efficient Strategies for Foraging and Navigation Using Complex Natural Stimuli

“…Here, we leverage the advantages of controlled laboratory conditions to demonstrate that mice can make use of airborne odor cues to locate a source. The complexity of airborne odor plumes is well-documented [12], creating a rich and dynamic stimulus for odor-based navigation. Work using simplified odor cues has suggested that rodents may be able to measure odor gradients with just one or two sniffs [13,14].…”