Menu

Javascript is not activated in your browser. This website needs javascript activated to work properly.
You are here

The sea urchin Diadema africanum uses low resolution vision to find shelter and deter enemies

Author:
  • John D. Kirwan
  • Michael J. Bok
  • Jochen Smolka
  • James J. Foster
  • José Carlos Hernández
  • Dan-Eric Nilsson
Publishing year: 2018-07-01
Language: English
Publication/Series: Journal of Experimental Biology
Volume: 221
Issue: 14
Document type: Journal article
Publisher: The Company of Biologists Ltd

Abstract english

Many sea urchins can detect light on their body surface and some species are reported to possess image-resolving vision. Here, we measure the spatial resolution of vision in the long-spined sea urchin Diadema africanum, using two different visual responses: a taxis towards dark objects and an alarm response of spine-pointing towards looming stimuli. For the taxis response we used visual stimuli, which were isoluminant to the background, to discriminate spatial vision from phototaxis. Individual animals were placed in the centre of a cylindrical arena under bright down-welling light, with stimuli of varying angular width placed on the arena wall at alternating directions from the centre. We tracked the direction of movement of individual animals in relation to the stimuli to determine whether the animals oriented towards the stimulus. We found that D. africanum responds by taxis towards isoluminant stimuli with a spatial resolution in the range of 29–69 deg. This corresponds to a theoretical acceptance angle of 38–89 deg, assuming a contrast threshold of 10%. The visual acuity of the alarm response of D. africanum was tested by exposing animals to different sized dark looming and appearing stimuli on a monitor. We found that D. africanum displays a spine-pointing response to appearing black circles of 13–25 deg angular width, corresponding to an acceptance angle of 60–116 deg, assuming the same contrast threshold as above.

Keywords

  • Zoology
  • Echinoidea
  • Photoreception
  • Sea urchin
  • Visual acuity
  • Visual response
  • Visually guided behaviour

Other

Published
  • Lund Vision Group
  • ISSN: 0022-0949
James Foster
E-mail: james [dot] foster [at] biol [dot] lu [dot] se

Postdoctoral fellow

Functional zoology

+46 46 222 95 82

B-B316

4