1. |
- Berdan, Emma L, 1983, et al.
(författare)
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A large chromosomal inversion shapes gene expression in seaweed flies (Coelopa frigida)
- 2021
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Ingår i: EVOLUTION LETTERS. - : Oxford University Press (OUP). - 2056-3744. ; 5:6, s. 607-624
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Tidskriftsartikel (refereegranskat)abstract
- Inversions often underlie complex adaptive traits, but the genic targets inside them are largely unknown. Gene expression profiling provides a powerful way to link inversions with their phenotypic consequences. We examined the effects of the Cf-Inv(1) inversion in the seaweed fly Coelopa frigida on gene expression variation across sexes and life stages. Our analyses revealed that Cf-Inv(1) shapes global expression patterns, most likely via linked variation, but the extent of this effect is variable, with much stronger effects in adults than larvae. Furthermore, within adults, both common as well as sex-specific patterns were found. The vast majority of these differentially expressed genes mapped to Cf-Inv(1). However, genes that were differentially expressed in a single context (i.e., in males, females, or larvae) were more likely to be located outside of Cf-Inv(1). By combining our findings with genomic scans for environmentally associated SNPs, we were able to pinpoint candidate variants in the inversion that may underlie mechanistic pathways that determine phenotypes. Together the results of this study, combined with previous findings, support the notion that the polymorphic Cf-Inv(1) inversion in this species is a major factor shaping both coding and regulatory variation resulting in highly complex adaptive effects.
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2. |
- Berdan, Emma L, 1983, et al.
(författare)
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A metabarcoding analysis of the wrackbed microbiome indicates a phylogeographic break along the North Sea-Baltic Sea transition zone
- 2023
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Ingår i: Environmental Microbiology. - 1462-2912. ; 25:9, s. 1659-73
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Tidskriftsartikel (refereegranskat)abstract
- Sandy beaches are biogeochemical hotspots that bridge marine and terrestrial ecosystems via the transfer of organic matter, such as seaweed (termed wrack). A keystone of this unique ecosystem is the microbial community, which helps to degrade wrack and re-mineralize nutrients. However, little is known about this community. Here, we characterize the wrackbed microbiome as well as the microbiome of a primary consumer, the seaweed fly Coelopa frigida, and examine how they change along one of the most studied ecological gradients in the world, the transition from the marine North Sea to the brackish Baltic Sea. We found that polysaccharide degraders dominated both microbiomes, but there were still consistent differences between wrackbed and fly samples. Furthermore, we observed a shift in both microbial communities and functionality between the North and Baltic Sea driven by changes in the frequency of different groups of known polysaccharide degraders. We hypothesize that microbes were selected for their abilities to degrade different polysaccharides corresponding to a shift in polysaccharide content in the different seaweed communities. Our results reveal the complexities of both the wrackbed microbial community, with different groups specialized to different roles, and the cascading trophic consequences of shifts in the near shore algal community.
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3. |
- Berdan, Emma L, 1983, et al.
(författare)
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How chromosomal inversions reorient the evolutionary process
- 2023
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Ingår i: Journal of Evolutionary Biology. - 1010-061X .- 1420-9101. ; 36:12, s. 1761-1782
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Forskningsöversikt (refereegranskat)abstract
- Inversions are structural mutations that reverse the sequence of a chromosome seg-ment and reduce the effective rate of recombination in the heterozygous state. They play a major role in adaptation, as well as in other evolutionary processes such as spe-ciation. Although inversions have been studied since the 1920s, they remain difficult to investigate because the reduced recombination conferred by them strengthens the effects of drift and hitchhiking, which in turn can obscure signatures of selection. Nonetheless, numerous inversions have been found to be under selection. Given re-cent advances in population genetic theory and empirical study, here we review how different mechanisms of selection affect the evolution of inversions. A key difference between inversions and other mutations, such as single nucleotide variants, is that the fitness of an inversion may be affected by a larger number of frequently interacting processes. This considerably complicates the analysis of the causes underlying the evolution of inversions. We discuss the extent to which these mechanisms can be disentangled, and by which approach.
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4. |
- Bosso, L., et al.
(författare)
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The rise and fall of an alien: why the successful colonizer Littorina saxatilis failed to invade the Mediterranean Sea
- 2022
-
Ingår i: Biological Invasions. - : Springer Science and Business Media LLC. - 1387-3547 .- 1573-1464. ; 24:10, s. 3169-3187
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Tidskriftsartikel (refereegranskat)abstract
- Understanding what determines range expansion or extinction is crucial to predict the success of biological invaders. We tackled this long-standing question from an unparalleled perspective using the failed expansions in Littorina saxatilis and investigated its present and past habitat suitability in Europe through Ecological Niche Modelling. This intertidal snail is a typically successful Atlantic colonizer and the earliest confirmed alien species in the Mediterranean Sea, where, however, it failed to thrive despite its high dispersal ability and adaptability. We explored the environmental constraints affecting its biogeography, identified potential glacial refugia in Europe that fuelled its post-glacial colonisations and tested whether the current gaps in its distribution are linked to local ecological features. Our results suggested that L. saxatilis is unlikely to be a glacial relict in the Mediterranean basin. Multiple Atlantic glacial refugia occurred in the Last Glacial Maximum, and abiotic environmental features such as salinity and water temperature have influenced the past and current distributions of this snail and limited its invasion of the Mediterranean Sea. The snail showed a significant overlap in geographic space and ecological niche with Carcinusmaenas, the Atlantic predator, but distinct from Pachygrapsusmarmoratus, the Mediterranean predator, further pointing to Atlantic-like habitat requirements for this species. Abiotic constrains during introduction rather than dispersal abilities have shaped the past and current range of L. saxatilis and help explaining why some invasions have not been successful. Our findings contribute to clarifying the processes constraining or facilitating shifts in species’ distributions and biological invasions.
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5. |
- Butlin, Roger, 1955, et al.
(författare)
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PARALLEL EVOLUTION OF LOCAL ADAPTATION AND REPRODUCTIVE ISOLATION IN THE FACE OF GENE FLOW
- 2014
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Ingår i: Evolution. - : Wiley. - 0014-3820. ; 68:4, s. 935-949
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Tidskriftsartikel (refereegranskat)abstract
- Parallel evolution of similar phenotypes provides strong evidence for the operation of natural selection. Where these phenotypes contribute to reproductive isolation, they further support a role for divergent, habitat-associated selection in speciation. However, the observation of pairs of divergent ecotypes currently occupying contrasting habitats in distinct geographical regions is not sufficient to infer parallel origins. Here we show striking parallel phenotypic divergence between populations of the rocky-shore gastropod, Littorina saxatilis, occupying contrasting habitats exposed to either wave action or crab predation. This divergence is associated with barriers to gene exchange but, nevertheless, genetic variation is more strongly structured by geography than by ecotype. Using approximate Bayesian analysis of sequence data and amplified fragment length polymorphism markers, we show that the ecotypes are likely to have arisen in the face of continuous gene flow and that the demographic separation of ecotypes has occurred in parallel at both regional and local scales. Parameter estimates suggest a long delay between colonization of a locality and ecotype formation, perhaps because the postglacial spread of crab populations was slower than the spread of snails. Adaptive differentiation may not be fully genetically independent despite being demographically parallel. These results provide new insight into a major model of ecologically driven speciation.
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6. |
- De Jode, Aurélien, et al.
