Variation of Nuclear DNA Content in the Biflorus Species of Lonchocarpus (Leguminosae)

This represents the first study of nuclear DNA content in alarge sample (135 spp.) from a tropical arboreal genus, in whicha large proportion of the species were examined (42 spp., 31.1%).Somatic chromosome numbers and 4C-DNA values for 51 taxa ofLonchocarpus are reported. All taxa were diploid with 2 n =22,but their DNA content ranged from 1.92 to 2.86 pg 4C nucleus,corresponding to a 48.95% variation in genome size. In the 74collections studied, no correlation was observed between DNAcontent and habitat altitude. Variation in nuclear DNA contentwas analysed at the level of genus, subgenus, section and subsection.Variation in genome size was also studied within some species,either among widely separated populations or among differentintraspecific taxa. Very little variation in genome size wasdetected between populations, subspecies, and varieties of thesame species. The taxonomic implications of variation in nuclearDNA content are discussed.Copyright 2000 Annals of Botany Company Lonchocarpus (Leguminosae), DNA content, chromosome number.     

Genetic architecture of the cryptic species complex of Acanthocyclops vernalis (Crustacea: Copepoda). II. Crossbreeding experiments, cytogenetics, and a model of chromosomal evolution

Collectively, populations of Acanthocyclops vernalis, a species complex of freshwater copepods, are remarkably similar as to morphology and DNA content, despite variability in chromosome number. Reproductive isolation had been reported among some populations, but with each new investigation the species boundaries and factors that may influence them appeared less clear. To clarify the pattern of biological species within this group of populations, we adopted a comprehensive approach and examined patterns of reproductive isolation in populations for which morphology, chromosome number, DNA content, and 18S rDNA sequences are known. In this study we established nine isofemale lines from four sites in Wisconsin and performed 266 crosses. Crosses within and among these lines were used to relate the degree of reproductive isolation to chromosome differences and to construct a model to explain the origin and maintenance of chromosome number variability. Different gametic and somatic chromosome numbers were observed among specimens within some isofemale lines. In a few cases, gametes with different haploid numbers were produced by a single female. Matings within isofemale lines always produced at least some reproductively successful replicate crosses (produced viable, fertile offspring). Crosses between lines from the same site showed reduced success relative to within-line crosses. Crosses between populations from distant sites showed limited genetic compatibility, producing viable, fertile F1 offspring but infertile F2 adults. One cross between lines with different chromosome numbers (one with 2n = 8 and one with 2n = 10) produced fertile viable offspring, which reproduced for at least 60 generations. These hybrids had either eight or nine chromosomes in the third generation of inbreeding, and eight chromosomes after 20 generations. These hybrids also had reduced nuclear DNA contents at the third generation, a level that persisted through the 20th generation. Successful backcrosses between some hybrids and their parental lines further demonstrated the potential for genetic compatibility among forms with different chromosome numbers. We propose a model in which alterations due to Robertsonian fusions, translocations, and/or loss of chromosomal fragments generate heritable variation, only some of which leads to reproductive isolation. Hence, some of the criteria traditionally used to recognize species boundaries in animals (morphology, DNA content, chromosome number) may not apply to this species complex.     

Variation in chromosome numbers, CMA bands and 45S rDNA sites in species of Selaginella (Pteridophyta)

