ALBERT

Description: Dinoflagellates are a major cause of harmful algal blooms, with consequences for coastal marine ecosystem functioning and services. Alexandrium tamarense is one of the most abundant and widespread toxigenic species in the temperate northern and southern hemisphere, and produces paralytic shellfish poisoning toxins as well as lytic allelochemical substances. These bioactive compounds may support the success of A. tamarense and its ability to form blooms. Here we investigate the impact of grazing on monoclonal and mixed set-ups of highly (Alex2) and moderately (Alex4) allelochemically active A. tamarense strains and on a non-allelochemically active conspecific (Alex5) by the heterotrophic dinoflagellate Polykrikos kofoidii. While Alex4 and particularly Alex5 were strongly grazed by P. kofoidii when offered alone, both strains grew well in the mixed assemblages (Alex4+Alex5 and Alex2+Alex5). Hence, the allelochemical active strains facilitated growth of the non-active strain by protecting the population as a whole against grazing. Based on our results, we argue that facilitation among clonal lineages within a species may partly explain the high genotypic and phenotypic diversity of Alexandrium populations. Populations of Alexandrium may comprise multiple cooperative traits that act in concert with intraspecific facilitation, and hence promote the success of this notorious harmful algal bloom species.

Description: Dinoflagellates are a major cause of harmful algal blooms (HABs), with consequences for coastal marine ecosystem functioning and services. Alexandrium fundyense (previously Alexandrium tamarense) is one of the most abundant and widespread toxigenic species in the temperate Northern and Southern Hemisphere and produces paralytic shellfish poisoning toxins as well as lytic allelochemical substances. These bioactive compounds may support the success of A. fundyense and its ability to form blooms. Herewe investigate the impact of grazing on monoclonal and mixed set-ups of highly (Alex2) and moderately (Alex4) allelochemically active A. fundyense strains and a non-allelochemically active conspecific (Alex5) by the heterotrophic dinoflagellate Polykrikos kofoidii. While Alex4 and particularly Alex5 were strongly grazed by P. kofoidii when offered alone, both strains grew well in the mixed assemblages (Alex4 þ Alex5 and Alex2 þ Alex5). Hence, the allelochemical active strains facilitated growth of the non-active strain by protecting the population as awhole against grazing. Based on our results, we argue that facilitation among clonal lineages within a species may partly explain the high genotypic and phenotypic diversity of Alexandrium populations. Populations of Alexandrium may comprise multiple cooperative traits that act in concert with intraspecific facilitation, and hence promote the success of this notorious HAB species.

Description: Phytoplankton is responsible for approximately 50 % of the annual global primary production and Emiliania huxleyi ((Lohm.) Hayard and Mohler) is an important part of the phytoplankton community. It contributes to the biological- and carbon counter-pump and therefore species success of E. huxleyi might play an important role on vertical carbon fluxes in the ocean. Several studies have shown that E. huxleyi is susceptible for Global change. Emiliania huxleyi has a high adaptive capacity and can thrive in highly diverse but also stable environments from the subtropics to subpolar regions. Emiliania huxleyi has a biphasic life cycle with phenotypically distinct haploid and diploid cell stages interconnected by syngamy, a form of sexual reproduction. A recent study unveiled that E. huxleyi populations subjected to stable environments had a significant proportion of strains which have lost key genes associated to haploid cell formation. The loss of sex implies several evolutionary constraints for species survival and adaptive capacity, since asexual reproducing lineages tend to possess a loss of heterozygosity. However with an increase of homozygosity deleterious alleles can be unmasked and the fitness of a given species can be reduced. As a counterpart acts here ameiotic recombination, which can retain adaptive capacity in asexual lineages, by balancing the emergence of deleterious alleles. As asexual and sexual populations of E. huxleyi from the same geographic origin, we further expect sympatric evolution of the two subpopulations, due to separation of their gene pools. Aim of this study was to unravel the influence of demographic, ecological as well as environmental factors on the population differentiation as well as to uncover mechanisms which influence micro-evolutionary processes in Asexual E. huxleyi lineages. As method of choice we used a reduced representation sequencing approach called double digest Restriction site Associated DNA (ddRAD) sequencing, where only genomic regions between two different restriction enzyme cutting sites were sequenced. For 1 population from Peru and 3 populations from Chile basic population genetic parameters were assessed as well as genomic erosion and Gene Diversity in asexual Chile strains within and between populations. Based on basic population genetic parameters, moderate genetic differentiation between Peru and Chile populations was detected, most likely explained due to separation of the populations by different water masses and currents. However indications for the presence of sympatric evolution of asexual and sexual gene pools were given as well. The observed heterozygosity in Asexual E. huxleyi strains was not reduced although inbreeding indices were elevated, which could indicate a loss of heterozygosity. Therefore it remains unresolved which micro-evolutionary processes are dominating the genomic evolution of asexual E. huxleyi strains. The overall exceptionally high interspecific genetic diversity of E huxleyi might mitigate effects of Asexual reproduction and helps to sustain a high adaptive capacity.

Description: In this thesis double digest restriction-site associated DNA sequencing was established for the marine microalgae Alexandrium tamarense and microsatellite marker analysis as well as 28S analysis of four A. tamarense populations was performed. A. tamarense belongs to the phylum dinoflagellata, a large group of flagellate protists with unique features in respect to their genome structure and cell organization. Furthermore this microalga is responsible for a lot of HABs. A group of three morphologically very similar species form the A. tamarense” species complex”, which is further subdivided into five distinct ribotype groups. Questions like the biogeography of this species complex as well as the question how to bring molecular data about separation of clades and morphological characteristics of defined species in line remain partly unsolved by now. Special emphasis in this thesis lays on the biogeography of ribotype group I of the A. tamarense species complex. Previous studies addressing the above mentioned questions used molecular markers which cover just a tiny fraction of the genome. ddRADSeq produces a lot more markers leading to a higher coverage of the genome and thus a much higher resolution for molecular ecological studies. In order to provide results for comparison with ddRADSeq, analysis were performed with an already established marker system. Hence microsatellite analysis with 10 microsatellite loci was performed. The four tested populations were from 3 different geographic origins: Alaska, Greenland and Northsea. Principle Coordinate and Structure analysis were performed to reveal inter- and intrapopulation structuring. A Mantel´s test was conducted to test if geographic distance correlates with genetic distance. The ddRADSeq approach could be established successfully. Results from microsatellite analysis revealed separation of Alaska´s population into two distinct clusters in Structure as well as in PCoA analysis. These findings support previously proposed models of biogeographic distribution of the group I ribotye from the A. tamarense species complex.