(författare)
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Ten years of demographic modelling of divergence and speciation in the sea
- 2022
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Ingår i: Evolutionary Applications. - : Wiley. - 1752-4571. ; 16:2, s. 542-59
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Tidskriftsartikel (refereegranskat)abstract
- Understanding population divergence that eventually leads to speciation is essential for evolutionary biology. High species diversity in the sea was regarded as a paradox when strict allopatry was considered necessary for most speciation events because geographical barriers seemed largely absent in the sea, and many marine species have high dispersal capacities. Combining genome-wide data with demographic modelling to infer the demographic history of divergence has introduced new ways to address this classical issue. These models assume an ancestral population that splits into two subpopulations diverging according to different scenarios that allow tests for periods of gene flow. Models can also test for heterogeneities in population sizes and migration rates along the genome to account, respectively, for background selection and selection against introgressed ancestry. To investigate how barriers to gene flow arise in the sea, we compiled studies modelling the demographic history of divergence in marine organisms and extracted preferred demographic scenarios together with estimates of demographic parameters. These studies show that geographical barriers to gene flow do exist in the sea but that divergence can also occur without strict isolation. Heterogeneity of gene flow was detected in most population pairs suggesting the predominance of semipermeable barriers during divergence. We found a weak positive relationship between the fraction of the genome experiencing reduced gene flow and levels of genome-wide differentiation. Furthermore, we found that the upper bound of the ‘grey zone of speciation’ for our dataset extended beyond that found before, implying that gene flow between diverging taxa is possible at higher levels of divergence than previously thought. Finally, we list recommendations for further strengthening the use of demographic modelling in speciation research. These include a more balanced representation of taxa, more consistent and comprehensive modelling, clear reporting of results and simulation studies to rule out nonbiological explanations for general results.
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7. |
- Faria, R., et al.
(författare)
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Evolving Inversions
- 2019
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Ingår i: Trends in Ecology & Evolution. - : Elsevier BV. - 0169-5347. ; 34:3, s. 239-248
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Forskningsöversikt (refereegranskat)abstract
- Empirical data suggest that inversions in many species contain genes important for intraspecific divergence and speciation, yet mechanisms of evolution remain unclear. While genes inside an inversion are tightly linked, inversions are not static but evolve separately from the rest of the genome by new mutations, recombination within arrangements, and gene flux between arrangements. Inversion polymorphisms are maintained by different processes, for example, divergent or balancing selection, or a mix of multiple processes. Moreover, the relative roles of selection, drift, mutation, and recombination will change over the lifetime of an inversion and within its area of distribution. We believe inversions are central to the evolution of many species, but we need many more data and new models to understand the complex mechanisms involved.
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8. |
- Faria, R., et al.
(författare)
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Multiple chromosomal rearrangements in a hybrid zone between Littorina saxatilis ecotypes
- 2019
-
Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 28:6, s. 1375-1393
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Tidskriftsartikel (refereegranskat)abstract
- Both classical and recent studies suggest that chromosomal inversion polymorphisms are important in adaptation and speciation. However, biases in discovery and reporting of inversions make it difficult to assess their prevalence and biological importance. Here, we use an approach based on linkage disequilibrium among markers genotyped for samples collected across a transect between contrasting habitats to detect chromosomal rearrangements de novo. We report 17 polymorphic rearrangements in a single locality for the coastal marine snail, Littorina saxatilis. Patterns of diversity in the field and of recombination in controlled crosses provide strong evidence that at least the majority of these rearrangements are inversions. Most show clinal changes in frequency between habitats, suggestive of divergent selection, but only one appears to be fixed for different arrangements in the two habitats. Consistent with widespread evidence for balancing selection on inversion polymorphisms, we argue that a combination of heterosis and divergent selection can explain the observed patterns and should be considered in other systems spanning environmental gradients.
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9. |
- Hearn, K. E., et al.
(författare)
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Differing associations between sex determination and sex-linked inversions in two ecotypes of Littorina saxatilis
- 2022
-
Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 6:5, s. 358-74
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Tidskriftsartikel (refereegranskat)abstract
- Sexual antagonism is a common hypothesis for driving the evolution of sex chromosomes, whereby recombination suppression is favored between sexually antagonistic loci and the sex-determining locus to maintain beneficial combinations of alleles. This results in the formation of a sex-determining region. Chromosomal inversions may contribute to recombination suppression but their precise role in sex chromosome evolution remains unclear. Because local adaptation is frequently facilitated through the suppression of recombination between adaptive loci by chromosomal inversions, there is potential for inversions that cover sex-determining regions to be involved in local adaptation as well, particularly if habitat variation creates environment-dependent sexual antagonism. With these processes in mind, we investigated sex determination in a well-studied example of local adaptation within a species: the intertidal snail, Littorina saxatilis. Using SNP data from a Swedish hybrid zone, we find novel evidence for a female-heterogametic sex determination system that is restricted to one ecotype. Our results suggest that four putative chromosomal inversions, two previously described and two newly discovered, span the putative sex chromosome pair. We determine their differing associations with sex, which suggest distinct strata of differing ages. The same inversions are found in the second ecotype but do not show any sex association. The striking disparity in inversion-sex associations between ecotypes that are connected by gene flow across a habitat transition that is just a few meters wide indicates a difference in selective regime that has produced a distinct barrier to the spread of the newly discovered sex-determining region between ecotypes. Such sex chromosome-environment interactions have not previously been uncovered in L. saxatilis and are known in few other organisms. A combination of both sex-specific selection and divergent natural selection is required to explain these highly unusual patterns.
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10. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Diverse pathways to speciation revealed by marine snails
- 2024
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Ingår i: Trends in Genetics. - 0168-9525 .- 1362-4555.
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Forskningsöversikt (refereegranskat)abstract
- Speciation is a key evolutionary process that is not yet fully understood. Combining population genomic and ecological data from multiple diverging pairs of marine snails (Littorina) supports the search for speciation mechanisms. Placing pairs on a one-dimensional speciation continuum, from undifferentiated populations to species, obscured the complexity of speciation. Adding multiple axes helped to describe either speciation routes or reproductive isolation in the snails. Divergent ecological selection repeatedly generated barriers between ecotypes, but appeared less important in completing speciation while genetic incompatibilities played a key role. Chromosomal inversions contributed to genomic barriers, but with variable impact. A multidimensional (hypercube) approach supported framing of questions and identification of knowledge gaps and can be useful to understand speciation in many other systems.
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11. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Is embryo abortion a post-zygotic barrier to gene flow between Littorina ecotypes?
- 2020
-
Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 33:3, s. 342-351
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Tidskriftsartikel (refereegranskat)abstract
- Genetic incompatibilities contribute to reproductive isolation between many diverging populations, but it is still unclear to what extent they play a role if divergence happens with gene flow. In contact zones between the "Crab" and "Wave" ecotypes of the snail Littorina saxatilis, divergent selection forms strong barriers to gene flow, while the role of post-zygotic barriers due to selection against hybrids remains unclear. High embryo abortion rates in this species could indicate the presence of such barriers. Post-zygotic barriers might include genetic incompatibilities (e.g. Dobzhansky-Muller incompatibilities) but also maladaptation, both expected to be most pronounced in contact zones. In addition, embryo abortion might reflect physiological stress on females and embryos independent of any genetic stress. We examined all embryos of >500 females sampled outside and inside contact zones of three populations in Sweden. Females' clutch size ranged from 0 to 1,011 embryos (mean 130 +/- 123), and abortion rates varied between 0% and 100% (mean 12%). We described female genotypes by using a hybrid index based on hundreds of SNPs differentiated between ecotypes with which we characterized female genotypes. We also calculated female SNP heterozygosity and inversion karyotype. Clutch size did not vary with female hybrid index, and abortion rates were only weakly related to hybrid index in two sites but not at all in a third site. No additional variation in abortion rate was explained by female SNP heterozygosity, but increased female inversion heterozygosity added slightly to increased abortion. Our results show only weak and probably biologically insignificant post-zygotic barriers contributing to ecotype divergence, and the high and variable abortion rates were marginally, if at all, explained by hybrid index of females.
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12. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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Oceanographic barriers to gene flow promote genetic subdivision of the tunicate Ciona intestinalis in a North Sea archipelago
- 2018
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 165:8
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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.
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13. |
- 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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14. |
- Johannesson, Kerstin, 1955, et al.
