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Sökning: kerstin johannesson > Johannesson Kerstin 1955

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  • Canbäck, Björn, et al. (författare)
  • The Littorina sequence database (LSD) - an online resource for genomic data.
  • 2012
  • Ingår i: Molecular Ecology Resources. - Wiley-Blackwell. - 1755-098X. ; 12, s. 142-148
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an interactive, searchable expressed sequence tag database for the periwinkle snail Littorina saxatilis, an upcoming model species in evolutionary biology. The database is the result of a hybrid assembly between Sanger and 454 sequences, 1290 and 147 491 sequences respectively. Normalized and non-normalized cDNA was obtained from different ecotypes of L. saxatilis collected in the UK and Sweden. The Littorina sequence database (LSD) contains 26 537 different contigs, of which 2453 showed similarity with annotated proteins in UniProt. Querying the LSD permits the selection of the taxonomic origin of blast hits for each contig, and the search can be restricted to particular taxonomic groups. The database allows access to UniProt annotations, blast output, protein family domains (PFAM) and Gene Ontology. The database will allow users to search for genetic markers and identifying candidate genes or genes for expression analyses. It is open for additional deposition of sequence information for L. saxatilis and other species of the genus Littorina. The LSD is available at http://mbio-serv2.mbioekol.lu.se/Littorina/.
  • Johannesson, Kerstin, 1955-, et al. (författare)
  • Oceanographic barriers to gene flow promote genetic subdivision of the tunicate Ciona intestinalis in a North Sea archipelago
  • 2018
  • Ingår i: Marine Biology. - 0025-3162. ; 165:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Pelagic larval development has the potential to connect populations over large geographic distances and prevent genetic structuring. The solitary tunicate Ciona intestinalis has pelagic eggs and a swimming larval stage lasting for maximum a few days, with the potential for a homogenizing gene flow over relatively large areas. In the eastern North Sea, it is found in a geomorphologically complex archipelago with a mix of fjords and open costal habitats. Here, the coastal waters are also stratified with a marked pycnocline driven by salinity and temperature differences between shallow and deep waters. We investigated the genetic structure of C. intestinalis in this area and compared it with oceanographic barriers to dispersal that would potentially reduce connectivity among local populations. Genetic data from 240 individuals, sampled in 2 shallow, and 4 deep-water sites, showed varying degrees of differentiation among samples (F (ST) = 0.0-0.11). We found no evidence for genetic isolation by distance, but two distant deep-water sites from the open coast were genetically very similar indicating a potential for long-distance gene flow. However, samples from different depths from the same areas were clearly differentiated, and fjord samples were different from open-coast sites. A biophysical model estimating multi-generation, stepping-stone larval connectivity, and empirical data on fjord water mass retention time showed the presence of oceanographic barriers that explained the genetic structure observed. We conclude that the local pattern of oceanographic connectivity will impact on the genetic structure of C. intestinalis in this region.
  • Johannesson, Kerstin, 1955-, et al. (författare)
  • Allozyme variation in a snail (Littorina saxatilis) - Deconfounding the effects of microhabitat and gene flow
  • 1997
  • Ingår i: Evolution. - 0014-3820. ; 51:2, s. 402-409
  • Tidskriftsartikel (refereegranskat)abstract
    • It is commonly observed that a restricted gene flow among populations of a species generates genetic differentiation in, for example, allozyme markers. However, recent studies suggest that microhabital-specific variation may contribute to the total differentiation. To appreciate the relative contributions of geographic variation and habitat-specific variation, we sampled 42 subpopulations of the intertidal snail Littorina saxatilis from three different microhabitats (boulders, low and high rocky intertidal) on five small islands within a distance of 15 km. We used a modified orthogonal version of Nei's gene diversity analysis with a modified analysis of variance (ANOVA) that estimated the significance of habitat and geographic separation and the interaction between them. Between subpopulation differentiation (GST) was usually in the range of 5% to 10% but was exceptionally high in one locus (Aat; 53%). Genetic differentiation attributable to different habitats accounted for 10% to 81% (mean 35%) of the between subpopulation variation and was significant (P < 0.05) in six loci. Differentiation doe to geographic separation accounted for 11% to 61% (mean 36%) and was significant (P < 0.05) in seven loci. Furthermore, three loci showed interactions between habitat and island, suggesting varying effects of habitat in different islands. microhabitat-specific variation, probably through spatially varying fitness, seems particularly likely in Aat and Pgm-2. Moderate levels of habitat associated variation added to the observed differentiation due to gene flow in Pgi, Pnp, and Pgm-1, whereas in the remaining three loci either the habitat effect was confused by strong habitat-island interaction (Ark) or was virtually absent (Pep and Mpi).
  • Johannesson, Kerstin, 1955- (författare)
  • Are we analyzing speciation without prejudice?
  • 2010
  • Ingår i: Annals of the New York Academy of Sciences. - 0077-8923. ; 1206, s. 143-149
  • Tidskriftsartikel (refereegranskat)abstract
    • Physical isolation has long been the null hypothesis of speciation, with exceptional evidence required to suggest speciation with gene flow. Following recent persuasive theoretical support and strong empirical examples of nonallopatric speciation, one might expect a changed view. However, a review of 73 recent empirical studies shows that when allopatric speciation is suggested, a nonallopatric alternative is rarely considered, whereas the opposite is true in studies suggesting sympatric speciation, indicating a biased treatment of different speciation models. Although increasing support for ecological speciation suggests natural selection as the most critical component of speciation, gene flow remains an issue. Methods for unbiased hypothesis testing are available, and the genetic and phylogeographic data required for appropriate tests can be generated. Focus on phylogenies and functions of individual genes have revealed strong idiosyncratic elements of speciation, such as single genes with possible allopatric origin that make significant contributions during nonallopatric phases of speciation. Hence a more complex picture of speciation is now emerging that will benefit from unbiased evaluation of both allopatric and sympatric mechanisms of speciation.
