| 1. |
- Aaltonen, Kristina, et al.
(författare)
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Molecular Population Genetics of the SRK and SCR Self-incompatibility Genes in the Wild Plant Species Brassica cretica (Brassicaceae).
- 2009
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 181:3, s. 985-995
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Tidskriftsartikel (refereegranskat)abstract
- Self-incompatibility (SI) in plants is a classic example of a trait evolving under strong frequency-dependent selection. As a consequence, population genetic theory predicts that the S locus, which controls SI, should maintain numerous alleles, display a high level of nucleotide diversity, and, in structured populations, show a lower level of among-population differentiation compared to neutral loci. Population-level investigations of DNA sequence variation at the S locus have recently been carried out in the genus Arabidopsis, largely confirming results from theoretical models of S-locus evolutionary dynamics, but no comparable studies have been done in wild Brassica species. In this study, we sequenced parts of the S-locus genes SRK and SCR, two tightly linked genes that are directly involved in the determination of SI specificity, in samples from four natural populations of the wild species Brassica cretica. The amount and distribution of nucleotide diversity, as well as the frequency spectrum of putative functional haplotypes, observed at the S locus in B. cretica fit very well with expectations from theoretical models, providing strong evidence for frequency-dependent selection acting on the S locus in a wild Brassica species.
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| 2. |
- Aaltonen, Kristina, et al.
(författare)
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Nuclear and chloroplast microsatellites reveal extreme population differentiation and limited gene flow in the Aegean endemic Brassica cretica (Brassicaceae)
- 2007
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Ingår i: Molecular Ecology. - 0962-1083. ; 16:23, s. 4972-4983
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear and chloroplast microsatellite markers were used to study population structure and gene flow among seven Cretan populations of the Aegean endemic plant species Brassica cretica (Brassicaceae). Both nuclear and chloroplast markers revealed exceptionally high levels of population differentiation (overall FST = 0.628 and 1.000, respectively) and relatively little within-population diversity (overall HS = 0.211 and 0.000, respectively). Maximum-likelihood estimates of directional migration rates were low among all pairs of populations (average Nm = 0.286). There was no evidence that differences in flower colour between populations had any influence on historical levels of gene flow. In addition, a haplotype network showed that all five chloroplast haplotypes found in the sample were closely related. Together, these results suggest that current patterns of diversification in B. cretica are mainly a result of genetic drift during the last half million years. The main conclusions from the present study are consistent with the prevailing hypothesis that plant diversification in the Aegean region is driven by random rather than adaptive differentiation among isolated populations.
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| 3. |
- Aaltonen, Kristina, et al.
(författare)
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The Evolution and Diversification of S-locus Haplotypes in the Brassicaceae Family.
- 2009
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Ingår i: Genetics. - : Oxford University Press (OUP). - 0016-6731 .- 1943-2631. ; 181:3, s. 977-984
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Tidskriftsartikel (refereegranskat)abstract
- Self-incompatibility (SI) in the Brassicaceae plant family is controlled by the SRK and SCR genes situated at the S locus. A large number of S haplotypes have been identified, mainly in cultivated species of the Brassica and Raphanus genera, but recently also in wild Arabidopsis species. Here, we used DNA sequences from the SRK and SCR genes of the wild Brassica species B. cretica, together with publicly available sequence data from other Brassicaceae species, to investigate the evolutionary relationships between S haplotypes in the Brassicaceae family. The results reveal that wild and cultivated Brassica species have similar levels of SRK diversity indicating that domestication has had but a minor effect on S-locus diversity in Brassica. Our results also show that a common set of S haplotypes were present in the ancestor of the Brassica and Arabidopsis genera, that only a small number of haplotypes survived in the Brassica lineage after its separation from Arabidopsis, and that diversification within the two Brassica dominance classes occurred after the split between the two lineages. We also find indications that recombination may have occurred between the kinase domain of SRK and the SCR gene in Brassica.
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| 4. |
- Aaltonen, Kristina, et al.
(författare)
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Unequal segregation of SRK alleles at the S locus in Brassica cretica.
- 2008
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Ingår i: Genetical Research. - 1469-5073. ; 90:3, s. 223-228
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Tidskriftsartikel (refereegranskat)abstract
- In the Brassicaceae plant family, which includes the Arabidopsis and Brassica genera, self-incompatibility (SI) is controlled by genes at the S locus. Using experimental crosses, we studied the pattern of inheritance of S-locus alleles in the wild species Brassica cretica. Four full-sib families were established and unequal segregation of alleles at the SRK SI gene was found in one family. The segregation distortion acted in favour of a recessive (class II) allele and was best explained by some form of gametic-level selection. Our findings are discussed in the light of theoretical predictions of differential accumulation of deleterious mutations among S-locus alleles.
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| 5. |
- Bengtsson, Bengt Olle, et al.