(författare)
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What explains rare and conspicuous colours in a snail? A test of time-series data against models of drift, migration or selection
- 2017
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 0018-067X .- 1365-2540. ; 118:1, s. 21-30
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Tidskriftsartikel (refereegranskat)abstract
- It is intriguing that conspicuous colour morphs of a prey species may be maintained at low frequencies alongside cryptic morphs. Negative frequency-dependent selection by predators using search images ('apostatic selection') is often suggested without rejecting alternative explanations. Using a maximum likelihood approach we fitted predictions from models of genetic drift, migration, constant selection, heterozygote advantage or negative frequency-dependent selection to time-series data of colour frequencies in isolated populations of a marine snail (Littorina saxatilis), re-established with perturbed colour morph frequencies and followed for >20 generations. Snails of conspicuous colours (white, red, banded) are naturally rare in the study area (usually <10%) but frequencies were manipulated to levels of ~50% (one colour per population) in 8 populations at the start of the experiment in 1992. In 2013, frequencies had declined to ~15-45%. Drift alone could not explain these changes. Migration could not be rejected in any population, but required rates much higher than those recorded. Directional selection was rejected in three populations in favour of balancing selection. Heterozygote advantage and negative frequency-dependent selection could not be distinguished statistically, although overall the results favoured the latter. Populations varied idiosyncratically as mild or variable colour selection (3-11%) interacted with demographic stochasticity, and the overall conclusion was that multiple mechanisms may contribute to maintaining the polymorphisms.
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15. |
- Jonsson, Lisbeth G., 1955, et al.
(författare)
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Symbiotic associations between anthozoans and crustaceans in a temperate coastal area
- 2001
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Ingår i: Marine Ecology Progress Series. - 0171-8630. ; 209, s. 189-195
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Tidskriftsartikel (refereegranskat)abstract
- While symbiotic associations between anemones and crustaceans appear to be common in tropical waters, few such associations are known from temperate waters, except for the symbiosis between hermit crabs and anemones. In this study, observations made with ROVs (remotely operated vehicles) suggested that certain shrimps (Pandalus borealis, P. propinquus, P. montagui and in particular Spirontocaris liljeborgii and Lebbeus polaris) associate with the anemone Bolocera tuediae and the cerianthid Pachycerianthus multiplicatus by aggregating beneath their tentacles. The lithodid crab Lithodes maja was also observed associating with B. tuediae. Laboratory experiments suggested that female crabs have a stronger association than males. The associations are presumably facultative commensalistic, as the species of crustaceans live as non-symbionts on the sea floor as well, and the 2 anthozoans do not seem to gain any benefits from the associations. In the field, S. liljeborgii had the closest association with both species of anthozoans, while B. tuediae was the preferred host of all associating species. The main benefit for the crustaceans to be associated with the anthozoans is protection against predators. In the case of the shrimps, access to a food source is probably also important.
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16. |
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17. |
- Koch, E. L., et al.
(författare)
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Genetic architecture of repeated phenotypic divergence in Littorina saxatilis ecotype evolution
- 2022
-
Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 76:10, s. 2332-2346
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Tidskriftsartikel (refereegranskat)abstract
- Chromosomal inversions have been shown to play a major role in a local adaptation by suppressing recombination between alternative arrangements and maintaining beneficial allele combinations. However, so far, their importance relative to the remaining genome remains largely unknown. Understanding the genetic architecture of adaptation requires better estimates of how loci of different effect sizes contribute to phenotypic variation. Here, we used three Swedish islands where the marine snail Littorina saxatilis has repeatedly evolved into two distinct ecotypes along a habitat transition. We estimated the contribution of inversion polymorphisms to phenotypic divergence while controlling for polygenic effects in the remaining genome using a quantitative genetics framework. We confirmed the importance of inversions but showed that contributions of loci outside inversions are of similar magnitude, with variable proportions dependent on the trait and the population. Some inversions showed consistent effects across all sites, whereas others exhibited site-specific effects, indicating that the genomic basis for replicated phenotypic divergence is only partly shared. The contributions of sexual dimorphism as well as environmental factors to phenotypic variation were significant but minor compared to inversions and polygenic background. Overall, this integrated approach provides insight into the multiple mechanisms contributing to parallel phenotypic divergence. © 2022 The Authors. Evolution published by Wiley Periodicals LLC on behalf of The Society for the Study of Evolution.
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18. |
- Le Moan, Alan, et al.
(författare)
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An allozyme polymorphism is associated with a large chromosomal inversion in the marine snail Littorina fabalis
- 2022
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Ingår i: Evolutionary Applications. - : Wiley. - 1752-4571. ; 16:2, s. 279-92
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the genetic targets of natural selection is one of the most challenging goals of population genetics. Some of the earliest candidate genes were identified from associations between allozyme allele frequencies and environmental variation. One such example is the clinal polymorphism in the arginine kinase (Ak) gene in the marine snail Littorina fabalis. While other enzyme loci do not show differences in allozyme frequencies among populations, the Ak alleles are near differential fixation across repeated wave exposure gradients in Europe. Here, we use this case to illustrate how a new sequencing toolbox can be employed to characterize the genomic architecture associated with historical candidate genes. We found that the Ak alleles differ by nine nonsynonymous substitutions, which perfectly explain the different migration patterns of the allozymes during electrophoresis. Moreover, by exploring the genomic context of the Ak gene, we found that the three main Ak alleles are located on different arrangements of a putative chromosomal inversion that reaches near fixation at the opposing ends of two transects covering a wave exposure gradient. This shows Ak is part of a large (3/4 of the chromosome) genomic block of differentiation, in which Ak is unlikely to be the only target of divergent selection. Nevertheless, the nonsynonymous substitutions among Ak alleles and the complete association of one allele with one inversion arrangement suggest that the Ak gene is a strong candidate to contribute to the adaptive significance of the inversion.
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19. |
- Le Moan, Alan, et al.
(författare)
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Coupling of twelve putative chromosomal inversions maintains a strong barrier to gene flow between snail ecotypes
- 2024
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Ingår i: EVOLUTION LETTERS. - 2056-3744. ; 8:4, s. 575-586
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Tidskriftsartikel (refereegranskat)abstract
- Chromosomal rearrangements can lead to the coupling of reproductive barriers, but whether and how they contribute to the completion of speciation remains unclear. Marine snails of the genus Littorina repeatedly form hybrid zones between populations segregating for multiple inversion arrangements, providing opportunities to study their barrier effects. Here, we analyzed 2 adjacent transects across hybrid zones between 2 ecotypes of Littorina fabalis ("large" and "dwarf") adapted to different wave exposure conditions on a Swedish island. Applying whole-genome sequencing, we found 12 putative inversions on 9 of 17 chromosomes. Nine of the putative inversions reached near differential fixation between the 2 ecotypes, and all were in strong linkage disequilibrium. These inversions cover 20% of the genome and carry 93% of divergent single nucleotide polymorphisms (SNPs). Bimodal hybrid zones in both transects indicated that the 2 ecotypes of Littorina fabalis maintain their genetic and phenotypic integrity following contact. The bimodality reflects the strong coupling between inversion clines and the extension of the barrier effect across the whole genome. Demographic inference suggests that coupling arose during a period of allopatry and has been maintained for > 1,000 generations after secondary contact. Overall, this study shows that the coupling of multiple chromosomal inversions contributes to strong reproductive isolation. Notably, 2 of the putative inversions overlap with inverted genomic regions associated with ecotype differences in a closely related species (Littorina saxatilis), suggesting the same regions, with similar structural variants, repeatedly contribute to ecotype evolution in distinct species.
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20. |
- Le Pennec, Guénolé, et al.
(författare)
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Adaptation to dislodgement risk on wave-swept rocky shores in the snail Littorina saxatilis.
