Further research on chemotaxonomy of paeonol and analogs in Paeonia (Ranunculaceae)

In this paper, the paeonol, paeoniflorin and their analogs were analyzed in the roots of 14 species and 2 subspecies of Paeonia L. The existence and content of these compounds were discussed in three sections, sect. Moutan, sect. Paeonia and sect. Onaepia. In sect. Moutan, paeonol and its analogs were high in content in all species. In sect. Paeonia, low content of paeonol and its analogs were found in plants of four taxa, P. lactiflora, P. anomala ssp. veitchii, P. mairei and P. intermedia. None of these compounds was found in sect. Onaepia. Paeonol has a simple structure and is distributed widely in plant; its decrease and loss may be the result of evolution. Therefore, it is deduced that the relationship among the three sections of Paeonia might be that woody sect. Moutan is the more primitive and derived from the ancestor of Paeonia first. For the herbaceous sections, sect. Paeonia is more closely related to sect. Moutan than to sect. Onaepia. In sect. Moutan, there are less paeonol and its analogs in the species of subsect. Vaginata than in those of subsect. Delavayanae. Thus, the former may be considered more advanced. In sect. Paeonia, the taxa with minor content of paeonol and its analogs are diploid except P. mairei. Among them, P. lactiflora and P. anomala ssp. veitchii are relatively primitive by morphology. None of paeonol and its analogs was detected in the species with specialized form.     

芍药组内不同类群间光合特性及叶绿素荧光特性比较

为了比较分析芍药组不同类群光合生理差异以及它们对各自不同光照环境的适应性, 测定了芍药组(Paeonia sect. Paeonia) 4种2变种的光合日变化、光响应曲线、CO₂响应曲线, 以及叶绿素荧光特性。结果显示, 芍药组中不同类群之间光合速率差异明显, 各个种类的“午休”程度不同, 芍药(Paeonia lactiflora )和毛果芍药(P. lactiflora var. trichocarpa)的强光抑制现象没有川赤芍(P. veitchii)、美丽芍药(P. mairei)和窄叶芍药(P. anomala)明显。叶绿素荧光特征能够反映芍药组不同类群光合生理的差异。芍药组内不同类群地理分布的差异能部分从光合生理特征的适应性方面得到解释。     

Paeonia anomala的核型研究

报道了Paeonia anomala L．的核型,澄清了新疆阿尔泰地区分布的该物种的染色体数目。分布于该地区的Paeonia anomala L．的核型组成：2n=2x=10=6m＋2sm＋2st。该类群核型与该属其它类群一致——2A型。在综合比较分析该属染色体参数以及核型不均一性参数,包括最长,最短染色体比（L1/Ln）和染色体不对称系数（CKOA）的基础上,我们发现该属三个组在核型上没有明显分化,仅在木本类群（Sect．Mouton DC．）和草本类群（Sect．Onaepia Lindley和Sect．Paeonia）之间存在微小差异。此外,作为二倍体类群,新疆阿尔泰地区分布的Paeonia anomala L．很可能是二倍体杂种,这将为研究被子植物的父母本同倍化杂交式物种起源提供一个很好的研究材料。     

Chloroplast DNA phylogeny, reticulate evolution, and biogeography of Paeonia (Paeoniaceae)

The coding region of the mat K gene and two intergenic spacers, psb A-trn H and trn L(UAA)-trn F(GAA), of cpDNA were sequenced to study phylogenetic relationships of 32 Paeonia species. In the psb A-trn H intergenic spacer, short sequences bordered by long inverted repeats have undergone inversions that are often homoplasious mutations. Insertions/deletions found in the two intergenic spacers, mostly resulting from slipped-strand mispairing, provided relatively reliable phylogenetic information. The mat K coding region, evolving more rapidly than the trnL-trn F spacer and more slowly than the psb A-trn H spacer, produced the best resolved phylogenetic tree. The mat K phylogeny was compared with the phylogeny obtained from sequences of internal transcribed spacers (ITS) of nuclear ribosomal DNA. A refined hypothesis of species phylogeny of section Paeonia was proposed by considering the discordance between the nuclear and cpDNA phylogenies to be results of hybrid speciation followed by inheritance of cpDNA of one parent and fixation of ITS sequences of another parent. The Eurasian and western North American disjunct distribution of the genus may have resulted from interrruption of the continuous distribution of ancestral populations of extant peony species across the Bering land bridge during the Miocene. Pleistocene glaciation may have played an important role in triggering extensive reticulate evolution within section Paeonia and shifting distributional ranges of both parental and hybrid species.     

