| 21. |
- Johannesson, Kerstin, 1955
(författare)
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Parallel speciation: a key to sympatric divergence
- 2001
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Ingår i: Trends in Ecology & Evolution. - 0169-5347. ; 16:3, s. 148-153
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Tidskriftsartikel (refereegranskat)abstract
- Until recently our view of speciation was that reproductive isolation evolves during long periods of allopatry through the accumulation of genetic differences that result in genetic incompatibility. This view now contrasts with new findings that characters affecting reproductive isolation can diverge rapidly in sympatry as a result of natural selection. Recent studies combining research on phylogeny and ecology of natural populations cast new light on patterns, timescales and mechanisms, and emphasize the role of ecological factors in speciation, Studies of parallel speciation provide a strong case for sympatric speciation and for natural selection generating reproductive barriers.
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| 22. |
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| 23. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Phenotypic variation in sexually and asexually recruited individuals of the Baltic Sea endemic macroalga Fucus radicans : in the field and after growth in a common-garden
- 2012
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Ingår i: BMC Ecology. - : Springer Science and Business Media LLC. - 1472-6785. ; 12, s. 2-
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Most species of brown macroalgae recruit exclusively sexually. However, Fucus radicans, a dominant species in the northern Baltic Sea, recruits new attached thalli both sexually and asexually. The level of asexual recruitment varies among populations from complete sexual recruitment to almost (> 90%) monoclonal populations. If phenotypic traits have substantial inherited variation, low levels of sexual activity will decrease population variation in these traits, which may affect function and resilience of the species. We assessed the level of inherited variation in nine phenotypic traits by comparing variation within and among three monoclonal groups and one group of unique multilocus genotypes (MLGs) sampled in the wild.RESULTS: Of the nine phenotypic traits, recovery after freezing, recovery after desiccation, and phlorotannin content showed substantial inherited variation, that is, phenotypic variation in these traits were to a large extend genetically determined. In contrast, variation in six other phenotypic traits (growth rate, palatability to isopod grazers, thallus width, distance between dichotomies, water content after desiccation and photochemical yield under ambient conditions) did not show significant signals of genetic variation at the power of analyses used in the study. Averaged over all nine traits, phenotypic variation within monoclonal groups was only 68% of the variation within the group of different MLGs showing that genotype diversity does affect the overall level of phenotypic variation in this species.CONCLUSIONS: Our result indicates that, in general, phenotypic diversity in populations of Fucus radicans increases with increased multilocus genotype (MLG) diversity, but effects are specific for individual traits. In the light of Fucus radicans being a foundation species of the northern Baltic Sea, we propose that increased MLG diversity (leading to increased trait variation) will promote ecosystem function and resilience in areas where F. radicans is common, but this suggestion needs experimental support.
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| 24. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Repeated evolution of reproductive isolation in a marine snail - unveiling mechanisms of speciation
- 2010
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Ingår i: Philosophical Transactions of the Royal Society Biology. - 0962-8436. ; 365:1547, s. 1735-1747
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Tidskriftsartikel (refereegranskat)abstract
- Distinct ecotypes of the snail Littorina saxatilis, each linked to a specific shore microhabitat, form a mosaic-like pattern with narrow hybrid zones in between, over which gene flow is 10–30% of within-ecotype gene flow. Multi-locus comparisons cluster populations by geographic affinity independent of ecotype, while loci under selection group populations by ecotype. The repeated occurrence of partially reproductively isolated ecotypes and the conflicting patterns in neutral and selected genes can either be explained by separation in allopatry followed by secondary overlap and extensive introgression that homogenizes neutral differences evolved under allopatry, or by repeated evolution in parapatry, or in sympatry, with the same ecotypes appearing in each local site. Data from Spain, the UK and Sweden give stronger support for a non-allopatric model of ecotype formation than for an allopatric model. Several different non-allopatric mechanisms can, however, explain the repeated evolution of the ecotypes: (i) parallel evolution by new mutations in different populations; (ii) evolution from standing genetic variation; and (iii) evolution in concert with rapid spread of new positive mutations among populations inhabiting similar environments. These models make different predictions that can be tested using comprehensive phylogenetic information combined with candidate loci sequencing.