(författare)
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The balance between sexual and asexual reproduction in plants living in variable environments
- 2000
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Ingår i: Journal of evolutionary biology. - : Wiley. - 1420-9101 .- 1010-061X. ; 13:3, s. 415-422
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Tidskriftsartikel (refereegranskat)abstract
- The balance between sexual and asexual propagule production is studied in an evolutionary model where plants produce the two kinds of propagules in genetically determined proportions. The male function of plants producing asexual propagules can be varied, and the sexual and asexual propagules carry different probabilities to turn into new reproductive individuals. These fitnesses may vary over years. The evolution of the population’s reproductive system is studied assuming modifier alleles with small effects. In this setting a balanced, mixed reproductive system can evolve, but only if the difference in fitness between the sexual and asexual propagules varies over years. When the two kinds of propagules are very similar to each other, as is often the case with sexual and asexual seed formation, evolution will tend towards a state dominated by the one or the other reproductive system.
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| 6. |
- Ceplitis, Alf, et al.
(författare)
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Bayesian inference of evolutionary history from chloroplast microsatellites in the cosmopolitan weed Capsella bursa-pastoris (Brassicaceae)
- 2005
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Ingår i: Molecular Ecology. - 0962-1083. ; 14:14, s. 4221-4233
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Tidskriftsartikel (refereegranskat)abstract
- Besides showing an extraordinary degree of phenotypic variability, Capsella bursa-pastoris (Brassicaceae) is also one of the world's most common plant species and a serious weed in many countries. We have employed a coalescent-based Bayesian analysis of chloroplast microsatellite data to infer demographic and evolutionary parameters of this species. Two different demographic models applied to data from seven chloroplast microsatellite loci among 59 accessions show that the effective population size of C. bursa-pastoris is very small indicating a rapid expansion of the species, a result that is in accordance with fossil and historical data. Against this background, analysis of flowering time variation among accessions suggests that ecotypic differentiation in flowering time has occurred recently in the species' history. Finally, our results also indicate that mononucleotide repeat loci in the chloroplast genome can deteriorate in relatively short periods of evolutionary time.
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| 7. |
- Ceplitis, Alf
(författare)
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Coalescence times and the Meselson effect in asexual eukaryotes
- 2003
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Ingår i: Genetical Research. - 1469-5073. ; 82:3, s. 183-190
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Tidskriftsartikel (refereegranskat)abstract
- In asexual eukaryotes, the two allelic gene copies at a locus are expected to become highly divergent as a result of the independent accumulation of mutations in the absence of segregation. If sexual reproduction was abandoned millions of generations ago, intra-individual allelic divergences can be significantly larger than in species that reproduce sexually. Owing to the disputed existence of truly ancient asexual species, this so-called 'Meselson effect' has been put forward as a means of confirming the complete loss of sexual reproduction. Very few attempts have, however, been made at quantifying the effect of sexual reproduction on the degree of divergence between gene copies in an asexual population. Here, I describe how asexual reproduction can be regarded as a special case of population subdivision. Using a slightly modified version of the standard two-deme structured coalescent, I derive the expected coalescence time for a pair of gene copies in an asexual population and show that the Meselson effect is compatible with low rates of sexual reproduction.
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| 8. |
- Ceplitis, Alf
(författare)
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Genetic and environmental factors affecting reproductive variation in Allium vineale
- 2001
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Ingår i: Journal of evolutionary biology. - 1420-9101. ; 14:5, s. 721-730
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Tidskriftsartikel (refereegranskat)abstract
- Traits related to allocation of resources to sexual and asexual reproduction, together with seed production, were-scored on Allium vineale plants sampled from five sites in southern Sweden during a period of 4 years. In addition, random amplified polymorphic DNA (RAPD) fingerprinting of the sampled plants allowed the identification of genets. Integration of genetic and phenotypic data from field and greenhouse provided for the analysis of among-year, among-site, and among-genet variance components. These variance components were taken to represent the influences of short-term environmental changes, persistent site divergence, and within-site genet differences, respectively. It was shown that differences among sites and among genets explained a large part of the phenotypic variation of allocation traits, whereas among-year differences had a larger influence on the variation in seed production. Together, the results support the conclusions of a recent model on the evolution of mixed reproductive systems, that predicts a stable balance between sexual and asexual reproduction because of annual fluctuations in fecundity through the two modes.
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| 9. |
- Ceplitis, Alf, et al.
(författare)
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Genetic variation, disequilibrium and natural selection on reproductive traits in Allium vineale
- 2004
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Ingår i: Journal of evolutionary biology. - : Wiley. - 1420-9101 .- 1010-061X. ; 17:2, s. 302-311
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Tidskriftsartikel (refereegranskat)abstract
- Bulbils and seeds collected from Allium vineale plants from natural populations were grown under uniform conditions. The bulbil-derived offspring represented the parental generation, whereas the seed-derived offspring represented the sexually produced offspring generation. Molecular markers were used to identify maternal genets. Variation in traits determining the allocation to sexual and asexual reproduction was partitioned among genets and ramet families in the parental and offspring generations. From observations of a release of genetic variation and slippage in the mean phenotype in the offspring generation, we inferred that there exists extensive genetic disequilibrium for reproductive traits in A. vineale populations, that most of the genetic variance is because of dominance effects, and that natural selection favours a reduced allocation to sexual reproduction. No genetic correlation between sexual and asexual allocation traits was found. We discuss the implications of these results with respect to the evolution of a mixed reproductive system in A. vineale.
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| 10. |
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