- 2017
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Ingår i: PloS one. - : Public Library of Science (PLoS). - 1932-6203. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- The periwinkle Littorina saxatilis has repeatedly evolved both a small, fragile and globose "wave ecotype" confined to wave-swept shores and a large, robust and elongated "crab ecotype" found in nearby crab-rich but less-exposed shores. This phenotypic divergence is assumed to reflect, in some part, local adaptation to wave exposure, but this hypothesis has received incomplete experimental testing. Here, we report a test of the prediction that the wave ecotype has a higher capacity to resist water flow than the crab ecotype. We sampled snails along a crab-wave transect and measured their resistance to dislodgement in a high-speed water flume with water speeds that match those of breaking waves in a range of relevant field conditions. Snails from the wave environment were consistently more resistant to water flow than snails from the crab environment and high resistance was positively correlated with the surface area of the foot and the area of the outer aperture contour both relative to shell size, and to the extent of lateral shell compression. In a separate experiment, we found that snails raised in still water in a common garden showed higher resistance to water flow if originating from a wave environment than from a crab environment, and this was true both at juvenile (2 weeks) and adult (10 months) developmental stages. This result suggests genetic control of a distinct "wave adapted" phenotype, likely to be maintained under strong divergent selection between the two adjacent habitats.
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21. |
- Morales, Hernán E., 1985, et al.
(författare)
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Genomic architecture of parallel ecological divergence: Beyond a single environmental contrast
- 2019
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:12
-
Tidskriftsartikel (refereegranskat)abstract
- The study of parallel ecological divergence provides important clues to the operation of natural selection. Parallel divergence often occurs in heterogeneous environments with different kinds of environmental gradients in different locations, but the genomic basis underlying this process is unknown. We investigated the genomics of rapid parallel adaptation in the marine snail Littorina saxatilis in response to two independent environmental axes (crab-predation versus wave-action and low-shore versus high-shore). Using pooled whole-genome resequencing, we show that sharing of genomic regions of high differentiation between environments is generally low but increases at smaller spatial scales. We identify different shared genomic regions of divergence for each environmental axis and show that most of these regions overlap with candidate chromosomal inversions. Several inversion regions are divergent and polymorphic across many localities. We argue that chromosomal inversions could store shared variation that fuels rapid parallel adaptation to heterogeneous environments, possibly as balanced polymorphism shared by adaptive gene flow.
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22. |
- Perini, Samuel, 1990, et al.
(författare)
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Assortative mating, sexual selection, and their consequences for gene flow in Littorina
- 2020
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 74:7, s. 1482-1497
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Tidskriftsartikel (refereegranskat)abstract
- When divergent populations are connected by gene flow, the establishment of complete reproductive isolation usually requires the joint action of multiple barrier effects. One example where multiple barrier effects are coupled consists of a single trait that is under divergent natural selection and also mediates assortative mating. Such multiple-effect traits can strongly reduce gene flow. However, there are few cases where patterns of assortative mating have been described quantitatively and their impact on gene flow has been determined. Two ecotypes of the coastal marine snail,Littorina saxatilis, occur in North Atlantic rocky-shore habitats dominated by either crab predation or wave action. There is evidence for divergent natural selection acting on size, and size-assortative mating has previously been documented. Here, we analyze the mating pattern inL. saxatiliswith respect to size in intensively sampled transects across boundaries between the habitats. We show that the mating pattern is mostly conserved between ecotypes and that it generates both assortment and directional sexual selection for small male size. Using simulations, we show that the mating pattern can contribute to reproductive isolation between ecotypes but the barrier to gene flow is likely strengthened more by sexual selection than by assortment.
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23. |
- Perini, Samuel, 1990, et al.
(författare)
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Very short mountings are enough for sperm transfer in Littorina saxatilis
- 2022
-
Ingår i: Journal of Molluscan Studies. - : Oxford University Press (OUP). - 0260-1230 .- 1464-3766. ; 88:1
-
Tidskriftsartikel (refereegranskat)abstract
- Conflict over reproduction between females and males exists because of anisogamy and promiscuity. Together they generate differences in fitness optima between the sexes and result in antagonistic coevolution of female and male reproductive traits. Mounting duration is likely to be a compromise between male and female interests whose outcome depends on the intensity of sexual selection. The timing of sperm transfer during mounting is critical. For example, mountings may be interrupted before sperm is transferred as a consequence of female or male choice, or they may be prolonged to function as mate guarding. In the highly promiscuous intertidal snail Littorina saxatilis, mountings vary substantially in duration, from less than a minute to more than an hour, and it has been assumed that mountings of a few minutes do not result in any sperm being transferred. Here, we examined the timing of sperm transfer, a reproductive trait that is likely affected by sexual conflict. We performed time-controlled mounting trials using L. saxatilis males and virgin females, aiming to examine indirectly when the transfer of sperm starts. We observed the relationship between mounting duration and the proportion of developing embryos out of all eggs and embryos in the brood pouch. Developing embryos were observed in similar proportions in all treatments (i.e. 1, 5 and 10 or more minutes at which mountings were artificially interrupted), suggesting that sperm transfer begins rapidly (within 1 min) in L. saxatilis and very short matings do not result in sperm shortage in the females. We discuss how the observed pattern can be influenced by predation risk, population density, and female status and receptivity.
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24. |
- Rafajlović, Marina, 1983, et al.
(författare)
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A universal mechanism generating clusters of differentiated loci during divergence-with-migration
- 2016
-
Ingår i: Evolution. - : Wiley. - 0014-3820. ; 70:7, s. 1609-1621
-
Tidskriftsartikel (refereegranskat)abstract
- Genome-wide patterns of genetic divergence reveal mechanisms of adaptation under gene flow. Empirical data show that divergence is mostly concentrated in narrow genomic regions. This pattern may arise because differentiated loci protect nearby mutations from gene flow, but recent theory suggests this mechanism is insufficient to explain the emergence of concentrated differentiation during biologically realistic timescales. Critically, earlier theory neglects an inevitable consequence of genetic drift: stochastic loss of local genomic divergence. Here, we demonstrate that the rate of stochastic loss of weak local differentiation increases with recombination distance to a strongly diverged locus and, above a critical recombination distance, local loss is faster than local "gain" of new differentiation. Under high migration and weak selection, this critical recombination distance is much smaller than the total recombination distance of the genomic region under selection. Consequently, divergence between populations increases by net gain of new differentiation within the critical recombination distance, resulting in tightly linked clusters of divergence. The mechanism responsible is the balance between stochastic loss and gain of weak local differentiation, a mechanism acting universally throughout the genome. Our results will help to explain empirical observations and lead to novel predictions regarding changes in genomic architectures during adaptive divergence.
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25. |
- Rafajlović, Marina, 1983, et al.
(författare)
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Introduction to the theme issue 'Species' ranges in the face of changing environments'
- 2022
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Ingår i: Philosophical Transactions of the Royal Society B: Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 377
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Understanding where, when and howspecies' ranges will be modified is both a fundamental problem and essential to predicting how spatio-temporal environmental changes in abiotic and biotic factors impact biodiversity. Notably, different species may respond disparately to similar environmental changes: some species may overcome an environmental change only with difficulty or not at all, while other species may readily overcome the same change. Ranges may contract, expand or move. The drivers and consequences of this variability in species' responses remain puzzling. Importantly, changes in a species' range creates feedbacks to the environmental conditions, populations and communities in its previous and current range, rendering population genetic, population dynamic and community processes inextricably linked. Understanding these links is critical in guiding biodiversity management and conservation efforts. This theme issue presents current thinking about the factors and mechanisms that limit and/or modify species' ranges. It also outlines different approaches to detect changes in species' distributions, and illustrates cases of range modifications in several taxa. Overall, this theme issue highlights the urgency of understanding species' ranges but shows that we are only just beginning to disentangle the processes involved. Oneway forward is to unite ecology with evolutionary biology and empirical with modelling approaches. This article is part of the theme issue 'Species' ranges in the face of changing environments (Part II)'.
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26. |
- Rafajlović, Marina, 1983, et al.
(författare)
-
Preface
- 2022
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Ingår i: Philosophical Transactions of the Royal Society B: Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 377
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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27. |
- Ravinet, Mark, 1986, et al.