四川西部川赤芍野生居群的表型多样性分析

为揭示四川西部川赤芍〔Paeonia anomala subsp.veitchii(Lynch)D.Y.Hong et K.Y.Pan〕表型性状的变异规律,对川赤芍6个野生居群的株高、茎基粗、叶片和花部性状等15个表型性状进行了比较;并在此基础上,对各表型性状进行了方差分析、变异系数(CV)分析、离散系数(R′)分析、Shannon-Weaver遗传多样性指数(H′)分析、主成分分析和聚类分析.结果表明:川赤芍15个表型性状在居群间均存在极显著差异;除顶小叶长宽比外,其他14个表型性状在居群内均存在极显著或显著差异.15个表型性状在居群内的F值均明显小于居群间.15个表型性状中,每枝着花量的CV平均值最大(33.68%),花瓣数的CV平均值最小(11.26%);6个居群中,阿坝州小金县两河乡(P1)和阿坝州小金县四姑娘山镇(P2)居群的CV平均值较大,阿坝州金川县万林乡(P4)和阿坝州马尔康县卓克基乡(P5)居群的CV平均值居中,阿坝州汶川县卧龙自然保护区(P3)和甘孜州炉霍县充古乡(P6)居群的CV平均值最小.15个表型性状中,株高的R′平均值最大(64.48%),萼片数和苞片数的R′平均值均最小(37.50%);6个居群中,P2居群的R′平均值最大(56.66%),P3居群的R′平均值最小(43.65%).川赤芍6个居群15个表型性状的CV值和R′值的平均值分别为18.70%和49.80%.川赤芍15个表型性状和6个居群的H′平均值均较高,分别为1.6475和1.4510.主成分分析结果显示:叶片形态和花部特征是川赤芍表型变异的主要因子.聚类分析结果显示:在欧氏距离7.12处,川赤芍6个居群被分成2支,其中,P6居群单独聚为一支,其他5个居群聚为另一支,表明生境相似的居群更早地聚在一起.研究结果显示:四川西部川赤芍表型性状在居群间变异丰富,这与其叶片形态、花部特征及生境关系密切.     

芍药胚和胚乳早期发育的研究

本文报道芍药(Paeonia lactiflora)的胚和胚乳的早期发育,主要结论是:1,开花后4—20天,合子核反复分裂形成多核原胚。2.原胚及胚乳游离核分裂均以有丝分裂为主,晚期有无丝分裂和多倍体核;3,细胞壁形成可由纺锤丝间和自由壁两种方式进行。原胚壁形成由合点端向珠孔端进行,胚乳则由胚附近向合点端发展。我们支持 Cave 等基于多核原胚提出的 Paeonia 与裸子植物平行演化的意见,同时认为 Paeonia 的多核原胚演化趋势是原胚由珠孔端至合点端功能分区的特化。     

Assessing hybridization in natural populations of Penstemon (Scrophulariaceae) using hypervariable intersimple sequence repeat (ISSR) bands

