A POLYPLOID SPECIES COMPLEX IN SPIROGYRA MAXIMA (CHLOROPHYTA,ZYGNEMATACEAE), A SPECIES WITH LARGE CHROMOSOMES1

A species complex in Spirogyra consists of the series of filament morphotypes of various ploidal levels arising from an original morphotype within a clonal culture or in nature. A clonal culture of filaments identified as Spirogyra maxima (Hassall) Kützing produced several morphotypes, i.e. filament types of distinctly different widths and ploidal levels. Banding patterns and satellites were visible on chromosomes stained at mitotic prophase and metaphase. The original culture of S. maxima contained filaments averaging 127 μ wide. Vegetative cells of the original culture contained six large chromosomes (>4 μ long), identifiable as three distinct pairs based on banding patterns and presence of satellites: (1) one pair of short chromosomes (ca. 5.0 μ); (2) one pair of long chromosomes (ca. 8.0 μm); and (3) a second pair of long chromosomes (ca. 9.0 μm) including a nucleolar organizing region and satellite. A larger morphotype averaging 175 μm in width contained 12 chromosomes, with two pairs of short chromosomes and four pairs of long chromosomes (satellites were usually indistinct). Aneuploid chromosome numbers ranging from 5 to 13 were observed in a few cells. Binucleate and trinucleate cells were also observed. A twobanded chromosome fragment was observed in a few cells with 6 chromosomes and a few cells with 12 chromosomes. The variety of morphotypes derived in this study could be identified as four different species of Spirogyra by conventional taxonomic criteria. The banding patterns and satellites on chromosomes suggest that three pairs of homologous chromosomes are present in filaments of the original clonal culture and that these filaments are themselves autopolyploid (diploid) descendants of ancestral form with a base chromosome number of x = 3.     

PLOIDAL CHANGES IN CLONAL CULTURES OF SPIROGYRA COMMUNIS AND IMPLICATIONS FOR SPECIES DEFINITION

A clonal culture of Spirogyra filaments of initially uniform width produced filaments of three additional significantly different widths. Group I filaments of the original clone were 30.9 ± 0.7 μm wide (mean ± SD, N = 50). Group I filaments produced Group II filaments (22.0 ± 1.1 μm) through vegetative growth and sexual reproduction. Zygospores from homothallic Group I filaments produced germlings representative of Groups I and II; zygospores from homothallic Group II filaments produced germlings representative of Group II only. Germlings of Groups III (27.7 ± 1.0 μm) and IV (44.9 ± 0.8 μm) were produced in the cross of I × II. Viable zygospores from homothallic Group III filaments were obtained. Cells of Group IV filaments were initially binucleate and did not conjugate. Of the six intergroup crosses possible, four resulted in conjugation-tube formation only; two crosses yielded zygospores (I × II and III × IV). Germlings from the successful cross of Groups III and IV produced filaments of all four groups. Chromosome counts were: Group I (24), Group II (12), Group III (18), and Group IV (24, one nucleus). Relative nuclear fluorescence values of mithramycin-stained DNA were (mean ± SD, N ≥ 30): Group I (11.1 ± 1.4), Group II (5.7 ± 0.7), Group III (8.8 ± 1.3), and Group IV (10.0 ± 0.9, one nucleus). Cytologically, Group II appears to be a diploid (2x), Group I a tetraploid (4x), and Group III a triploid (3x). Systematically, Groups I, II, and III key out to Spirogyra singularis, S. communis, and S. fragilis, respectively, using Transeau's mongraph of the family Zygnemataceae. These species are interpreted to represent a species complex of S. communis (whose name has priority) with the ancestral haploid (x = 6) missing.     