BACKGROUND AND AIMS: Selaginella is the largest genus of heterosporous pteridophytes, but karyologically the genus is known only by the occurrence of a dysploid series of n=7-12, and a low frequency of polyploids. Aiming to contribute to a better understanding of the structural chromosomal variability of this genus, different staining methods were applied in species with different chromosome numbers. METHODS: The chromosome complements of seven species of Selaginella were analysed and, in four of them, the distribution of 45S rDNA sites was determined by fluorescent in situ hybridization. Additionally, CMA/DA/DAPI and silver nitrate staining were performed to investigate the correlation between the 45S rDNA sites, the heterochromatic bands and the number of active rDNA sites. KEY RESULTS: The chromosome numbers observed were 2n=18, 20 and 24. The species with 2n=20 exhibited chromosome complement sizes smaller and less variable than those with 2n=18. The only species with 2n=24, S. convoluta, had relatively large and asymmetrical chromosomes. The interphase nuclei in all species were of the chromocentric type. CMA/DA/DAPI staining showed only a weak chromosomal differentiation of heterochromatic bands. In S. willdenowii and S. convoluta eight and six CMA+ bands were observed, respectively, but no DAPI+ bands. The CMA+ bands corresponded in number, size and location to the rDNA sites. In general, the number of rDNA sites correlated with the maximum number of nucleoli per nucleus. Ten rDNA sites were found in S. plana (2n=20), eight in S. willdenowii (2n=18), six in S. convoluta (2n=24) and two in S. producta (2n=20). CONCLUSIONS: The remarkable variation in chromosome size and number and rDNA sites shows that dramatic karyological changes have occurred during the evolution of the genus at the diploid level. These data further suggest that the two putative basic numbers of the genus, x=9 and x=10, may have arisen two or more times independently.     

Telomeric and interstitial telomeric-like DNA sequences in Orthoptera genomes.

A (TTAGG)n-specific telomeric DNA probe was hybridized to 11 orthopteroid insect genomes by fluorescence in situ hybridization. Nine different genera, mainly distributed within two evolutionary branches with male chromosome numbers 2n = 23 and 2n = 17 were included in the analysis. Telomere sequences yielded positive signals in every telomere and there was a considerable number of interstitial telomeric-like sequences, mainly located at the distal end of some, but not all, subterminal chromosome regions. One of the species, Pyrgomorpha conica, showed massive hybridization signals associated with constitutive heterochromatin. The results are discussed along two lines: (i) the chromosomal evolutionary trends within this group of insects and (ii) the putative role that ITs may play in a genome when they are considered telomere-derived, but not telomere-functional, DNA sequences.     

Karyological studies on the Sino-Himalayan genus, Cremanthodiurn (Asteraceae: Senecioneae)

Twenty-two populations of seven species of Cremanthodium from high altitude regions of western China were observed karyologically. C. ellisii, C. microglossum, C. brunneo-pilosum, C. stenoglossum, C. discoideum and C. lineare all had the same chromosome number of 2 n = 58 whereas C. humile had 2 n = 60. All chromosome numbers of these species are documented here for the first time. The basic number of x = 30 is new for this genus. The karyotypes of all species belong to 2A type according to Stebbins' asymmetry classification of karyotypes. Two basic chromosome numbers, x = 30 and x = 29 in Cremanthodium , correspond exactly to two branching patterns in this genus, sympodial versus monopodial. The systematic and taxonomic statuses of the sympodial species need further study. The karyomorphological data provide no support to the sectional subdivision in Cremanthodium .     

Karyotype studies of some species of Dalechampia Plum. (Euphorbiaceae)

Karyotype studies in eight species of Dalechampia , including 10 natural populations, revealed chromosome numbers (2 n = 36, 46, 138 and 198) differing from two numbers cited in the literature (2 n = 44 and 72). The basic number x = 6, as in the genus Acalypha , may be considered ancestral in Dalechampia. Analysis of chromosome number, haploid chromosome length and karyotype symmetry suggests that the major chromosome mechanism acting in karyotype evolution of Dalechampia is polyploidy, but differences in chromosome morphology may be caused by chromosome rearrangements.     

