Near-surface wind variability over spatiotemporal scales relevant to plume tracking insects

Abstract

Odor plume tracking is an important biological process for many organisms, and flying insects have served as popular model systems for studying these behaviors both in the field and in lab settings. The shape and statistics of the airborne odor plumes that insects follow are largely governed by the wind that advects them. Prior atmospheric studies have investigated aspects of microscale wind patterns with an emphasis on characterizing pollution dispersion, enhancing weather prediction models, and for assessing wind energy potential. Here, we aim to characterize microscale wind dynamics through the lens of short-term ecological functions by focusing on spatial and temporal scales most relevant to an insect actively searching for an odor source. We collected and compared near-surface wind data across three distinct environments (sage steppe, forest, and urban) in locations across Northern Nevada. Our findings show that near-surface wind direction variability decreases with increasing wind speeds and increases in environments with greater surface complexity. Across environments, there is a strong correlation between the variability in wind speed (i.e. turbulence intensity) and wind direction (i.e. the standard deviation in wind direction). In some environments, the standard deviation in wind direction varied as much as 15 deg to 75 deg on time scales of 1-10 minutes. We draw insights between our findings and previous plume tracking experiments to provide a general intuition for future field research and guidance for wind tunnel experimental design. From our analyses, we hypothesize that there may be an ideal range of wind speeds and environment complexity in which insects will be most successful when tracking an odor plume to its source.

Wind Gates Olfaction Driven Search States in Free Flight

“…In nature however, the air or water surrounding an organism can be very still, and may not provide a reliable directional cue [Crall et al, 2017, Houle and van Breugel, 2023, Carvalho and Gonc ¸alves, 2020.…”

“…In nature however, the air or water surrounding an organism is rarely consistent, and can be very still or turbulent [Crall et al, 2017, Houle and van Breugel, 2023, Carvalho and Gonc ¸alves, 2020. How then should a flying organism track a plume when ambient flow is below detection thresholds?…”

“…However it is unclear whether cast and surge represents a one size fits all sensorimotor motif for successful plume tracking in flight, or if there are alternative search states which optimize successful plume tracking depending on the wind conditions. Both elements of cast and surge rely on a directional cue from the wind, but in nature the wind direction can shift on timescales relevant for plume tracking, or be very still 4,3,5 . To address this knowledge gap we focus on the extreme scenario, and ask a simple but deceptively complex question: what sensorimotor transformations underlay search in still air?…”

“…For both swimming and flying animals engaged in olfaction driven search, turning into the direction of oncoming wind or water current is often a critical first step 1, 2 . However, in nature, wind and water currents may not always provide a reliable directional cue 3,4,5 . It is unclear how organisms adjust their search strategies accordingly due to the challenges of separately controlling flow and chemical encounters.…”

“…For both swimming and flying animals engaged in olfactory search, turning into the direction of oncoming wind or water current is often a critical first step [Marsh et al, 1978, Carton and Montgomery, 2003]. However, in nature, fluid flow may be turbulent or very still [Crall et al, 2017, Houle and van Breugel, 2023, Carvalho and Gonçalves, 2020], and it is unclear how organisms adjust their search strategies accordingly due to the challenges of separately controlling flow and chemical encounters. Here, we use the genetic toolkit of Drosophila melanogaster , a model organism for olfaction [Benton, 2022], to develop an optogenetic paradigm to deliver temporally precise “virtual” olfactory experiences in free-flying animals while independently manipulating the wind conditions.…”