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

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Bibliographic Details
Main Author: Guðbrandsson, Jóhannes
Other Authors: Arnar Pálsson, Líf- og umhverfisvísindadeild (HÍ), Faculty of Life and Environmental Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
Format: Doctoral or Postdoctoral Thesis
Language:English
Published: University of Iceland, School of Engineering and Natural Sciences, Faculty of Life and Environmental Sciences 2019
Subjects:
Online Access:https://hdl.handle.net/20.500.11815/1063
Description
Summary: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 ...