Sand dollars clone themselves when they sense danger

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Scientists from North America have discovered that some animals can clone themselves to escape a potential attack by fish predators.

Dawn Vaughn and Richard Strathmann from the University of Washington found that four day old larval Sand dollars (Dendraster excentricus) would produce clones within 24 hours of being exposed to fish mucus - the cue to a potential predator.

Sand dollars, which are closely related to sea urchins, live on the intertidal and subtidal ocean floor and are named after their round flat shape, similar to a large coin.

During breeding season, both sexes release their gametes (sperm and eggs) into the water where they fuse with that of the opposite sex and form free swimming larvae.

These larvae undergo several stages of metamorphosis before they reach their final form. Females can produce up to 350,000 eggs per year.

Starry flounders, Platichthys stellatus, are a common predator of sand dollars.

Cloning occurred in all treatments containing fish mucus and the buds detached to form larvae smaller than un-cloned larvae. It is thought that by forming two smaller, less detectable organisms, the larvae provided itself with a temporary escape from predation.

"If you are eaten, but the smaller version of you survives, you're still a winner from an evolutionary standpoint," said Dawn Vaughn in the Seattle Times.

Although this process may be slow compared to the attack of a fish, it is also in response to the ~presence of fish not an actual attack. Adult sand dollars are unable to assess the risks faced by their planktonic offspring and thus adjust egg size.

Vaughn and Strathmann hypothesize that instead larvae may use information about potential risk factors to adjust their size by cloning.

This is the first time that cloning has ever been seen in echinoderms in response to anything other than food and temperature.

Common predators of the sand dollar include the California sheephead (Semicossyphus pulcher), the Starry flounder (Platichthys stellatus) and the Pink sea star (Pisaster brevispinus).

For more information see: Vaughn D and R Strathmann (2008) - Predators induce cloning in Echinoderm larvae. Science, Vol 319 14 March 2008 pp 1503.