Snails Shed Shells in One Fell Swoop: Common Evolutionary Step among Mollusks Likely a Leap

Article excerpt

Evolution doesn't have to operate at a snail's pace, even for snails. In recent experiments designed to simulate the evolutionary transition that produced slugs, researchers exposed baby snails to the metal platinum, causing the animals to develop without external shells.

The simple experiments illustrate how a big leap in the history of animal body plans might have occurred. The research also reopens a can of worms concerning the development and evolution of an entire class of shelled creatures.

Scientists reared common aquarium snails in petri dishes containing varying concentrations of platinum. At certain exposures, all of the roughly 80 percent of snails that survived were shellless, Heinz Kohler of the University of Tubingen in Germany and his colleagues report in the September-October Evolution & Development. The researchers posit that the platinum is causing effects similar to the genetic mutation that turned off shell production in some ancient snails, paving the way for their slug descendants.

"This shows that you can get really dramatic changes that could be similar to the genetic mutations that drive evolution, without worrying about doing everything in small incremental steps," says Roger Croll of Dalhousie University in Halifax, Nova Scotia.

Evidence suggests that transitions from having a concrete outer shell to a greatly reduced internal one have happened numerous times in evolution. Such losses or gains occurred repeatedly within the Mollusca, an enormous group that includes clams, oysters, squid, octopuses and of course the gastropods--snails and slugs. …