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Evolutionary genetics of salmonids: host-pathogen interaction and temperature variation

Author Laetitia WILKINS SCHMID
Director of thesis Claus Wedekind
Co-director of thesis Luca Fumagalli
Summary of thesis

Typically, selectively neutral markers have been used for conservation genetic studies of wild populations. Questions about demographic parameters and population structure can be answered based solely on genetic data with tiny little pieces of tissue from a representative sample of the study population. I have been very interested in applying coalescence theory to the study of population structure and history based on neutral markers. I like different statistical approaches towards genetic data to find out more about the evolutionary history.


However, evolutionary relevant and adaptive processes within populations can only be investigated with coding genes, and empirical support for selective mechanisms in free-ranging animal populations in their natural environment is still rare. Therefore I find the characterization of the major histocompatibility complex, cathelicidins or other genes related to the immune system, as well as the simulation of different adaptive scenarios in a wild species even more enthralling. With this knowledge it is going to be possible to investigate questions concerning mate choice, life-history strategies, whether specific genotypes of parents correlate with breeding success and offspring quality, and how particular genotypes relate to pollution and pathogen pressure.


Recent findings suggest that symbiotic microbes have major effects on the survival and growth of naturally spawned fish embryos. Moreover, we know that the immune system influences the embryos’ resistance to microbial challenges at later developmental stages. Despite these advancements and relative ease with which fish embryos can now be studied under natural and controlled laboratory conditions, our understanding of the ecological and evolutionary role of associated microbial communities is still poor. The composition of symbiotic microbes affects host development and life history, whereas the expression of certain parental host genes affects the symbiotic microbes. The influence of microbes on host development and survival depends furthermore on environmental factors such as temperature. For my doctoral studies I am going to identify and characterize typical microbial communities of model salmonids using next-generation sequencing techniques; test the roles of specific microbial communities and of particular host factors; and analyze the effects of temperature on the interaction between microbial communities and host. Salmonids will be used as the host species in order to exploit the various experimental advantages that embryos of this family offer as compared to other vertebrate hosts: taking samples from natural populations, rearing under experimental laboratory conditions, fertilizing externally, collecting very large family sizes, quantifying of additive and non-additive genetic and maternal environmental effects on offspring characteristics, measuring of various stress responses, translocating easily and exposing individual replicated genotypes to natural selection regimes.


“After sleeping through a hundred million centuries we have finally opened our eyes on a sumptuous planet, sparkling with color, bountiful with life. Within decades we must close our eyes again. Isn’t it a noble, and enlightened way of spending our brief time in the sun, to work at understanding the universe and how we have come to wake up in it? This is how I answer when I am asked – as I am surprisingly often – why I bother to get up in the mornings.” - Richard Dawkins

Administrative delay for the defence 7 November 2014
URL http://laetitia.schmid.se