WOODS HOLE, MA -- A January 2004 finding by biologists at the JosephineBay Paul Center for Comparative Molecular Biology and Evolution addedimportant evidence to the radical conclusion that a group of diminutiveaquatic animals called bdelloid rotifers have evolved for tens ofmillions of years without sexual reproduction, in apparent violation ofthe rule that abandonment of sexual reproduction is a biological deadend. Now, MBL scientists are beginning to understand just what'sdifferent about these creatures' DNA that has enabled them to succeedwhere other asexual species have failed.
In a paper published in this week's Proceedings of the NationalAcademy of Sciences (PNAS), MBL scientists Irina R. Arkhipova andMatthew Meselson provide evidence that suggests bdelloidrotifers--which probably gave up sex at least 50 million years ago buthave still evolved into 370 species--handle DNA transposons moreefficiently than other asexual species. Transposons are small snippetsof "junk DNA" that sexual reproduction compensates for, but which oftengo unchecked and are believed to contribute to mutation (and eventuallyextinction) in species that reproduce asexually.
To learn more about the bdelloid rotifers' unique ability toevolve without sex, Arkhipova and Meselson studied portions ofdifferent bdelloid rotifer genomes and surveyed the diversity,structural organization, and patterns of evolution of DNA transposons.
The scientists found that DNA transposons in bdelloid rotifersare in a different, perhaps less damaging, location than those found inother creatures. Many bdelloid DNA transposons have the samesurrounding sequences, which may indicate preferences for specificlocations. Indeed, many of them appear to be located at the tip of thechromosome in an area called the telomere, different from the gene-richportions of the genome, whereas most species tend to have DNAtransposons dispersed throughout their genome.
Note to Editors: The paperentitled "Diverse DNA transposons in rotifers of the class Bdelloidea"by Irina R. Arkhipova and Matthew Meselson is scheduled for publicationin the August 1 - 5 issue of PNAS.
The Marine Biological Laboratory is an internationally known,independent, nonprofit institution dedicated to improving the humancondition through creative research and education in the biological,biomedical and environmental sciences. Founded in 1888, the MBL is theoldest private marine laboratory in the Western Hemisphere. TheJosephine Bay Paul Center for Comparative Molecular Biology andEvolution explores the evolution and interaction of genomes of diverseorganisms that play significant roles in environmental biology andhuman health. This dynamic research program integrates the powerfultools of genome science, molecular phylogenetics, and molecular ecologyto advance our understanding of how living organisms are related toeach other, to provide the tools to quantify and assess biodiversity,and to identify genes and underlying mechanisms of biomedicalimportance. Projects span all evolutionary time scales, ranging fromdeep phylogenetic divergence of ancient eukaryotic and prokaryoticlineages, to ecological analyses of how members of diverse communitiescontribute and respond to environmental change. Three interlockingprograms define the scope of research in the Bay Paul Center: theProgram in Global Infectious Diseases, the Program in MolecularEvolution, and the Program in Molecular Microbial Diversity.
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