Abstract
We have a growing understanding of the light-sensing organs and light-influenced behaviours of animals with distributed visual systems, but we have yet to learn how these animals convert visual input into behavioural output. It has been suggested they consolidate visual information early in their sensory-motor pathways, resulting in them being able to detect visual cues (spatial resolution) without being able to locate them (spatial vision). To explore how an animal with dozens of eyes processes visual information, we analysed the responses of the bay scallop Argopecten irradians to both static and rotating visual stimuli. We found A. irradians distinguish between static visual stimuli in different locations by directing their sensory tentacles towards them and were more likely to point their extended tentacles towards larger visual stimuli. We also found that scallops track rotating stimuli with individual tentacles and with rotating waves of tentacle extension. Our results show, to our knowledge for the first time that scallops have both spatial resolution and spatial vision, indicating their sensory-motor circuits include neural representations of their visual surroundings. Exploring a wide range of animals with distributed visual systems will help us learn the different ways non-cephalized animals convert sensory input into behavioural output.
Highlights
A diverse set of invertebrates have many separate light-sensing organs distributed across their bodies
The light-sensing organs that contribute to these distributed visual systems range from pigment-shielded photoreceptors like those of the brittle star Ophiocoma [1], to eyespots like those of chitons such as Chiton [2], to compound eyes like those of sabellid and serpulid fan worms [3], to camera-type eyes like those of cubozoans such as Tripedalia [4] and chitons such as Acanthopleura [5,6]
Extracting spatial information from visual input is thought to require a brain, so it has been hypothesized that animals with distributed visual systems consolidate visual information early in their sensory-motor pathways [16]
Summary
A diverse set of invertebrates have many separate light-sensing organs distributed across their bodies. In our first experiment with static visual stimuli, we recorded the responses of scallops (n = 21) to five treatments These included a control treatment consisting of an isoluminant white stimulus and four experimental treatments in which we presented a single black stripe with an angular width of 24° (as measured from the centre of the behavioural arena). In our second experiment with static visual stimuli, we recorded the responses of scallops (n = 21) to four treatments These included a control treatment consisting of an isoluminant white stimulus and three experimental treatments in which we presented a single black stripe to the ventral sides (0°) of test animals. We transformed the vectors of mean direction (ɸ1) and concentration parameter (κ1) into Cartesian coordinates, which allowed us to quantify and plot how the circular distribution of relative tentacle lengths changed over the time course of trials
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