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From seashell colors, a snapshot of evolution

U. PITTSBURGH (US) — Researchers studying 19 different sea snail species have used a new technique to model the pigmentation patterns of mollusk shells, a discovery that sheds light on how ancient nervous systems evolved.

“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),” says G. Bard Ermentrout, professor of computational biology at the University of Pittsburgh.

Seashells differ substantially between the closely related Conus species, and the complexity of the patterns makes it difficult to properly characterize their similarities and differences. It also has proven difficult to describe the evolution of pigmentation patterns or to draw inferences about how natural selection might affect them.

Now, however, scientists from the University of Pittsburgh and the University of California, Berkeley, have created mathematical equations and simulations to collect space-time information to reveal the evolution of ancient nervous systems through the analysis of seashell color patterns.

In a paper published online in the Proceedings of the National Academy of Sciences, Ermentrout and colleagues combined models based on natural evolutionary relationships with a realistic developmental model that can generate pigmentation patterns of the shells of the various Conus species.

In order for scientists at UC Berkeley to create simulations, Ermentrout and his collaborators developed equations and a neural model for the formation of the pigmentation patterns on shell surfaces.

With the equations in hand, Zhenquiang Gong, a UC Berkeley graduate student in engineering, used a computer to simulate the patterns on the shells, hand fitting the parameters to create a basic model for the patterns of a given species.

The findings have allowed researchers to estimate the shell pigmentation patterns of ancestral species, identify lineages in which one or more parameters have evolved rapidly, and measure the degree to which different parameters correlate with the evolutionary development and history of the organisms.

Since the parameters are telling the researchers something about the circuitry of the mollusks’ nervous system, this is an indirect way to study 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,” says Ermentrout.

“In the future, we hope to use similar ideas to understand other pattern-forming systems that are controlled by the nervous system. 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.”

The research was funded by the National Science provided funding.

More news from University of Pittsburgh: http://www.news.pitt.edu/

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