Odor Tracking in Aquatic Animals

Panayiota Siskos ’23

Animals use intermittent chemical cues to help avoid predators, find mates, and find food. The speed at which some animals forage shows that more instantaneous sensory feedback is also used. Lobsters have multiple sensors to gather information, including sensilla on antennules with chemosensory cells that detect chemical concentrations and mechanosensory cells that find flow and direction. Several are conditionally rhythmically active and are called “bursting” primary olfactory receptor neurons. Their response depends on both concentration of the odor and when it arrives relative to their bursting cycle. Different odorant encounter intervals cause various subsets of bORNs that encode a range of time intervals, allowing them to be able to accurately encode intervals between encounters. Instantaneity of temporal and spatial distribution of odors is dependent on distance from the source and intensity of turbulence, as well as the topography. The hypothesis addressed in this study asks what the spatial and temporal structure of plume intermittency of a turbulent landscape is and what are search implications to distinguish plume structure by intermittency encoding.

A hydrodynamic model and plume was simulated. Intermittency was defined as the number of concentration spikes above a threshold concentration over a given period. Since intermittency is inversely related to time, an area of plume with high intermittency means it has short periods between concentration spikes. Two models of antennules were made by two point sensors and a movement decision was made to be consistent with that of P. argus. The strategies used were the chemo tropotactic search strategy and the incorporated intermittency of odorant encounters.

Threshold concentration had a strong influence on intermittency measured at specific points. The plume edge was more intermittent than the inside or outside of the plume, and the threshold was enough to mark the plume edge of the length simulated. A similar spatial pattern for intermittency was observed. The edge of the plume was prominent in concentration sampling rates and supports that plume intermittency is detectable and has useful information in sampling the environment. Results convey that plume intermittency can be detected reliably when simulated odorants are sampled on the order of seconds, and provides optimal information when animals search along the plume edge. Search algorithm with intermittency of odorant encounters tracked plume edge, while gradient search behavior moved to the centerline. This study sheds light on bursting primary olfactory receptor neurons, which are not as well-known as tonically active primary olfactory receptor neurons. New directions for study are necessary to better understand the mechanisms of adaptation in bORNs. Also, more work is required to identify the range of similar flow regimes the result may be applied to.

Works Cited:

[1] B. Michaelis, et al. , Odor tracking in aquatic organisms: the importance of temporal and spatial intermittency of the turbulent plume. scientific reports 10, (2020). doi: https://doi.org/10.1038/s41598-020-64766-y 

[2] Image retrieved from: https://unsplash.com/photos/j1auYOfmB-g 

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