The Asplenium normale complex contains the widespread A. normale and several geographically restricted species: A. boreale, A. hobdyi, A. kiangsuense, A. oligophlebium and A. shimurae. The taxonomy of this group is unclear with some entities treated infraspecifically or as synonyms. Furthermore, the existence of diploids and tetraploids in this species complex is suggestive of reticulate evolution. In order to formulate a natural classification and to investigate the relationships in this complex, phylogenetic analyses of plastid and nuclear sequence data and inference of ploidy level were used to assess the distinctiveness of putative taxonomic units and their relationships. The Asplenium normale complex was recovered as a monophyletic group comprising six principal chloroplast lineages. The results support the hypothesis that A. normale s.l. contains several species. Based on our inferences, we outline an improved species classification recognizing three diploid and four tetraploid entities. Incongruence of chloroplast and nuclear phylogenies was interpreted to be a result of recurrent reticulation events in the A. normale complex.
Polyploidy is widely considered as a major process in the evolution of plants but the accumulation of polyploid species diversity is still controversial. Some recent studies proposed increased extinction risk in neopolyploids compared with their diploid ancestors. The high proportion of polyploid ferns is expected to be formed mainly by neopolyploids, whereas paleopolyploid species are predicted to be clustered in clades founded by whole genome duplications. Here, we test this prediction by exploring the evolution of polyploidy in the derived fern family Aspleniaceae. The family has a global distribution and shows the highest frequency of polyploid taxa among all ferns. To test the hypothesis, we obtained a comprehensive phylogeny using chloroplast DNA sequences of 883 specimens representing 292 species. All published chromosome counts were mapped onto this phylogenetic framework in order to explore the evolution of polyploids. We recovered evidence for several whole genome duplications in the history of Aspleniaceae. Phylogenetic relationships of polyploids exceeding the tetraploid level suggest that tetraploid Asplenium species may have replaced their diploid ancestors as the main evolutionary players in some clades of this family.
The Asplenium normale D. Don complex comprises several taxa that are either diploid or tetraploid. The tetraploids are assumed to have originated from diploid ancestors by relatively recent autopolyploidization or allopolyploidization. Some of the diploids are readily recognized morphologically but most of the taxa have until now been placed into a single species. However, phylogenetic studies have challenged this treatment and emphasized the notion that the taxonomic treatment of this complex needs to be revised. An integrative taxonomic approach was employed to delimit species in the complex using cytological, morphological, and DNA sequence data. Initially, we employed a diploid first approach to establish a robust taxonomic framework. Special efforts were made to collect and identify the diploid progenitors of each polyploid lineage identified in the plastid DNA based phylogenetic hypothesis. A total of six distinct diploid species were identified. The distinctive nature of the six diploids is strongly supported by sequence differences in plastid DNA and nuclear loci, as well as by the results of morphometric analysis. Diagnostic morphological characters were identified to distinguish the six diploid species, resulting in their revised taxonomy, which includes two novel species, namely, Asplenium normaloides and A. guangdongense. Further studies to strengthen the taxonomic classification of all of the tetraploid taxa are warranted.
Locally available resources can be shared within clonal plant systems through physiological integration, thus enhancing their survival and growth. Most epiphytes exhibit clonal growth habit, but few studies have tested effects of physiological integration (resource sharing) on survival and growth of epiphytes and whether such effects vary with species. We conducted two experiments, one on individuals (single ramets) and another on groups (several ramets within a plot), with severed and intact rhizome treatments (without and with physiological integration) on two dominant epiphytic ferns (Polypodiodes subamoena and Lepisorus scolopendrium) in a subtropical montane moist forest in Southwest China. Rhizome severing (preventing integration) significantly reduced ramet survival in the individual experiment and number of surviving ramets in the group experiment, and it also decreased biomass of both species in both experiments. However, the magnitude of such integration effects did not vary significantly between the two species. We conclude that resource sharing may be a general strategy for clonal epiphytes to adapt to forest canopies where resources are limited and heterogeneously distributed in space and time.
Background: Bacteria are readily nourished in airtight environments with high humidity, such as storage cabinets, clothing closets, and corners, where ventilation is normally low and humidity is high. Objectives: We characterized the role of humidity and ventilation in bacterial growth and genus distribution at different temperatures (26 °C and 34 °C). Methods: Fresh pork, which was used as the substrate for bacterial culture, was placed in storage cabinets. Bacterial growth and genera distribution on the surface of pork placed in a storage cabinet under different temperatures (26 °C and 34 °C); relative humidity levels (RH: 50%, 70%, 90%); and ventilation conditions (no ventilation and low, medium, and high levels of ventilation) were assessed by rDNA sequencing. Results: Increased ventilation and reduced humidity significantly decreased bacterial growth at 26 °C and 34 °C. The contribution of increased ventilation to the reduction in bacterial growth exceeded that of decreased humidity. Ventilation had the greatest effect on reducing bacterial growth compared to the unventilated conditions at 70% RH. At 34 °C, medium and high levels of ventilation were required to reduce bacterial growth. High temperatures greatly increased bacterial growth, but ventilation could reduce the degree of this increase.
The name Hymenasplenium laterepens was first proposed by Cheng and Murakami in 1998 but was not validly published. We recently collected and studied this taxon at its locus classicus in Xishuangbanna, Yunnan Province in China. Molecular phylogenetic analyses and morphological observation of H. laterepens and related species clearly indicate that this is a distinct taxonomic entity worthy of species rank. Phylogenetically, H. laterepens is closely related to H. apogamum and may be involved in the reticulate evolution of the H. apogamum complex, which is comprised of several taxa with different levels of ploidy. Morphologically, H. laterepens is distinguished by the combination of its triangular laminae, large pinnae with acute apices and deeply serrated margins, and ca. 117 chromosomes at meiosis I and 32 spores in each sporangium. This work provides a complete species description and comparison to related species within the genus Hymenasplenium, particularly to other relatives of the “H. unilaterale” group. Hymenasplenium laterepens is described here with diagnosis and type designation.
A number of samples with the nominal formula Y 0.4( Ba x Sr 1−x)0.6 Cu O 3, Y 0.5( Ba x Sr 1−x)0.5 CuO 3 and Y 1.2 ( Ba x Sr 1−x)0.8 CuO 4 have been made. It is found that for x=0 the samples show no superconductivity but for x>0.008 samples do show superconductivity, and for x=0.008, 0.005 the samples have high normal resistivity and no resistive transition but show diamagnetism at about 70k. The structure analysis find a smaller distortion in the the sample Y 0.5( Ba 0.01 Sr 0.99)0.5 CuO 3 than that in YBa 2 Cu 3 O 9−y. The relation between superconductivity and the ionic radius is discussed.
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