Evolution of complex organelles in dinoflagellates

• Main Author: Gavelis, Gregory S.
• Language: English
• Published: University of British Columbia 2016
• Online Access: http://hdl.handle.net/2429/56291

Dinoflagellates are an abundant and diverse group of aquatic eukaryotes, with members that have photosynthetic, heterotrophic, or mixotrophic life strategies, as well as a number of unique cytological features. My thesis focuses on two groups of closely related dinoflagellates: polykrikoids and warnowiids. Both include heterotrophic as well as plastid-bearing members, though the number of times photosynthesis has been lost (or gained) in each group is unclear, and the presence and provenance of plastids in some species (e.g., Nematodinium sp. and Polykrikos lebouriae) have been debated. Polykrikoids and warnowiids also contain some of the most complex subcellular structures described--such as nematocysts and, in warnowiids, eye-like ocelloids. Yet these groups are rare in nature and uncultivated, and as such, the origins of their complex organelles are unclear. For my thesis, I modified existing techniques for use on single-cell environmental isolates, and applied these techniques to wild polykrikoid and warnowiid cells. By exploiting the common splice leader sequence found on dinoflagellate transcripts, I was able to amplify a single-cell transcriptome from Polykrikos lebouriae—a dinoflagellate with aberrant plastids. Coupled with single-cell genomics using multiple displacement amplification (MDA), I demonstrated that Polykrikos lebouriae has retained peridinin-type plastids, while photosynthesis has been lost in multiple other polykrikoid species independently. Using MDA and single-cell transmission electron microscopy, I also determined that the eye-like ocelloid of Nematodinium sp. is made in part from a peridinin plastid, and also from mitochondria. Specifically, single-cell focused ion beam scanning electron microscopy (FIB-SEM) allowed me to demonstrate that a retina-like portion of the ocelloid is a small part of a much larger peridinin-plastid that ramifies throughout the Nematodinium cell. Lastly, I investigated the evolution of nematocysts in Polykrikos spp. and Nematodinium sp. using a combination of transcriptomics, TEM, SEM, and FIB-SEM, and inferred that “nematocysts” in these groups evolved independently from those in cnidarians. Thus, nematocyst-like extrusive organelles appear to have evolved multiple times in eukaryotes. The data presented in this thesis show how extreme subcellular complexity has evolved in dinoflagellates through both endosymbiotic and autogenous origins. === Science, Faculty of === Zoology, Department of === Graduate