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| 25. |
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| 26. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Selective predation favouring cryptic individuals of marine snails (Littorina)
- 2002
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Ingår i: Biological Journal of the Linnean Society. - 0024-4066. ; 76:1, s. 137-144
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Tidskriftsartikel (refereegranskat)abstract
- Many gastropods have inherited conspicuous shell colour polymorphisms. A challenging question is, are colour frequencies under selection or is polymorphism owing to random evolutionary processes? The intertidal species Littorina saxatilis (a rock-dweller) and L. obtusata (confined to macroalgae) both have genetically determined shell colour variation. In Iceland, Littorina obtusata are mostly cryptic on brown macroalgae by having brown or yellow shells (similar to95% of the snails), while Littorina saxatilis often appears conspicuous to the background of dark rocks owing to non-cryptic colours (15-20%). This difference may be due to selective elimination of conspicuously coloured L. obtusata by visual predators, while L. saxatilis, largely living in another habitat, is not under a similarly intense colour selection. To test this hypothesis we increased the frequencies of conspicuous L. saxatilis in experimental populations (from <12 to 55%) and placed these in the seaweed zone, the main habitat of L. obtusata. Fifteen populations were released on isolated spots of seaweed and three of these were covered by net cages to exclude bird predators. One month later, yellow snails had increased in frequency within the patches, and to our surprise the result did not differ between bare and caged patches. This suggests selection favouring a colour that matches the background of fucoid seaweeds by visual predators able to enter the cages. Birds acted as important predators by picking 16% of the experimental snails in the uncaged spots, but were unable to enter the caged spots. However, the bird predation was non-selective with respect to snail colour. For various reasons the most likely predators able to enter the cages were intertidal fish, these were thus responsible for the selection of non-cryptic snails. (C) 2002 The Linnean Society of London.
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| 27. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Snabb evolution i Östersjön
- 2007
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Ingår i: Forskning och Framsteg. ; 3, s. 34-38:3, s. 34-38
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 28. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Ten years of marine evolutionary biology - challenges and achievements of a multidisciplinary research initiative
- 2023
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Ingår i: Evolutionary Applications. - : Wiley. - 1752-4571. ; 16:2, s. 530-41
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Tidskriftsartikel (refereegranskat)abstract
- The Centre for Marine Evolutionary Biology (CeMEB) at the University of Gothenburg, Sweden, was established in 2008 through a 10-year research grant of 8.7 m€ to a team of senior researchers. Today, CeMEB members have contributed >500 scientific publications, 30 PhD theses and have organised 75 meetings and courses, including 18 three-day meetings and four conferences. What are the footprints of CeMEB, and how will the centre continue to play a national and international role as an important node of marine evolutionary research? In this perspective arcticle we first look back over the 10 years of CeMEB activities and briefly survey some of the many achievements of CeMEB. We furthermore compare the initial goals, as formulated in the grant application, with what has been achieved, and discuss challenges and milestones along the way. Finally, we bring forward some general lessons that can be learnt from a research funding of this type, and we take also look ahead, discussing how CeMEB’s achievements and lessons can be used as a springboard to the future of marine evolutionary biology.
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| 29. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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The future of Baltic Sea populations : local extinction or evolutionary rescue?
- 2011
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 40:2, s. 179-190
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Tidskriftsartikel (refereegranskat)abstract
- Environmental change challenges local and global survival of populations and species. In a species-poor environment like the Baltic Sea this is particularly critical as major ecosystem functions may be upheld by single species. A complex interplay between demographic and genetic characteristics of species and populations determines risks of local extinction, chances of re-establishment of lost populations, and tolerance to environmental changes by evolution of new adaptations. Recent studies show that Baltic populations of dominant marine species are locally adapted, have lost genetic variation and are relatively isolated. In addition, some have evolved unusually high degrees of clonality and others are representatives of endemic (unique) evolutionary lineages. We here suggest that a consequence of local adaptation, isolation and genetic endemism is an increased risk of failure in restoring extinct Baltic populations. Additionally, restricted availability of genetic variation owing to lost variation and isolation may negatively impact the potential for evolutionary rescue following environmental change.
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| 30. |
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