  • Johannesson, Kerstin, 1955- (författare)
  • Biologisk mångfald – inte bara arter.
  • 2005
  • Ingår i: Bevara arter – till vilket pris? Formas Fokuserar (red. B. Johansson), Formas, Stockholm..
  • Tidskriftsartikel (övrigt vetenskapligt)
  • Johannesson, Kerstin, 1955- (författare)
  • Evolution in Littorina: ecology matters
  • 2003
  • Ingår i: Journal of Sea Research. - 1385-1101. ; 49:2, s. 107-117
  • Tidskriftsartikel (refereegranskat)abstract
    • Organisms of marine rocky shores are exposed to physical stress from abiotic factors, such as temperature, salinity and wave action. These factors vary over compressed temporal and spatial scales, producing an exceedingly heterogeneous habitat with steep gradients of selection, and it seems likely that this has a strong influence on the evolution of populations of rocky shore organisms. With the periwinkles (genus Littorina) as a model group, I review strategies for coping with small-scale heterogeneous environments and what implications these strategies have on the evolution of these species. Some species of Littorina have long-lived pelagic larvae and sites of various habitats are thus recruited from a common gene pool. This largely prevents local adaptation but minor adjustments are possible through a plastic phenotype. Other species of the genus are directly developing with no larval dispersal and among these there is evidence of strong local adaptation forming distinct ecotypes in contrasting habitats by parallel evolution. In at least one of the directly developing species (L. saxatilis) divergent selection among ecotypes has resulted in partial reproductive barriers that further impede gene flow among ecotypes. Furthermore, convergent evolution among species has produced superficially similar morphs in different habitats. Ecotype formation, ecological reproductive barriers and convergence among species all indicate that ecological processes are critical for evolution of Littorina species. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Johannesson, Kerstin, 1955-, et al. (författare)
  • Growth rate differences between upper and lower shore ecotypes of the marine snail Littorina saxatilis (Olivi) (Gastropoda)
  • 1997
  • Ingår i: Biological Journal of the Linnean Society. - 0024-4066. ; 61:2, s. 267-279
  • Tidskriftsartikel (refereegranskat)abstract
    • Shell polymorphisms are widespread among those intertidal gastropods that lack a pelagic spreading stage. These polymorphisms may indicate diversifying selection in a heterogeneous habitat, but to do this the variation must be at least partly inherited. Galician populations of Littorina saxatilis (Olivi) living in exposed rocky shores are highly polymorphic in several shell traits, e.g. ornamentation, banding and size. Mature snails of the upper-shore ridged and banded (RB) morph is, for example, often twice as large as mature individuals of the lower-shore smooth and unbanded (SU) morph of the same shore. We investigated the hypothesis that lower-shore snails grow more slowly and that differences in growth rate were at least partly inherited and could be explained by diversifying selection. We released snails of different origin (upper, mid- and lower shore) and morph (RB, SU and hybrids) at different shore levels and compared their shell increment after one month of growth. We found that despite considerable variation among individuals and among replicate samples (together about 53% of the total variation), average rates of growth differed between morphs. RB snails both from the upper and mid-shores grew at a high rate at all shore levels, SU snails grew considerably less, and hybrids grew at intermediate rates, at all levels. Inherited difference among morphs explained about 34% of the total variation while effects of shore levels and the interaction morph x shore level explained only 5 and 7%, respectively. Thus a large part of the difference in growth rate leading to different adult sizes of the two morphs has probably evolved due to spatially varying selection favouring large sizes in upper-shore and small sizes in lower-shore environments. (C) 1997 The Linnean Society of London.
  • Johannesson, Kerstin, 1955- (författare)
  • Havets nyckelarter måste fungera
  • 2005
  • Ingår i: Bevara arter – till vilket pris? Formas Fokuserar (ref. B. Johansson), Formas, Stockholm..
  • Tidskriftsartikel (övrigt vetenskapligt)
  • Johannesson, Kerstin, 1955-, et al. (författare)
  • Hybrid fitness seems not to be an explanation for the partial reproductive isolation between ecotypes of Galician Littorina saxatilis
  • 2000
  • Ingår i: Journal of Molluscan Studies. - 0260-1230. ; 66, s. 149-156
  • Tidskriftsartikel (refereegranskat)abstract
    • Partial reproductive isolation between closely related groups of organisms is suggested to be of central importance during speciation. Galician populations of Littorina saxatilis are phenotypically differentiated into an upper-shore and a lower-shore morph. These mate assortatively in the mid-shore: zone of overlap, and genetic assessment shows an impeded gene flow between the parental morphs. The traditional explanation as to why assortative mating occurs is that reproductive isolation is reinforced due to hybrid unfitness. Earlier studies have, however, not found hybrids to be less viable. Likewise, growth and migratory behaviours are merely intermediate between those of the parental morphs. In the present study we compared male and female fertility components of the parental morphs and the hybrids to test hypotheses of decreased hybrid fertility. The results showed that hybrid males were as fertile as other males, and hybrid females did not produce fewer embryos, nor aborted embryos at a higher rate, than the parental morphs.
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