Mollusks taste memories to build shells(th Meinhardt's chemical model which hypo...)
th Meinhardt's chemical model, which hypothesized reactions among chemicals diffusing through the snail shell, is that it required different chemical reactions to produce each shell pattern.
"Our real contribution is not reproducing the patterns, but showing that the nervous system can do it with one equation based on the principle discovered by Ernst Mach in the 1860s," Oster said.
Striped shells are the easiest to explain with this neural network model. A pigment-secreting cell inhibits secretion of pigment by neighboring cells but not itself, so that the same pattern is repeated day after day, yielding a stripe. Similarly, if one cell pumps up calcium carbonate secretion while depressing secretion by surrounding cells, ridges result. Interestingly, the stripes or ridges split naturally as the shell grows, a mathematical necessity because the size of the inhibition area remains the same as the shell's edge grows.
Bands parallel to the growing edge can be explained by inhibition of future activity. Pigment secreted on one day can inhibit secreting cells for a few days, resulting in an on/off pattern that produces a series of bands.
The most interesting patterns, however, are waves of activity that interfere to produce zigzags, diamonds, chevrons, arrowheads and a host of other shapes. These come about when a pigment inhibits future secretion at that site but excites secretion in surrounding cells. The pigment thus moves laterally on successive days, producing the equivalent of a traveling wave.
Ironically, most sea snails don't care a whit about their shell pattern. They are buried in the mud of the seafloor where their patterns are hidden even from potential mates.
"The pigment is a cue to get the mantle in register so it builds the right shaped shell, and is only an epiphenomenon reflecting neural activity," Oster said. "It is incidental to the snail."
"There is no strong selective pressure to drive p
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| Contact: Robert Sanders rsanders@berkeley.edu 510-643-6998 University of California - Berkeley Source:Eurekalert |
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