(författare)
-
Shared and nonshared genomic divergence in parallel ecotypes of Littorina saxatilis at a local scale
- 2016
-
Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 25:1, s. 287-305
-
Tidskriftsartikel (refereegranskat)abstract
- Parallel speciation occurs when selection drives repeated, independent adaptive divergence that reduces gene flow between ecotypes. Classical examples show parallel speciation originating from shared genomic variation, but this does not seem to be the case in the rough periwinkle (Littorina saxatilis) that has evolved considerable phenotypic diversity across Europe, including several distinct ecotypes. Small ‘wave’ ecotype snails inhabit exposed rocks and experience strong wave action, while thick-shelled, ‘crab’ ecotype snails are larger and experience crab predation on less exposed shores. Crab and wave ecotypes appear to have arisen in parallel, and recent evidence suggests only marginal sharing of molecular variation linked to evolution of similar ecotypes in different parts of Europe. However, the extent of genomic sharing is expected to increase with gene flow and more recent common ancestry. To test this, we used de novo RAD-sequencing to quantify the extent of shared genomic divergence associated with phenotypic similarities amongst ecotype pairs on three close islands (<10 km distance) connected by weak gene flow (Nm ~ 0.03) and with recent common ancestry (<10 000 years). After accounting for technical issues, including a large proportion of null alleles due to a large effective population size, we found ~8–28% of positive outliers were shared between two islands and ~2–9% were shared amongst all three islands. This low level of sharing suggests that parallel phenotypic divergence in this system is not matched by shared genomic divergence despite a high probability of gene flow and standing genetic variation.
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28. |
- Stankowski, S., et al.
(författare)
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The evolution of strong reproductive isolation between sympatric intertidal snails
- 2020
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Ingår i: Philosophical Transactions of the Royal Society B-Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 375:1806
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of strong reproductive isolation (RI) is fundamental to the origins and maintenance of biological diversity, especially in situations where geographical distributions of taxa broadly overlap. But what is the history behind strong barriers currently acting in sympatry? Using whole-genome sequencing and single nucleotide polymorphism genotyping, we inferred (i) the evolutionary relationships, (ii) the strength of RI, and (iii) the demographic history of divergence between two broadly sympatric taxa of intertidal snail. Despite being cryptic, based on external morphology, Littorina arcana and Littorina saxatilis differ in their mode of female reproduction (egg-laying versus brooding), which may generate a strong post-zygotic barrier. We show that egg-laying and brooding snails are closely related, but genetically distinct. Genotyping of 3092 snails from three locations failed to recover any recent hybrid or backcrossed individuals, confirming that RI is strong. There was, however, evidence for a very low level of asymmetrical introgression, suggesting that isolation remains incomplete. The presence of strong, asymmetrical RI was further supported by demographic analysis of these populations. Although the taxa are currently broadly sympatric, demographic modelling suggests that they initially diverged during a short period of geographical separation involving very low gene flow. Our study suggests that some geographical separation may kick-start the evolution of strong RI, facilitating subsequent coexistence of taxa in sympatry. The strength of RI needed to achieve sympatry and the subsequent effect of sympatry on RI remain open questions. This article is part of the theme issue 'Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers'.
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29. |
- Stankowski, Sean, et al.
(författare)
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The genetic basis of a recent transition to live-bearing in marine snails
- 2024
-
Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 383:6678, s. 114-119
-
Tidskriftsartikel (refereegranskat)abstract
- Key innovations are fundamental to biological diversification, but their genetic basis is poorly understood. A recent transition from egg-laying to live-bearing in marine snails (Littorina spp.) provides the opportunity to study the genetic architecture of an innovation that has evolved repeatedly across animals. Individuals do not cluster by reproductive mode in a genome-wide phylogeny, but local genealogical analysis revealed numerous small genomic regions where all live-bearers carry the same core haplotype. Candidate regions show evidence for live-bearer-specific positive selection and are enriched for genes that are differentially expressed between egg-laying and live-bearing reproductive systems. Ages of selective sweeps suggest that live-bearer-specific alleles accumulated over more than 200,000 generations. Our results suggest that new functions evolve through the recruitment of many alleles rather than in a single evolutionary step.
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30. |
- Westram, A. M., et al.
(författare)
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Clines on the seashore: The genomic architecture underlying rapid divergence in the face of gene flow
- 2018
-
Ingår i: Evolution Letters. - : Oxford University Press (OUP). - 2056-3744. ; 2:4, s. 297-309
-
Tidskriftsartikel (refereegranskat)abstract
- Adaptive divergence and speciation may happen despite opposition by gene flow. Identifying the genomic basis underlying divergence with gene flow is a major task in evolutionary genomics. Most approaches (e.g., outlier scans) focus on genomic regions of high differentiation. However, not all genomic architectures potentially underlying divergence are expected to show extreme differentiation. Here, we develop an approach that combines hybrid zone analysis (i.e., focuses on spatial patterns of allele frequency change) with system-specific simulations to identify loci inconsistent with neutral evolution. We apply this to a genome-wide SNP set from an ideally suited study organism, the intertidal snail Littorina saxatilis, which shows primary divergence between ecotypes associated with different shore habitats. We detect many SNPs with clinal patterns, most of which are consistent with neutrality. Among non-neutral SNPs, most are located within three large putative inversions differentiating ecotypes. Many non-neutral SNPs show relatively low levels of differentiation. We discuss potential reasons for this pattern, including loose linkage to selected variants, polygenic adaptation and a component of balancing selection within populations (which may be expected for inversions). Our work is in line with theory predicting a role for inversions in divergence, and emphasizes that genomic regions contributing to divergence may not always be accessible with methods purely based on allele frequency differences. These conclusions call for approaches that take spatial patterns of allele frequency change into account in other systems.
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31. |
- Westram, A. M., et al.
(författare)
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Inversions and parallel evolution
- 2022
-
Ingår i: Philosophical Transactions of the Royal Society B-Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 377:1856
-
Forskningsöversikt (refereegranskat)abstract
- Local adaptation leads to differences between populations within a species. In many systems, similar environmental contrasts occur repeatedly, sometimes driving parallel phenotypic evolution. Understanding the genomic basis of local adaptation and parallel evolution is a major goal of evolutionary genomics. It is now known that by preventing the break-up of favourable combinations of alleles across multiple loci, genetic architectures that reduce recombination, like chromosomal inversions, can make an important contribution to local adaptation. However, little is known about whether inversions also contribute disproportionately to parallel evolution. Our aim here is to highlight this knowledge gap, to showcase existing studies, and to illustrate the differences between genomic architectures with and without inversions using simple models. We predict that by generating stronger effective selection, inversions can sometimes speed up the parallel adaptive process or enable parallel adaptation where it would be impossible otherwise, but this is highly dependent on the spatial setting. We highlight that further empirical work is needed, in particular to cover a broader taxonomic range and to understand the relative importance of inversions compared to genomic regions without inversions.This article is part of the theme issue 'Genomic architecture of supergenes: causes and evolutionary consequences'.
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32. |
- Andersson, Björn, 1985, et al.
(författare)
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Cross-contamination risks in sediment-based resurrection studies of phytoplankton
- 2022
-
Ingår i: Limnology and Oceanography Letters. - : Wiley. - 2378-2242. ; 8:2, s. 376-84
-
Tidskriftsartikel (refereegranskat)abstract
- Resurrection studies can answer some fundamental questions in aquatic ecology and evolutionary biology. For phytoplankton resting stages, longevity of thousands to millions of years has recently been reported. However, contamination during sediment sampling could distort these estimates, and this risk has not been systematically evaluated. Here we used 4.5 mu m diameter microspheres to quantify contamination while reviving the resting stages of seven abundant estuarine diatom and cyanobacterial taxa. We observed a sharp decline in resting stages abundance from 10(6) (g wet sediment)(-1) at the surface to < 0.8 (g wet sediment)(-1) at 12.5 cm depth. Added microspheres (similar to 4.5 x 10(7) cm(-2)) were translocated even deeper down the sediment and could well explain the vertical distributions and abundances of revived cells. Without this control, we could have claimed to have revived seven multi-decades to centennial-old taxa. Our findings suggest that improved contamination controls are needed for sediment core sampling of rare cells, microfossils, or DNA molecules.
