In today’s Academic Minute, Dr. Anders Garm of the University of Copenhagen reveals what starfish vision can teach us about the evolution of more complex eyes.
Anders Garm is an associate professor of biology at the University of Copenhagen where he studies vision in marine species such as starfish and jellyfish. His work has been widely published and he holds a Ph.D. from the University of Copenhagen.
Dr. Anders Garm – Starfish and Eye Evolution
The worlds oceans hold about 1500 species of starfish found from shallow costal waters to the deep sea. To most people they seem relatively doll with very little behaviour, but there is more to them than meets the eye. Most known starfish species possess a compound eye at the tip of each arm, which, except for the lack of lenses, resembles the compound eye of arthropods such as crabs and insects. It is about 0.5 mm wide, bright red and made of 150-200 optical units called ommatidia each assumed to provide a separate part of the image. Although the starfish compound eyes have been known for more than two centuries, no visually guided behaviour has ever been directly associated with their presence.
In a recent study we have studied the eyes and behaviour of the coral-reef-associated starfish Linckia laevigata. Our results show that even though the eyes are slow and color blind they are capable of true image formation with low resolution allowing only large objects to be seen. Through behavioural experiments we reveal that only specimens with intact vision can navigate back to their reef habitat when displaced, demonstrating that this is a visually guided behaviour. Blinded starfish still try to escape the sand flats in front of the reef where they will starve but they walk in a random direction. This is the first report of a function of the starfish eyes. Eyes supporting only low resolution vision, like the starfish eye, are believed to be an essential and early stage in eye evolution, preceding the high resolution vision required for detecting prey, predators and conspecifics. Our study helps to understand, therefore, for what purpose image forming eyes first evolved.