"Taxonomists have been arguing about these things for decades, and people kept coming at this with one data set after another," Cunningham said. This latest study has created a fuller picture of the arthropod family tree by using more species and more genes, he said.
Beginning in 2001, Jeffrey Shultz, an associate professor of entomology at Maryland, led the efforts to figure out which species needed to be sequenced for a robust comparison, and then to round up suitable specimens of each. The study included nematodes, scorpions, dragonflies, barnacles, copepods and centipedes.
Remipedes, one of the two species of Xenocarida in the study, had to be fetched from partially submerged limestone caves in the Yucatan Peninsula and preserved just so. Bitty creatures called mystacocarids that live between grains of sand were captured by the Natural History Museum's Regina Wetzer, using a microscope on a Massachusetts beach.
Once assembled, the 75 species were then stripped down to their DNA for a painstaking search to find genetic sequences that would appear across all arthropods, enabling statistical comparisons.
The lab of Jerome Regier at Maryland's Center for Biosystems Research combed through 2,500 different combinations of PCR primers to find 62 protein-coding gene sequences that could be compared across all 75 species. Regier was an early proponent of using protein coding genes to sort out the arthropod tree, while most other researchers were using relatively less complex analyses from the DNA found in ribosomes and mitochondria.
The researchers ran four different statistical approaches, including two new ones invented at Maryland, "and they all came up with the same answer," Cunningham
|Contact: Karl Leif Bates|