DNA cloning and hybridization in deer species supporting the chromosome field theory

The Cervidae show the largest variation in chromosome number found within any mammalian family. The eight species of deer which are the subject of this study vary in chromosome number from 2n = 70 to 2n = 6. Three species of Bovidae are also included since they belong to a closely related family. Digestion of nuclear DNAs with the restriction endonucleases Hae III, Hpa II, Msp I, Eco RI, Xba I, Pst I and Bam HI reveals that there is a series of highly repetitive sequences forming similar band patterns in the different species. There are two bands (1100 and 550 base pairs) which are common to all species although the two families separated more than 40 million years ago. To obtain information on the degree of homology among these conserved sequences we isolated a Bam HI restriction fragment of approximately 770 base pairs from red deer DNA. This sequence was 32P labeled and hybridized by the Southern blot technique with DNAs cleaved with Bam HI, Eco RI, Hpa II and Msp I. Moreover, the same sequence was cloned in the plasmid vector pBR322 nick translated with 32P and hybridized with the DNAs of 8 species of Cervidae and 3 of Bovidae. The same cloned probe was labeled with 3H and hybridized in situ with the metaphase chromosomes of red deer (2n = 68) and Muntiacus muntjak (2n = 7 male). Homologies are still present between the highly repetitive sequences of the 8 species of Cervidae despite the drastic reorganization that led to extreme chromosome numbers. Moreover, the cloned DNA sequence was found to occupy the same position, in the proximal regions of the arms, in both red deer (2n = 68) and M. muntjak (2n = 7 male) chromosomes. The ribosomal RNA genes and the centromeres in these species have also maintained their main territory despite the drastic chromosome reorganization. These results are experimental confirmation of the chromosome field theory which predicted that each DNA sequence has an optimal territory within the centromere-telomere field and tends to occupy this same territory following chromosome reorganization.     

Genome evolution in the genus Sorghum (Poaceae)

BACKGROUND AND AIMS: The roles of variation in DNA content in plant evolution and adaptation remain a major biological enigma. Chromosome number and 2C DNA content were determined for 21 of the 25 species of the genus Sorghum and analysed from a phylogenetic perspective. METHODS: DNA content was determined by flow cytometry. A Sorghum phylogeny was constructed based on combined nuclear ITS and chloroplast ndhF DNA sequences. KEY RESULTS: Chromosome counts (2n = 10, 20, 30, 40) were, with few exceptions, concordant with published numbers. New chromosome numbers were obtained for S. amplum (2n = 30) and S. leiocladum (2n = 10). 2C DNA content varies 8.1-fold (1.27-10.30 pg) among the 21 Sorghum species. 2C DNA content varies 3.6-fold from 1.27 pg to 4.60 pg among the 2n = 10 species and 5.8-fold (1.52-8.79 pg) among the 2n = 20 species. The x = 5 genome size varies over an 8.8-fold range from 0.26 pg to 2.30 pg. The mean 2C DNA content of perennial species (6.20 pg) is significantly greater than the mean (2.92 pg) of the annuals. Among the 21 species studied, the mean x = 5 genome size of annuals (1.15 pg) and of perennials (1.29 pg) is not significantly different. Statistical analysis of Australian species showed: (a) mean 2C DNA content of annual (2.89 pg) and perennial (7.73 pg) species is significantly different; (b) mean x = 5 genome size of perennials (1.66 pg) is significantly greater than that of the annuals (1.09 pg); (c) the mean maximum latitude at which perennial species grow (-25.4 degrees) is significantly greater than the mean maximum latitude (-17.6) at which annual species grow. CONCLUSIONS: The DNA sequence phylogeny splits Sorghum into two lineages, one comprising the 2n = 10 species with large genomes and their polyploid relatives, and the other with the 2n = 20, 40 species with relatively small genomes. An apparent phylogenetic reduction in genome size has occurred in the 2n = 10 lineage. Genome size evolution in the genus Sorghum apparently did not involve a 'one way ticket to genomic obesity' as has been proposed for the grasses.     

