HENRY, J.D.*; O’CARROLL, D.C.: What visual information do hawking dragonfly predators use to intercept prey?

Dragonflies are voracious predators that locate and intercept prey with astonishing accuracy. Many dragonflies (e.g. Corduliidae and Aeshnidae) are hawking predators, hunting while patrolling a territory. Dragonfly hunting is a visually guided behavior, utilizing large, highly acute eyes. Hawking dragonflies could use one or both of two mechanisms to extract visual information from their environment to determine prey location: (i) stereopsis and (ii) motion parallax. Stereopsis requires binocular overlap to determine object depth. Motion parallax uses relative image motion (due to motion of the viewer) to determine object distance; near objects will appear to move more quickly than far objects. Stereopsis would require an interneuron acting as a coincidence detector for movement in both halves of the small dorsal region of binocular overlap. Motion parallax would require integrating the output of two neurons that view the same region in space but are tuned to different velocities. To investigate which mechanism hawking dragonflies employ, we use intracellular recording and dye injection in the third optic ganglion (lobula) of Aeshnidae and Corduliidae. We find: (i) There are neurons that selectively respond to the motion of small targets. (ii) Neuroanatomical and physiological data indicate the presence of a binocular feature detecting neuron in the Corduliid Hemicordulia tau. (iii) There are at least three distinct classes of velocity tuning in target sensitive neurons (two classes have been found in Corduliids, three in Aeshnids). Data thus far support both models, indicating the potential for behavioral plasticity within the general strategy of being a hawking predator.