Inferences regarding hybridization rely on genetic markers to differentiate parental taxa from one another. Intersimple sequence repeat (ISSR) markers are based on single-primer PCR reactions where the primer sequence is derived from di- and trinucleotide repeats. These markers have successfully been used to assay genetic variability among cultivated plants, but have not yet been tested in natural populations. We used genetic markers generated from eight ISSR primers to examine patterns of hybridization and purported examples of hybrid speciation in Penstemon (Scrophulariaceae) in a hybrid complex involving P. centranthifolius , P. grinnellii , P. spectabilis and P. clevelandii . This hybrid complex has previously been studied using three molecular data sets (allozymes, and restriction-site variation of nuclear rDNA and chloroplast DNA). These studies revealed patterns of introgression involving P. centranthifolius , but were unsuccessful in determining whether gene flow occurs among the other species, and support for hypotheses of diploid hybrid speciation was also lacking. In this study, we were able to fingerprint each DNA accession sampled with one to three ISSR primers and most accessions could be identified with a single primer. We found population- and species-specific markers for each taxon surveyed. Our results: (i) do not support the hybrid origin of P. spectabilis ; (ii) do support the hypothesis that P. clevelandii is a diploid hybrid species derived from P. centranthifolius and P. spectabilis ; and (iii) demonstrate that pollen-mediated gene flow via hummingbird vectors is prevalent in the hybrid complex.     

ALLOPOLYPLOIDY IN NATURAL AND CULTIVATED POPULATIONS OF PORPHYRA (BANGIALES,RHODOPHYTA)1

To confirm whether allopolyploidy occurs in samples of previously identified Porphyra yezoensis Ueda, P. tenera Kjellm., and P. yezoensis × P. tenera from natural and cultivated populations, we examined these samples by using PCR‐RFLP and microsatellite analyses of multiple nuclear and chloroplast regions [nuclear regions: type II DNA topoisomerase gene (TOP2), actin‐related protein 4 gene (ARP4), internal transcribed spacer (ITS) rDNA and three microsatellite loci; chloroplast region: RUBISCO spacer]. Except for the ITS region, these multiple nuclear markers indicated that the wild strain MT‐1 and the cultivated strain 90‐02 (previously identified as P. yezoensis × P. tenera and cultivated P. tenera, respectively) are heterozygous and possess both genotypes of P. tenera and P. yezoensis in the conchocelis phase. Furthermore, gametophytic blades of two pure lines, HG‐TY1 and HG‐TY2 (F₁ strains of MT‐1 and 90‐02, respectively), were also heterozygous, and six chromosomes per single cell could be observed in each blade of the two pure lines. These results demonstrate that allopolyploidy occurs in Porphyra strains derived from both natural and cultivated populations, even though ITS genotypes of these strains showed homogenization toward one parental ITS.     

Molecular evidence for polyploid origins in Saxifraga (Saxifragaceae): the narrow arctic endemic S. svalbardensis and its widespread allies

The recently described polyploid Saxifraga svalbardensis is endemic to the arctic archipelago of Svalbard. We investigated relationships among four closely related species of Saxifraga in Svalbard and tested three previously proposed hypotheses for the origin of S. svalbardensis: (1) differentiation from the morphologically and chromosomally variable polyploid S. cernua; (2) hybridization between the diploid S. hyperborea and S. cernua; and (3) hybridization between the tetraploid S. rivularis and S. cernua. Fifteen populations were analyzed using random amplified polymorphic DNAs (RAPDs) and nucleotide sequences of the chloroplast gene matK and the internal transcribed spacers (ITS) of nuclear ribosomal DNA (rDNA). RAPD and matK data suggest that S. svalbardensis has originated from a hybrid with S. rivularis as the maternal parent and S. cernua as the paternal parent, possibly a single time, whereas ITS data could not be used to discriminate among the hypotheses. The data also suggest that the diploid S. hyperborea is a progenitor of the tetraploid S. rivularis. The four populations examined of S. svalbardensis were virtually identical for RAPD and ITS markers, whereas S. cernua showed high levels of variation, suggesting that the latter polyploid either has formed recurrently or has undergone considerable differentiation since its origin.     

