Vergleichende Populationsgenetik, Larvenverdriftung und evolutionäre Aspekte von Antarktisfischen (Notothenioidei)

In this thesis, population genetic structures and evolutionary aspects of speciation in notothenioid fishes from the Southern Ocean have been investigated. Special emphasis was given to the role of pelagic larval dispersal on gene flow between geographically separated populations, since notothenioids are characterized by unusually long pelagic larval durations of up to one year, which is assumed to counteract genetic divergence of populations and ultimately allopatric speciation processes. By elucidating the population genetic structures of selected notothenioid species, inferences were made about the level of gene flow between populations. The major goal of this thesis was to compare the population genetic structures of sympatric species within the Atlantic sector of the Southern Ocean to determine factors responsible for regulating gene flow. Species-specific traits, such as larval durations, were expected to result in differences between the observed patterns, while environmental factors, such as oceanographic currents or frontal systems, were assumed to influence multiple species in a similar way. In addition, it has been tested whether the evolution of notothenioids fulfills the criteria of an adaptive radiation, of which only a few examples are known from the marine realm.In dieser Doktorarbeit wurden die populationsgenetischen Strukturen und weitere evolutionäre Aspekte von Artbildungsprozessen innerhalb von Antarktisfischen (Notothenioidei) aus dem Südpolarmeer untersucht. Ein besonderer Schwerpunkt war es, den Einfluss pelagischer Larvenverdriftung auf den Genfluss zwischen geografisch getrennten Populationen zu ermitteln, da notothenioide Fische durch ungewöhnlich lange, pelagische Larvenphasen von bis zu über einem Jahr charakterisiert sind, wodurch erhöhter Genfluss einer Auseinanderentwicklung von Populationen und damit auch allopatrischer Artbildung entgegen wirken kann. Die Untersuchung der populationsgenetischen Strukturen erlaubt es, Rückschlüsse auf das Ausmaß des genetischen Austauschs zwischen Populationen zu ziehen. Das Hauptziel dieser Arbeit war es, durch einen Vergleich der genetischen Populationsstrukturen sympatrischer Arten, Faktoren zu identifizieren, die maßgeblich den Genfluss beeinflussen. Dabei wurde angenommen, das artspezifische Merkmale, wie z. B. die Dauer der Larvenphase, in Unterschieden zwischen den beobachteten Populationsstrukturen zum Ausdruck kommen, während Umweltfaktoren, wie ozeanografische Strömungen und Fronten, verschiedene Arten gleichermaßen beeinflussen. Des weiteren wurde untersucht, ob die Evolution der Antarktisfische den Kriterien einer Adaptativen Radiation entspricht, für welche es im marinen Lebensraum bisher nur wenige bekannte Beispiele gibt

Comparative population genetics, larval dispersal and evolutionary aspects of Antarctic fishes (Notothenioidei)

In this thesis, population genetic structures and evolutionary aspects of speciation in notothenioid fishes from the Southern Ocean have been investigated. Special emphasis was given to the role of pelagic larval dispersal on gene flow between geographically separated populations, since notothenioids are characterized by unusually long pelagic larval durations of up to one year, which is assumed to counteract genetic divergence of populations and ultimately allopatric speciation processes. By elucidating the population genetic structures of selected notothenioid species, inferences were made about the level of gene flow between populations. The major goal of this thesis was to compare the population genetic structures of sympatric species within the Atlantic sector of the Southern Ocean to determine factors responsible for regulating gene flow. Species-specific traits, such as larval durations, were expected to result in differences between the observed patterns, while environmental factors, such as oceanographic currents or frontal systems, were assumed to influence multiple species in a similar way. In addition, it has been tested whether the evolution of notothenioids fulfills the criteria of an adaptive radiation, of which only a few examples are known from the marine realm

Assessing SNP-markers to study population mixing and ecological adaptation in Baltic cod