Molecular phylogeny of the genus Dahlia Cav. (Asteraceae, Heliantheae-Coreopsidinae) using sequences derived from the internal transcribed spacers of nuclear ribosomal DNA

Sequences of the internal transcribed spacers (ITS) of the 18S-26S nuclear ribosomal DNA were used to resolve phylogenetic relationships among 13 species of the genus Dahlia . Phylogenetic reconstruction from both parsimony analysis and pairwise distance data produced a single tree in which four clades could be distinguished, these broadly separating the species into the different chromosome numbers found in Dahlia ( x = 16, x = 17 and x = 18). Although species based on x = 16 were divided into two clades, there is the suggestion that this separation may be artificial and that these should be combined as a single clade. The phylogeny produced here has been discussed with reference to the existing taxonomic treatment of the genus. It currently appears that the genus Dohlia is monophyletic and it is evident that the different basic chromosome numbers withim the dysploid series in Dahlia have evolved only once. This proposed monophyly of the genus coupled with the successful production of hybrids withim the dysploid series (2 n = 32, 2 n = 34 and 2 n = 36) suggests that the species of Dahlia have evolved from a common ancestor.     

八种国产大戟属植物的核型报道

8种大戟属Euphorbia L．植物的核型分析结果表明,大戟属不同亚属的染色体基数与其形态变 异的复杂性有一定关系。地锦草亚属subgen．Chamaesyce 3个种染色体基数分别为x=8,9,11;一品红 亚属subgen．Poinsettia两个种染色体基数均为x=7,分别为四倍体和八倍体;乳浆大戟亚属subgen． Esula 3个种,染色体基数分别为x=7,10,10。根据以前学者发表的资料分析,一品红亚属和大戟亚属 Subgen. Euphorbia的染色体基数是很稳定的,分别为x=7和x=10;通奶草E．hypericifolia为x=8 的四倍体,它不仅有染色体整倍性的变异,还有异基数性的变化。结合以前学者的研究,笔者支持x= 10为大戟属的最原始基数的观点。齿裂大戟E．dentata和通奶草具不同的染色体倍性,猫眼草E． esula的细胞染色体数目观察证实了我国存在四倍体的居群,与欧洲和北美的植物构成一个典型的多倍体复合体。     

Karyotypes of eight species of Euphorbia L. (Euphorbiaceae) from China

In this paper, eight species of the genus Euphorbia L. were cytologically studied. The three species of the subgenus Chamaesyce Raf., E. hirta, E. humifusa and E. hypericifolia, had chromosome numbers of 2n = 18, 22 and 32, with their basic chromosome numbers being x = 9, 11 and 8 respectively. The two species of the subgenus Poinsettia (Grah.) House. E. dentata, with 2n=28, a tetraploid, and E. cyathophora, with 2n= 56, a octoploid, had both the basic chromosome number of x= 7. The three species of the subgenus Esula Pers, E. lathyris, E. helioscopia and E. hylonoma, had chromosome number of 2n= 20, 42 and 20, with their basic numbers being x= 10, 7 and 10 respectively. The basic chromosome number of x = 8 is new for E. hypericifolia, in which x = 7 was previously reported. This indicates that this species had both ploidy(2n = 4x = 28, 8x = 56) and dysploidy(x = 7, 8) variations. In E. dentata, there occurred also ploidy variation (2n = 2x, 4x and 8x). A tetraploid cytotype of E. esula was found in China, its diploid cytotype and hexaploid cytotype being previously reported in North America, the Iberian Peninsula and some other European areas. Based on our results and those previously reported, we support the viewpoint that x＝10 may be the original basic chromosome number of Euphorbiaand discuss the role of polyploidy and dysploidy in the speciation and evolution of this genus     

Quantitative karyology of some species ofLuzula

The dimensions of metaphase chromosomes and nuclear DNA contents were measured in eight species ofLuzula. The 2 C DNA contents ranged from 8.51 pg inL. purpurea to 0.55 pg inL. pilosa. Total chromosome volume shows a linear relationship with DNA content; however, the total chromosome length of the complement of the different species is approximately constant. Nucleolar volume and the number of chromocentres in the different species also show a relationship with DNA content. Taken together, these data suggest that while chromosome fragmentation could have generated the present-day range of chromosome numbers in the genus, there have also been changes in the total quantity of DNA with the result that species with similar chromosome numbers have different DNA contents. The relationships of DNA content with chromosome volume inLuzula and other genera are compared and the differences discussed.     

