| 1. |
- Bolinder, Kristina, et al.
(författare)
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AERODYNAMICS AND POLLEN ULTRASTRUCTURE IN EPHEDRA
- 2015
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Ingår i: American Journal of Botany. - : Wiley. - 0002-9122 .- 1537-2197. ; 102:3, s. 457-470
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Tidskriftsartikel (refereegranskat)abstract
- Premise of the study: Pollen dispersal is affected by the terminal settling velocity (U-t) of the grains, which is determined by their size, bulk density, and by atmospheric conditions. The likelihood that wind-dispersed pollen is captured by ovulate organs is influenced by the aerodynamic environment created around and by ovulate organs. We investigated pollen ultrastructure and U-t of Ephedra foeminea (purported to be entomophilous), and simulated the capture efficiency of its ovules. Results were compared with those from previously studied anemophilous Ephedra species. Methods: U-t was determined using stroboscopic photography of pollen in free fall. The acceleration field around an average ovule was calculated, and inflight behavior of pollen grains was predicted using computer simulations. Pollen morphology and ultrastructure were investigated using SEM and STEM. Key results: Pollen wall ultrastructure was correlated with U-t in Ephedra. The relative proportion and amount of granules in the infratectum determine pollen bulk densities, and (together with overall size) determine U-t and thus dispersal capability. Computer simulations failed to reveal any functional traits favoring anemophilous pollen capture in E. foeminea. Conclusion: The fast U-t and dense ultrastructure of E. foeminea pollen are consistent with functional traits that distinguish entomophilous species from anemophilous species. In anemophilous Ephedra species, ovulate organs create an aerodynamic microenvironment that directs airborne pollen to the pollination drops. In E. foeminea, no such microenvironment is created. Ephedroid palynomorphs from the Cretaceous share the ultrastructural characteristics of E. foeminea, and at least some may, therefore, have been produced by insect-pollinated plants.
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| 2. |
- Bolinder, Kristina, et al.
(författare)
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From near extinction to diversification by means of ashift in pollination mechanism in the gymnosperm relict Ephedra (Ephedraceae, Gnetales)
- 2016
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Ingår i: Botanical journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4074 .- 1095-8339. ; 180:4, s. 461-477
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Tidskriftsartikel (refereegranskat)abstract
- Pollination in gymnosperms is usually accomplished by means of wind, but some groups are insect-pollinated. We show that wind and insect pollination occur in the morphologically uniform genus Ephedra (Gnetales). Based on field experiments over several years, we demonstrate distinct differences between two Ephedra species that grow in sympatry in Greece in pollen dispersal and clump formation, insect visitations and embryo formation when insects are denied access to cones. Ephedra distachya, nested in the core clade of Ephedra, is anemophilous, which is probably the prevailing state in Ephedra. Ephedra foeminea, sister to the remaining species of the genus, is entomophilous and pollinated by a range of diurnal and nocturnal insects. The generalist entomophilous system of E.foeminea, with distinct but infrequent insect visitations, is in many respects similar to that reported for Gnetum and Welwitschia and appears ancestral in Gnetales. The Ephedra lineage is well documented already from the Early Cretaceous, but the diversity declined dramatically during the Late Cretaceous, possibly to near extinction around the Cretaceous-Palaeogene boundary. The clade imbalance between insect- and wind-pollinated lineages is larger than expected by chance and the shift in pollination mode may explain why Ephedra escaped extinction and began to diversify again.
