Comparison of morphological and molecular traits for species identification and taxonomic grouping of oncaeid copepods

Abstract

The pelagic marine copepod family Oncaeidae is highly diversified (over 100 species worldwide) and includes a great number of sibling species, which are difficult to identify morphologically, because of their very small size (0.18-1.2 mm total length as adults). Global investigations of oncaeid biodiversity are severely hampered by insufficient taxonomic knowledge, in particular for species which have first been described from the European Mediterranean Sea (type locality). Many of these species have been reported as key taxa of smallsized copepod communities in very distant oceanic regions. However, due to the taxonomic uncertainties it cannot be excluded that at least some of these allegedly cosmopolitan species in reality represent a complex of distinct, yet closely related, species. To improve the basis for the identification of Oncaeidae of Mediterranean origin, new diagnostic characters in combination with traditional methods were applied in the present study. Copepods were sampled with fine nets of 0.1 mm mesh size down to a maximum depth of 1,000 m on a west-east-transect in the Mediterranean Sea. Oncaeid species and form variants were predefined morphologically and the genetic identity of the morphospecies was analysed by about 650 and 500 bp region of the mitochondrial COI and 12S srRNA gene sequence, respectively (barcoding). A total of 67 individuals from 24 oncaeid species and forms were successfully analysed, including 12 species and one form of Mediterranean origin. For Oncaeidae, the 12S amplification turned out to be more successful (23 species) than the COI amplification (13 species and 1 form). Together, the morphological and molecular results are discussed with respect to three topics: (1) confirmation of a genetic distinction of three Triconia species, which have been interpreted as sibling species by morphological characters, (2) genetic distance of species within the ovalis-complex of oncaeids and (3) the taxonomic status of two form variants of Oncaea mediterranea (Claus).

Occurrence of the <i>Paracalanus parvus</i> species complex in offshore waters south of Japan and their genetic and morphological identification to species

“…One of the two first antennae of each individual was used for Sanger sequencing to determine genetic group affiliation, with the remaining body parts retained for subsequent morphological analysis. Genomic DNA was extracted according to Böttger-Schnack & Machida (2011), and PCR and Sanger sequencing were both performed as described previously. Because sufficient data related to mt-COI sequences were not obtained using these methods, genetic groups were determined based on the results of nLSU sequences.…”

Taxonomic re-examination and distribution of copepods reported as Oncaea notopus Giesbrecht, 1891 (Copepoda, Oncaeidae) in the Mediterranean Sea

“…Böttger-Schnack and Schnack 2009;Böttger-Schnack and Machida 2010). Oncaeid copepods in the deep-sea plankton material from the eastern Mediterranean Sea had quantitatively been counted and sorted from an aliquot of the subsamples during earlier zooplankton studies on the vertical distribution and trophic relationships in this area (cf.…”

Molecular phylogeny of Oncaeidae (Copepoda) using nuclear ribosomal internal transcribed spacer (ITS rDNA)

“…conifera and O . media , are complexes of closely related, yet distinct, species [5,10,13,15]. Molecular taxonomy can also improve and refine our knowledge of the ecology of this copepod family, which is at the moment limited to a few studies [16–18].…”