Atlantic cod (Gadus morhua) is a species of great ecological and economical importance in the Baltic Sea. Here, two genetically differentiated stocks, the western and the eastern Baltic cod, display substantial mechanical mixing, hampering our understanding of cod ecology and impeding stock assessments and management. Based on whole-genome re-sequencing data from reference samples obtained from the study area, we designed two different panels of Single Nucleotide Polymorphisms markers (SNPs), which take into account the exceptional genome architecture of cod. A minimum panel of 20 diagnostic SNPs and an extended panel (20 diagnostic and 18 biologically informative SNPs, 38 in total) were developed and validated to distinguish unambiguously between the western and the eastern Baltic cod stocks and to enable studies of local adaptation to the specific environment in the Baltic Sea, respectively. We tested both panels on cod sampled from the southern Baltic Sea (n = 603) caught in 2015 and 2016. Genotyping results showed that catches from the mixing zone in the Arkona Sea, were composed of similar proportions of individuals of the western and the eastern stock. Catches from adjacent areas to the east, the Bornholm Basin and Gdańsk Deep, were exclusively composed of eastern Baltic cod, whereas catches from adjacent western areas (Belt Sea and Öresund) were composed of western Baltic cod. Interestingly, the two Baltic cod stocks showed strong genetic differences at loci associated with life-history trait candidate genes, highlighting the species’ potential for ecological adaptation even at small geographical scales. The minimum and the extended panel of SNP markers presented in this study provide powerful tools for future applications in research and fisheries management to further illuminate the mixing dynamics of cod in the Baltic Sea and to better understand Baltic cod ecology

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Diversity and disparity through time in the adaptive radiation of Antarctic notothenioid fishes

According to theory, adaptive radiation is triggered by ecological opportunity that can arise through the colonization of new habitats, the extinction of antagonists or the origin of key innovations. In the course of an adaptive radiation, diversification and morphological evolution are expected to slow down after an initial phase of rapid adaptation to vacant ecological niches, followed by speciation. Such 'early bursts' of diversification are thought to occur because niche space becomes increasingly filled over time. The diversification of Antarctic notothenioid fishes into over 120 species has become one of the prime examples of adaptive radiation in the marine realm and has likely been triggered by an evolutionary key innovation in the form of the emergence of antifreeze glycoproteins. Here, we test, using a novel time-calibrated phylogeny of 49 species and five traits that characterize notothenioid body size and shape as well as buoyancy adaptations and habitat preferences, whether the notothenioid adaptive radiation is compatible with an early burst scenario. Extensive Bayesian model comparison shows that phylogenetic age estimates are highly dependent on model choice and that models with unlinked gene trees are generally better supported and result in younger age estimates. We find strong evidence for elevated diversification rates in Antarctic notothenioids compared to outgroups, yet no sign of rate heterogeneity in the course of the radiation, except that the notothenioid family Artedidraconidae appears to show secondarily elevated diversification rates. We further observe an early burst in trophic morphology, suggesting that the notothenioid radiation proceeds in stages similar to other prominent examples of adaptive radiation

Genomic Differentiation and Demographic Histories of Atlantic and Indo-Pacific Yellowfin Tuna (Thunnus albacares) Populations

Recent developments in the field of genomics have provided new and powerful insights into population structure and dynamics that are essential for the conservation of biological diversity. As a commercially highly valuable species, the yellowfin tuna (Thunnus albacares) is intensely exploited throughout its distribution in tropical oceans around the world, and is currently classified as near threatened. However, conservation efforts for this species have so far been hampered by limited knowledge of its population structure, due to incongruent results of previous investigations. Here, we use whole-genome sequencing in concert with a draft genome assembly to decipher the global population structure of the yellowfin tuna, and to investigate its demographic history. We detect significant differentiation of Atlantic and Indo-Pacific yellowfin tuna populations as well as the possibility of a third diverged yellowfin tuna group in the Arabian Sea. We further observe evidence for past population expansion as well as asymmetric gene flow from the Indo-Pacific to the Atlantic

The Adaptive Radiation of Notothenioid Fishes in the Waters of Antarctica

Fishes of the perciform suborder Notothenioidei, which dominate theichthyofauna in the freezing waters surrounding the Antarctic continent, representone of the prime examples of adaptive radiation in a marine environment. Driven byunique adaptations, such as antifreeze glycoproteins that lower their internal freezingpoint, notothenioids have not only managed to adapt to sub-zero temperaturesand the presence of sea ice, but also diversified into over 130 species. We herereview the current knowledge about the most prominent notothenioid characteristics,how these evolved during the evolutionary history of the suborder, how theycompare between Antarctic and non-Antarctic groups of notothenioids, and howthey could relate to speciation processes.Fil: Michael Matschiner. Universidad de Basilea; SuizaFil: Colombo, Marco. Universidad de Basilea; SuizaFil: Damerau, Malte. Thünen Institute Of Fisheries Ecology; AlemaniaFil: Ceballos, Santiago Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Hanel, Reinhold. Thünen Institute Of Fisheries Ecology; AlemaniaFil: Salzburger, Walter. Universidad de Basilea; Suiz