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| 3. |
- Bolinder, Kristina, 1987-
(författare)
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Pollen and pollination in Ephedra (Gnetales)
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ephedra (Gnetales) is a gymnosperm genus with a long evolutionary history; the first dispersed pollen grains with affinity to the group are known already from the Permian. This thesis focuses on the evolutionary history of the group and different aspects of its pollination mechanisms. Despite the limited number of extant species of the genus (50-60), and a low morphological and genetic divergence among species, there is variation in pollination syndrome in the genus. The prevailing state in Ephedra, and most gymnosperms, is wind pollination. It is therefore surprising that one species, E. foeminea, is insect-pollinated. Together with co-workers I documented the pollination syndromes of E. foeminea and a sympatric species, E. distachya, based on long term field experiments in north-eastern Greece and aerodynamic investigations and calculations. Placing the results into an evolutionary framework reveals that the insect-pollinated species E. foeminea is sister to the remaining (mostly wind-pollinated) genus, and indicates that insect pollination is the ancestral state in the Gnetales. During the course of evolution of the group there has been a shift to wind pollination, which may have played a crucial role for the diversification of the crown group in the Paleogene. Pollination biology is often correlated with the morphology of the pollen such that pollen grains of anemophilous plants are small with a smooth surface, whereas pollen grains of entomophilous plants are larger with an ornamented surface and a covering of pollenkitt. The pollen morphology of Ephedra can be broadly divided into two types: an ancestral type with an unbranched pseudosulcus between each pair of plicae, and a derived type with a branched pseudosulcus between each pair of plicae. Further, the pollen morphology and ultrastructure of the pollen wall in Ephedra are to some degree correlated with the pollination syndrome and capability of long distance dispersal. Pollen of E. foeminea has a denser ultrastructure, as a result a higher settling velocity and is therefore capable of flying shorter distances than does pollen of the anemophilous E. distachya, and other investigated anemophilous species that show a more spacious ultrastructure of the pollen grain. These results can be useful in the reconstruction of the pollination mechanism of extinct taxa of the Ephedra-lineage in the future.
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| 4. |
- Bolinder, Kristina, et al.
(författare)
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Pollen morphology of Ephedra (Gnetales) and its evolutionary implications
- 2016
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Ingår i: Grana. - : Informa UK Limited. - 0017-3134 .- 1651-2049. ; 55:1, s. 24-51
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Tidskriftsartikel (refereegranskat)abstract
- The Ephedra lineage can be traced at least to the Early Cretaceous. Its characteristically polyplicate pollen is well-represented in the fossil record and is frequently used as an indicator of paleoclimate. However, despite previous efforts, knowledge about variation and evolution of ephedroid pollen traits is poor. Here, we document pollen morphology of nearly all extant species of Ephedra, using a combination of scanning electron microscopy (SEM) and light microscopy (LM), and reconstruct ancestral states of key pollen traits. Our results indicate that the ancestral Ephedra pollen type has numerous plicae interspaced by unbranched pseudosulci, while the derived pollen type has branched pseudosulci and (generally) fewer plicae. The derived type is inferred to have evolved independently twice, once along the North American stem branch and once along the Asian stem branch. Pollen of the ancestral type is common in Mesozoic fossil records, especially from the Early Cretaceous, but it is less commonly reported from the Cenozoic. The earliest documentation of the derived pollen type is from the latest Cretaceous, after which it increases strongly in abundance during the Paleogene. The results of the present study have implications for the age of crown group Ephedra as well as for understanding evolution of pollination syndromes in the genus.
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| 5. |
- Evkaikina, Anastasiia I., et al.
