| 1. |
- Balao, Francisco, et al.
(författare)
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Adaptive sequence evolution is driven by biotic stress in a pair of orchid species (Dactylorhiza) with distinct ecological optima
- 2017
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083. ; 26:14, s. 3649-3662
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Tidskriftsartikel (refereegranskat)abstract
- The orchid family is the largest in the angiosperms, but little is known about the molecular basis of the significant variation they exhibit. We investigate here the transcriptomic divergence between two European terrestrial orchids, Dactylorhiza incarnata and Dactylorhiza fuchsii, and integrate these results in the context of their distinct ecologies that we also document. Clear signals of lineage-specific adaptive evolution of protein-coding sequences are identified, notably targeting elements of biotic defence, including both physical and chemical adaptations in the context of divergent pools of pathogens and herbivores. In turn, a substantial regulatory divergence between the two species appears linked to adaptation/acclimation to abiotic conditions. Several of the pathways affected by differential expression are also targeted by deviating post-transcriptional regulation via sRNAs. Finally, D. incarnata appears to suffer from insufficient sRNA control over the activity of RNA-dependent DNA polymerase, resulting in increased activity of class I transposable elements and, over time, in larger genome size than that of D. fuchsii. The extensive molecular divergence between the two species suggests significant genomic and transcriptomic shock in their hybrids and offers insights into the difficulty of coexistence at the homoploid level. Altogether, biological response to selection, accumulated during the history of these orchids, appears governed by their microenvironmental context, in which biotic and abiotic pressures act synergistically to shape transcriptome structure, expression and regulation.
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| 2. |
- Balao, F, et al.
(författare)
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Genetic differentiation and admixture between sibling allopolyploids in the Dactylorhiza majalis complex.
- 2015
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 1365-2540 .- 0018-067X.
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Tidskriftsartikel (refereegranskat)abstract
- Allopolyploidization often happens recurrently, but the evolutionary significance of its iterative nature is not yet fully understood. Of particular interest are the gene flow dynamics and the mechanisms that allow young sibling polyploids to remain distinct while sharing the same ploidy, heritage and overlapping distribution areas. By using eight highly variable nuclear microsatellites, newly reported here, we investigate the patterns of divergence and gene flow between 386 polyploid and 42 diploid individuals, representing the sibling allopolyploids Dactylorhiza majalis s.s. and D. traunsteineri s.l. and their parents at localities across Europe. We make use in our inference of the distinct distribution ranges of the polyploids, including areas in which they are sympatric (that is, the Alps) or allopatric (for example, Pyrenees with D. majalis only and Britain with D. traunsteineri only). Our results show a phylogeographic signal, but no clear genetic differentiation between the allopolyploids, despite the visible phenotypic divergence between them. The results indicate that gene flow between sibling Dactylorhiza allopolyploids is frequent in sympatry, with potential implications for the genetic patterns across their entire distribution range. Limited interploidal introgression is also evidenced, in particular between D. incarnata and D. traunsteineri. Altogether the allopolyploid genomes appear to be porous for introgression from related diploids and polyploids. We conclude that the observed phenotypic divergence between D. majalis and D. traunsteineri is maintained by strong divergent selection on specific genomic areas with strong penetrance, but which are short enough to remain undetected by genotyping dispersed neutral markers.Heredity advance online publication, 25 November 2015; doi:10.1038/hdy.2015.98.
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| 3. |
- Brandrud, Marie K., et al.
