| 61. |
- Hollander, Johan, 1969, et al.
(författare)
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Evolution of adaptation through allometric shifts in a marine snail
- 2006
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 60:12, s. 2490-2497
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Tidskriftsartikel (refereegranskat)abstract
- Variation in ontogenetic development among individuals may be a major contributor to morphological variation within species. Evolution of different growth trajectories might, for example, evolve as a response to varying ecological contexts of individuals living in different environments, or by life-stage or gender differences. The intertidal periwinkle Littorina saxatilis is strongly polymorphic in shell shape. We compared ontogenetic trajectories between life stages, local populations, and sexes to understand how different morphological end points are reached during ontogeny and what might cause these differences. Applying landmark-based geometric morphometrics, we captured shell shape variation for four Swedish populations of this species. We also derived a method to visualize ontogenetic trajectories described by the relationship of size to the multivariate shape space. We found that growth trajectories differed between individuals living in different habitats, as well as between sexes and maturity stages. Males living on rocky cliffs grew isometrically throughout life, whereas females from the same habitat switched from isometric growth as juveniles to allometric growth as adults. In contrast, males and females living on boulders grew allometrically as juveniles but changed to isometric growth at sexual maturity. Thus, in this species, ontogenetic growth seems influenced by habitat-associated selection as well as by gender and age-specific selection. These differing selection regimes result in ontogenetic shifts in allometry in three of the four groups examined.
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| 62. |
- Hollander, Johan, 1969, et al.
(författare)
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Local adaptation but not geographical separation promotes assortative mating in a snail
- 2005
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Ingår i: Animal Behaviour. - : Elsevier BV. - 0003-3472. ; 70:5, s. 1209-1219
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Tidskriftsartikel (refereegranskat)abstract
- A crucial assumption in models of ecological speciation is that reproductive barriers evolve as a consequence of ecological divergence of populations, rather than geographical separation. To test the prediction that barriers between populations might evolve in the face of gene flow, we studied reproductive barriers between populations of two Swedish ecotypes of the marine snail Littorina saxatilis with inherited differences in shell size and shape, living in adjacent rocky shore microhabitats with zones of overlap making gene flow between ecotypes possible. We compared mounting frequency and duration between mates of different ecotypes with that between mates of the same ecotype but from populations at various geographical distances. (In this species gene flow is substantially reduced over distances of a few kilometres owing to poor dispersal.) Mates of the same ecotype mated more frequently and for longer than mates of different ecotypes, whereas increased geographical distance did not affect this pattern. Snails of similar sizes more frequently initiated copulation than did snails of different sizes, whereas the duration of copulation was affected by shape. Mating between mates of similar sizes but of different ecotype was more frequently interrupted than mating between the same ecotype. Thus ecological rather than geographical separation in this species has resulted in the evolution of local reproductive barriers. This lends support to models of ecological speciation
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| 63. |
- Hollander, Johan, 1969, et al.
(författare)
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Phenotypic plasticity in two marine snails: constraints superseding life history
- 2006
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 19:6, s. 1861-1872
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Tidskriftsartikel (refereegranskat)abstract
- In organisms encountering predictable environments, fixed development is expected, whereas in organisms that cannot predict their future environment, phenotypic plasticity would be optimal to increase local adaptation. To test this prediction we experimentally compared phenotypic plasticity in two rocky-shore snail species; Littorina saxatilis releasing miniature snails on the shore, and Littorina littorea releasing drifting larvae settling on various shores, expecting L. littorea to show more phenotypic plasticity than L. saxatilis. We compared magnitude and direction of vectors of phenotypic difference in juvenile shell traits after 3 months exposure to different stimuli simulating sheltered and crab-rich shores, or wave-exposed and crab-free shores. Both species showed similar direction and magnitude of vectors of phenotypic difference with minor differences only between ecotypes of the nondispersing species, indicating that plasticity is an evolving trait in L. saxatilis. The lack of a strong plastic response in L. littorea might be explained by limits rather than costs to plasticity.
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| 64. |
- Hudson, J., et al.