(författare)
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The Huperzia selago Shoot Tip Transcriptome Sheds New Light on the Evolution of Leaves
- 2017
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Ingår i: Genome Biology and Evolution. - : Oxford University Press (OUP). - 1759-6653 .- 1759-6653. ; 9:9, s. 2444-2460
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Tidskriftsartikel (refereegranskat)abstract
- Lycopodiophyta-consisting of three orders, Lycopodiales, Isoetales and Selaginellales, with different types of shoot apical meristems (SAMs)-form the earliest branch among the extant vascular plants. They represent a sister group to all other vascular plants, from which they differ in that their leaves are microphylls-that is, leaves with a single, unbranched vein, emerging from the protostele without a leaf gap-not megaphylls. All leaves represent determinate organs originating on the flanks of indeterminate SAMs. Thus, leaf formation requires the suppression of indeterminacy, that is, of KNOX transcription factors. In seed plants, this is mediated by different groups of transcription factors including ARP and YABBY. We generated a shoot tip transcriptome of Huperzia selago (Lycopodiales) to examine the genes involved in leaf formation. Our H. selago transcriptome does not contain any ARP homolog, although transcriptomes of Selaginella spp. do. Surprisingly, we discovered a YABBY homolog, although these transcription factors were assumed to have evolved only in seed plants. The existence of a YABBY homolog in H. selago suggests that YABBY evolved already in the common ancestor of the vascular plants, and subsequently was lost in some lineages like Selaginellales, whereas ARP may have been lost in Lycopodiales. The presence of YABBY in the common ancestor of vascular plants would also support the hypothesis that this common ancestor had a simplex SAM. Furthermore, a comparison of the expression patterns of ARP in shoot tips of Selaginella kraussiana (Harrison CJ, et al. 2005. Independent recruitment of a conserved developmental mechanism during leaf evolution. Nature 434(7032): 509-514.) and YABBY in shoot tips of H. selago implies that the development of microphylls, unlike megaphylls, does not seem to depend on the combined activities of ARP and YABBY. Altogether, our data show that Lycopodiophyta are a diverse group; so, in order to understand the role of Lycopodiophyta in evolution, representatives of Lycopodiales, Selaginellales, as well as of Isoetales, have to be examined.
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| 6. |
- Forest, Felix, et al.
(författare)
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Gymnosperms on the EDGE
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Driven by limited resources and a sense of urgency, the prioritization of species for conservation has been a persistent concern in conservation science. Gymnosperms (comprising ginkgo, conifers, cycads, and gnetophytes) are one of the most threatened groups of living organisms, with 40% of the species at high risk of extinction, about twice as many as the most recent estimates for all plants (i.e. 21.4%). This high proportion of species facing extinction highlights the urgent action required to secure their future through an objective prioritization approach. The Evolutionary Distinct and Globally Endangered (EDGE) method rapidly ranks species based on their evolutionary distinctiveness and the extinction risks they face. EDGE is applied to gymnosperms using a phylogenetic tree comprising DNA sequence data for 85% of gymnosperm species (923 out of 1090 species), to which the 167 missing species were added, and IUCN Red List assessments available for 92% of species. The effect of different extinction probability transformations and the handling of IUCN data deficient species on the resulting rankings is investigated. Although top entries in our ranking comprise species that were expected to score well (e.g. Wollemia nobilis, Ginkgo biloba), many were unexpected (e.g. Araucaria araucana). These results highlight the necessity of using approaches that integrate evolutionary information in conservation science.
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| 7. |
- Han, Fang, et al.
(författare)
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Steppe development on the Northern Tibetan Plateau inferred from Paleogene ephedroid pollen
- 2016
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Ingår i: Grana. - : Informa UK Limited. - 0017-3134 .- 1651-2049. ; 55:1, s. 71-100
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Tidskriftsartikel (refereegranskat)abstract
- Steppe vegetation represents a key marker of past Asian aridification and is associated with monsoonal intensification. Little is, however, known about the origin of this pre-Oligocene vegetation, its specific composition and how it changed over time and responded to climatic variations. Here, we describe the morphological characters of Ephedraceae pollen in Eocene strata of the Xining Basin and compare the pollen composition with the palynological composition of Late Cretaceous and Paleocene deposits of the Xining Basin and the Quaternary deposits of the Qaidam Basin. We find that the Late Cretaceous steppe was dominated by Gnetaceaepollenites; in the transition from the Cretaceous to the Paleocene, Gnetaceaepollenites became extinct and Ephedripites subgenus Ephedripites dominated the flora with rare occurrences of Ephedripites subgen. Distachyapites; the middle to late Eocene presents a strong increase of Ephedripites subgen. Distachyapites; and the Quaternary/Recent is marked by a significantly lower diversity of Ephedraceae (and Nitrariaceae) compared to the Eocene. In the modern landscape of China, only a fraction of the Paleogene species diversity of Ephedraceae remains and we propose that these alterations in Ephedreaceae composition occurred in response to the climatic changes at least since the Eocene. In particular, the strong Eocene monsoons that enhanced the continental aridification may have played an important role in the evolution of Ephedripites subgen. Distachyapites triggering an evolutionary shift to wind-pollination in this group. Conceivably, the Ephedraceae/Nitrariaceae dominated steppe ended during the Eocene/Oligocene climatic cooling and aridification, which favoured other plant taxa.
