| 51. |
- 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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| 52. |
- Eriksson, Anders, 1975, et al.
(författare)
-
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
-
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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| 53. |
- 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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| 54. |
- Faria, R., et al.
(författare)
-
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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| 55. |
- Faria, R., et al.
(författare)
-
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
-
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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| 56. |
- 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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| 57. |
- 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
-
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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| 58. |
- 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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| 59. |
- 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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| 60. |
- 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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