Doctoral defence in Biology - Samantha Victoria Beck

Ph.D. student: Samantha Victoria Beck

Dissertation title: The influence of egg size for the diversification of Arctic charr (Salvelinus alpinus) morphs

Opponents: Dr. Benedikt Hallgrímsson, Professor at the University of Calgary, Canada
Dr.Kimmo K. Kahilainen, Professor at Inland Norway University of Applied Sciences, Norway 

Advisor: Camille A. Leblanc

Supervisor: Dr. Zophonías O. Jónsson, Professor at the Faculty of Life and Environmental Sciences at the University of Iceland 

Doctoral committee: 

Dr. Katja Räsänen, Lecturer at EAWAG Switzerland
Dr. Bjarni K. Kristjánsson, Professor at Hólar University College
Dr. Skúli Skúlason, Professor at Hólar University College  
Dr. John Postlethwait, Professor Emeritus  at the University of Oregon, USA

Chair of Ceremony: Dr. Anna Dóra Sæþórsdóttir, Head of the Faculty of Life and Environmental Sciences at the University of Iceland.

Abstract:
Intraspecific variation in egg size and its effects on offspring fitness is well documented in fishes. Yet whether or not differential per propagule maternal investment (egg size) can influence phenotypic diversification is little understood. Arctic charr (Salvelinus alpinus) are famed for their resource polymorphisms, whereby their degree of sympatric diversification often varies between lakes. Using a gradient of divergence, we aimed to understand how egg size influenced: (1) developmental times, (2) relative expression of genes related to growth and skeletogenesis across early-life stages, (3) craniofacial shape at hatching and first feeding, and (4) the covariance between craniofacial shape and the relative expression of genes related to growth and skeletogenesis. We found morphs to differ in egg size and egg size variation, as well their extent of egg size-mediated effects on offspring gene expression and craniofacial shape. Most striking is the higher expression of genes related to skeletogenesis at eye stage in the weakly diverged Vatnshlíðarvatn silver morph, all of which also correlated with egg size and was the only morph to have egg size-correlated differences in craniofacial shape. These results demonstrate the likely role that canalisation has played in reducing phenotypic variation in offspring (i.e. gene expression and shape), in concert with egg size-mediated maternal effects, along a gradient of sympatric divergence. This thesis provides novel insight into the potential for early-life stage divergence of gene expression and associated shape change, alongside variation in egg size, to drive phenotypic diversification in the early evolution of resource polymorphism.

About the doctoral candidate: Samantha began her studies in Equine Science in Oatridge College, Scotland. After which, she moved to North Wales to study an undergraduate degree in Zoology and Conservation at Bangor University. For her final year project, she worked with the Molecular Ecology and Fisheries Genetics Lab to determine the phylogeography of a Southeast Asian killifish. This interest in using molecular techniques to understand fish dispersal led her on to undertaking her research masters in the population genetics of Arctic charr in North Wales. Her thesis went on to receive the award for best-written master’s thesis in 2014. Wanting to continue her research with Arctic charr, Sam moved to Iceland in 2014 to start her PhD looking at the influence of egg size on the evolutionary diversification of Arctic charr across Iceland.

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