How to Build a Better Tree of Life
NEW IDEA / BY JOE KLOC / JULY 1, 2009
AN UNCONVENTIONAL APPROACH TO ANALYZING MOLECULAR SEQUENCES ALLOWS RESEARCHERS TO CONSTRUCT LARGER EVOLUTIONARY TREES.
Organizing the world’s species into branches on a phylogenetic tree is a major goal of biologists trying to understand how life evolved. DNA-sequencing technologies are providing them with more information than ever with which to accomplish this goal, but with less than 1 percent of all species currently placed in any kind of phylogeny, there is still much work to be done. In a recent paper in Science, researchers at the University of Texas at Austin introduced new tree-building software that could expand the tree of life and change our understanding of evolution.
One way to construct evolutionary trees is with software that compares and interprets discrepancies between the molecular sequences of different species using various statistical techniques. The robustness of the math driving these techniques largely determines the speed and accuracy of a given tree-building method. Thus taking a mathematically well-grounded approach to constructing evolutionary trees can limit a method’s scope. “The statisticians who have been developing these methods have been really trying to get the mathematics right,” explains Tandy Warnow, a phylogeneticist at the University of Texas at Austin. “And getting the mathematics right really does tend to limit you to small datasets.” Many programs are only fast enough to handle about 20 molecular sequences at a time—a paltry number considering the datasets biologists are trying to analyze are usually anywhere from a few hundred to a few thousand sequences.To find out just how slow these programs were, Warnow attempted to run them on a data set of 100 sequences. “They looked like they were not going to complete for months and months and months,” she says. Larger datasets, then, could take decades.
“There is a clear and desperate need for methods that compute phylogenetic trees much faster,” says Antonis Rokas, a biologist at Vanderbilt University, adding that scientists ultimately hope to build trees containing millions of species.
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