Genetic characterization of the marine ichthyotoxic flagellate Pseudochattonella farcimen (Heterokonta) and phylogenetic relationships among heterokonts.
Appears in the following Collection
- Biologisk institutt 
AbstractIn most cases, the proliferation of marine planktonic alga is ecologically beneficial for the marine food web. However, harmful algal blooms can have negative effects by causing fish kills. In this PhD thesis particularly one ichthyotoxic phytoflagellate that has caused massive blooms in Scandinavian waters since its first live record in 1998, has been studied.The first objective of this thesis was to determine the phylogeny and systematic position of this organism. The species name Pseudochattonella farcimen sp. nov. was proposed as it was found to be different from, but closely related to P. verruculosa,previously described as the Raphidophyte Chattonella verruculosa Y. Hara et Chihara from Japan. Ultrastructure, morphology and pigment composition as well as phylogenetic analyses of nuclear rDNA confirmed that the genus Pseudochattonella belong to the heterokont class Dictyochophyceae – and not Raphidophyceae as previously believed. Florenciellales, a new order within the Dictyochophyceae was proposed, which embraces the three species Florenciella parvula Eikrem, P. farcimen and P. verruculosa. A further aim of this thesis was to genetically characterize P. farcimen and related species, and determine the genetic diversity within and between Pseudochattonella species. Genetic evidence for a separation of the two Pseudochattonella species was found in nuclear rDNA as well as in protein coding DNA sequences from mitochondria and chloroplast. Another objective was to develop molecular methods for detection of this species, as well as determine the identity of bloom-forming Pseudochattonella species in various geographical regions.Finally this work was brought into a broader perspective as P. farcimen was included in a multigene phylogenetic analysis. Bayesian and maximum likelihood analyses improved the heterokont tree compared to previous rDNA analyses. Except for the positioning of Chrysophyceae, Eustigmatophyceae and Pinguiophyceae, all main branches of Ochrophyta were resolved. Further all plastid-free heterotrophic heterokonts were placed sister to Ochrophyta with robust support.
List of papers. This thesis is based on the following four papers, which will be referred to in the text by their Roman numerals.
I.Edvardsen B., Eikrem W., Shalchian-Tabrizi K., Riisberg I., Johnsen G., Naustvoll L., Throndsen J.Verrucophora farcimen gen. et sp. nov. (Dictyochophyceae, Heterokonta) a bloom forming ichthyotoxic flagellate from the Skagerrak, Norway. Journal of Phycology (2007) 43: 1054-1070.
II.Riisberg I., and Edvardsen B. Genetic variation in bloom-forming ichthyotoxic Pseudochattonella species (Dictyochophyceae, Heterokonta) using nuclear, mitochondrial and plastid DNA sequence data. Submitted to European Journal of Phycology (October 2007).
III.Riisberg I., and Edvardsen B. Molecular probes and specific PCR primers for detection and identification of ichthyotoxic marine flagellates in the genus Pseudochattonella(Dictyochophyceae, Heterokonta). Submitted to Journal of Plankton Research (February 2008).
IV.Riisberg I., Orr R. J. S, Kluge R., Shalchian-Tabrizi K., Bowers H. A., PatilV.,Edvardsen B. and Jakobsen K.S.Seven gene phylogeny of heterokonts. To be submitted to Protist.