Population structure of the cyanobacterium Microcystis mediated by history, grazing and interstrain interactions

Ondertitel:Populatiestructuur van de cyanobacterie Microcystis gemedieerd door historische factoren, begrazing en interacties tussen stammen

Massive growth of cyanobacterial phytoplankton, in response to eutrophication, can lead to dense water blooms. A very widespread toxic bloom forming cyanobacteria is Microcystis (order Chroococcales), which has received much scientific attention. Studies based on several molecular markers have shown that naturally occurring Microcystis populations are generally composed of several genotypes. Although these blooms have been extensively studied, little is known about the mechanisms generating local and regional diversity of Microcystis bloom populations nor about the factors affecting population structure. In this thesis, we investigated the diversity and distribution patterns of Microcystis ITS types (16S-23S rDNA Internal Transcribed Spacer) to assess the roles of historical and environmental processes in structuring genotypic diversity. We used the ITS as a marker to determine the genetic diversity of Microcystis. As Microcystis strains differ highly in functional traits we also focused on interactions between Microcystis strains as these may be important determinants of population structure. Moreover, we paid attention to interactions between these interstrain interactions, zooplankton grazing and colonisation history in determining Microcystis population structure. We can conclude from this thesis that history (dispersal limitation and priority effects), grazing and interstrain interactions influence Microcystis population structure in a strongly strain-specific way depending on the functional traits of the strains, and that these factors also interact with each other. At global scale and over long time spans, dispersal limitation seems not very important for Microcystis, though in regions with a low density of young water bodies, differences in dispersal rate, and possibly priority effects, can be important in structuring local populations and limiting regional and local diversity. Interstrain interactions, mediated by functional traits, are probably one of the major factors structuring Microcystis populations given the highly complex positive and negative interactions between sympatric strains. Furthermore, grazing of zooplankton can influence the population structure and temporal dynamics of Microcystis populations. The interaction between Daphnia and Microcystis seems to depend to a large extent on toxicity and colony formation of Microcystis strains. In addition, grazing can change the strength and direction of interstrain interactions and priority effects, as illustrated by predator-mediated facilitation in the presence of Daphnia.

Jaar van publicatie:2009

Toegankelijkheid:Open