PHYLOGENY OF SPIROGYRA AND SIROGONIUM (ZYGNEMATOPHYCEAE) BASED ON RBCL SEQUENCE DATA1

DNA sequence data were obtained for the gene encoding the large subunit of RUBISCO (rbcL) from 26 strains of Spirogyra and seven of Sirogonium, using as outgroups 10 genera in the Zygnematales and Desmidiales (Closterium, Cosmarium, Cylindrocystis, Gonatozygon, Mesotaenium, Netrium, Penium, Zygnema, Zygnemopsis, Zygogonium). Sequence data were analyzed using maximum parsimony (MP), maximum likelihood (ML), and Bayesian inference (BI), with bootstrap replication (MP, ML) and posterior probabilities (BI) as measures of support. MP, ML, and BI analyses of the rbcL data strongly support a single clade containing Spirogyra and Sirogonium. The Spirogyra taxa are monophyletic, with the exception of Spirogyra maxima (Hassall) Wittrock, which is nested within a clade with Sirogonium and shares with them the characters of loosely spiraled chloroplasts (<1 complete turn per cell) and anisogamy of gametangial cells; S. maxima differs from Sirogonium in displaying well‐defined conjugation tubes rather than a tubeless connection involving bending (genuflection) of filaments. The ML and BI analyses place this Sirogonium/Spirogyra maxima clade sister to the remaining Spirogyra. Morphological differences among strains of Spirogyra grouped together on the basis of rbcL data, including laboratory strains derived from clonal cultures (Spirogyra communis, S. pratensis), indicate that some characters (filament width, chloroplast number) used in the traditional taxonomy of this group are poor measures of species identity. However, some characters such as replicate end walls and loose spiraling of chloroplasts may be synapomorphies for Spirogyra clades.     

Notes of Spirogyra from Guizhou,China

Reported in the present paper are two new species and one new record of Spirogyra. The two new species are Spirogyra subferruginea and S.kweichowensis; the new record for China is Spirogyra brunea Czurda.     

CYTOGEOGRAPHIC EVIDENCE FOR THE EVOLUTION OF DISTYLY FROM TRISTYLY IN THE NORTH AMERICAN SPECIES OF OXALIS SECTION IONOXALIS

A survey of haploid chromosome numbers of 18 North American taxa of Oxalis section Ionoxalis was initiated to determine the relationship between ploidal level, geographic distribution, and the occurrence of tristyly and distyly. Although chromosome numbers in the section are variable, the majority of tristylous populations are diploid. Among the distylous taxa a greater diversity of ploidal levels exists, with the higher chromosome numbers predominating. In section Ionoxalis the majority of the tristylous taxa are geographically restricted endemics of southern Mexico, while the distylous taxa have more extensive distributions ranging to the north. The association of diploidy and geographic endemism in the majority of the tristylous taxa suggests that these species are relictual. A few widespread tristylous taxa are polyploid, and often somewhat weedy. The probable derivation of widespread polyploid species from the restricted diploid endemics of southern Mexico appears to have been accompanied by the evolution of distyly from tristyly. The frequent association of polyploidy and distyly in section Ionoxalis has apparently resulted from the concurrence of two evolutionary trends: increase in ploidal level and the derivation of distyly from tristyly.     

Linkage mapping in tetraploid willows: segregation of molecular markers and estimation of linkage phases support an allotetraploid structure for Salix alba x Salix fragilis interspecific hybrids

Salix alba-Salix fragilis complex includes closely related dioecious polyploid species, which are obligate outcrossers. Natural populations of these willows and their hybrids are represented by a mixture of highly heterozygous genotypes sharing a common gene pool. Since nothing is known about their genomic constitution, tetraploidy (2n=4x=76) in willow species makes basic and applied genetic studies difficult. We have used a two-way pseudotestcross strategy and single-dose markers (SDMs) to construct the first linkage maps for both pistillate and staminate willows. A total of 242 amplified fragment length polymorphisms (AFLPs) and 50 selective amplifications of microsatellite polymorphic loci (SAMPL) markers, which showed 1:1 segregation in the F(1) mapping populations, were used in linkage analysis. In S. alba, 73 maternal and 48 paternal SDMs were mapped to 19 and 16 linkage groups covering 708 and 339 cM, respectively. In S. fragilis, 13 maternal and 33 paternal SDMs were mapped in six and 14 linkage groups covering 98 and 321 cM, respectively. For most cosegregation groups, a comparable number of markers linked in coupling and repulsion was identified. This finding suggests that most of chromosomes pair preferentially as occurs in allotetraploid species exhibiting disomic inheritance. The detection of 10 pairs of marker alleles from single parents showing codominant inheritance strengthens this hypothesis. The fact that, of the 1122 marker loci identified in the two male and female parents, the vast majority (77.5%) were polymorphic and as few as 22.5% were shared between parental species highlight that S. alba and S. fragilis genotypes are differentiated. The highly difference between S. alba- and S. fragilis-specific markers found in both parental combinations (on average, 65.3 vs 34.7%, respectively) supports the (phylogenetic) hypothesis that S. fragilis is derived from S. alba-like progenitors.     

