Friday, 16 January 2009

Seeing ‘eye-to-eye’

The flatfish (namely the sole, plaice and halibut), named for the shape of its body, is a remarkable fish I only recently heard about. What is so interesting about this creature is that the young flatfish starts off ‘normal’ with its eyes placed on both sides of its body (think of a typical looking fish) and a symmetrical skull. But, as the fish rapidly develops into an adult, one eye migrates from one side of its body close to the other eye and the skull becomes asymmetrical! At this point, the body of the flatfish remains the same but both eyes are on one side – named the ‘eyed’ side, as opposed to the ‘blind’ side. For a long time, evolutionary biologists speculated the origin and asymmetrical nature of the flatfish but with no conclusive evidence. Some biologists proposed the asymmetrical flatfish arose through natural section whilst others proposed the fish arose through evolutionary leaps - a process known as 'saltation'. However in 2008, Dr Matt Friedman became the first scientist to provide the most conclusive evidence of the origin of the asymmetrical nature of the flatfish. Dr Friedman was given permission to study 45 million year-old fish fossils using computer tomography imaging which lead to the finding of an ‘intermediate’ fish which had an eye on either side of its body but with an asymmetrical skull. This was the ‘intermediate’ fish which all evolutionary biologists had been looking for. Interestingly, one eye of this intermediate fish was found to be normal whilst the other eye was a squinting eye.
A good image of a flatfish can be found here. An explanation for the migration of the flatfish eye (from an evolutionary point-of-view) is presented by Richard Dawkins in the YouTube clip here.

(1) Janvier P (2008) Squint of the fossil flatfish. Nature. 454. p169-170.

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