Meeting Abstract

108.2  Sunday, Jan. 6  Fixational eye movements in the earliest stage of metazoan evolution BIELECKI, J*; GARM , A; University of Copenhagen jbielecki@bio.ku.dk

Fixational eye movements in vertebrate vision prevent sensory adaptation by refreshing the retinal image. Without fixational eye movements an animal would be rendered blind during visual fixation until the time when the eyes were moved voluntarily or the world moved in front of them. Box jellyfish face the same sensory adaptation problem as vertebrates and a counter strategy is necessary to prevent image fading, but unlike vertebrates these animals do not have motor control of their eyes. Here we present the first evidence that vertebrate fixational eye movements have evolutionary parallels in Cnidarians, the first phylum to develop a central nervous system. We have proven that the bell contractions in the box jellyfish Tripedalia cystophora induce a swinging of the eye-carrying rhopalia which, in amplitude and duration, matches the spatio-temporal resolution of the lens eyes. Video recordings of free swimming and tethered animals determined the spatio-temporal relationship between the rhopalial swinging and the visual physiology of T. cystophora, and the findings were further confirmed by performing extracellular electrophysiological recordings on transected rhopalia exposed to comparable visual stimuli in vitro.