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Genes point to common origin for insects, crustaceans

Genes point to common origin for insects, crustaceans

Summary

The discovery of a common genetic circuit for limb formation in arthropods is not only important for developmental biology, but also holds promise as an important new window to the past.

For more than a century, scientists have debated the family tree of the arthropods, the largest and most diverse division of the animal kingdom. Now scientists have found genetic evidence that all arthropods--from the lowly millipede to the gastronomically revered lobster--probably have a common ancestor.

The discovery of a common genetic circuit for limb formation in arthropods is not only important for developmental biology, but also holds promise as an important new window to the past.

In the November 24 issue of the journal Science, researchers in the laboratory of Sean Carroll at the Howard Hughes Medical Institute at the University of Wisconsin at Madison describe the discovery of a common set of genes that govern limb formation among arthropods, including insects, crustaceans, spiders, centipedes and millipedes.

"This is a new way of looking at evolution. The arthropod fossil record has a lot of missing links," said the study's lead author Grace Panganiban. "The record is not clear about what evolved into what. Here, at the molecular level, we can see the tracks of evolution."

The findings, said Panganiban, constitute new evidence that arthropods--which include tens of thousands of distinct species of animals--probably arose millions of years ago from a single common ancestor. "This is not a new idea, but it is one that has been argued about for a long time," said Panganiban.

The newly discovered genes are essentially the same in all arthropods examined, despite the wide range of body plans. Each species seems to use the genes in different ways to build its own unique body structure.

According to Panganiban, the genes that guide an animal's development can be reengaged in evolution to build on a successful body architecture. "In an evolutionary context, it seems that some genetic circuits are so useful they can be turned to making new things," she said. "It is easier to modify and reuse an existing genetic program than to create a new one. A branched limb, a leg or antenna, for example, is a duplicate and modification of a limb that's unbranched," said Panganiban.

Scientists are still unsure what the "mother of all arthropods" looked like. They suspect it was worm-like and lacked the exterior skeleton that is a hallmark of the arthropod family. But whatever that animal looked like, said Panganiban, it must have had these genes and they were acting in a coordinated way.

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