Flying lemurs are monkeys' uncle

Treeshrews were once thought to be the closest relatives of primates, but a comparative genomic study published this week in Science shows that another mammal, the flying lemur, is the sister group to primates.

"The relationships between primates and other mammals has been unclear for quite some time," William Murphy of Texas A&M University, a coauthor on the study, told The Scientist. "Our study is the first one to resolve that, and we had to take a genome wide approach to do it."

DNA and morphological studies have supported the view that primates are closely allied with treeshrews (Scandentia) and flying lemurs (Dermoptera), also called colugos, but precisely how the three groups are related has been strongly debated. Resolving these relationships is key to understanding the early transformations in primate evolution, but has been challenging because of rapid diversification in these groups and inadequate sampling.

Jan Janecka at Texas A&M and colleagues addressed this problem by searching for rare genomic changes among the three groups. One key to their approach was obtaining genetic material from the rare pentail treeshrew (Ptilocercus lowii), the most primitive member of the order. Murphy's group had been studying mammalian evolution for over a decade, but only recently learned that German ecologists had access to the creature.

The team screened a set of 197,322 known exons in order to find rare insertions and deletions -- known as indels -- that could indicate the validity of different groupings. They found that seven indels supported a close relationship between primates and colugos, while only a single indel suggested linking treeshrews to primates. No indels supported linking treeshrews to colugos. To confirm these findings, the team also constructed a phylogenetic tree with 14 kilobases of nuclear genes from each of the representative groups.

The study also pushes the origin of the treeshrews back 20 million years prior to their appearance in the fossil record. The three groups had a common ancestor 88 million years ago, and primates branched off as little as two million years later -- which explains the difficulty previous researchers had in pinning down these relationships. "We're talking about two million years," Murphy said. "One wouldn't expect many rare genomic changes."

Outside researchers were impressed by the breadth of the new study, but said it may not be the final word. "It's definitely an improvement, and I think I believe it," Mark Allard of George Washington University said. "Now, you have a good outgroup for all of primates so you can reexamine evolutionary relationships and character evolution [within the group]."

Jonathan Bloch at the Florida Museum of Natural History in Gainsville said the molecular study is an interesting contribution, but more work is needed to understand the morphological transitions that took place on the lineage leading up to primates. "With the fossil record, we're very far from having the story being over," he said. "We have huge parts of the world that need to be explored looking for early primates."

Murphy said he believes the results will bolster support to produce a draft genome of the flying lemur in order to further elucidate primate origins. "One of the important goals of the Human Genome Project is to sequence primates and the primates' closest relatives to better understand changes on the lineage leading to humans and also earlier," he said.

Brendan Borrell
mail@the-scientist.com


Links within this article:

J.E. Janecka et al, "Molecular and Genomic Data Identify the Closest Living Relative of Primates," Science, November 2, 2007.
http://www.sciencemag.org

William Murphy
http://gene.tamu.edu/faculty_pages/faculty_MurphyW.php

J.I. Bloch et. al, "New Paleocene skeletons and the relationship of plesiadapiforms to crown-clade primates," Proceedings of the National Academy of Sciences, January 23, 2007.
http://www.the-scientist.com/pubmed/17229835

B. Grant, "Do chimps have culture?" The Scientist, August 1, 2007.
http://www.the-scientist.com/article/display/53392/

M.L. Phillips, "Genomic alterations 2.0," The Scientist, October 1, 2007.
http://www.the-scientist.com/2007/10/1/89/1/

J. L. Peirce, "Following phylogenetic footprints," The Scientist, September 27, 2004.
http://www.the-scientist.com/article/display/14954/

Mark Allard
http://www.gwu.edu/˜clade/faculty/allard/

Jonathan Bloch
http://www.flmnh.ufl.edu/directory/cvs/jbloch_cv.htm

V.K. McElheny, "The human genome project +5," The Scientist, February 1, 2006.
http://www.the-scientist.com/article/display/23065/