A Molecular Phylogenetic Framework for the Phylum Ctenophora Using 18S rRNA Genes

Molecular evidence for the occurrence of ctenophore Mertensia ovum in the northern Baltic Sea and implications for the status of the Mnemiopsis leidyi invasion

“…It also includes the variable DNA sequence areas of the intervening internal transcribed spacer regions, ITS1 and ITS2. Both rRNA genes and spacers are very useful in delineating species and genera in a variety of organisms, including ctenophores (Podar et al 2001). To identify the species in question, we amplified and sequenced the 18S rRNA, ITS1, and 5.8S rRNA from the ctenophore DNA samples.…”

“…We used 50 randomly selected samples from the collection made in 2008 and all 3 specimens available from 2007 to amplify 18S rRNA, ,1800 base pairs (bp). The amplifications were performed on an MJ Research MiniCycler using universal eukaryotic primers (Kober and Nichols 2007) and a ,600-bp fragment covering the 39 terminus of 18S rRNA, ITS1, and 5.8S rRNA using the primers located at the 39 terminus of the 18S rRNA (Podar et al 2001) and the 39 terminus of the 5.8S rRNA ( Table 2). PCR of 25 mL contained 12.5 mL of Promega PCR Master Mix, 2 mL of each primer (final concentration 0.2 mmol L 21 ), 3 mL of DNA template, and 5.5 mL nuclease-free water (Gibco).…”

“…The sequence obtained was deposited in GenBank (FJ668937). Sequence identity was evaluated by performing BLASTN searches against GenBank and aligned against Atlantic M. leidyi (NCBI accession number AF293700, originated from Woods Hole, Massachusetts, Podar et al 2001;L10826, unknown origin, Wainright et al 1993;and EF175463, coastal waters of the Netherlands, Faasse and Bayha 2006), P. pileus (AF293678; Woods Hole, Massachusetts, Podar et al 2001), M. ovum (AF293679; Newfoundland coastal waters, Canada) and two undescribed mertensiids Table 1. Details on sampling locations, depth, sample sizes, and environmental factors; n/a, not available.…”

“…Details on sampling locations, depth, sample sizes, and environmental factors; n/a, not available. (AF293680 and AF293681; Bahamas and Santa Barbara, California, Podar et al 2001). In addition to the reference specimen of M. ovum collected from Newfoundland, a second sequence covering the 18S rRNA, ITS1, and 5.8S rRNA region was obtained from an adult M. ovum specimen collected in the Arctic Ocean, north of Alaska, and compared to that in the Baltic specimens.…”

“…By contrast, in growing cydippid ctenophores, no transition occurs and tentacles remain in older stages. Although species identification is challenging for adult ctenophores (Podar et al 2001), it is even more difficult for specimens in early life stages, for which there are often no easily identifiable morphological characters (Mayer 1912). In such cases, molecular methods could greatly improve the accuracy of identification.…”