MDI Bio Lab finds place for turtles in evolution

Posted July 26, 2011, at 7:27 p.m.
Last modified July 27, 2011, at 5:21 a.m.

BAR HARBOR, Maine — With the help of researchers from other institutions, scientists at Mount Desert Island Biological Laboratory finally have found a place for turtles on the evolutionary tree.

The “tree” is really a diagram that shows evolutionary relationships between different types of animals. Lines on the diagram branch off from one another as different categories develop from a common ancestor, according to evolutionary scientists.

Finding a place for turtles on the diagram has been problematic, however, as scientists have offered different theories about which other species are turtles’ closest living evolutionary relative, MDI Bio Lab officials indicated Monday in a press release. Some scientists have argued that previous genetic evidence suggest that turtles, which are reptiles, are most closely related to birds and alligators. Other scientists have cited the physical form and structure of turtles in arguing that lizards are their closest relatives.

With the help of microRNA, comparatively small molecules that activate or suppress the expression of genetic material in cells, scientists at MDI Bio Lab and Ivy League universities have found that turtles are most closely related to lizards. Their findings were first published recently in the scientific journal Biology Letters.

“Different microRNAs develop fairly rapidly in different animal species over time, but once developed, they then remain virtually unchanged,” Kevin Peterson, a paleobiologist at MDI Bio Lab and Dartmouth College, indicated in the lab’s written statement. “They provide a kind of molecular map that allows us to trace a species’ evolution.”

Peterson uses fossils to study the molecular biology of ancient animal life and the evolutionary relationships between ancient and modern species.

Ben King, a bioinformatician at the lab, indicated in the release that a computer analysis of the lizard genome revealed that four of 77 new microRNA families found in lizards also are found in the painted turtle. According to a scientific abstract of the study, the common microRNA families are not found in other animal genomes, and there is no microRNA evidence that links them more closely to another type of animal.

According to an article published last week by the scientific journal Nature, Peterson said this evidence should put the debate to rest.

“What we’ve been able to provide is unambiguous evidence for one hypothesis over the others,” Peterson told Nature.

Other researchers involved in the effort include Tyler Lyson and Jacques Gauthier of Yale University, Eric Sperling of Harvard University, and Alysha Heimberg of Dartmouth College, according to MDI Bio Lab officials.

The lab indicated in the release that it plans to use computer software it developed as part of the turtle study on other species. It also plans to develop a web-based platform for the software so other researchers around the world can have Internet access to it for use in their studies.

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