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| 8. |
- Hou, Chen, 1986-
(författare)
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Evolutionary studies of the Gnetales
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Gnetales consist of three distinct genera, Ephedra, Gnetum and Welwitschia with considerable divergence among them regarding morphological, ecological and molecular characters. A longstanding debate of the similarity between the Gnetales and angiosperms and the unresolved seed plant phylogeny intrigues plant scientists to further investigate the evolutionary history of the Gnetales. The presented projects deal with interdisciplinary questions on proteomics, chloroplast genomes, phylogenetic relationships, gross morphology and taxonomy. The thesis aims to summarize general problems encountered in previous studies, and to provide new insights and future perspectives based on the results of completed and ongoing projects. In Ephedra, the Mediterranean species E. foeminea has been shown to be entomophilous and it possesses an important phylogenetic status as the sister of the remaining genus. Therefore, the chloroplast genome of E. foeminea was assembled and compared to that previously presented (of the anemophilous Asian species E. equisetina, nested in the core clade of Ephedra). The genome has a quadripartite structure and comprises 118 genes and 109,584 base pairs. A pairwise genome comparison was conducted between E. foeminea and E. equisetina, resulting in the detection of 2,352 variable sites, the obtained data can be used for prospective phylogenetic studies. A proteomic study was also conducted on E. foeminea along with three anemophilous Ephedra species, in order to investigate the biochemistry of the pollination drops. The results show that detected proteins in the pollination drops of Ephedra vary dramatically among species but always occur in very low amounts. The majority of the detected proteins are degradome proteins, i.e., waste products from degrading cells of the nucellus. Some secretome proteins were also found, which are putatively functional, but also these proteins occur in very low amounts. The repeatability of the proteomic studies can, however, be questioned. The sampling methods and proteomic analyses are probably problematic although some suggestions for improvement are provided. Thus I chose to continue with other projects.In Gnetum, reconstruction of the genus phylogeny and assessments of divergence times of clades were performed using an extensive sampling of ingroup and outgroup accessions. The results show that the South American lineage separated from the remaining genus in the Late Cretaceous. The continued diversification event gave rise to an African lineage and an Asian lineage. The crown age of the Asian clade, which comprises two arborescent species sister to the remaining liaonid species, was estimated to the Cretaceous-Paleogene (K-Pg) boundary. In light of the genus phylogeny and estimated node ages, we suggest that the breakup of Gondwana influenced diversification patterns in Gnetum. Later dispersal events also contributed to the current distribution of Gnetum, and to the phylogenetic patterns within each of the major clades. From my results, it is however clear that taxonomy and species delimitations are poorly defined, and needs to be further studied for all subclades of Gnetum. I have initiated this task by studying the Chinese lianoid clade of Gnetum more in depth. Eleven chloroplast genomes were generated, aligned and compared. Based on the information, four chloroplast markers were designed and applied to further resolve the species relationships with an extensive sampling. The results show, with strong support, that G. parvifolium is sister to all the remaining species of the Chinese linaoid clade. Another five lianoid species are confirmed using both morphological and molecular data, but several names are represented by type material that cannot be considered separate species. Modified keys for identification of male and female plants are presented, based on vegetative and reproductive structures. A subsequent dating analysis indicates that diversification in the Chinese lianoid Gnetum clade took place mainly in the Neogene, during which environmental changes probably facilitated diversification in the lineage.
