Researchers find a pattern in evolution of liz...( Evolutionary biologists have developed ...)

Evolutionary biologists have developed a wide range of techniques to reconstruct the evolutionary history of particular groups of plants and animals. These techniques reveal much about the diverse patterns of evolution of life on earth, but few generalities have emerged, leading many scientists, such as the late Stephen Jay Gould, to conclude that each group of living things evolves in its own idiosyncratic manner. But now biologists at Washington University in St. Louis have proposed a general pattern among groups in the timing of evolutionary diversification.

Using novel statistical and analytical techniques, a group headed by Jonathan Losos, Ph.D. and Allan Larson, Ph.D., both Washington University professors of biology in Arts & Sciences, examined two important dimensions in the evolutionary diversification of four groups of lizards: the ages of branching points on the evolutionary trees of the lizard groups and variation among branches in morphological (body) traits, such as limb length and head size.

The researchers found that the four lizard groups differed in both respects. For example, in Australian agamid lizards, a disproportionate number of branching events occur deep (early) in the evolutionary tree, whereas, at the other extreme, among the South American Liolaemus lizards, the branching points are evenly distributed throughout the tree.

Similarly, the distribution of morphological variation differed in the four groups. In the agamids, closely related species tend to be morphologically similar and distantly related species morphologically different, whereas this relationship is much weaker for Liolaemus . In both cases, the other two lizard groups were intermediate.

What was most surprising to the researchers was that, despite the many differences among the four lizard groups, a strong overall relationship was found between the two aspects of evolutionary diversification. "This correlation was a big surprise," said L
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Contact: Tony Fitzpatrick
tony_fitzpatrick@aismail.wustl.edu
314-935-5272
Washington University in St. Louis
14-Aug-2003

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