Detection of conjugal transfer systems in oral, black-pigmented Bacteroides spp.

Oral, black-pigmented Bacteroides spp. are important pathogens in oral anaerobic infections and dental disease. We detected conjugation systems in isolates of Bacteroides denticola and Bacteroides intermedius that transferred tetracycline resistance (Tetr) and penicillin resistance to Bacteroides buccae and to Bacteroides fragilis, an intestinal Bacteroides species. A cloned Tetr gene from B. fragilis hybridized to the transferable Tetr locus in the oral strains, indicating that genetic exchange occurs between these two groups of anaerobes.     

An integrated genetic and physical map for the malaria vector Anopheles funestus

We have constructed a genetic map of the major African malaria vector, Anopheles funestus, using genetic markers segregating in F(2) progeny from crosses between two strains colonized from different field sites. Genotyping was performed on 174 progeny from three families using 33 microsatellite markers, a single RFLP, and 15 single nucleotide polymorphism (SNP) loci. Four linkage groups were resolved and these were anchored to chromosomes X and 2 and chromosomal arms 3R and 3L by comparison with a physical map of this species. Five markers were linked to the X chromosome, 16 markers to chromosome 2, and 10 and 11 markers to chromosomal arms 3R and 3L, respectively. This significantly increases the number of chromosomally defined genetic markers for this species and will facilitate the identification of genes controlling epidemiologically important traits such as resistance to insecticides or vector competence.     

谷蠹和米象对磷化氢抗性遗传的研究

本文就谷蠹Rhyzopertha dominica 和米象Sitophilus oryzae对磷化氢的抗性遗传进行了研究,分别对两个种的实验室敏感品系和粮仓现场采集的抗性品系作为亲本进行杂交。同时测定了各自的亲本及其F₁杂种、F₁对抗性亲本回交和F2混交后代的剂量-死亡率反应曲线,并对它们的结果进行了遗传分析。结果指出,谷蠹和米象的F₁杂种对磷化氢的抗性遗传都为不完全隐性,各自的显性度(D)分别是-0.768和-0.348。同时F₁,回交和F₂混交的观察值和计算值之间的X²分析也表明,抗性表现为一个以上的常染色体因子遗传,但是主要是受隐性因子所控制。     

DISTRIBUTION,MORPHOLOGICAL DIVERSITY AND EVIDENCE FOR POLYPLOIDY IN NORTH AMERICAN ZYGNEMATACEAE (CHLOROPHYTA)1

Large-scale collections of Zygnemataceae in the continental United States of America were made between March and August in 1982, 1983, and 1984. Collections were made on a 31000-km transect through 35 states. Zygnemataceae were found at 318 sites was inspected. Temperature average 19°C and p^H averaged 6.1 over all sites. Algal strains in collections were identified to genus, characterized for filament width, chloroplast number, and end wall type, then photographed and isolated into unialgal culture. Spirogyra was the most common genus collected(632 strains), followed in abundance by Zygnema (174 Strains) and Mougeotia (135 strains). These three genera contained 95% of the strains collected and were equally widely distributed. Strains of the three genera frequently occurred together; no genus displayed evidence of habitat specialization among the three habitat types: flowing water, permanent ponds or lakes, and temporary pools. In Spirogyra, strains with plane (flat) end walls were four times more abundant than those with replicate (interlocking) end walls. Spirogyra with plane end walls showed more variation in filament width than Zygnema, Mougeotia, or Spirogyra with replicate end walls. In Spirogyra with plane end walls, filament width was correlted with nuclear DNA content and number of strains found per collection site was twice that of other genera or Spirogyra, with replicate end walls. Spirogyra strains wider than 70 μm were more frequent on the northern part of the transect. It is proposed that polyploidy may be of widespread occurrence in Spirogyra with plane end walls and that associated morphological plasticity may account for the high apparent specied diversity and survival of the genus in a wider variety of microhabitats than occupied by other Zygnemataceae.     

