Seashell pattern offers clue to evolution of nervous systems

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When looking to discover the evolution of ancient nervous systems, you wouldn't expect the answer to lay in the colour of a mollusc shell, but recent research shows this may actually be the case.

Researchers studying 19 species of the predatory sea snail, Conus, researchers from University of Pittsburgh and the University of California believe they have managed to demonstrate it is possible by using mathematic modelling.

"There is no evolutionary record of nervous systems, but what you're seeing on the surface of seashells is a space-time record, like the recording of brain-wave activity in an electroencephalogram (EEG)," said project co-investigator G. Bard Ermentrout, Pitt Distinguished University Professor of Computational Biology and a professor in the Kenneth P. Dietrich School of Arts and Sciences' Department of Mathematics.

Seashell patterns differ significantly amongst Conus species, and the complex patterns add to the difficulty of characterising any similarities and differences which compounds the issue of describing the evolution of pigmentation patterns and how natural selection might affect those patterns.

The researchers attempt to tackle this problem by combining models based on natural evolutionary relationships with a realistic developmental model that can generate pigmentation patterns of the shells of the various Conus species.

By developing equations and a neural model for the formation of shell pigmentation patterns, the researchers were able to use a computer to simulate the patterns on shells.

The study has allowed researchers to estimate the shell pigmentation patterns of the ancestral species of Conus, identifying lineages where one or more parameters have evolved rapidly and measuring the degree of how different parameters correlate with evolutionary development and history of the organisms. As the parameters are saying something about the circuitry of the molluscs’ nervous system, there now exists an indirect way of studying the evolution of a simple nervous system.

"We've found that some aspects of the nervous system have remained quite stable over time, while there is a rapid evolution of other portions," said Ermentrout. 

"In the future, we hope to use similar ideas to understand other pattern-forming systems that are controlled by the nervous system," Ermentrout added. "For instance, we would really like to develop models for some of the cephalopods like the cuttlefish and the octopus, which are able to change patterns on their skin in an instant."

For further information see the open-access paper: Zhenqiang Gong, Nichilos J. Matzke, Bard Ermentrout, Dawn Song, Jann E. Vendetti, Montgomery Slatkin, and George Oster
PNAS Plus: Evolution of patterns on Conus shells
PNAS 2012 : 1119859109v1-201119859.

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