Phenotypic variation within and across barriers to gene flow in the marine diatom Seminavis robusta

Master Thesis subject (30 ECTS)
Microalgae do not only constitute the basis for aquatic food webs, but are also important drivers of elemental cycling. Thus, understanding the ecology and evolution of these key players is of great interest. A particular feature of microalgae is the enormous genetic diversity as well as phenotypic plasticity of co-existing genotypes in natural populations. Vital step in furthering our understanding of the eco-evolutionary significance of this diversity is being able to link genetic information (genotypes) to environmentally important traits (phenotypes) and their expression in individual genotypes. The marine benthic diatom Seminavis robusta, has within recent years emerged as a model organism for studying reproductive barriers in diatoms. It has been recognized that within the S. robusta species complex there exists three closely related incipient species (mating groups) that co-exist in nature. Previous laboratory studies show that sexual reproduction mainly occurs within the same mating group, and is more rare between mating groups meaning reduced intraspecific gene flow. In comparison, several other diatom species instead indicate reduced gene flow between populations adapted to different local environmental conditions. Ultimately, S. robusta provides a unique system for studying phenotypic variation and genetic diversity in the presence and absence of reproductive, physical and environmental barriers to gene flow. In this project we wish to phenotypically characterize a set of S. robusta strains, belonging to the three different mating groups that have been collected from various locations along the coast of Belgium and the Netherlands. Currently these strains are in the process of whole-genome sequencing, which will then allow for comparison of phenotypic characterization with genome data. Phenotyping will be done by subjecting the strains to a series of different environmental stressors during which growth will be monitored using PAM fluorescence as well as semi-automated image and video-processing. In addition, crossing experiments will be carried out in order to find out the reproductive success under various culturing conditions. The data generated from this thesis will ultimately provide a better understanding of i) the coupling between genetic diversity and phenotypic variation, ii) identifying environmental parameters that pose strong selective pressure on S. robusta and finally iii) if and how phenotypic variation occurs in the presence and absence of barriers to gene flow.
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Reference Number: RP-48421