Heterogeneity of three molecular data partition phylogenies of mints related to M. x piperita (Mentha; Lamiaceae)

Phylogenetic reconstructions with molecular tools are now widely used, thanks to advances in PCR and sequencing technologies. The choice of the molecular target still remains a problem because too few comparative data are available. This is particularly true for hybrid taxa, where differential introgression of genome parts leads to incongruity between data sets. We have studied the potential of three data partitions to reconstruct the phylogeny of mints related to M. x piperita. These included nuclear DNA (ITS), chloroplast DNA (non-coding regions trnL intron, intergenic spacers trnL-trnF, and psbA-trnH), and AFLP and ISSR, markers. The taxonomic sampling was composed of hybrids, diploid and polyploid genomes. Since the genealogy of cultivated mint hybrids is known, they represent a model group to compare the usefulness of various molecular markers for phylogeny inference. Incongruities between ITS, chloroplast DNA, and AFLP-ISSR phylogenetic trees were recorded, although DNA fingerprinting data were congruent with morphological classification. Evidence of chloroplast capture events was obtained for M. x piperita. Direct sequencing of ITS led to biased results because of the existence of pseudogenes. Sequencing of cloned ITS further failed to provide evidence of the existence of the two parental copy types for M. x piperita, a sterile hybrid that has had no opportunity for concerted evolution of ITS copies. AFLP-ISSR data clustered M. x piperita with the parent that had the largest genome. This study sheds light on differential of introgression of different genome regions in mint hybrids.     

Wax plants disentangled: a phylogeny of Hoya (Marsdenieae, Apocynaceae) inferred from nuclear and chloroplast DNA sequences

Hoya (Marsdenieae, Apocynaceae) includes at least 200 species distributed from India to the Pacific Islands. We here infer major species groups in the genus based on combined sequences from the chloroplast atpB-rbcL spacer, the trnL region, and nuclear ribosomal DNA ITS region for 42 taxa of Hoya and close relatives. To assess levels of ITS polymorphism, ITS sequences for a third of the accessions were obtained by cloning. Most ITS clones grouped by species, indicating that speciation in Hoya usually predates ITS duplication. One ITS sequence of H. carnosa, however, grouped with a sequence of the morphologically similar H. pubicalyx, pointing to recent hybridization or the persistence of paralogous copies through a speciation event. The topology resulting from the combined chloroplast and nuclear data recovers some morphology-based sections, such as Acanthostemma and Eriostemma, as well as a well-supported Australian/New Guinean clade. The combined data also suggest that morphological adaptations for ant-symbiosis evolved at least three times within Hoya.     

Phylogenetic utility of the glycerol-3-phosphate acyltransferase gene: evolution and implications in Paeonia (Paeoniaceae)

The nuclear-encoded chloroplast-expressed glycerol-3-phosphate acyltransferase (GPAT) gene has been found to be single-copy in a number of angiosperm families. In this study we investigated the phylogenetic utility of the GPAT gene at the interspecific level using the genus Paeonia (Paeoniaceae) as an example. An approximately 2.3- to 2.6-kb fragment of the GPAT gene, containing a large intron of more than 2 kb, was amplified, cloned, and sequenced from 19 accessions representing 13 Paeonia species. The GPAT gene phylogeny inferred by parsimony analysis supported interspecific relationships that were previously unresolved, suggesting that large introns of low-copy nuclear genes are particularly informative in the resolution of close relationships at low taxonomic levels. Whereas the GPAT phylogeny is largely congruent with the previous phylogenetic hypothesis of Paeonia, it shows a significant discordance involving the paraphyly of section Paeonia. Given evidence of an ancient duplication and the subsequent silencing of one GPAT locus in P. anomala, this discordance is most likely the result of paralogy. Two distinct genomic clones containing partial GPAT genes were isolated from P. anomala. The GPAT sequence from one clone corresponded to the functional copy of the gene, and the second genomic clone was determined to contain a GPAT pseudogene. The insertion of a retrotransposon in an intron of this pseudogene may have been responsible for the silencing of this GPAT locus in P. anomala. This study suggests that, although it is unlikely that universal nuclear gene markers free from paralogy are usually available, low-copy nuclear genes can be very useful in plant phylogenetic reconstruction, especially at low taxonomic levels, as long as the evolutionary dynamics of the genes are carefully examined.     

