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Doctoral defence in Biology - Jóhannes Guðbrandsson

Fri, 26/04/2019 - 14:00 to 16:00


Room 132

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Ph.D. student: Jóhannes Guðbrandsson

Dissertation title: Gene expression during early development and genetic variation among recently evolved sympatric Arctic charr (Salvelinus alpinus) morphs in Lake Þingvallavatn, Iceland.

Dr. Kathryn Elmer, Reader at the Institute of Biodiversity Animal Health & Comparative Medicine, University of Glasgow.
Dr. Jón H. Hallson, Associate Professor at the Faculty of Natural Resources and Environmental Sciences, Agricultural University of Iceland.

Advisor: Dr. Arnar Pálsson, Professor at the Faculty of Life- and Environmental Science, University of Iceland.

Doctoral committee: 
Dr. Zophonías O. Jónsson, Professor at the Faculty of Life- and Environmental Science, University of Iceland.
Dr. Sigurður S. Snorrason, Professor at the Faculty of Life- and Environmental Science, University of Iceland.
Dr. Einar Árnason, Professor at the Faculty of Life- and Environmental Science, University of Iceland.
Dr. Páll Melsted, Professor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland.

Chair of Ceremony: Dr. Snæbjörn Pálsson, Professor and Vice Head of the Faculty of Life- and Environmental Science, University of Iceland.


The four morphs of Arctic charr (Salvelinus alpinus) in Lake Þingvallavatn, Iceland, which differ in many phenotypic traits related to morphology, life history, and feeding ecology, are believed to have evolved locally within the lake after the retreat of the Ice-age glacier. The principal aims of the study were to get a handle on the molecular mechanisms underlying the phenotypic differences and assess genetic differentiation among the morphs. Gene expression during early development was surveyed to look for differential expression of genes thereby identifying developmental processes affecting divergent phenotypes. Genetic variation among the morphs was studied and patterns of biological function (gene ontology) and genomic position of highly differentiated variants were examined. Both candidate gene and transcriptome-wide profiling (RNA-sequencing) approaches were used. The results reveal both differentiation in expression and genetic composition of the sympatric morphs. Gene expression differences in multiple genes and biological pathways were discovered, pointing to substantial differentiation of morphs and that many genes may have been under selection. However, RNA degradation during sample handling created technical problems that complicated data analysis. The transcriptome-wide profiling was nonetheless useful as it revealed expression differences in genes relating to extra-cellular matrix formation and skeletogenesis and highlights differentiation in more biological pathways. The data show extensive genome-wide differentiation in allele frequencies, pointing to reproductive isolation of the morphs and/or natural selection operating on multiple parts of the genome. Strong genetic differentiation among morphs was for example discovered in immunological genes using a candidate gene approach and in genes involved in collagen metabolism and environmental sensing, by gene ontology enrichment tests of differentiated variants in the transcriptome. The expression differences in embryos and the clear genetic differentiation of the morphs suggest that they have advanced along "the speciation continuum" towards becoming reproductively isolated.

About the doctoral candidate:

Jóhannes was born in 1985 and grew up in Staðarhraun in Mýrar. He graduated with a BS degree in biology from the University of Iceland in 2008 and with a BS degree in mathematics from the same school in 2010. He started his doctoral studies in 2009. From the year 2012 he has worked part-time for the Institute of Freshwater Fisheries, that became the Marine and Freshwater Research Institute in 2016, where he studies salmonids. During his studies he also worked as an teaching assistant in multiple courses in biology at the University of Iceland. 

Jóhannes lives in Hvanneyri with his fiancé Jónína Svavardóttir, from Ölkelda in Staðarsveit and their four children, Steinunn Lára (born 2005), Jónas Emil (born 2011), Brynhildur Eyja (born 2014) and Örnólfur Kári (born 2017).

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Jóhannes Guðbrandsson

Doctoral defence in Biology - Jóhannes Guðbrandsson