title: Regional differentiation and extensive hybridization between mitochondrial clades of the Southern Ocean giant sea spider Colossendeis megalonyx.
abstract: Assessing the enormous diversity of Southern Ocean benthic species and their evolutionary histories is a central task in the era of global climate change. Based on mitochondrial markers, it was recently suggested that the circumpolar giant sea spider Colossendeis megalonyx comprises a complex of at least six cryptic species with mostly small and non-overlapping distribution ranges. Here, we expand the sampling to include over 500 mitochondrial COI sequences of specimens from around the Antarctic. Using multiple species delimitation approaches, the number of distinct mitochondrial OTUs increased from six to 15-20 with our larger dataset. In contrast to earlier studies, many of these clades show almost circumpolar distributions. Additionally, analysis of the nuclear internal transcribed spacer region for a subset of these specimens showed incongruence between nuclear and mitochondrial results. These mito-nuclear discordances suggest that several of the divergent mitochondrial lineages can hybridize and should not be interpreted as cryptic species. Our results suggest survival of C. megalonyx during Pleistocene glaciations in multiple refugia, some of them probably located on the Antarctic shelf, and emphasize the importance of multi-gene datasets to detect the presence of cryptic species, rather than their inference based on mitochondrial data alone.
authors.affiliation: Faculty of Biology and Biotechnology, Department of Animal Ecology, Evolution and Biodiversity , Ruhr University Bochum , Universitaetsstrasse 150, Bochum 44801, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Dietz
authors.affiliation: Natural Environments Program , Queensland Museum , PO Box 3300, South Brisbane, Queensland 4101, Australia.
authors.forename: Claudia P
authors.initials: CP
authors.lastname: Arango
authors.affiliation: Faculty of Biology and Biotechnology, Department of Animal Ecology, Evolution and Biodiversity , Ruhr University Bochum , Universitaetsstrasse 150, Bochum 44801, Germany.
authors.forename: Jana S
authors.initials: JS
authors.lastname: Dömel
authors.affiliation: Auburn University , 101 Rouse Life Sciences Building, AL 36849, USA.
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Halanych
authors.affiliation: Department of Biology , Institute for Great Lakes Research, Central Michigan University , Mount Pleasant, MI, USA.
authors.forename: Avril M
authors.initials: AM
authors.lastname: Harder
authors.affiliation: Alfred Wegener Institute , Helmholtz Center for Marine and Polar Biology , Am Alten Hafen 26, Bremerhaven 25768, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Held
authors.affiliation: Department of Biology , Institute for Great Lakes Research, Central Michigan University , Mount Pleasant, MI, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Mahon
authors.affiliation: Zoological Research Museum Alexander Koenig , Adenauerallee 160 , Bonn 53113, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Mayer
authors.affiliation: Bavarian State Collection of Zoology-SNSB , Münchhausenstraße 21 , Munich 81247, Germany ; Department Biology II , Ludwig-Maximilians-Universität München , Großhaderner Straße 2, Planegg-Martinsried 82152, Germany ; GeoBio-Center , Richard-Wagner-Straße 10 , Munich 80333, Germany.
authors.forename: Roland R
authors.initials: RR
authors.lastname: Melzer
authors.affiliation: Scripps Institution of Oceanography , University of California , San Diego, 9500 Gilman Drive, La Jolla 92093-0202, CA, USA.
authors.forename: Greg W
authors.initials: GW
authors.lastname: Rouse
authors.affiliation: Bavarian State Collection of Zoology-SNSB , Münchhausenstraße 21 , Munich 81247, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Weis
authors.affiliation: Scripps Institution of Oceanography , University of California , San Diego, 9500 Gilman Drive, La Jolla 92093-0202, CA, USA ; Western Australian Museum , Locked Bag 49, Welshpool DC, Western Australia 6986, Australia.
authors.forename: Nerida G
authors.initials: NG
authors.lastname: Wilson
authors.affiliation: Faculty of Biology and Biotechnology, Department of Animal Ecology, Evolution and Biodiversity , Ruhr University Bochum , Universitaetsstrasse 150, Bochum 44801, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Leese
keywords: Antarctic; Pycnogonida; benthos; glacial refugia; phylogeography; speciation