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33. |
- Andersson, Björn, et al.
(författare)
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Strain-specific metabarcoding reveals rapid evolution of copper tolerance in populations of the coastal diatom Skeletonema marinoi
- 2023
-
Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X.
-
Tidskriftsartikel (refereegranskat)abstract
- Phytoplankton have short generation times, flexible reproduction strategies, large population sizes and high standing genetic diversity, traits that should facilitate rapid evolution under directional selection. We quantified local adaptation of copper tolerance in a population of the diatom Skeletonema marinoi from a mining-exposed inlet in the Baltic Sea and in a non-exposed population 100 km away. We hypothesized that mining pollution has driven evolution of elevated copper tolerance in the impacted population of S. marinoi. Assays of 58 strains originating from sediment resting stages revealed no difference in the average tolerance to copper between the two populations. However, variation within populations was greater at the mining site, with three strains displaying hyper-tolerant phenotypes. In an artificial evolution experiment, we used a novel intraspecific metabarcoding locus to track selection and quantify fitness of all 58 strains during co-cultivation in one control and one toxic copper treatment. As expected, the hyper-tolerant strains enabled rapid evolution of copper tolerance in the mining-exposed population through selection on available strain diversity. Within 42 days, in each experimental replicate a single strain dominated (30%–99% abundance) but different strains dominated the different treatments. The reference population developed tolerance beyond expectations primarily due to slowly developing plastic response in one strain, suggesting that different modes of copper tolerance are present in the two populations. Our findings provide novel empirical evidence that standing genetic diversity of phytoplankton resting stage allows populations to evolve rapidly (20–50 generations) and flexibly on timescales relevant for seasonal bloom progressions.
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34. |
- Andersson, Leif, et al.
(författare)
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Ecological adaptation in cod and herring and possible consequences of future climate change in the Baltic Sea
- 2023
-
Ingår i: Frontiers in Marine Science. - : Frontiers Media S.A.. - 2296-7745. ; 10
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Forskningsöversikt (refereegranskat)abstract
- The Atlantic herring and Atlantic cod are two marine fish species that have successfully adapted to the brackish Baltic Sea, and the former is able to spawn in near-freshwater conditions in the inner Gulf of Bothnia. Here, we review the state of current knowledge concerning ecological adaptation in the two species and make an attempt to predict how they will be able to cope with future climate change. Previous whole genome sequencing studies in Atlantic herring have revealed hundreds of genetic loci underlying ecological adaptation, including several loci that show very strong associations to variation in salinity and temperature. These results suggest the existence of standing genetic variation available for adaptation to a changing environment. However, although Atlantic herring probably has the genetic potential to adapt, its future status also depends on how climate change will affect plankton production and competing species, such as sprat and three-spined stickleback. In cod, the situation is challenging, as there is only one true Baltic population, spawning east of Bornholm and then dispersing towards the east and north. This Baltic cod population is threatened by overfishing, low oxygen levels in benthic waters and generally bad physiological condition of individual fish, in addition to being completely isolated from gene flow from nearby cod populations at the entrance of the Baltic Sea.
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35. |
- Ardehed, Angelica, et al.
(författare)
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Complex spatial clonal structure in the macroalgae Fucus radicans with both sexual and asexual recruitment
- 2015
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 5:19, s. 4233-4245
-
Tidskriftsartikel (refereegranskat)abstract
- In dioecious species with both sexual and asexual reproduction, the spatial distribution of individual clones affects the potential for sexual reproduction and local adaptation. The seaweed Fucus radicans, endemic to the Baltic Sea, has separate sexes, but new attached thalli may also form asexually. We mapped the spatial distribution of clones (multilocus genotypes, MLGs) over macrogeographic (>500km) and microgeographic (<100m) scales in the Baltic Sea to assess the relationship between clonal spatial structure, sexual recruitment, and the potential for natural selection. Sexual recruitment was predominant in some areas, while in others asexual recruitment dominated. Where clones of both sexes were locally intermingled, sexual recruitment was nevertheless low. In some highly clonal populations, the sex ratio was strongly skewed due to dominance of one or a few clones of the same sex. The two largest clones (one female and one male) were distributed over 100-550km of coast and accompanied by small and local MLGs formed by somatic mutations and differing by 1-2 mutations from the large clones. Rare sexual events, occasional long-distance migration, and somatic mutations contribute new genotypic variation potentially available to natural selection. However, dominance of a few very large (and presumably old) clones over extensive spatial and temporal scales suggested that either these have superior traits or natural selection has only been marginally involved in the structuring of genotypes.
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36. |
- Ardehed, Angelica, et al.
(författare)
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Divergence within and among Seaweed Siblings (Fucus vesiculosus and F. radicans) in the Baltic Sea
- 2016
-
Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 11:8
-
Tidskriftsartikel (refereegranskat)abstract
- Closely related taxa provide significant case studies for understanding evolution of new species but may simultaneously challenge species identification and definition. In the Baltic Sea, two dominant and perennial brown algae share a very recent ancestry. Fucus vesiculosus invaded this recently formed postglacial sea 8000 years ago and shortly thereafter Fucus radicans diverged from this lineage as an endemic species. In the Baltic Sea both species reproduce sexually but also recruit fully fertile new individuals by asexual fragmentation. Earlier studies have shown local differences in morphology and genetics between the two taxa in the northern and western Bothnian Sea, and around the island of Saaremaa in Estonia, but geographic patterns seemin conflict with a single origin of F. radicans. To investigate the relationship between northern and Estonian distributions, we analysed the genetic variation using 9 microsatellite loci in populations from eastern Bothnian Sea, Archipelago Sea and the Gulf of Finland. These populations are located in between earlier studied populations. However, instead of bridging the disparate genetic gap between N-W Bothnian Sea and Estonia, as expected from a simple isolation-by-distance model, the new populations substantially increased overall genetic diversity and showed to be strongly divergent from the two earlier analysed regions, showing signs of additional distinct populations. Contrasting earlier findings of increased asexual recruitment in low salinity in the Bothnian Sea, we found high levels of sexual reproduction in some of the Gulf of Finland populations that inhabit extremely low salinity. The new data generated in this study supports the earlier conclusion of two reproductively isolated but very closely related species. However, the new results also add considerable genetic and morphological complexity within species. This makes species separation at geographic scales more demanding and suggests a need for more comprehensive approaches to further disentangle the intriguing relationship and history of the Baltic Sea fucoids.
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37. |
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38. |
- Barth, Julia M.I., et al.
(författare)
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Genome architecture enables local adaptation of Atlantic cod despite high connectivity
- 2017
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 26:17, s. 4452-4466
-
Tidskriftsartikel (refereegranskat)abstract
- Adaptation to local conditions is a fundamental process in evolution; however, mechanisms maintaining local adaptation despite high gene flow are still poorly understood. Marine ecosystems provide a wide array of diverse habitats that frequently promote ecological adaptation even in species characterized by strong levels of gene flow. As one example, populations of the marine fish Atlantic cod (Gadus morhua) are highly connected due to immense dispersal capabilities but nevertheless show local adaptation in several key traits. By combining population genomic analyses based on 12K single nucleotide polymorphisms with larval dispersal patterns inferred using a biophysical ocean model, we show that Atlantic cod individuals residing in sheltered estuarine habitats of Scandinavian fjords mainly belong to offshore oceanic populations with considerable connectivity between these diverse ecosystems. Nevertheless, we also find evidence for discrete fjord populations that are genetically differentiated from offshore populations, indicative of local adaptation, the degree of which appears to be influenced by connectivity. Analyses of the genomic architecture reveal a significant overrepresentation of a large ~5 Mb chromosomal rearrangement in fjord cod, previously proposed to comprise genes critical for the survival at low salinities. This suggests that despite considerable connectivity with offshore populations, local adaptation to fjord environments may be enabled by suppression of recombination in the rearranged region. Our study provides new insights into the potential of local adaptation in high gene flow species within fine geographical scales and highlights the importance of genome architecture in analyses of ecological adaptation.
