Date of Award

6-2020

Document Type

Union College Only

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Robert Olberg

Keywords

Anax junius, Target Selective Descending Neurons, MDT3, DIT3, looming stimuli, predator escape, wing pronation and supination

Abstract

The behavioral wing responses of the dragonfly (Anax) to small moving objects such as insect prey are governed by 8 large visual neurons: “Target-Selective” Descending Neurons (TSDNs). These target detectors descend from the brain to the thoracic ganglia and serve to direct turning responses of the wings, specifically wing twisting (supination and pronation), and elevation and depression. Of the eight TSDNs, MDT3 and DIT3 are excited in response to looming stimuli. I hypothesize the wing adjustments serve to turn the dragonfly toward and eventually capture its moving prey.

In this study, I recorded the behavioral responses to simulated looming visual objects. A small black circle on a white background served as the stimulus which expanded with a time course to mimic a physical approaching object. The observation of the change in wing angles and elevation was video-recorded at 240 frames per second. Two markings were made on each wing to digitize the change in elevation and angle of the wings. Preliminary results indicate TSDNs are activated and produce wing movements at the start of target loom and continue after target contact time. The greatest wing response occurs within about 100 ms of virtual contact, timing that agrees with the responses of the target neurons to the same visual stimuli. The relative early response suggests that these wing movements were not triggered by the change in screen illumination, most of which occurred in the final 20 ms. I consider whether these wing movements constitute an upsweep in flight to capture prey or an evasive maneuver to avoid collision.

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