Three-dimensional spatial learning and space use by cuttlefish (#460)
The world is three-dimensional, hence even surface-bound animals need to learn spatial information in the vertical plane. However, a difference exists in the way 3D-moving species, as fish, learn 3D spatial information as compared to surface-bound species, which prioritize the horizontal dimension and encode it with higher resolution. Cuttlefish have remarkable spatial abilities and although can move freely in a volume, they are mostly benthic, making them an interesting model for the study of three-dimensional navigation. We tested the relative preference of vertical vs. horizontal information in Sepia officinalis cuttlefish. Animals were trained to approach one of two visual cues arranged in a 45° configuration, and then tested with an exclusively horizontal, an exclusively vertical and an opposite 45° configuration. We found that cuttlefish can separately encode the horizontal and vertical components of space and prefer vertical over horizontal information. Since little is known about the navigational strategies of cuttlefish and whether or not they equally move in all dimensions, we tested whether cuttlefish would prefer to swim over or around barriers to reach a shelter. We trained Sepia prashadi cuttlefish to reach a shelter at the opposite side of a tank. Afterwards, rock barriers were placed between the starting point and the shelter. We showed that cuttlefish prefer to move horizontally when a direct route is available close to the ground; however when faced with significant obstacles they can and would preferentially choose a more direct path requiring a vertical movement over a longer exclusively horizontal path. Therefore, vertical displacement in cuttlefish might be more important than previously thought. This together with the increased predation risk of moving upwards in the water column might contribute to the greater salience of vertical information reported for cuttlefish.
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