Dissertation: 7.4.2017 FM Roghaieh Ashrafi (Faculty of Mathematics and Science, Ecology and Evolutionary Biology)
Start date: Apr 07, 2017 12:00 PM
End date: Apr 07, 2017 03:00 PM
Location: Ylistönrinne, YAA 303
FM Roghaieh Ashrafi defends his doctoral dissertation in Ecology and Evolutionary Biology ”Exploring potential evolutionary responses to increasing temperature in an environmental opportunistic pathogen”. Opponent Professor Anna-Liisa Laine (University of Helsinki) and custos Adjunct Professor Tarmo Ketola (University of Jyväskylä). The doctoral dissertation is held in English.
Environmentally growing opportunistic pathogens can grow outside the host. This makes them very sensitive to selection pressures outside the host, which in turn, could further alter disease severity. In this thesis, I used novel techniques and analyses to investigate the effect of environmental selection pressures, in particular temperature, on thermal performance, virulence, and intraspecific interactions of Flavobacterium columnare, a waterborne opportunistic bacterial pathogen of fish. The phylogenetic analysis of 83 strains from eight different geographic locations in Finland over ten years (2003-2012) were carried out using the multilocus sequence analysis (MLST/MLSA). This analysis demonstrated that strains were clearly separated into two main lineages, (I and II) which can be further divided into five genotypes. Meanwhile, isolates clustered independent from the geographic origin, host, and year with a semi-clonal and epidemic population structure (where frequent recombination occurs among isolates, but time to time, one or a few fit genotypes can arise and increase rapidly to produce an epidemic clone). F. columnare isolates showed variation in their thermal tolerances and in virulence, with virulence increasing over the years. Virulence was negatively correlated with a broader thermal performance curve with a right-shift towards warmer temperatures. Most likely climate change driven changes in the disease epidemics of this bacterium are associated with increased length of growing season, extending the suitable period for disease outbreaks. Finally, competition outcome in liquid cultures seemed to be well predicted by growth and yield of isolated strains at two different temperatures. However, interference competition results measured in inhibition tests on solid agar were inconsistent with head-to-head competition, suggesting that benefits of interference while growing on a surface are relaxed in liquid culture.