If there's something strange in the neighborhood ... clone yourself. That's the philosophy of sand dollar larvae, which copy themselves when they sense predators are near.
Scientists exposed 4-day-old sand dollar larvae to fish mucus, a sign that danger is close. They found that the larvae created clones of themselves within 24 hours.
"It’s the first time we've seen anything clone itself in response to cues that predators are near," said researcher Dawn Vaughn, a biology doctoral student at the University of Washington's Friday Harbor Laboratories.
Sand dollar larvae are tiny globs that float along with plankton in the sea, an easy target for hungry fish. When they are 6 weeks old, they settle to the seafloor and eventually become adult sand dollars with their distinctive petal-patterned shells.
After being exposed to fish mucus, the larvae formed embryo-like buds that eventually detached and developed into new, genetically-identical larvae that were much smaller than the originals. The parent larvae were left smaller, too, measuring about half their beginning size.
Larvae that were not exposed to the fish mucus did not clone themselves.
The scientists think cloning may provide a double benefit to larvae facing danger. By doubling themselves, they have a second chance to ensure their genetic information survives even if one larva gets eaten.
Additionally, being smaller may be beneficial to larvae trying to hide from fish.
"Fish are visual predators and often choose their prey based on size," Vaughn told LiveScience. "You're apt to see something bigger. Based on past research, we're hypothesizing that small size protects larvae, but we have to test that."
Even if being tiny helps the larvae, they could suffer for it later as full-grown sand dollars that live on the sea floor. For many species, being bigger helps scare off predators. The researchers don't know yet if this is true for sand dollars.
"We're suggesting that that’s the tradeoff," Vaughn said. "You may reduce your vulnerability as a larva, but when you reach the sea floor, potentially small size ends up hurting you. But if you don't make it to the sea floor in the first place, it might be worth the tradeoff."
Cloning had previously been observed in sand dollar larvae in response to a greater availability of food or favorable temperatures, but never in response to danger.
Vaughn and her colleagues detail the findings in the March 14 issue of the journal Science.