The evolution of Dactylorhiza (Orchidaceae) allotetraploid complex: insights from nrDNA sequences and cpDNA PCR-RFLP data

Sequence data from a portion of the external transcribed spacer (ETS) and from the internal transcribed spacers (ITS1 and ITS2) of 18S-26S nuclear ribosomal DNA were used together with chloroplast DNA PCR-RFLP data to unravel patterns of allotetraploid speciation within the Western European Dactylorhiza polyploid complex. A maximum likelihood tree based on combined ETS and ITS sequences suggests that the Western European Dactylorhiza allotetraploids have evolved by hybridization between four main diploid lineages. Cloned sequences and the topology of the ITS plus ETS tree indicate that the allotetraploid species D. elata, D. brennensis, and D. sphagnicola have originated from the autotetraploid D. maculata together with the diploid D. incarnata, while D. majalis, D. traunsteineri, and D. angustata seem to have evolved by hybridization between the D. fuchsii s.str and D. incarnata lineages. Finally, the diploid D. saccifera lineage seems to have been involved together with the D. incarnata lineage in the formation of the allotetraploid D. praetermissa. The observed congruence between the chloroplast tree and the ITS/ETS tree suggests a directional evolution of the nrDNA after polyploidization in favor of the maternal genome. Considered together with morphological, biogeographical, and ecological evidence, the molecular analysis leads us to recognize four species within the investigated allotetraploid complex, namely D. majalis, D. praetermissa, D. elata, and D. sphagnicola.     

Distribution of parental DNA markers inEncelia virginensis (Asteraceae: Heliantheae), a diploid species of putative hybrid origin

Morphological, geographical and ecological evidence suggests thatEncelia virginensis is a true-breeding diploid species derived from hybrids ofE. actoni andE. frutescens. To test this hypothesis, we examined the chloroplast and nuclear DNA of severalEncelia species. PCR amplification targeted three separate regions of chloroplast DNA:trnK-2621/trnK-11,rbcL/ORF106, andpsbA3/TrnI-51, which amplify 2600bp, 3300bp and 3200bp fragments respectively. Restriction fragment analysis of chloroplast DNA revealed no variation that could be used to discriminate between the parent species. A RAPD analysis using 109 dekamer primers was used to analyze the nuclear genome.Encelia actoni andE. frutescens were distinguished by several high-frequency RAPD markers. In populations ofE. virginensis, these markers were detected in varying proportions, and no unique markers were found. Evidence from the nuclear genome supports the hypothesis thatE. virginensis is of hybrid origin. ThatE. virginensis may have arisen by normal divergent speciation followed by later introgression remains a possibility, however, and is not formally ruled out here. Diploid hybrid speciation inEncelia differs from other documented cases in that there are no discernible chromosome differences between the species, and all interspecific hybrids are fully fertile. In addition, apparent ecological selection against backcross progeny provides an external barrier to reproduction between F₁ progeny and the parental species. These characteristics suggest that hybrid speciation inEncelia may represent an alternative model for homoploid hybrid speciation involving external reproductive barriers. In particular, this may be the case for other proposed diploid hybrid taxa that also exhibit little chromosomal differentiation and have fertile F₁s.     

