A research team led by a Brown professor has shed new light on the evolutionary history of bilateral organisms. In a study published last week, the team, led by Assistant Professor of Biology Casey Dunn, used a San Diego supercomputer and new DNA sequencing techniques to establish Acoelomorpha flatworms as our most distant bilateral relatives.
This collection of tiny, soft-bodied worms has puzzled researchers for decades. Like humans, flatworms are bilateral: Their body plans are symmetric. Scientists had struggled, however, to determine just how closely these flatworms are related to us and to all other bilateral animals.
The team's research proved that these flatworms represent the first creatures to split from a long-dead ancestor common to all bilateral animals. Though previous researchers had posited that Acoelomorpha might have been the first to branch off from the bilateral group, no one had ever marshaled enough data to make a definitive statement.
The team, which included 17 researchers from six different countries, used a technique known as expressed sequence tags to examine 1,487 genes — ten times more than previous studies of Acoelomorpha's ancestry. In order to analyze such a large number of genes, the team needed new software, which was written expressly for the study. The researchers also needed the help of the supercomputer, which logged more than 2.25 million processor hours on the project.
When the study began, the researchers knew the topic was a difficult one. In fact, that was why they chose it, Dunn said. Previous studies had indicated that Acoelomorpha would be the "hardest (animals) to place," he said.
Because the researchers planned to use new computing technology in such an unprecedented way, they wanted a difficult problem, Dunn said, to demonstrate the power of the new tools.
Understanding the evolutionary tree is crucial to understanding similarities and differences between groups of animals, he said. The field has expanded in recent years due to rapid declines in the cost of DNA sequencing.
"Sequencing prices probably dropped more than a hundred-fold from the beginning to the end of the study," Dunn said.
Sequencing used to be labor-intensive lab work with more than a little bit of "guesswork," Dunn said. Now, new technologies allow scientists to sequence enormous numbers of genes, while powerful software helps them select those worthy of further study, he said.
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