MacIver was inspired to think about these original concepts by the unusual animal he prefers to study: the black ghost knifefish, found in the murky waters of the Amazon River. The fish does not use a passive sensing system such as sight or hearing to hunt. Instead, the knifefish has an active sensing system: it generates a weak electric field all around its body, and sensors, also all around its body, register any perturbations. By fluttering a ribbon-like fin along the entire length of its body, the knifefish can swim both forward and backward to catch its prey, the water flea.
After developing their mathematical definitions of the volumes, the researchers applied them to the knifefish, using the plentiful data available on the animal. They coupled video analysis of prey capture behavior with computational modeling of the fishs electrosensory capabilities and let the simulations run for several weeks in a computer cluster operated by the Chicago Biomedical Consortium.
MacIver and his team are the first to quantify and compare in any animal the three-dimensional volumes for movement and sensation. They showed that the knifefish is truly omnidirectional in moving and sensing and discovered that the two volumes (stopping motor and sensory) are roughly equal, with sensory volume just a little greater than stopping motor volume. This places the knifefish in the reactive mode, critical if the fish wants to eat, and not collide with, its prey.
Our results reveal that the knifefish invests just enough energy into active sensing to detect prey in time to stop, said MacIver. They have evolved an amazing movement system to match their omnidirectional sensing skills -- they can move backwards and
|Contact: Megan Fellman|