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- Demandt, Marnie H
(författare)
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Biodiversity in Swedish Cyprinid Fish: Insights Into Processes of Divergence
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Uncovering and understanding the processes that have led to the biological diversity we observe today are of fundamental interest in biology. Since direct observation of speciation is usually impossible, knowledge about the processes behind species formation can be gathered by studying mutations, natural/sexual selection, and genetic drift. In this thesis I aim to identify evolutionary processes that cause species divergence and, ultimately, speciation using Swedish cyprinid fish as a model system. Assuming that the demographic history of a population is mirrored in the genome, I studied the effects of a bottleneck on genetic variability in populations of roach. As expected, I found that a decrease in population size caused a decrease in genetic variability, a pattern that was obtained from both microsatellite and mitochondrial data. The importance of hybridization for speciation is debated, however, by analyzing morphology and microsatellites I could show that common bream and white bream and their interspecific hybrids are phenotypically and genetically differentiated and that ongoing geneflow is mainly unidirectional. Ongoing geneflow antagonizes the effect of genetic drift, but by studying isolated populations (= no gene flow) the impact of genetic drift can be assessed. Long-term isolated populations of roach and perch surprisingly showed stable levels of genetic diversity over time despite decreasing effective population size. However, each population genetically diverged during the period of investigation, a finding that is consistent with the effect of drift. An analysis of the systematic relationship of the 18 species of Swedish cyprinids revealed low congruence of phylogenies based on two different genetic markers. The position of the tench remains unresolved and the relationship of common bream and white bream as sister species cannot be confirmed. Within cyprinid fishes, diversification rates reveal a slowdown with time, a pattern that I found also in other fish clades and that is consistent with density-dependent cladogenesis. Overall, based on the findings presented in this thesis I emphasize that the maintenance of genetic variation in populations is essential since genetic variation is the key element for processes of divergence to act upon.
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| 2. |
- Demandt, Marnie H, et al.
(författare)
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Identification of cyprinid hybrids by using geometric morphometrics and microsatellites
- 2009
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Ingår i: Journal of Applied Ichthyology. - : Hindawi Limited. - 0175-8659 .- 1439-0426. ; 25:6, s. 695-701
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Tidskriftsartikel (refereegranskat)abstract
- Traditional morphological studies need to be complemented with modern genetic methods to facilitate the identification of hybrids. By using a combination of landmark-based techniques and microsatellite markers, natural hybridization was investigated between the cyprinids Abramis brama (L.) and Blicca bjoerkna (L.) and their hybrids. Geometric morphometrics revealed significant differences in body shape between A. brama, B. bjoerkna, and hybrids. Hybrids were of intermediate body shape with a tendency of being more like A. brama. Genetic differentiation was found between both parental species and their hybrids. However, hybrids revealed a higher genetical similarity with A. brama. Based on sequencing of the mitochondrial ATP synthase subunit 6 and 8 region a clear split was found between the two sibling species. Seventeen out of 19 hybrid specimens clustered within the A. brama clade. Data indicate that hybridization between A. brama and B. bjoerkna is mainly unidirectional and has not yet resulted in fusion of the two parental gene pools. Genetic integrity is maintained in B. bjoerkna, but F1 hybrid backcrosses might lead to introgression into the genepool of A. brama.
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| 5. |
- Demandt, Marnie H.
(författare)
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Sequence variation in mitochondrial ATP synthase subunit 6 & 8 and nuclear genes ITS1 and ITS2 in 17 cyprinid species
- 2013
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Ingår i: Journal of Applied Ichthyology. - : Hindawi Limited. - 0175-8659 .- 1439-0426. ; 29:1, s. 278-280
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Tidskriftsartikel (refereegranskat)abstract
- Sequence variation for the mitochondrial ATP synthase subunit 6 & 8 and the nuclear ITS1 marker was investigated for 17 cyprinid fish species in order to increase the number of possible loci for character sampling. The mitochondrial locus provided appropriate information for further phylogenetic studies, which can be readily applied to other taxa; the nuclear ITS1, however, cannot be recommended for inference of relationships among different taxa. No congruence was obtained between the trees resulting from the mitochondrial and nuclear gene using Bayesian Inference.
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| 6. |
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| 7. |
- Demandt, Marnie H.
(författare)
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Temporal changes in genetic diversity of isolated populations of perch and roach
- 2010
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Ingår i: Conservation Genetics. - : Springer Science and Business Media LLC. - 1566-0621 .- 1572-9737. ; 11:1, s. 249-255
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Tidskriftsartikel (refereegranskat)abstract
- Genetic drift, together with natural selection and gene flow, affects genetic variation and is the major source of changes in allele frequencies in small and isolated populations. Temporal shifts in allele frequencies at five polymorphic loci were used to estimate the amount of genetic drift in an isolated population of perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.). Here, I used the populations from the Biotest basin at Forsmark, Sweden, to investigate genetic diversity between 1977 and 2000, during which time the population can be considered to be totally isolated from other populations. Microsatellite data reveal stable levels of gene diversity over time for both species. Estimates of genetic differentiation (F-ST) showed a significant divergence between 1977 and 2000 for both perch and roach. A positive correlation between genetic distance and time was found (Mantel test, perch: r = 0.724, P = 0.0112; roach: r = 0.59, P = 0.036). Estimates of effective population size (N-e) differed with a factor six between two different estimators (NeEstimator and TempoFS) applying the temporal method. Ratios of Ne/N ranged between 10(-2) and 10(-3), values normally found in marine species. Despite low Ne the populations have not lost their evolutionary potential due to drift. But two decades of isolation have lead to isolation by time for populations of perch and roach, respectively.
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