Date Published: June 13, 2018
Publisher: Public Library of Science
Author(s): Alexander Liberzon, Kyra Harrington, Nimrod Daniel, Roi Gurka, Ally Harari, Gregory Zilman, Francois G. Schmitt.
Some female moths attract male moths by emitting series of pulses of pheromone filaments propagating downwind. The turbulent nature of the wind creates a complex flow environment, and causes the filaments to propagate in the form of patches with varying concentration distributions. Inspired by moth navigation capabilities, we propose a navigation strategy that enables a flier to locate an upwind pulsating odor source in a windy environment using a single threshold-based detection sensor. This optomotor anemotaxis strategy is constructed based on the physical properties of the turbulent flow carrying discrete puffs of odor and does not involve learning, memory, complex decision making or statistical methods. We suggest that in turbulent plumes from a pulsating point source, an instantaneously measurable quantity referred as a “puff crossing time”, improves the success rate as compared to the navigation strategies based on temporally regular zigzags due to intermittent contact, or an “internal counter”, that do not use this information. Using computer simulations of fliers navigating in turbulent plumes of the pulsating point source for varying flow parameters such as turbulent intensities, plume meandering and wind gusts, we obtained statistics of navigation paths towards the pheromone sources. We quantified the probability of a successful navigation as well as the flight parameters such as the time spent searching and the total flight time, with respect to different turbulent intensities, meandering or gusts. The concepts learned using this model may help to design odor-based navigation of miniature airborne autonomous vehicles.
Female arctiid moths have been shown to release pulsed pheromone signals to attract male moths [1, 2] whereas various species of moths have been shown to perceive pulsed pheromone signals [3–8]. Successful mating requires the male moth to find the female within a time constraint, i.e. before the female stops emitting the pheromone and before other males find her. It is known that male moths can reach conspecific females from a long distance, overcoming obstacles such as forests or canopies [9, 10]. Moths sense the pheromone via chemo-receptors on their antennae [11–13]. If the chemical structure of the pheromone triggers the olfactory receptors in the moth antennae and is judged to be a sufficiently high quality signal [14, 15], the male will than navigate towards the female. Along the path, the male moth has to follow the pheromone cue which is subjected to windy environment and under various turbulent conditions.
In order to test the efficiency of the proposed strategy we implement numerical simulations based on two models: the odor dispersion in the atmosphere emitted from a pulsating point source and a algorithm used by a flier to navigate to the source. First, we simulated the odor dispersion in the Lagrangian framework. The odor patches are released from a point source at a constant pulsing rate. The patches are convected and dispersed in space and time due to the mean flow and we simulated the effects of turbulence, meandering and gusts as described below. Similarly to the previous studies [26, 44, 46] we use a highly idealized model of the dispersion of a scalar field in a turbulent flow. The flow is comprised of a mean flow, while turbulence, meandering, and gusts are modeled as linearly added signals without solving fluid dynamics equations. The simplicity reduces the computational cost of collecting statistics without resolving the real complexity of turbulent flows. Multiple fliers at rest are positioned at random locations downstream from the source. When one of the dispersed patches arrives at a flier location the navigation simulation starts according to the algorithm described in the following section.
The aim of our work was to develop a bio-inspired algorithm to search for a pulsating source of an odor (i.e. chemical substance) in a turbulent environment. A patchy turbulent plume containing odor parcels is simulated as described by the Lagrangian model in Eq 1. The trajectories (flight paths) of numerous fliers in generated turbulent fields of odor parcels are calculated using the developed navigation algorithm, presented in Fig 3.
A bio-inspired algorithm is developed for the navigation of a self-propelled agent towards a pulsating source of a scalar, convected in a turbulent flow. The algorithm is general and could equally apply to any fluid, for instance for water convected concentration of a fluorescent dye and the navigation of a self-propelled swimmer, however in the present work we focused on parameters relevant for airborne plumes of odor. The flier sensory system is assumed to be simple and can only detect the presence of odor above a certain concentration level. The model does not require a stereoscopic (two antennae) or additional (e.g. wind velocity and direction) measurement sensory system, neither previous knowledge or information obtained during the previous search history. We built the model based on the physics of a plume from a pulsating source, in which the size and distance between the puffs are related to each other through properties of a turbulent flow. Therefore, it is possible that the size of the puffs provides the flier with sufficient information in order to robustly locate the source in this complex environment with ample turbulence intensity. We modeled the puffs using a Lagrangian model in Eq 1.