The Early Development of Embryo and Endosperm of Paeonia lactifiora

The present paper reports the early development of embryo and endosperm of Paeonia lactiflora. The main conclusions are as follows: 1 The zygote nucleus divides directly to form a coenocytic proembryo with different number of free nuclei. The result confirms the conclusion of Yakovlev[6] as well as Yakovlev and Yoffe[7] On the occurnce of coenocytic proembryo in Paeonia suffruticosa Andr. (P. moutan Sims), P. albiflora Pall. (P. lactiflora Pall), P. officinalis L., P. tenuifolia L., P. anomala L., P. veitchii Lynch (P. beresowskii Komarov), P. wittmanniana, also it agrees with the report of Cave et al.[4] on the occurence of the coenocytie proembryo in Paeonia californica and P. brownii. From the result of our investigation, there is no basis to support Murgai's conclusion obtained in certain species of Paeonia, i.e., the first division of zygote nucleus is accompanied by wall formation and the coenocyte is a suspensor. The primary endosperm nucleus of P. lactiflora divides often earlier than zygote nucleus, or almost at the same time or later in a few cases; 2 Both mitosis and amitosis occur in the free nuclei in the coenocytic proembryo, and mitosis is dominant. In the later stage of development the amitosis occurs at the micropylar region of the coenocytic proembryo, in the free nuclear endosperm at the chalazal region and the appressed part of the chalazal end of the coenocytic proembryo. In addition, in the region of conenocytic proembryo and endosperm polyploid nuclei, irregular nuclei are also frequently met with; 3 Cell wall formation in the coenocyte and the endosperm initiates by means of both cell plate and freely growthing walls, but in the coenocyte wall formation is earlier than in the free nuclear endosperm. At first, wall formation of the coenocytic proembryo begins at the chalazal end, and then extends toward the micropylar region, and in endosperm it begins at the part appressed to the part of the chalazal end of coenocytic proembryo, and then extends toward the chalazal end. We support Cave’s suggestion of the parallel evolution for Paeonia possessed the coenocytic proembryo has no relation to the coenocytic proembryo of the gymnosperms. Further we consider the evolution tendency of the coenocytic proembryo of Paeonia toward a functional specialization.     

Paeonia anomala 的核型研究

报道了Paeonia anomala L. 的核型, 澄清了新疆阿尔泰地区分布的该物种的染色体数目。分布于该地区的Paeonia anomala L. 的核型组成: 2n = 2x = 10 = 6m+ 2sm+ 2st。该类群核型与该属其它类群一致———2A 型。在综合比较分析该属染色体参数以及核型不均一性数, 包括最长􊄯最短染色体比(L1/Ln ) 和染色体不对称系数( CKOA) 的基础上, 我们发现该属三个组在核型上没有明显分化, 仅在木本类群(Sect . Moutan DC .) 和草本类群(Sect. Onaepia Lindley 和Sect. Paeonia) 之间存在微小差异。此外, 作为二倍体类群, 新疆阿尔泰地区分布的Paeonia anomala L. 很可能是二倍体杂种, 这将为研究被子植物的父母本同倍化杂交式物种起源提供一个很好的研究材料。     

Polymerase chain reaction-single strand conformation polymorphism analyses of nuclear and chloroplast DNA provide evidence for recombination,multiple introductions and nascent speciation in the Caulerpa taxifolia complex

Independent lines of evidence support an Australian origin for the Mediterranean populations of the tropical alga Caulerpa taxifolia. To complement previous biogeographical studies based on nuclear rDNA internal transcribed spacer (ITS), a new chloroplast marker was developed--the cp 16S rDNA intron-2. Sequence variability for both nuclear and chloroplast markers were assessed in 110 individuals using single strand conformation polymorphism. Comparison of intrapopulation genetic diversity between invasive Mediterranean and 'native' Australian populations revealed the occurrence of two divergent and widespread clades. The first clade grouped nontropical invasive populations with inshore-mainland populations from Australia, while the second clustered all offshore-island populations studied so far. Despite our finding of nine distinct nuclear and five distinct chloroplast profiles, a single nucleocytoplasmic combination was characteristic of the invasive populations and sexual reproduction was found to be very rare. C. taxifolia is clearly a complex of genetically and ecologically differentiated sibling species or subspecies.     

