| Summary: | 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 offpspring (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. Breytileiki á hrognastærð innan og milli tegunda fiska er umtalsverður og hrognastærð hefur áhrif á afkomu og hæfni afkvæma. Skilningur okkar á því hvaða áhrif eggjastærð getur haft á þroskunarferla afkvæma er aftur á móti takmarkaður. Bleikja (Salvelinus alpinus) er þekkt fyrir óvenjumikinn svipgerðarbreytileika og mismunandi ...
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