Cincinnati - What's missing might turn out to be as important as what's actually there in uncovering the roots of the mammalian tree of life.
A team of biologists led by Mark Springer at the University of California, Riverside and including Ronald DeBry of the University of Cincinnati report in the Feb. 1 issue of Nature that an intensive analysis of DNA sequences provides strong support for a grouping Springer dubs "Afrotheria." The group includes a variety of placental mammals from elephants to elephant shrews. And add in aardvarks, manatees, and hyraxes to boot.
"One of the problems with mammal phylogenies is there hasn't been a lot known," explained DeBry. "We were searching for the basic outline of the tree of life."
Traditional phylogenies, or evolutionary trees, were based on fossil evidence and physical similarities. To complicate things further, there was a huge explosion of mammalian groups right after dinosaurs went extinct.
"Finding the base of the tree has been difficult," said DeBry. "There are lots and lots of questions."
Over the last 10 years, DNA studies have confirmed some patterns proposed by those studying fossil evidence and physical similarities. Other DNA studies turned up new and unexpected relationships. The picture quickly got muddier and muddier.
"What we needed was a BIG data set," said DeBry. "Our data set has six different genes and 8600 base pairs." Two of the genes are found in mitochondrial DNA. The other four are found in the chromosomes of the nucleus, including BRCA-1, commonly known as the breast cancer gene.
Springer, DeBry and the other co-authors report that a specific deletion of nine base pairs in BRCA-1 is shared by 12 groups of placental mammals. These are the groups Springer puts together in "Afrotheria."
In addition, the exhaustive comparison helps to answer a more recent question: How closely are rabbits and guinea pigs related to rodents? The results in Nature indicate
Contact: Chris Curran
University of Cincinnati