Two new taxa of Spirogyra

Summary A new species and a new variety ofSpirogyra have been recorded.Spirogyra varshaii spec. nov. has been described and compared to two related species ofSpirogyra. This species has a very distinct subdenticulate to denticulate type of ornamentation of the zygospore wall and differs from the other two related speciesS. chakiense andS. verruculosa in having different dimensions of the zygospores and in the number of chloroplasts. A new variety,Spirogyra chakiense var.lucknowense var. nov. has been described. It differs from the speciesS. chakiense in possessing some differences in the dimensions of the cells and the zygospores from the type species.

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Zusammenfassung Eine neue Spezies und eine neue ArtSpirogyra sind eingetragen worden.Spirogyra varshaii Spec. nov. ist beschrieben worden und mit zwei verwandten Spezies verglichen. Diese Spezies hat einen sehr deutlichen unterzahnigen bis zum zahnigen Typus der gestickten Zygosporeswand, und sie unterscheidet sich von den anderen zwei verwandten SpeziesS. chakiense undS. verruculosa daß sie verschiedene Ausdehnungen der Zygosporen und auch eine verschiedene Zahl der Kromatophoren hat. Eine neue ArtSpirogyra chakiense var.lucknowense var. nov. ist auch beschrieben worden. Sie unterscheidet sich von der SpeziesS. chakiense weil sie einigen Unterschieden in Ausdehnungen der Zellen und auch der Zygosporen hat im Vergleich mit der Typusspezies.

     

Gametocidal genes in wheat and its relatives. IV. Functional relationships between six gametocidal genes.

Gametocidal (Gc) genes in Aegilops species are known to cause gamete abortion and chromosome breakage when they are introduced into the wheat genetic background. Interactions of five Gc genes so far identified were investigated by analysis of wheat hybrids among lines carrying different gametocidal genes. As a result, the genes were classified into three functional groups. The first group includes two Gc genes of Ae. speltoides (Gc1a and Gc1b) and one gene (Gc-Sl3) on chromosome 2S1 of Ae. sharonensis. These genes were hypostatic to the genes (Gc-Sl1, Gc-Sl2) on chromosome 4S1 of Ae. longissima and Ae. sharonensis, which constitute the second group. In addition, plants carrying Gc genes of both the first and the second group produced progeny with higher frequencies of chromosome breakage than those found in the progeny of single gene carriers. It was concluded that there were specific interactions between these genes to enhance chromosome breakage. On the other hand, there was no interaction between the Gc gene (Gc-C) of Ae. triuncialis, the third group, and Gc genes belonging to the former two groups. These functional groups might be a reflection of the mechanisms by which Gc genes induce gamete abortion and chromosome breakage. Based on functional and local relationships, the symbols of the Gc genes were systematically redesignated.     