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39. |
- Bergstrom, L., et al.
(författare)
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Genetic and morphological identification of Fucus radicans sp Nov (Fucales, Phaeophyceae) in the brackish Baltic Sea
- 2005
-
Ingår i: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 41:5, s. 1025-1038
-
Tidskriftsartikel (refereegranskat)abstract
- Brown seaweeds of the genus Fucus occupy a wide variety of temperate coastal habitats. The genus is evolutionary dynamic with recent radiations to form morphologically distinct taxa. In the brackish Baltic Sea, fucoids are the only perennial canopy-forming macroalgae. The most northern populations of Fucus occur permanently submerged in extremely low salinity (3-5 psu). These are currently referred to as Fucus vesiculosus L. but are morphologically distinct with a narrow frond without bladders. We report here that a population of this unique morphotype is reproductively isolated from a truly sympatric population of common F. vesiculosus and conclude that the northern morphotype represents a previously undescribed species. We describe Fucus radicans sp. nov., which is attached and dioecious with broadly elliptic receptacles, characterized by a richly branched narrow flat frond (2-5 mm), short thallus (< 26 cm), and a high capacity for vegetative recruitment of attached plants. Analysis of five highly polymorphic microsatellite DNA loci showed genetic differentiation between sympatric populations of F. radicans and F. vesiculosus, whereas allopatric populations of the same species revealed a coherent pattern of genetic variation. Sequences of the RUBISCO region in F. radicans were identical to or differing at only one to two dinucleotide positions from those of F. vesiculosus, indicating a recent common origin of the two species.
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40. |
- Blakeslee, A. M. H., et al.
(författare)
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Population structure and phylogeography of two North Atlantic Littorina species with contrasting larval development
- 2021
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 168:7
-
Tidskriftsartikel (refereegranskat)abstract
- Phylogeography provides insights into how historical and contemporary processes influence the genetic structure and gene flow in marine organisms around the globe. In benthic marine invertebrates, a species' reproductive strategy can strongly impact phylogeographic patterns and distribution, with some direct-developing (non-planktonic) dispersers demonstrating strong genetic structure but also broad geographic spread. While seemingly paradoxical, past work has shown ovoviviparous species, like Littorina saxatilis, can be more successful colonizers of remote locations than species with planktonic larvae, like L. littorea. Both Littorina species overlap in much of their North Atlantic ranges but have different colonization histories: L. saxatilis is native on both North Atlantic coasts and islands, and L. littorea is native to the eastern Atlantic but introduced to the west. Using an extensive mitochondrial dataset (1236 sequences; 85 sites), we examined how their opposing reproductive strategies correspond to their distributions and phylogeographies. Littorina saxatilis exhibited a heterogeneous genetic structure reflecting post-glacial recolonization from multiple refugial sites, while L. littorea had a homogeneous structure with a post-glacial history characterized by recolonization from one main refugial area in the northeast Atlantic. Further, haplotype diversity was significantly depressed in northwest Atlantic L. littorea populations, signifying a strong bottleneck characteristic of a human-mediated introduction. In contrast, haplotype diversity in L. saxatilis was similar between the two regions, demonstrating long-term history on both coasts. Thus, our study suggests contrasting life-history characteristics were a major structuring force in the phylogeographic patterns of these related species following large-scale disturbances (natural and anthropogenic) that compel contraction and redistribution over large areas.
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41. |
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42. |
- De Wit, Pierre, 1978, et al.
(författare)
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Diet-dependent gene expression highlights the importance of Cytochrome P450 in detoxification of algal secondary metabolites in a marine isopod
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Isopods of the genus Idotea have an unusual ability to feed on algae containing high amounts of chemical defense molecules, such as species of the genera Fucus and Ulva. In this study, we compared gene expression patterns of Idotea balthica individuals fed with Fucus vesiculosus to individuals fed with Ulva lactuca. We generated the rst-ever transcriptome assembly for this species, and found 3,233 di erentially expressed genes across feeding regimes. However, only a handful of biological functions were enriched with regard to di erentially expressed genes, the most notable being “alkaloid metabolic process”. Within this category, we found eight di erentially expressed cytochrome P450 (CYP) unigenes, all of which had a higher expression in the U. lactuca diet treatment. A phylogenetic analysis showed that the di erentially expressed CYP genes are closely related to a CYP gene described from the hepatopancreas of the spiny lobster Panulirus argus, and we hypothesize that these transcripts are involved in metabolite detoxi cation. This is a rst step in the understanding of this algae-grazer interaction, and will form a basis for future work to characterize cytochrome P450 functioning in marine crustaceans.
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43. |
- De Wit, Pierre, 1978, et al.
(författare)
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Spatial genetic structure in a crustacean herbivore highlights the need for local considerations in Baltic Sea biodiversity management
- 2020
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Ingår i: Evolutionary Applications. - : Wiley. - 1752-4563 .- 1752-4571. ; 13:5, s. 974-990
-
Tidskriftsartikel (refereegranskat)abstract
- Incorporating species' eco-evolutionary responses to human-caused disturbances remains a challenge in marine management efforts. A prerequisite is knowledge of geographic structure and scale of genetic diversity and connectivity—the so-called seascape genetic patterns. The Baltic Sea is an excellent model system for studies linking seascape genetics with effects of anthropogenic stress. However, seascape genetic patterns in this area are only described for a few species and are completely unknown for invertebrate herbivores, which constitute a critical part of the ecosystem. This information is crucial for sustainable management, particularly under future scenarios of rapid environmental change. Here, we investigate the population genetic structure among 31 locations throughout the Baltic Sea, of which 45% were located in marine protected areas, in one of the most important herbivores of this region, the isopod crustacean Idotea balthica, using an array of 33,774 genome-wide SNP markers derived from 2b-RAD sequencing. In addition, we generate a biophysical connectivity matrix for I. balthica from a combination of oceanographic current models and estimated life history traits. We find population structure on scales of hundreds of kilometers across the Baltic Sea, where genomic patterns in most cases closely match biophysical connectivity, indicating passive transport with oceanographic currents as an important mean of dispersal in this species. We also find a reduced genetic diversity in terms of heterozygosity along the main salinity gradient of the Baltic Sea, suggesting periods of low population size. Our results provide crucial information for the management of a key ecosystem species under expected changes in temperature and salinity following global climate change in a marine coastal area. © 2019 The Authors. Evolutionary Applications published by John Wiley & Sons Ltd.
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44. |
- Ekendahl, Anette, et al.
(författare)
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Shell colour variation in Littorina saxatilis Olivi (Prosobranchia : Littorinidae): a multi-factor approach
- 1997
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Ingår i: Biological Journal of the Linnean Society. - 0024-4066. ; 62:3, s. 401-419
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Tidskriftsartikel (refereegranskat)abstract
- The marine snail Littorina saxatilis is highly polymorphic for shell colour. It lives in the heterogeneous intertidal zone, where there are sharp transitions in a number of abiotic factors that may influence the relative fitness of morphs. We investigated the hypothesis of selected variation by relating the colour distribution to five factors (wave exposure, substratum, shore level, sex, snail age), and to interactions between them. We compared patterns from geographical areas in Sweden, Iceland and Russia. Cryptic morphs (tessellated and different dark colours) generally dominated (80-98%) while conspicuous morphs (white, yellow, red and banded) were less common (2-20%). The colour frequencies were often related to wave exposure, substratum and shore level. Frequencies rarely varied with age and never with sex. In order to test the assumption that the different colours are genetically determined we cross-bred snails from Iceland in the laboratory. Both the presence of bands and the ground colours of the shell were inherited, and we have tentative support for a one-locus two-allele model for banding. Our results support a model of selected inherited colour variation, involving a number of different selective agents, the importance of which may vary between populations on local and geographical scales. (C) 1997 The Linnean Society of London.
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45. |
- Eriksson, Anders, 1975, et al.
