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 Paläontologie und Historische Geologie
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From cryptic speciation to phylogeography in Electra pilosa:

The case of genetic study of one cosmopolitan species

E.Nikulina 1 , J.Süling 2 , P.Schäfer 1 , K.J.Tilbrook 3 , S.J. Hageman 4

1 Christian Albrechts Universität, Kiel

2 Leibniz Institute of Marine Sciences, Kiel

3 - Earth and Oceanic Science Research Institute, New Zealand

4 - Appalachian State University, USA

Electra pilosa (L.) is an extant cheilostome bryozoan species, originally described from the north-east Atlantic but subsequently assigned a cosmopolitan distribution; recorded from the North Atlantic, European Arctic, south-east Atlantic and Indo-Pacific, as far as New Zealand. Molecular genetic studies have often shown that such cosmopolitan species are actually complexes of cryptic species. This study of E. pilosa , based on 16S mtDNA, shows deep genetic differences, not only between geographically isolated populations, but also within the same geographic area. The North Atlantic population of E. pilosa consists of seven clades, with genetic distances between them varying from 6-13%. Such a population structure is indicative of advanced cryptic speciation. The Arctic haplotypes are embedded within one of the North Atlantic clades, showing a recent gene flow between these two regions. A comparison of the North Atlantic and Indo-West Pacific populations show genetic distances are about 25%. This indicates that these two clades have been independently evolving since at least the Oligocene, and thus represent two separate species. A phylogenetic study of E. pilosa species group, with an analysis of the recorded modern geographic distribution, allows a tentative reconstruction of the main features of their evolution. In the late Paleogene, the Tethys Sea acted as a connection between the Atlantic and Indian Ocean. An ancestral species may have been widespread throughout this area. After the closure of the Tethys along its south-eastern margin in the mid-Miocene the proto-North Atlantic and Indo-Pacific became fully isolated from one another. However, the genetic differentiation between the Atlantic and Indo-Pacific probably started earlier than this, due to isolation through distance within the Tethys. A deep genetic divergence within the Atlantic shows the long evolution of E. pilosa (at least from the mid-Miocene) in this region; high haplotype diversity demonstrates that this species had the potential to survive the strong and rapid climatic fluctuations of the Neogene.