title: Survey of the efficacy of a short fragment of the rbcL gene as a supplemental DNA barcode for diatoms.
abstract: DNA barcoding is a tool that uses a short, standard segment of DNA to identify organisms. In diatoms, a consensus on an appropriate DNA barcode has not been reached, but several markers show promise. These include the 5.8S gene plus a fragment of the internal transcribed spacer 2 (ITS-2) of nuclear-encoded ribosomal RNA, a 420-bp segment of the 18S rRNA gene, and a 748-bp fragment at the 3'-end of the ribulose bisophosphate carboxylase large subunit (rbcL) gene. Here, we tested a 540-bp fragment 417-bp downstream of the start codon of the rbcL gene for its efficacy in distinguishing diatom species in a wide range of taxa. Overall, 381 sequences representing 66 genera and 245 species from the classes Mediophyceae and Bacillariophyceae were examined. Intra/interspecific thresholds were set at p = 0.01 differences per site (diff./site) for Mediophyceae and p = 0.02 diff./site for Bacillariophyceae and correctly segregated 96% and 93% of morphological congeners, respectively. When testing reproductively isolated or biological species, which are only available from Bacillariophyceae, 80% of species were discriminated. Therefore, we concluded that, alone, the rbcL region tested herein as potential a DNA barcode was not a sufficient discriminator of all diatoms. We suggest that this fragment could be used in a dual-locus barcode with the more variable 5.8S+ITS-2 to discriminate species without sufficient interspecific divergences in the tested rbcL region and to provide insight into species identity from a separately evolved genome.
authors.affiliation: Department of Biology, Mount Allison University, 63B York Street, Sackville, New Brunswick, E4L 1G7, Canada. mlmcgll@mta.ca
authors.forename: Michael L
authors.initials: ML
authors.lastname: MacGillivary
authors.forename: Irena
authors.initials: I
authors.lastname: Kaczmarska
mesh_terms: D058893:DNA Barcoding, Taxonomic / Q000379:methods*; D017377:Diatoms / Q000145:classification* / Q000235:genetics*; D008969:Molecular Sequence Data; D012337:RNA, Ribosomal, 18S / Q000235:genetics*; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics*; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA
chemical_list: D012337:RNA, Ribosomal, 18S; D012273:Ribulose-Bisphosphate Carboxylase