If you hear that a sea creature splits after sensing a foe, that may not be just a figure of speech for it swimming away—it may literally split in two. That is the case for the sand dollar (Dendraster excentricus), a spiny critter related to starfish. When the larvae detect mucus from nearby predatory fish, they start cloning themselves, asexually reproducing within 24 hours. Although cloning is slow compared with a fish attack, if the larvae get enough of a head start, it may boost their chances of evading detection. That is because the clones are about two-thirds the typical length of the original. Many animals clone themselves, but scientists thought that the process was generally driven solely by growth and reproduction, not by a need to defend against carnivores. The scientists, who published their findings in the March 14 Science, speculate that cloning in response to predators may be found where small size confers a safety advantage.
This article was originally published with the title "Split Defense" in Scientific American 298, 5, 38 (May 2008)