| 1. |
- Hedenäs, Lars, et al.
(författare)
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Evidence of horizontal gene transfer between land plant plastids has surprising conservation implications
- 2021
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Ingår i: Annals of Botany. - : Oxford University Press (OUP). - 0305-7364 .- 1095-8290. ; 127:7, s. 903-908
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Tidskriftsartikel (refereegranskat)abstract
- Background and Aims Horizontal gene transfer (HGT) is an important evolutionary mechanism because it transfers genetic material that may code for traits or functions between species or genomes. It is frequent in mitochondrial and nuclear genomes but has not been demonstrated between plastid genomes of different green land plant species.Methods We Sanger-sequenced the nuclear internal transcribed spacers (ITS1 and 2) and the plastid rpl16 G2 intron (rpl16). In five individuals with foreign rpl16 we also sequenced atpB-rbcL and trnLUAA-trnFGAA.Key Results We discovered 14 individuals of a moss species with typical nuclear ITSs but foreign plastid rpl16 from a species of a distant lineage. None of the individuals with three plastid markers sequenced contained all foreign markers, demonstrating the transfer of plastid fragments rather than the entire plastid genome, i.e. entire plastids were not transferred. The two lineages diverged 165–185 Myr BP. The extended time interval since lineage divergence suggests that the foreign rpl16 is more likely explained by HGT than by hybridization or incomplete lineage sorting.Conclusions We provide the first conclusive evidence of interspecific plastid-to-plastid HGT among land plants. Two aspects are critical: it occurred at several localities during the massive colonization of recently disturbed open habitats that were created by large-scale liming as a freshwater biodiversity conservation measure; and it involved mosses whose unique life cycle includes spores that first develop a filamentous protonema phase. We hypothesize that gene transfer is facilitated when protonema filaments of different species intermix intimately when colonizing disturbed early succession habitats.
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| 2. |
- Swenson, Ulf, 1959-, et al.
(författare)
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Island life - classification and cryptic species of Pycnandra (Sapotaceae) in New Caledonia
- 2015
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Ingår i: Botanical journal of the Linnean Society. - 0024-4074 .- 1095-8339. ; 179, s. 57-77
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Tidskriftsartikel (refereegranskat)abstract
- Pycnandra (Sapotaceae), the largest endemic genus in New Caledonia, comprises 66 species classified in six subgenera. We tested phylogenetic relationships and a proposed infrageneric classification by sampling 60 species for sequences of nuclear ribosomal DNA (ETS, ITS, RPB2) and plastid DNA (trnH–psbA) and nine morphological characters. Data were analysed with Bayesian inference, parsimony jackknifing and lineage through time. We recovered a phylogenetic tree supporting the recognition of six proposed subgenera (Achradotypus, Leptostylis, Pycnandra, Sebertia, Trouettia and Wagapensia). Because a subgeneric classification is used, the nomenclature will be stable when the members are transferred to Pycnandra. Morphological traits were optimized in the BEAST analysis, adding evidence to earlier work that morphology has limited value for successfully diagnosing groups in Sapotaceae. We confirm a previously suspected case of cryptic species that exhibit the same morphological features and require the same abiotic conditions, but are distantly related in the phylogenetic tree. We detected two possible new cases of cryptic sibling species that might warrant recognition. A slowdown in speciation rate in several genera has been suggested as evidence that New Caledonia was once submerged after rifting from Australia. Plotting lineages through time reveals two important intervals at 7.5–8.6 Ma and present to 1.5 Ma, when net molecular diversification within the genus was zero. This indicates that the genus presently has reached a dynamic equilibrium, providing additional evidence that New Caledonia is an old Darwinian island, being submerged during the Eocene and colonized after re-emergence c. 37 Ma.
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| 3. |
- Swenson, Ulf, 1959-, et al.
