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Dartmouth Prof. Studies Evolution in Worms

Biology professor Kevin Peterson, working with researchers from several institutions, has developed a breakthrough technique to study the evolutionary relationships between species. His research, published on Sept. 15 in the Proceedings of the Royal Society B, provides answers to long-standing questions about the evolution of segmented worms.

Peterson’s team — which included researchers from Yale University, North Carolina State University and the University of Lyon, France — examined whether certain segmented worm species share specific sequences of microRNA, which are short, non-coding genes. Worm — or annelid — species that share microRNA sequences are likely related evolutionarily.

Although earthworms, leeches, mollusks and peanut worms have long been considered part of the annelid family, the study found that all four organisms could not have developed from the same branch of the evolutionary tree.

Peterson’s team is the first to use microRNA to study the evolutionary relationship between species.

Peterson said that this is also the first high profile study that uses microRNA to clarify evolutionary lineage.

“This is our first big test case as to why microRNA has such potential utility to addressing problems that remain outstanding,” he said in an interview with The Dartmouth.

The relationship between annelids and other groups has been the subject of debate in the scientific community.

Studies of the organisms’ genomes have seemed to indicate that some species like mollusks developed from segmented worms.

The fossil record, however, contradicted these studies, and suggested that mollusk species developed before the last common ancestor of annelids, Peterson said.

“Despite 10 years of molecular sequence work, the picture just became more muddled,” he said. “We couldn’t resolve this part of the tree with traditional molecular methods.”

Peterson’s research agreed with the evidence derived from the fossil record, lending support to the idea that species like peanut worms should not be classified as annelids. Peterson’s findings also supported the fossil evidence that terrestrial segmented worms evolved from marine forms.

Peterson’s lab has been working with microRNA since 2005 and began to look at annelids using a new methodology in 2008.

“We had to actually totally change the way we did things in lab, and it required us to learn all kinds of new techniques,” he said.

Peterson is now working with microRNA to study the relationship between jawed and jawless fish, as well as sponge classification.

“We can use the same genes to work on pattern and process itself, which up until this point people have not been able to do,” Peterson said of using microRNAs in research.