University of Washington biologists have recently found out that sand dollar larvae created clones of themselves when 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. This decrease in size can effectively make them invisible to the predatory fish, thus prevent them being killed by the predators.
So have you heard of Sand Dollar? Please don’t be mistaken it as a dollar made of sand =D.
Sand dollars (Dendraster Excentricus) are from the class of marine animals known as Echinoids, spiny skinned creatures. They are 75 mm wide to 6 mm high, light gray, brown to dark purple; disk-shaped, flat upper and lower surfaces are covered by fine, spiny tube feet; central mouth on lower surface.
I believe many of you, like me, will be very curious and unsure of what a sand dollar is. Below are some of the pictures of both adult and baby sand dollar.
Baby sand dollar in the process of cloning.
Dendraster Excentricus
Sand dollars can also be found in Chek Jawa in Singapore. The common sand dollars are Cake sand dollar and Keyhole sand dollar.
Interesting Points to Highlight:
- Studies have shown that the larvae of Echinoderms such as sea urchins and starfish clone themselves for the purpose of asexual reproduction. However, in this case, the baby sand dollars were found cloning themselves in face of danger, as a defense mechanism.
- In nature, many animals do try to prevent being preyed on or scare their predators away by becoming bigger in size. Nevertheless, these baby sand dollars make themselves smaller so as to become invisible to the predators.
The baby sand dollars only clone themselves when they detect danger. The external stimuli that caused the defense mechanism in them is the chemical cues of the fish mucous emitted by the fish. Once they detect the potential threat from the predators, they will change in their shapes and clone into two. The question raised was whether these smaller larvae can survive through during their adulthood since they are obviously smaller than those which have never cloned before.
Websites:
http://www.wildsingapore.com/chekjawa/text/s620.htm
http://www.gma.org/Tidings/sanddollar.html
http://www.nwmarinelife.com/htmlswimmers/d_excentricus.html
References:
University of Washington (2008, March 14). Sand Dollar Larvae Use Cloning To 'Make Change,' Confound Predators. ScienceDaily. Retrieved March 19, 2008, from http://www.sciencedaily.com /releases/2008/03/080313143100.htm
University Of Alberta (2003, September 11). Young Sea Animals Clone Themselves—century-old Debate Halted. ScienceDaily. Retrieved March 19, 2008, from http://www.sciencedaily.com /releases/2003/09/030911072551.htm