| Summary: | Octocorals are very diverse marine organisms that inhabit virtually every marine ecosystem, therefore are widely distributed around the globe. The origin of their huge diversity has been questioned for several decades, however very few studies have addressed this issue until now. This doctoral thesis explored the systematic relationships of octocoral deep-sea fauna distributed in Antarctic and Sub-Antarctic regions, and evaluated the role of the Antarctic Circumpolar Current (ACC) as a driving force for the diversification of octocoral deep-sea populations. It also assessed the evolution of four octocoral traits and the role of these traits on diversification rate shift. To answer the previous questions we used different approaches and methods that included phylogenetics, molecular dating, character evolution, phylogeography and population genetics. Here, we present the first assessment of phylogeographical patterns and the role of the ACC in the genetic connectivity for two deep-sea octocorals in the Pacific and Southern Ocean: Tokoprymno maia, which is a brooding octocoral, and Hemicorallium imperiale, which is a broadcast spawner. We also explored the systematic relationships of the deep-sea bamboo corals of the subfamily Keratoisidinae, and described two new species Keratoisis magnifica and Keratoisis peara. Finally, we inferred the most comprehensive time-calibrated phylogeny of all Octocorallia to date. We estimated the time of origin of this group around the Triassic, where he first octocorals appear to have been soft-bodied colonies, azooxanthellate, deep-water and cold-water organism. The study of marine benthic organisms has increased in the last decade, particularly for deep-sea fauna. This thesis has contributed greatly in the general knowledge of diversity patterns, temporal diversification processes, and population dynamics for Octocorallia. Our contribution has also laid a basis for further evolutionary studies on these incredible diverse organisms. (Doctor rerum naturalium (Dr rer nat)) Justus ...
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