A comparison of mtDNA restriction sites vs. control region sequences in phylogeographic assessment of the musk turtle (Sternotherus minor)


  • The work described in this report is the first instalment of a dissertation project by DeEtte Walker that involves molecular assessments of phylogeographic pattems in several species of freshwater turtles distributed amss the southeastem USA. This work is part of a broader research program in John Avise's laboratory on comparative phylogeogaphic pattems in freshwater, terrestrial, and marine organisms in this biogeographic region. Vincent Burke and Imrich Badk provided expertise in herpetology and molecular biology, respectively.

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A total of nearly 800 base pairs of mitochondrial DNA sequence was assayed in each of 52 musk turtles (Sternotherus minor) collected across the species' range in the south-eastern USA. About one-half of the sequence information in effect was accessed by conventional recognition-site assays of the entire mtDNA molecule; the remainder came from direct sequence assays of a normally hypervariable 5′ section of the noncoding control region. The two assay methods produced essentially nonoverlapping sets of variable character states that were compared with respect to magnitudes and phylogeographic patterns of mtDNA variation. The two assay procedures yielded nearly identical outcomes with regard to: (a) total levels of species-wide mtDNA genetic variation; (b) mean levels of within-locale variation; (c) extremely high population genetic structure; (d) a phylogenetcally significant separation of samples from the north-western half of the species' range vs. those in the south-eastern segment; and (e) considerably lower genetic variability within the north-western clade. The micro- and macro-phylogeographic mtDNA patterns in the musk turtle are consistent with a low-dispersal natural history, and with a suspected longer-term biogeographic history of the species, respectively.