(författare)
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Secondary contacts and genetic admixture shape colonization by an amphiatlantic epibenthic invertebrate
- 2020
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Ingår i: Evolutionary Applications. - : Wiley. - 1752-4571. ; 13:3, s. 600-612
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Tidskriftsartikel (refereegranskat)abstract
- Research on the genetics of invasive species often focuses on patterns of genetic diversity and population structure within the introduced range. However, a growing body of literature is demonstrating the need to study how native genotypes affect both ecological and evolutionary mechanisms within the introduced range. Here, we used genotyping-by-sequencing to study both native and introduced ranges [based on 1,653 single nucleotide polymorphisms (SNPs)] of the amphiatlantic marine invertebrate Ciona intestinalis. A previous study using microsatellites analysed samples collected along the Swedish west coast and showed the presence of genetically distinct lineages in deep and shallow waters. Using 1,653 single nucleotide polymorphisms (SNPs) from newly collected samples (285 individuals), we first confirmed the presence of this depth-defined genomic divergence along the Swedish coast. We then used approximate Bayesian computation to infer the historical relationship among sites from the North Sea, the English Channel and the northwest Atlantic and found evidence of ancestral divergence between individuals from deep waters off Sweden and individuals from the English Channel. This divergence was followed by a secondary contact that led to a genetic admixture between the ancestral populations (i.e., deep Sweden and English Channel), which originated the genotypes found in shallow Sweden. We then revealed that the colonization of C. intestinalis in the northwest Atlantic was as a result of an admixture between shallow Sweden and the English Channel genotypes across the introduced range. Our results showed the presence of both past and recent genetic admixture events that together may have promoted the successful colonizations of C. intestinalis. Our study suggests that secondary contacts potentially reshape the evolutionary trajectories of invasive species through the promotion of intraspecific hybridization and by altering both colonization patterns and their ecological effects in the introduced range.
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| 65. |
- Härkönen, T., et al.
(författare)
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Colonization history of the baltic harbor seals: Integrating archaeological, behavioral, and genetic data
- 2005
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Ingår i: Marine Mammal Science. - : Wiley. - 0824-0469 .- 1748-7692. ; 21:4, s. 695-716
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Tidskriftsartikel (refereegranskat)abstract
- Detailed knowledge about the history of colonization, population dynamics and behavior greatly enhance evaluation of genetic models of population units and migration rates in spatially structured populations. Here, the genetic uniqueness of harbor seals (Phoca vitulina) in the eastern Baltic is evaluated in the light of new information on the distribution and abundance of Baltic and eastern North Sea populations during the last 11,000 yr, recent hunting statistics, and population counts. Archaeological records reveal that the Baltic population of harbor seals was founded about 8,000 yr ago. Adjacent populations in the North Sea areas were either small, or went extinct, and became significant only during the last 300 yr. This information generates the hypothesis that the Baltic population has been isolated during the last 8,000 yr, despite the lack of geographical barriers. We show that stochastic effects, isolation, and a documented recent population bottleneck can account for the low observed genetic variation in Baltic harbor seals.
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| 66. |
- Johansson, Daniel, et al.
(författare)
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Reciprocal transplants support a plasticity-first scenario during colonisation of a large hyposaline basin by a marine macro alga
- 2017
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Ingår i: BMC Ecology. - : Springer Science and Business Media LLC. - 1472-6785. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 The Author(s).Background: Establishing populations in ecologically marginal habitats may require substantial phenotypic changes that come about through phenotypic plasticity, local adaptation, or both. West-Eberhard's "plasticity-first" model suggests that plasticity allows for rapid colonisation of a new environment, followed by directional selection that develops local adaptation. Two predictions from this model are that (i) individuals of the original population have high enough plasticity to survive and reproduce in the marginal environment, and (ii) individuals of the marginal population show evidence of local adaptation. Individuals of the macroalga Fucus vesiculosus from the North Sea colonised the hyposaline (≥2-3%) Baltic Sea less than 8000 years ago. The colonisation involved a switch from fully sexual to facultative asexual recruitment with release of adventitious branches that grow rhizoids and attach to the substratum. To test the predictions from the plasticity-first model we reciprocally transplanted F. vesiculosus from the original population (ambient salinity 24%) and from the marginal population inside the Baltic Sea (ambient salinity 4%). We also transplanted individuals of the Baltic endemic sister species F. radicans from 4 to 24%. We assessed the degree of plasticity and local adaptation in growth and reproductive traits after 6 months by comparing the performance of individuals in 4 and 24%. Results: Branches of all individuals survived the 6 months period in both salinities, but grew better in their native salinity. Baltic Sea individuals more frequently developed asexual traits while North Sea individuals initiated formation of receptacles for sexual reproduction. Conclusions: Marine individuals of F. vesiculosus are highly plastic with respect to salinity and North Sea populations can survive the extreme hyposaline conditions of the Baltic Sea without selective mortality. Plasticity alone would thus allow for an initial establishment of this species inside the postglacial Baltic Sea at salinities where reproduction remains functional. Since establishment, the Baltic Sea populations have evolved adaptations to extreme hyposaline waters and have in addition evolved asexual recruitment that, however, tends to impede local adaptation. Overall, our results support the "plasticity-first" model for the initial colonisation of the Baltic Sea by Fucus vesiculosus.
