Ehrlich, Moritz (2017) Invasion Genomics: Population structure and diversity patterns in the invasive ctenophore Mnemiopsis leidyi based on whole-genome re-sequencing. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 93 pp.

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Abstract

Increased global connectivity has led to an elevated prevalence of invasive species. Marine invaders in particular have caused significant damage to both ecosystems and economies outside of their native ranges. The mechanisms by which ecological, genetic and demographic factors combine to confer invasion success have yet to be understood. Specifically the patterns and importance of genetic diversity during colonisation, establishment and expansion have been debated in recent years. Here we describe population structure and contrast genomic diversity between native and invasive populations of a marine invader for the first time at the whole-genome scale. We examine the Mnemiopsis leidyi invasion system, sampling two native sites along the Western Atlantic and three invasive sites in the North, Black and Western Mediterranean Seas. Whole-genome re-sequencing of 72 specimens produced a mean coverage of 26x per individual and resulted in over 6.5 million SNPs. We confirm two independent invasion events from diverged source regions: the first from the vicinity of the Floridian Peninsula into the Black Sea with a subsequent range expansion throughout the Mediterranean, and the second from the coast of New England into the North Sea. Inbreeding coefficients and tests of HWE suggest M. leidyi populations are in equilibrium and do not self-fertilise in the native or the invasive range. Comparisons of invasive and source populations display patterns of increase, maintenance and decrease of genetic diversity at the whole-genome scale. We reject the former paradigm of diversity reduction through founder effects in invasive populations and hypothesise that propagule pressure or unrelated demographic processes both in invasive and native ranges predominantly shape genomic diversity. Claims are supported by demographic indicators and estimates of effective population size derived from the genome-wide SNP set.

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