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| 9. |
- Hou, Chen, et al.
(författare)
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New insights into the evolutionary history of Gnetum (Gnetales)
- 2015
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Ingår i: Taxon. - : Wiley. - 0040-0262 .- 1996-8175. ; 64:2, s. 239-253
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Tidskriftsartikel (refereegranskat)abstract
- Gnetum (Gnetales: Gnetaceae) constitutes an evolutionarily isolated gymnosperm clade, comprising about 40 species that inhabit tropical areas of the world. While its closest living relative, the monotypic Welwitschia, has a well-documented fossil record from the Early Cretaceous, Gnetum-like fossils are rare and poorly understood. The phylogeny of Gnetum has been studied previously but the distant relationship to outgroups and the difficulty of obtaining plant material mean it is not yet fully resolved. Most species are tropical lianas with an angiospermous vegetative habit that are difficult to find and identify. Here a new phylogeny is presented based on nuclear and chloroplast data from 58 Gnetum accessions, representing 27 putative species, and outgroup information from other seed plants. The results provide support for South American species being sister to the remaining species. The two African species constitute a monophyletic group, sister to an Asian clade, within which the two arborescent species of the genus are the earliest diverging. Estimated divergence times indicate, in contrast with previous results, that the major lineages of Gnetum diverged in the Late Cretaceous. This result is obtained regardless of tree prior used in the BEAST analyses (Yule or birth-death). Together these findings suggest a correlation between early divergence events in extant Gnetum and the breakup of Gondwana in the Cretaceous. Compared to the old stem ages of major subclades of Gnetum, crown nodes date to the Cenozoic: the Asian crown group dates to the Cretaceous-Paleogene (K-Pg) boundary, the African crown group to the mid-Paleogene, and the South American crown group to the Paleogene-Neogene boundary. Although dispersal must have contributed to the current distribution of Gnetum, e.g., within South America and from Southeast Asian islands to the East Asian mainland, dispersal has apparently not occurred across major oceans, at least not during the Cenozoic.
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| 10. |
- Hou, Chen, et al.
(författare)
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Resolving phylogenetic relationships and species delimitations in closely related gymnosperms using high-throughput NGS, Sanger sequencing and morphology
- 2016
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Ingår i: Plant Systematics and Evolution. - : Springer Science and Business Media LLC. - 0378-2697 .- 1615-6110 .- 2199-6881. ; 302:9, s. 1345-1365
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Tidskriftsartikel (refereegranskat)abstract
- Plastid genomes have been widely applied to elucidate plant evolution at higher taxonomic levels, but have rarely been considered useful for addressing close relationships. Here, we resolve the phylogeny and taxonomy of the Chinese lianoid Gnetum clade (Gnetales), using high throughput and Sanger sequencing techniques and studies of plant morphology. Despite previous efforts, relationships among taxa and the taxonomy within the clade have remained unclear. We generated 11 plastid genomes representing one arborescent and four lianoid species. Phylogenetic analyses were conducted using (a) the entire plastid genomes and (b) the protein-coding genes only. Sequence divergence among the lianoid species was substantial, with 9345 variable sites. Four variable regions were identified, targeted and sequenced for an additional 54 specimens and analyzed together with one nuclear ribosomal marker. Results from the phylogenetic analyses corroborate G. parvifolium as sister to the remaining lianoid species and support the presence of at least five additional species in the Chinese lianoid clade: G. catasphaericum, G. formosum, G. luofuense, G. montanum and G. pendulum. Following morphological investigations, G. giganteum and G. gracilipes are included in and synonymized with G. pendulum. Gnetum hainanense is included in and synonymized with G. luofuense. Two names, G. indicum and G. cleistostachyum, remain questionable. A taxonomic revision and a key to Chinese lianoid Gnetum are presented. Internal nodes in the Chinese lianoid Gnetum clade are from the Miocene and onwards and coincide with the expansion of tropical to subtropical forests in South China, which may have facilitated speciation in the clade.
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