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2016 ; 13
(1
): 41
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Crown-of-thorns starfish have true image forming vision
#MMPMID27605999
Petie R
; Garm A
; Hall MR
Front Zool
2016[]; 13
(1
): 41
PMID27605999
show ga
BACKGROUND: Photoreceptors have evolved numerous times giving organisms the
ability to detect light and respond to specific visual stimuli. Studies into the
visual abilities of the Asteroidea (Echinodermata) have recently shown that
species within this class have a more developed visual sense than previously
thought and it has been demonstrated that starfish use visual information for
orientation within their habitat. Whereas image forming eyes have been suggested
for starfish, direct experimental proof of true spatial vision has not yet been
obtained. RESULTS: The behavioural response of the coral reef inhabiting
crown-of-thorns starfish (Acanthaster planci) was tested in controlled aquarium
experiments using an array of stimuli to examine their visual performance. We
presented starfish with various black-and-white shapes against a mid-intensity
grey background, designed such that the animals would need to possess true
spatial vision to detect these shapes. Starfish responded to black-and-white
rectangles, but no directional response was found to black-and-white circles,
despite equal areas of black and white. Additionally, we confirmed that starfish
were attracted to black circles on a white background when the visual angle is
larger than 14°. When changing the grey tone of the largest circle from black to
white, we found responses to contrasts of 0.5 and up. The starfish were attracted
to the dark area's of the visual stimuli and were found to be both attracted and
repelled by the visual targets. CONCLUSIONS: For crown-of-thorns starfish, visual
cues are essential for close range orientation towards objects, such as coral
boulders, in the wild. These visually guided behaviours can be replicated in
aquarium conditions. Our observation that crown-of-thorns starfish respond to
black-and-white shapes on a mid-intensity grey background is the first direct
proof of true spatial vision in starfish and in the phylum Echinodermata.
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