(författare)
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Multiple paternity: determining the minimum number of sires of a large brood
- 2010
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Ingår i: Molecular Ecology Resources. - 1755-098X. ; 10:2, s. 282-291
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Tidskriftsartikel (refereegranskat)abstract
- We describe an efficient algorithm for determining exactly the minimum number of sires consistent with the multi-locus genotypes of a mother and her progeny. We consider cases where a simple exhaustive search through all possible sets of sires is impossible in practice because it would take too long to complete. Our algorithm for solving this combinatorial optimization problem avoids visiting large parts of search space that would not result in a solution with fewer sires. This improvement is of particular importance when the number of allelic types in the progeny array is large and when the minimum number of sires is expected to be large. Precisely in such cases, it is important to know the minimum number of sires: this number gives an exact bound on the most likely number of sires estimated by a random search algorithm in a parameter region where it may be difficult to determine whether it has converged. We apply our algorithm to data from the marine snail, Littorina saxatilis.
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46. |
- Erlandsson, Johan, et al.
(författare)
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Migratory differences between ecotypes of the snail Littorina saxatilis on Galician rocky shores
- 1998
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Ingår i: Evolutionary Ecology. - 0269-7653. ; 12:8, s. 913-924
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Tidskriftsartikel (refereegranskat)abstract
- Local migration patterns may be crucial to gene flow in species of marine gastropods which do not broadcast pelagic larvae. In some species, dispersal over distances of a few metres may influence micro-scale population structures. We investigated the migration pattern in Galician populations of the snail Littorina saxatilis in which populations of contrasting morphologies occupy different tidal levels of the same rocky shore. Two distinct morphs, one at the upper and one at the lower shore, overlap in distribution in a small mid-shore region where hybrids are produced. We documented the distances and directions of migration of both parental morphs and hybrids 1 month after they had been marked and released at different shore levels. When placed at their native shore level, snails migrated less than about 2 m and usually in independent directions. This supports the suggestion of a low local gene flow. At an alien shore level, however, the morphs often moved further and more directionally compared with native morphs. These differences may help to keep the two morphs separated at different shore levels. As fitness of an individual is highest in its native habitat, this seems to be an adaptive strategy.
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47. |
- Faria, R., et al.
(författare)
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Speciation in marine environments: Diving under the surface
- 2021
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 34:1, s. 4-15
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Tidskriftsartikel (refereegranskat)abstract
- Marine environments are inhabited by a broad representation of the tree of life, yet our understanding of speciation in marine ecosystems is extremely limited compared with terrestrial and freshwater environments. Developing a more comprehensive picture of speciation in marine environments requires that we 'dive under the surface' by studying a wider range of taxa and ecosystems is necessary for a more comprehensive picture of speciation. Although studying marine evolutionary processes is often challenging, recent technological advances in different fields, from maritime engineering to genomics, are making it increasingly possible to study speciation of marine life forms across diverse ecosystems and taxa. Motivated by recent research in the field, including the 14 contributions in this issue, we highlight and discuss six axes of research that we think will deepen our understanding of speciation in the marine realm: (a) study a broader range of marine environments and organisms; (b) identify the reproductive barriers driving speciation between marine taxa; (c) understand the role of different genomic architectures underlying reproductive isolation; (d) infer the evolutionary history of divergence using model-based approaches; (e) study patterns of hybridization and introgression between marine taxa; and (f) implement highly interdisciplinary, collaborative research programmes. In outlining these goals, we hope to inspire researchers to continue filling this critical knowledge gap surrounding the origins of marine biodiversity.
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48. |
- Galindo, J., et al.
(författare)
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Genetic and morphological divergence between Littorina fabalis ecotypes in Northern Europe
- 2021
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 34:1, s. 97-113
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Tidskriftsartikel (refereegranskat)abstract
- Low dispersal marine intertidal species facing strong divergent selective pressures associated with steep environmental gradients have a great potential to inform us about local adaptation and reproductive isolation. Among these, gastropods of the genus Littorina offer a unique system to study parallel phenotypic divergence resulting from adaptation to different habitats related with wave exposure. In this study, we focused on two Littorina fabalis ecotypes from Northern European shores and compared patterns of habitat-related phenotypic and genetic divergence across three different geographic levels (local, regional and global). Geometric morphometric analyses revealed that individuals from habitats moderately exposed to waves usually present a larger shell size with a wider aperture than those from sheltered habitats. The phenotypic clustering of L. fabalis by habitat across most locations (mainly in terms of shell size) support an important role of ecology in morphological divergence. A genome scan based on amplified fragment length polymorphisms (AFLPs) revealed a heterogeneous pattern of differentiation across the genome between populations from the two different habitats, suggesting ecotype divergence in the presence of gene flow. The contrasting patterns of genetic structure between nonoutlier and outlier loci, and the decreased sharing of outlier loci with geographic distance among locations are compatible with parallel evolution of phenotypic divergence, with an important contribution of gene flow and/or ancestral variation. In the future, model-based inference studies based on sequence data across the entire genome will help unravelling these evolutionary hypotheses, improving our knowledge about adaptation and its influence on diversification within the marine realm.
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49. |
- Granovitch, A., et al.
(författare)
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Digenetic trematodes in four species of Littorina from the west coast of Sweden
- 2000
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Ingår i: Ophelia. - 0078-5326. ; 53:1, s. 55-65
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Tidskriftsartikel (refereegranskat)abstract
- Four species of Littorina (L. littorea, L. obtusata, L. fabalis and L. saxatilis) from the Swedish west coast were examined fur infections with digenetic trematodes. Four species of the genus Microphallus, Podocyte atomon, Renicola roscovita, Himasthla elongata, Cryptocotyle lingua, and Paramonostomum chabaudi were found, in addition to encysted metacercariae of the two genera Himasthla and Renicola. The prevalence of sporocysts and rediae varied substantially among sampled populations (0-44%), as did the prevalence of metacercarial infections (3-100%), and this variation was due both to different microhabitats and to different host species. In L. saxatilis exposed rocky shore populations had lower prevalence than sheltered boulder shore populations. Within the same shores, L. littorea was the trust species with highest prevalence of digeneans. The general pattern of distribution of the nine trematode species ol er host species was similar to what have been reported from other North Atlantic areas. However, prevalence and intensity differed both at a geographic scale (in comparison with other studies) and at a local scale. The temporal variation over years was less significant.
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50. |
- Grudemo, Johan, et al.
(författare)
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Size of mudsnails, Hydrobia ulvae (Pennant) and H-ventrosa (Montagu), in allopatry and sympatry: conclusions from field distributions and laboratory growth experiments
- 1999
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Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981. ; 239:2, s. 167-181
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Tidskriftsartikel (refereegranskat)abstract
- In most areas, sizes of the two mudsnails Hydrobia ulvae and H. ventrosa diverge when their distributions overlap, while in allopatry they are about equally large. This has been suggested as an example of character displacement, although later studies suggest alternative interpretations. In this study, distribution and snail size of both species was assessed in 30 localities on the Swedish West coast, both allopatric sites of each species and sympatric sites. Overall, mean sizes varied considerably among populations; in H. ulvae mean size range was 2.0-4.5 mm and in H. ventrosa 2.2-3.6 mm. Mean sizes in allopatry were roughly similar, while in sympatry H. ulvae was always larger than H. ventrosa. In the field, snail size of both species increased with increasing silt content of the sediment. However, silt content alone seemed unable to explain the character displacement-like pattern as growth in the laboratory was not differently affected by sandy or silty sediments. In the laboratory, however, snails of both species grew at various rates over sediments from different bays, suggesting environmental effects other than grain size. Furthermore, H. ulvae constantly grew at about 150% the rate of H, ventrosa when grown under the same conditions. This suggests that the divergence in size in sympatric sites is due to intrinsic growth rate differences, which persist over a range of environments. The similar sizes in allopatric sites may be explained by phenotypic adjustments to environmental factors. Our results reject inherited differences in growth rate among populations as an explanation of the character displacement-like pattern of size variation. We also argue that differences in recruitment time seems an unlikely explanation. (C) 1999 Elsevier Science B;V. All rights reserved.
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