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Studies on the species level variation of selected coccolithophores

Geisen, Markus; (2003) Studies on the species level variation of selected coccolithophores. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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The oceans cover roughly seventy percent of the surface of the earth. With few exceptions minute photosynthetic primary producers like diatoms, dinoflagellates, silicoflagellates and coccolithophores inhabit the upper 200 m of this vast expanse. This phytoplankton forms the base of the marine food chain and plays an important role in geochemical cycles. Knowledge about species level biodiversity and speciation thus is important to understand marine ecology and biogeochemistry. Amongst the mentioned groups coccolithophores appear to be the ideal test group since their biomineralised periplasts - the coccoliths - provide a rich suite of qualitative and quantitative morphological characters and a uniquely extensive fossil record. In addition to this extant coccolithophore species can be grown in culture and hence are available for molecular genetic studies and cytological research. Combining data from both palaeontology and biology hence allows for a more detailed interpretation of coccolithophore biodiversity, evolution and speciation. For the CODENET project (the EC funded Coccolithophorid Evolutionary Biodiversity and Ecology Network) extant species with seemingly global occurrences - spanning the biodiversity of coccolithophores - were selected and different case studies were carried out on them to elucidate their species level biodiversity. Here we present the results and discuss tentative models of speciation for the coccolithophores in general. Following a brief introduction the second chapter (Methods) deals with sampling for both life and fossil coccolithophores and introduces culture techniques as well as biometrical methods used. Chapter 3 (Results) is divided in four parts - in part 1-3 detailed results from three CODENET species will be presented, mainly dealing with their morphological variability and physiology, but also with their evolutionary history. Part 4 is a published research paper in which the novel phenomenon of cryptic speciation is demonstrated for the first time in the coccolithophores. This paper equally highlights the importance of studies on living species to achieve a better understanding and interpretation of coccolithophore evolution, diversity and speciation. Chapter 4 (Discussion) comprises a comprehensive review about species level variation in all the CODENET key species. Here we tie together the various sources of data obtained during the project and introduce models of speciation for the coccolithophores. Further published manuscripts - both dealing with methods used in this study, but also supplementary data important for this thesis are given in an appendix.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Studies on the species level variation of selected coccolithophores
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Coccolithophores
URI: https://discovery.ucl.ac.uk/id/eprint/10097939
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