Oithona similis (Copepoda: Cyclopoida)- a cosmopolitan species?

• Main Author: Wend-Heckmann, Britta
• Other Authors: Niehoff, Barbara, Boersma, Maarten
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2013
• Subjects: Copepoda; Cyclopoida; Oithona similis; cosmopolitan; cryptic species; CO 1; 570; 570 Life sciences; biology; ddc:570; Arctic; Arctic Ocean; Helgoland; Southern Ocean
• Online Access: https://media.suub.uni-bremen.de/handle/elib/480; https://nbn-resolving.org/urn:nbn:de:gbv:46-00103163-14

The present study investigated whether the cyclopoid copepod Oithona similis Claus 1866 is a cosmopolitan or a conglomerate of cryptic species. Adult and subadult females (C5 stages) of O. similis were closely examined morphologically and via DNA-barcoding from four study areas: the Arctic Ocean, the Southern Ocean, the North Sea and the Mediterranean Sea. Sampling was done during two expeditions with RV Polarstern in the Arctic Ocean (ARK XXIII-3, ARK XXV-1) and at one expedition in the Southern Ocean (ANT XXIV-2). Further samples from three stations in the North Sea and one station in the Mediterranean Sea were provided. Based on the shape of the rostrum, body size and the formula and structure of the outer setae of the exopodits of the swimming legs, five different morphotypes were identified: Oithona similis (Arctic Ocean, Mediterranean Sea, North Sea, Southern Ocean), O. atlantica (Arctic Ocean), O. frigida (Southern Ocean), O. nana (North Sea) and Oithona sp. (North Sea). Via CO1-sequencing in total eight different haplotypes of O. similis were found in this study: three in the Arctic Ocean, three in the Southern Ocean, one in the North Sea as well as in the Mediterranean Sea and one in the Mediterranean Sea. Only one haplotype was found in one than one sampling area. In addition to the number of haplotypes, this clearly indicates that O. similis is not a cosmopolitan but a conglomerate of cryptic species. Additionally to the Oithona similis groups, three other copepod species groups were identified morphologically as well as via sequencing: O. frigida in the Southern Ocean and in the North Sea O. nana (close to the island of Helgoland)and Oithona sp. (close to the island of Sylt). Oithona nana was chosen as the basis of a neighbor joining tree because it is not as closely related to O. similis as the other species are. Morphological differences regarding the appendages of the swimming legs of O. frigida and O. similis were obvious and were clearly reflected in the results of the CO1 sequences. The ...