(författare)
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Resolving the relationships of the enigmatic genera Beauvisagea and Boerlagella, and the position of Planchonella suboppositifolia
- 2020
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Ingår i: Taxon. - : Wiley. - 0040-0262 .- 1996-8175. ; 69, s. 998-1015
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Tidskriftsartikel (refereegranskat)abstract
- ThepantropicalplantfamilySapotaceaecurrentlyincludes65–70genera.Twogenera,BeauvisageaandBoerlagella,were described in 1890s using incomplete material from West New Guinea (Bird’s Head Peninsula) and Sumatra, neither of which has been collected since. Their systematic position has long been regarded doubtful and Boerlagella was once placed in its own family, Boer- lagellaceae. We show here how useful and important it can be to obtain small leaf fragments from type specimens that are up to 150 years old for molecular analysis aiming to determine their phylogenetic position and clarify their taxonomic status. We used nuclear ribosomal DNA (ETS, ITS) and the nuclear gene RPB2 from 170 terminals to estimate phylogenetic relationships in a Bayes- ian framework using BEAST. The old type material yielded full length sequences of ETS and ITS from both genera (less successful with RPB2), revealing that both are firmly placed in Planchonella. Boerlagella is placed in synonymy with Planchonella and its type is accepted as Planchonella spectabilis, a species from Sumatra that possibly has gone extinct due to deforestation. Beauvisagea from the Bird’s Head Peninsula of western New Guinea is likewise regarded as a synonym of Planchonella and its type, accepted as P. pomi- fera, is conspecific with Pouteria doonsaf (currently circumscribed to include material of at least two different species), not Plancho- nella maclayana as earlier believed. Our study also included Planchonella suboppositifolia, an odd species with a character combination in conflict with the current definition of the genus. Our results show that it is sister to a lineage comprising several gen- era, including Planchonella, and that it represents a distinct lineage constituting a monotypic genus that will be described in a sub- sequent paper. The most recent classification of subfamily Chrysophylloideae and the character combinations used to distinguish its constituent genera are supported, and our results confirm that taxa can reliably be assigned to a genus based on morphology alone.
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| 5. |
- Zimmermann, Judith, et al.
(författare)
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Closely coupled evolutionary history of ecto- and endosymbionts from two distantly-related animal phyla : Closely linked ecto- and endosymbiont evolution
- 2016
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 25:13, s. 3203-3223
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Tidskriftsartikel (refereegranskat)abstract
- The level of integration between associated partners can range from ectosymbioses to extracellular and intracellular endosymbioses, and this range has been assumed to reflect a continuum from less intimate to evolutionarily highly stable associations. In this study, we examined the specificity and evolutionary history of marine symbioses in a group of closely related sulphur-oxidizing bacteria, called Candidatus Thiosym- bion, that have established ecto- and endosymbioses with two distantly related animal phyla, Nematoda and Annelida. Intriguingly, in the ectosymbiotic associations of stil- bonematine nematodes, we observed a high degree of congruence between symbiont and host phylogenies, based on their ribosomal RNA (rRNA) genes. In contrast, for the endosymbioses of gutless phallodriline annelids (oligochaetes), we found only a weak congruence between symbiont and host phylogenies, based on analyses of sym- biont 16S rRNA genes and six host genetic markers. The much higher degree of con- gruence between nematodes and their ectosymbionts compared to those of annelids and their endosymbionts was confirmed by cophylogenetic analyses. These revealed 15 significant codivergence events between stilbonematine nematodes and their ectosym- bionts, but only one event between gutless phallodrilines and their endosymbionts. Phylogenetic analyses of 16S rRNA gene sequences from 50 Cand. Thiosymbion spe- cies revealed seven well-supported clades that contained both stilbonematine ectosym- bionts and phallodriline endosymbionts. This closely coupled evolutionary history of marine ecto- and endosymbionts suggests that switches between symbiotic lifestyles and between the two host phyla occurred multiple times during the evolution of the Cand. Thiosymbion clade, and highlights the remarkable flexibility of these symbiotic bacteria.
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