(författare)
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Restriction-site associated DNA sequencing supports a sister group relationship of Nigritella and Gymnadenia (Orchidaceae)
- 2019
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier BV. - 1055-7903. ; 136, s. 21-28
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Tidskriftsartikel (refereegranskat)abstract
- The orchid genus Nigritella is closely related to Gymnadenia and has from time to time been merged with the latter. Although Nigritella is morphologically distinct, it has been suggested that the separating characters are easily modifiable and subject to rapid evolutionary change. So far, molecular phylogenetic studies have either given support for the inclusion of Nigritella in Gymnadenia, or for their separation as different genera. To resolve this issue, we analysed data obtained from Restriction-site associated DNA sequencing, RADseq, which provides a large number of SNPs distributed across the entire genome. To analyse samples of different ploidies, we take an analytical approach of building a reduced genomic reference based on de novo RADseq loci reconstructed from diploid accessions only, which we further use to map and call variants across both diploid and polyploid accessions. We found that Nigritella is distinct from Gymnadenia forming a well-supported separate clade, and that genetic diversity within Gymnadenia is high. Within Gymnadenia, taxa characterized by an ITS-E ribotype (G. conopsea s.str. (early flowering) and G. odoratissima), are divergent from taxa characterized by ITS-L ribotype (G. frivaldii, G. densiflora and late flowering G. conopsea). Gymnigritella runei is confirmed to have an allopolyploid origin from diploid Gymnadenia conopsea and tetraploid N. nigra ssp. nigra on the basis of RADseq data. Within Nigritella the aggregation of polyploid members into three clear-cut groups as suggested by allozyme and nuclear microsatellite data was further supported.
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| 4. |
- Hedrén, Mikael, et al.
(författare)
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A replacement name for a species of Hypoestes (Acanthaceae) from Somalia
- 2015
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Ingår i: Willdenowia. - : Botanic Garden and Botanical Museum Berlin, Freie Universitaet Berlin. - 0511-9618 .- 1868-6397. ; 45:1, s. 93-93
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Tidskriftsartikel (refereegranskat)abstract
- Hypoestes canescens Hedren & Thulin, nom. nov., is proposed for the illegitimate name H. cinerea Hedren, non C. B. Clarke.
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| 5. |
- Hedrén, Mikael, et al.
(författare)
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Evidence for bidirectional hybridization between Gymnadenia and Nigritella
- 2018
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Ingår i: Journal Europäischer Orchideen. - 0945-7909. ; 50:1, s. 43-60
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Despite morphological divergence, the two orchid genera Gymnadenia andNigritella are closely related and hybrids are often encountered at places wheremembers of the two genera grow together. On basis of pollination studies, it hasbeen suggested that members of Nigritella should have served as pollen parent tothese hybrids. Hybridization does not go beyond primary hybrid formation, butone of the hybrids, Gymnigritella runei, is recognized as a separate species sincethe hybrid genotype is maintained by apomixis and it is reproducingindependently of the parents. Surprisingly, a recent molecular analysis of G. runeidemonstrated that this hybrid evolved by the merger of an egg cell from Nigritellaand a microgamete from Gymnadenia, contrary to what has been predicted frompollination studies. Here, we conducted an extended study in which we analyzedtwo additional hybrid combinations known from the Alps and which each hasoriginated repeatedly at different sites: G. conopsea × N. rhellicani, andG. odoratissima × N. rhellicani. We show that each hybrid combination hasoriginated alternatively from Nigritella and Gymnadenia as egg parent. Ourresults call for renewed studies on the pollination biology of Nigritella andGymnadenia, in particular on the movement of insects between plants of thedifferent genera and their potential function as pollen vectors.
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| 6. |
- Hedrén, Mikael, et al.
