Washington, Nov 2 : New molecular and genomic data gathered by biologists indicates that flying lemurs might be the closest group to primates within the entire class of living mammals.

Debates over the identification of the closest relative to the primate have become more intense in the last ten years because of new fossil and molecular evidence. Some scientists have suggested that the group --Scandentia -- which includes the small tree shrews that scamper up and down trees in Asia, belong to the category.

Others scientists favour dermopterans, a relatively little-known group, that includes two living species of colugos in Southeast Asia. Although colugos are colloquially termed "flying lemurs," they are not lemurs and they do not fly.

Since 1999, all three groups -- primates, scandentians, and dermopterans -- have been recognized as comprising a single taxonomic unit, known as Euarchonta, or "true ancestors." The exact evolutionary relationships among the three groups within Euarchonta have proven elusive due to their overall closeness and the existence of a number of features that are shared among the groups.

The latest study has been derived after testing three previous hypotheses. While one states that colugos and primates together comprise a single group, another states that tree shrews and colugos have many features in common and are closely related to each other than to primates. The third hypothesis is that primates are most closely related to tree shrews alone, with colugos being more distant from both.

"We decided to design an exacting study that would test the three hypotheses using two independent molecular approaches," says Webb Miller, a professor of biology, and a member of the research team. "Before evaluating the different hypotheses, we wanted to make sure that the Euarchonta was, indeed, a valid evolutionary group that had arisen from a single ancestral lineage," he added.

The team screened a set of 197,322 known exons (areas of the human genome that code for proteins looking for insertions or deletions), collectively called "indels", which are rare genetic changes. From 300 candidate indels, the team found 196 that potentially could indicate the validity of the Euarchonta group and could determine primate affinities.

After eliminating those 196 indels, and adding genomic information from a number of living primates for comparison, the team found strong support for the growing consensus that the Euarchonta was a valid clade. After analyzing seven rare genetic changes, researchers established a close relationship between primates and colugos, supporting the idea that the Primatomorpha is a valid taxonomic group within the Euarchonta.

"In short, these molecular data strongly suggest that colugos are the sister group to primates," says Webb Miller, a professor of biology, and a member of the research team.

Because of the new-found importance of understanding colugos as the nearest relative to primates, the team urges that a draft genome of a colugo be established as soon as possible. According to Miller, "Colugos are going to be much more important species to study now that we know their relationship to primates." (ANI)