国产蕺菜的染色体数目变异及核穿壁现象

蕺菜 Houttuynia cordata Thunb.属三白草科蕺菜属,俗称鱼腥草、侧耳根等,主要分 布于 亚洲东部和东南部,我国以长江流域及其以南各省区常见。蕺菜药蔬兼用,为极具开发前景 的植物资源。部分学者曾对蕺菜染色体数目进行过报道,但报道的染色体数目不尽一致（梁汉兴,1991,1995; Hsu,1968; Nilsamranchit et al, 1999）,并且对此 现象未作较为详细而深入的解释。本文对国内部分省区收集的蕺菜种质资源进行染色体数目分析,旨在从细胞学角度探讨蕺菜的遗传多样性,为     

Karyological studies of two populations of Juniperus communis L. in west Siberia

Results of a karyological study of Juniperus communis L. populations under swamp and dry conditions are presented. The chromosome number of J. communis are 2n = 22. Analysis of morphological chromosome parameters showed a similarity between karyotypes of both populations. It is possible to identify one pair of asymmetric chromosomes (VIII pair); this chromosome pair is close to submetacentric type. Three pairs of chromosomes (I, VII, VIII) have secondary constrictions. Other metacentric chromosomes form groups of five long (II--VI) and three short (IX-XI) pairs. Differences between two populations in absolute chromosomal length are observed.     

Color polymorphism and sex ratio distortion in a cichlid fish as an incipient stage in sympatric speciation by sexual selection

We investigated a Lake Victoria cichlid with a complex colour polymorphism that apparently represents one original species and two incipient species, all of which are sympatric. In laboratory breeding experiments we observed sex ratio distortion in certain matings between original and incipient species. Mate choice experiments show that males of the incipient species exhibit mating preferences against the original species, and males and females of the original species exhibit strong mating preferences against the incipient species. Mating preferences might evolve by sex ratio selection to avoid matings with distorted progeny sex ratios. Phenotype frequencies in nature suggest that mating preferences translate into mating frequencies, thus restricting gene flow and exerting disruptive sexual selection between the original and incipient species. The incipient species do not differ in morphology or ecology from the original species, implying that colour polymorphism, associated with sex ratio distortion, can be an incipient stage in sympatric speciation, and that disruption of gene flow can precede ecological differentiation.     

乡土植物芦苇对外来入侵植物加拿大一枝黄花的抑制作用

在城市建筑荒地中设立实验样地,通过对样方植物进行实地观测,并结合实验室比叶重和生物量测算,了解和分析野外建筑荒地中自然混生条件下芦苇(Phragmites communis)和加拿大一枝黄花(Solidago canadensis)的竞争过程和结果。结果表明芦苇和加拿大一枝黄花混生群落中芦苇发展近似于单优群落,芦苇以较高的平均株高和密度抑制加拿大一枝黄花生长,混生群落逐渐趋向于芦苇单优群落。混生群落芦苇比叶重和平均每株生物量近似于单优群落,加拿大一枝黄花比叶重和平均每株生物量显著低于其单优群落,光合作用受到显著抑制。de Wit模型分析显示,混生群落中芦苇和加拿大一枝黄花相互竞争、拮抗,前者竞争攻击力高于后者,模型预测混生群落中芦苇最终将把加拿大一枝黄花从样地中排除出去。浸提液种子培养显示加拿大一枝黄花具有化感作用,在低浓度条件(12.5mg/mL)下,对自生种子发芽有促进作用,高浓度条件下出现强烈抑制,但各浓度下芦苇种子不受加拿大一枝黄花化感作用影响;芦苇种子繁殖能力相对较弱,混生样地中加拿大一枝黄花在芦苇竞争胁迫下,种子千粒重和发芽率显著上升,扩散能力增强。芦苇具有在一定区域生态控制加拿大一枝黄花的潜力。     

Synthesis of a callosic substance during rhizoid differentiation in Spirogyra

Spirogyra living in running water is anchored to the substratum by rhizoids that form at the ends of the filaments. A new terminal cell differentiates into a rhizoid cell if the filament is injured. The mode of growth changes from diffuse to tip growth when rhizoid differentiation begins. In this study, we found that a callosic substance was synthesized during rhizoid differentiation. Decreasing the cell turgor, lowering extracellular Ca2+ or adding Gd3+, all inhibited the commencement of rhizoid differentiation as well as synthesis of the callose-like substance at the tip of the terminal cell. A callosic substance was also synthesized during formation of the conjugation tube.     

Detailed alignment of saccharum and sorghum chromosomes: comparative organization of closely related diploid and polyploid genomes.