(författare)
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Evolution and systematics of polyploid Nigritella (Orchidaceae)
- 2018
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Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X. ; 36:3
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Tidskriftsartikel (refereegranskat)abstract
- Members of the orchid genus Nigritella are widespread in European mountains, but species circumscriptions and evolutionary patterns in the genus are subjects to conflicting opinions. We analyzed a representative material of Nigritella for differentiation at nuclear and plastid marker loci. In agreement with predictions from embryological studies, diploid members of Nigritella are sexual and mostly out-crossing, whereas triploid, tetraploid and pentaploid members are apomicts. The diploid taxa were poorly differentiated in the investigated molecular markers, except for the western N. gabasiana, which was separated in plastid haplotypes. Polyploid Nigritella aggregate into three groups and within each of these groups apomictic polyploids have given rise to new species. Within the N. nigra group, the tetraploid N. nigra subsp. austriaca is somewhat differentiated from the triploid subsp. nigra at nuclear as well as plastid loci. Fusion of an unreduced egg cell from subsp. nigra with a haploid microgamete from Gymnadenia conopsea gave rise to Gymnigritella runei. Within the N. widderi group, N. archiducis-joannis is poorly separated from N. widderi in molecular markers, and the pentaploid N. buschmanniae has evolved by fusion of an unreduced egg cell from N. widderi with a haploid microgamete from a diploid Nigritella. Within the N. miniata group, N. stiriaca is somewhat differentiated from N. miniata at nuclear loci, but no other segregates of N. miniata are supported at species level. Polyploid Nigritella species accumulate genetic diversity by somatic mutations. In the widespread N. nigra subsp. austriaca and N. miniata this diversity is correlated to geography. Although some polyploids may be of recent origins, each polyploid contain genetic markers no longer encountered in diploid members of the genus. According to plastid marker data, Nigritella and Gymnadenia may constitute monophyletic sister genera.
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| 7. |
- Hedrén, Mikael, et al.
(författare)
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High levels of genetic diversity in marginal populations of the marsh orchid Dactylorhiza majalis subsp. majalis
- 2018
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Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X. ; 36:4
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Tidskriftsartikel (refereegranskat)abstract
- Because of harsh conditions, suboptimal habitat quality and poor connectivity to other populations, plant populations at the margin of a distribution are expected to be less genetically diverse, but to be more divergent from each other than populations in the centre of a distribution. In northern Europe, northern marginal populations may also be younger than populations further to the south, and may have had less time to accumulate genetic diversity by mutation and gene flow. However, orchids have very small seeds, which are easily dispersed long distances by wind, and orchids are therefore expected to show less differentiation between marginal and central populations than other groups of seed plants. Here, we analysed whether Scandinavian populations of the tetraploid marsh orchid Dactylorhiza majalis subsp. majalis differ from central European populations in genetic diversity patterns. A total of 220 plants from eight central European and ten Scandinavian populations was examined for variation at five nuclear microsatellite loci, nuclear ITS and 13 polymorphic sites in noncoding regions of the plastid genome. The total genetic diversity was slightly lower in Scandinavia than in central Europe, both in plastid and nuclear markers, but the differences were small. Also, the Scandinavian populations were less diverse and somewhat more strongly differentiated from each other than the central European ones. Dactylorhiza majalis subsp. majalis has apparently colonized Scandinavia on multiple independent occasions and from different source areas in the south. Seed flow between Scandinavian populations has still not fully erased the patterns imprinted by early colonization. Our results suggest that marginal populations of orchids may be as important as central ones in preserving genetic diversity through Pleistocene glacial cycles. We also predict that orchids with their light seeds are better adapted than many other plants to respond to future climate changes by dispersing into new suitable areas.
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| 8. |
- Hedrén, Mikael, et al.
(författare)
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Hva er Dactylorhiza traunsteineri?
- 2018
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Ingår i: Blyttia. - 0006-5269. ; 76:2, s. 105-116
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Comments are given on the identity of some populations of allotetraploid Dactylorhiza in southern Norway and their relationships to populations elsewhere in Scandinavia and in continental Europe. The most widespread allotetraploid member of Dactylorhiza in southern Norway is D. majalis ssp. sphagnicola. This subspecies is confined to poor and medium-rich fens dominated by peat mosses, Sphagnum, in the bottom layer. Subspecies sphagnicola has sometimes been included in D. traunsteineri, which is another allotetraploid member of Dactylorhiza described from Austria, but molecular analyses show that these taxa are distinct. Subspecies sphagnicola is distributed from northern France, Belgium and western Germany to Central Scandinavia, but it does not grow on Gotland or to the east of the Baltic Sea. D. majalis ssp. lapponica is only sparsely represented in southern Norway, but is known from at least one site in Lier southwest of Oslo. This subspecies grows in rich fens with high pH. It is also rare on the southern Swedish mainland, but is common on Gotland and is widespread in regions with calcareous bedrock in mid and northern Scandinavia. Mountain populations are often low-grown, have leaves with spotted upper surface, and have anthocyanine-rich stems and flowers. D. majalis ssp. lapponica is related to the Central European D. traunsteineri, but the epithet “lapponica” has priority over “traunsteineri” at subspecies level.
