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J Mol Evol. 2005 Nov;61(5):627-35. Epub 2005 Oct 4.

Genomic approaches reveal unexpected genetic divergence within Ciona intestinalis.

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The Wellcome Trust Centre for Cell, Biology The University of Edinburgh, Michael Swann Building, The King's Buildings, Edinburgh EH9 3JR, UK.


The invertebrate chordate Ciona intestinalis is a widely used model organism in biological research. Individuals from waters ranging from arctic to temperate are morphologically almost indistinguishable. However, we found significant differences in whole genomic DNA sequence between northern European and Pacific C. intestinalis. Intronic and transposon sequences often appear unrelated between these geographic origins and amino acid substitutions in protein coding sequences indicate a divergence time in excess of 20 MYA. This finding suggests the existence of two cryptic species within the present C. intestinalis species. We found five marker loci which distinguish the two genetic forms by PCR. This analysis revealed that specimens from Naples, Italy, have the Pacific-type genome, perhaps due to human-mediated marine transport of species. Despite major genomic divergence, the two forms could be hybridized in the laboratory.

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