The complex polyploid genomes of three Saccharum species have been aligned with the compact diploid genome of Sorghum (2n = 2x = 20). A set of 428 DNA probes from different Poaceae (grasses) detected 2460 loci in F1 progeny of the crosses Saccharum officinarum Green German x S. spontaneum IND 81-146, and S. spontaneum PIN 84-1 x S. officinarum Muntok Java. Thirty-one DNA probes detected 226 loci in S. officinarum LA Purple x S. robustum Molokai 5829. Genetic maps of the six Saccharum genotypes, including up to 72 linkage groups, were assembled into "homologous groups" based on parallel arrangements of duplicated loci. About 84% of the loci mapped by 242 common probes were homologous between Saccharum and Sorghum. Only one interchromosomal and two intrachromosomal rearrangements differentiated both S. officinarum and S. spontaneum from Sorghum, but 11 additional cases of chromosome structural polymorphism were found within Saccharum. Diploidization was advanced in S. robustum, incipient in S. officinarum, and absent in S. spontaneum, consistent with biogeographic data suggesting that S. robustum is the ancestor of S. officinarum, but raising new questions about the antiquity of S. spontaneum. The densely mapped Sorghum genome will be a valuable tool in ongoing molecular analysis of the complex Saccharum genome.     

Morphometric and molecular analysis of the Encarsia inaron species-group (Hymenoptera: Aphelinidae), parasitoids of whiteflies (Hemiptera: Aleyrodidae)

Several series of host-reared specimens of an Encarsia species, initially thought to be the cosmopolitan Encarsia inaron (Walker), were collected in the Azores Islands (Portugal). Subsequent morphometric analysis supported the presence of two species: E. inaron and a new species, described herein as Encarsia estrellae Manzari & Polaszek sp. n. Encarsia estrellae was reared from Aleyrodes singularis Danzig, A. ?singularis, and Bemisia sp. afer-group on several host plants. In addition, the D2 region of the 28S rDNA gene was sequenced in eight individuals belonging to these species, as well as single representatives of two closely related and one distantly related species. Phylogenetic analysis of these DNA sequences, together with 23 additional Encarsia sequences retrieved from the European Molecular Biology Laboratory (EMBL) and GenBank databases, further supported the specific status of E. estrellae, and the placement of E. dichroa (Mercet) in the E. inaron species-group. Additionally, E. inaron is redescribed and some taxonomic problems in the E. inaron species-group are discussed.     

The Taxonomy of Sphacelaria cirrosa (Roth.) Ag., Sphacelaria fusca (Huds.) Ag., and Sphacelaria furcigera (Kutz.) Sauv: A Simple Statistical Approach

An attempt has been made to apply some simple statistical techniquesto the taxonomy of a problematical group of species within thegenus Sphacelaria Lyngb. Measurements were carried out on materialcollected from the field, material made available from Herbariumcollections and on material grown under experimental conditionsThe main characteristics considered are cell and filament dimensions,although certain reproductive structures have also been measured. It has been found that the number of longitudinal divisionsin each segment of the main axes and the primary branches hasa profound effect on the over-all appearance of the fronds ofthe three species investigated. Segment length breadth ratioand frond stiffness have been shown to be dependent on the numberof longitudinal walls. This characteristic has enabled one ofthe species, S. cirrosa (Roth) Ag., to be readily distinguishedfrom the other two. Another factor shown to be important is the determinate patternof growth displayed by S. cirrosa as opposed to the indeterminatepattern displayed by S. fusca (Huds ) Ag. and S. furcigera (Kutz.)Sauv. The pattern of growth affects the number of longitudinalwalls, filament width, and the relative lengths of the primarybranches. The angle at which branches emanate from the main axes has beenshown to be a useful characteristic in this group of species. The variability in the number of arms produced by each propagulepresents an interesting problem which has only been described,experimental work suggesting no explanation for this phenomenon.The degree of variability is clearly different in each speciesand is useful taxonomically if a large enough sample is availablefor examination.