Nature is full of examples of creatures that try to look as big as possible in an effort to scare away potential predators. But to avoid being eaten alive the larvae of sand dollars appear to have a different strategy, in a way exchanging a dollar for a couple of dimes.
University of Washington biologists have found that 4-day-old sand dollar larvae created clones of themselves within 24 hours of being exposed to fish mucous, a cue that predators are near. In each case, the cloning process resulted in a small new larva and the original larva substantially smaller than it had been.
The larvae responded to the general threat of predation rather than the immediate possibility of predator attack, said Dawn Vaughn, a UW biology doctoral student at the University of Washington's Friday Harbor Laboratories. The process caused the original larvae to shrink from about 300 microns, or about a hundredth of an inch, to about half that size, and the new larvae were even smaller.
"We think that by reducing their size they also reduce their visibility to predators," said Vaughn, who is lead author of a paper describing the work in the March 14 edition of Science.
Larval cloning has been observed previously among echinoderms, which include about 7,000 species of sea creatures, including starfish, sea urchins and sand dollars. However, this is the first time cloning by larvae has been seen as a survival mechanism in the face of possible predation.
The larvae of the sand dollar species Dendraster excentricus float as part of the plankton at various levels in open water, feeding as they slowly grow. After six weeks, the larvae reach a size of perhaps a three-hundredths of an inch and then settle to the ocean floor to finish developing to adulthood.
But as they float, the larvae are neither fast nor agile and have a high mortality rate, easily devoured by fish. Vaughn exposed 4-day-old larvae to fish mucous to see how th
|Contact: Vince Stricherz|
University of Washington