Evolution of alcohol dehydrogenase genes in peonies (Paeonia): phylogenetic relationships of putative nonhybrid species

Alcohol dehydrogenase genes were amplified by PCR, cloned, and sequenced from 11 putative nonhybrid species of the angiosperm genus Paeonia. Sequences of five exons and six intron regions of the Adh gene were used to reconstruct the phylogeny of these species. Two paralogous genes, Adh1A, and Adh2, were found; an additional gene, Adh1B, is also present in section Moutan. Phylogenetic analyses of exon sequences of the Adh genes of Paeonia and a variety of other angiosperms imply that duplication of Adh1 and Adh2 occurred prior to the divergence of Paeonia species and was followed by a duplication resulting in Adh1A and Adh1B. Concerted evolution appears to be absent between these paralogous loci. Phylogenetic analysis of only the Paeonia Adh exon sequences, positioning the root of the tree between the paralogous genes Adh1 and Adh2, suggests that the first evolutionary split within the genus occurred between the shrubby section Moutan and the other two herbaceous sections Oneapia and Paeonia. Restriction of Adh1B genes to section Moutan may have resulted from deletion of Adh1B from the common ancestor of sections Oneapia and Paeonia. A relative-rate test was designed to compare rates of molecular change among lineages based on the divergence of paralogous genes, and the results indicate a slower rate of evolution within the shrubby section Moutan than in section Oneapia. This may be responsible for the relatively long branch length of section Oneapia and the short branch length between section Moutan and the other two sections found on the Adh, ITS (nrDNA), and matK (cpDNA) phylogenies of the genus. Adh1 and Adh2 intron sequences cannot be aligned, and we therefore carried out separate analyses of Adh1A and Adh2 genes using exon and intron sequences together. The Templeton test suggested that there is not significant incongruence among Adh1A, ITS, and matK data sets, but that these three data sets conflict significantly with Adh2 sequence data. A combined analysis of Adh1A, ITS, and matK sequences produced a tree that is better resolved than that of any individual gene, and congruent with morphology and the results of artificial hybridization. It is therefore considered to be the current best estimate of the species phylogeny. Paraphyly of section Paeonia in the Adh2 gene tree may be caused by longer coalescence times and random sorting of ancestral alleles.      

Diploid hybrid origin of Hippophaë gyantsensis (Elaeagnaceae) in the western Qinghai–Tibet Plateau

Homoploid hybrid speciation, the origin of a hybrid species without change in chromosome number, is currently considered to be a rare form of speciation. In the present study, we examined the phylogenetic origin of Hippophaë gyantsensis, a diploid species occurring in the western Qinghai–Tibet Plateau. Some of its morphological and molecular traits suggest a close relationship to H. rhamnoides ssp. yunnanensis while others indicate H. neurocarpa. We conducted phylogenetic analyses of sequence data of two maternally inherited chloroplast (cp) DNA fragments and the bi‐parentally inherited nuclear ribosomal internal transcribed spacer (ITS) from 17 populations of H. gyantsensis, 15 populations of H. rhamnoides ssp. yunnanensis and 27 populations of H. neurocarpa across their distributional ranges, and modelled the niche differentiation of the three taxa. Multiple lines of evidence suggested that H. gyantsensis is a morphologically stable, genetically independent and ecologically distinct species. The inconsistent phylogenetic placements of the H. gyantsensis clade that comprised the dominant cpDNA haplotypes and ITS ribotypes suggested a probable diploid hybrid origin from multiple crosses between H. rhamnoides ssp. yunnanensis and H. neurocarpa. This tentative hypothesis is more parsimonious than alternative explanations according to the data available, although more evidence based on further testing is needed.     

利用多基因序列探讨稻属药稻复合体二倍体物种的系统发育关系

稻属药稻复合体Oryza officinalis complex中有5个二倍体物种,涉及B、C和E3个染色体组,分布在亚洲、非洲和大洋洲。其中,O.australiensis是稻属中惟一含E染色体组的物种;O.punctata则是惟一含B染色体组的物种。虽然O.officinalis、O.rhizomatis和O.eichingeri都含C染色体组,但由于它们间断分布在亚洲和非洲,可能在稻属异源多倍体成种中发挥了不同作用。染色体组B、C和E之间,以及上述二倍体物种之间的系统发育关系及其在稻属多倍体物种形成