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| 9. |
- Hedrén, Mikael, et al.
(författare)
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Orchid colonization: multiple parallel dispersal events and mosaic genetic structure in Dactylorhiza majalis ssp. lapponica on the Baltic island of Gotland.
- 2018
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Ingår i: Annals of Botany. - : Oxford University Press (OUP). - 0305-7364 .- 1095-8290. ; 122:6, s. 1019-1031
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Tidskriftsartikel (refereegranskat)abstract
- Background and AimsThe island of Gotland in the Baltic Sea has had no contact with surrounding continental areas since the withdrawal of the Weichselian ice sheet at approx. 17 ka BP. Plants present on Gotland must have arrived by long-distance dispersal, so populations are expected to exhibit reduced levels of genetic diversity compared with populations on surrounding mainlands. However, orchids have very small seeds, which appear well adapted to long-distance dispersal, and they should therefore be less affected than other plant species by colonization bottlenecks. The aim of this study was to analyse the genetic structure of orchids colonizing isolated islands, using the marsh orchid Dactylorhiza majalis ssp. lapponica as a case study.MethodsMore than 500 samples from 27 populations were analysed for 15 plastid and eight nuclear marker loci. Population diversity and differentiation patterns were compared for nuclear and plastid marker systems and analysed in relation to geographical location.Key ResultsWe found high genetic diversity but no clear geographical structure of genetic differentiation between populations on Gotland. However, the between-population differentiation in plastid and nuclear markers were correlated and the greatest diversity was found at sites at comparatively high elevations, which were the first to emerge above the water after the Ice Age.ConclusionsThe regional population on Gotland has been established by a minimum of four dispersal events from continental regions. Subsequent gene flow between sites has not yet homogenized the differentiation pattern originating from initial colonization. We conclude that long-distance seed dispersal in orchids has a strong impact on structuring genetic diversity during periods of expansion and colonization, but contributes less to gene flow between populations once a stable population structure has been achieved.
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| 10. |
- Hedrén, Mikael, et al.
(författare)
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Plastid DNA microsatellite data do not support recognition of subspecies of Coeloglossum viride (L.)Hartm. (Orchidaceae) in northern Europe
- 2016
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Ingår i: Symbolae Botanicae Upsalienses. - 0082-0644. ; 38, s. 81-91
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Tidskriftsartikel (refereegranskat)abstract
- The orchid Coeloglossum viride (L.) Hartm. has a circumboreal distribution and is widespread in the Nordic countries, especially in the boreal and montane regions. Whereas plants from the lowlands are generally slender and have greenish-yellowish flowers, plants from mountain areas tend to be low-growing with fewer, reddish-brown flowers, leading some authors to recognize the latter as a separate subspecies, C. viride subsp. islandica (Lindl.) Kreutz. In course of collecting data for the treatment of the Orchidaceae in the Flora Nordica, we have analysed material of C. viride for plastid microsatellite variation in order to assess the taxonomic justification of subsp. islandica. We found two major groups of haplotypes in C. viride in the Flora Nordica area. The two groups were widespread in both mountain and lowland regions in Scandinavia, but only one of the groups was present in material from Iceland. Accordingly, plastid microsatellite data give no support for the recognition of mountain/Icelandic plants as a separate taxon. Based on the distribution of haplotypes and their relationships, we suggest that the present-day population of C. viride in the Nordic countries originated from populations in refugia close to the Weichselian ice sheet.
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