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| 67. |
- 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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| 68. |
- Jonsson, Per R., 1957, et al.
(författare)
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High climate velocity and population fragmentation may constrain climate-driven range shift of the key habitat former Fucus vesiculosus
- 2018
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Ingår i: Diversity and Distributions. - : Wiley. - 1366-9516. ; 24:7, s. 892-905
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Tidskriftsartikel (refereegranskat)abstract
- Aim: The Baltic Sea forms a unique regional sea with its salinity gradient ranging from marine to nearly freshwater conditions. It is one of the most environmentally impacted brackish seas worldwide, and the low biodiversity makes it particularly sensitive to anthropogenic pressures including climate change. We applied a novel combination of models to predict the fate of one of the dominant foundation species in the Baltic Sea, the bladder wrack Fucus vesiculosus. Methods: We used a species distribution model to predict climate change-induced displacement of F.vesiculosus and combined these projections with a biophysical model of dispersal and connectivity to explore whether the dispersal rate of locally adapted genotypes may match estimated climate velocities to recolonize the receding salinity gradient. In addition, we used a population dynamic model to assess possible effects of habitat fragmentation. Results: The species distribution model showed that the habitat of F.vesiculosus is expected to dramatically shrink, mainly caused by the predicted reduction of salinity. In addition, the dispersal rate of locally adapted genotypes may not keep pace with estimated climate velocities rendering the recolonization of the receding salinity gradient more difficult. A simplistic model of population dynamics also indicated that the risk of local extinction may increase due to future habitat fragmentation. Main conclusions: Results point to a significant risk of locally adapted genotypes being unable to shift their ranges sufficiently fast considering the restricted dispersal and long generation time. The worst scenario is that F.vesiculosus may disappear from large parts of the Baltic Sea before the end of this century with large effects on the biodiversity and ecosystem functioning. We finally discuss how to reduce this risk through conservation actions, including assisted colonization and assisted evolution.
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| 69. |
- Kautsky, Lena, et al.
(författare)
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Rapid speciation in a newly opened postglacial marine environment, the Baltic Sea
- 2009
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 9:70
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Tidskriftsartikel (refereegranskat)abstract
- Background: Theory predicts that speciation can be quite rapid. Previous examples comprise a wide range of organisms such as sockeye salmon, polyploid hybrid plants, fruit flies and cichlid fishes. However, few studies have shown natural examples of rapid evolution giving rise to new species in marine environments. Results: Using microsatellite markers, we show the evolution of a new species of brown macroalga (Fucus radicans) in the Baltic Sea in the last 400 years, well after the formation of this brackish water body ~8–10 thousand years ago. Sympatric individuals of F. radicans and F. vesiculosus (bladder wrack) show significant reproductive isolation. Fucus radicans, which is endemic to the Baltic, is most closely related to Baltic Sea F. vesiculosus among north Atlantic populations, supporting the hypothesis of a recent divergence. Fucus radicans exhibits considerable clonal reproduction, probably induced by the extreme conditions of the Baltic. This reproductive mode is likely to have facilitated the rapid foundation of the new taxon. Conclusion: This study represents an unparalleled example of rapid speciation in a species-poor open marine ecosystem and highlights the importance of increasing our understanding on the role of these habitats in species formation. This observation also challenges presumptions that rapid speciation takes place only in hybrid plants or in relatively confined geographical places such as postglacial or crater lakes, oceanic islands or rivers.
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| 70. |
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