二十五种中国角蝉的染色体(英文)

本文记载了中国25种角蝉的染色体,研究表明染色体的数目、大小及其在减数分裂过程中的行为具有种或属一级的分类特征。该科昆虫染色体的数目变异在n＝5到12之间,众数为n＝11,另外,n＝10的类型也较为普遍。绝大多数种类的性别决定机制为XO型,仅个别种类具有新XY性染色体系统。     

香港喜盐草属植物的核型分析

报道了分布于我国香港特别行政区的喜盐草属(Halophila Thou.) 2种植物的染色体数目和核型,其体细胞中期染色体数目均为2n=18。它们的核型公式分别为：喜盐草(H. ovalis (R. Br.) Hook. f.) 2n=2x=18=4m+14sm;贝克喜盐草(H. beccarii Asch) 2n=2x=18=8m+10sm(首次报道)。核型均属于2B型。     

Molecular phylogeny of Cryptocercus wood-roaches based on mitochondrial COII and 16S sequences, and chromosome numbers in Palearctic representatives

Woodroaches of the genus Cryptocercus are subsocial and xylophagous cockroaches, distributed in North America and Asia. Studies on male chromosome number in Nearctic species have shown that diploid numbers vary from 2n=37 to 2n=47; numbers from Palearctic species were heretofore unknown. Two hypotheses have been proposed to explain the varying number of chromosomes among Nearctic species: the serial reduction hypothesis, and the parallel scenario. We performed phylogenetic analyses of the COII gene in these species and found evidence for the topology (47(45(43(39,37), which is congruent with the serial reduction hypothesis. We also determined chromosome numbers for the first time in Palearctic species, and found Cryptocercus primarius and Cryptocercus relictus to have relatively low chromosome numbers (2n=17-21) compared to their Nearctic relatives. Finally, our study determined the phylogenetic position of Cryptocercus primarius among other Asian taxa.     

Rapid detection of aneuploidy in <Emphasis Type="Italic">Musa</Emphasis> using flow cytometry

We report a procedure for the rapid and convenient detection of aneuploidy in triploid Musa using DNA flow cytometry. From a population of plants derived from gamma-irradiated shoot tips, plants were selected based on aberrant morphology and their chromosome numbers were counted. Aneuploids plants with chromosome numbers 2n=31 or 32 were found as well as the expected triploid plants (2n=3x=33). At the same time, the nuclear DNA content of all plants was measured using flow cytometry. The flow cytometric assay involved the use of nuclei isolated from chicken red blood cells (CRBC), which served as an internal reference standard. The relative DNA content of individual plants was expressed as a ratio of DNA content of CRBC and Musa (DNA index). In order to estimate the chromosome number using flow cytometry, the relative DNA content of plants with unknown ploidy was expressed as a percentage of the DNA content of triploid plants. The classification based on flow cytometry fully agreed with the results obtained by chromosome counting. The results indicated that flow cytometry is a convenient and rapid method for the detection of aneuploidy in Musa.     

A cytological study ofPelargonium sect.Eumorpha (Geraniaceae)

The chromosome numbers of seven species ofPelargonium sect.Eumorpha have been determined from material of known wild origin, and karyotypic comparisons have been made. Within the section there is variation in basic chromosome number (x = 4, 8, 9, 11), variation in chromosome size, and two species have polyploid races. The three species with chromosome numbers based on x = 11 have the smallest chromosomes (1.0–1.5 µm); chromosomes are larger (1.0–3.0 µm) in the other species.P. elongatum has the lowest chromosome number in the genus (2n = 8).P. alchemilloides is exceptional in that it has four cytotypes, 2n = 16, 18, 34 and 36, and the form with 2n = 36 has large chromosomes (2.0–5.0 µm). Evidence from a synthesized hybrid suggests thatP. alchemilloides with 2n = 16 may be of polyploid origin. The three species based on x = 11 appear to be more closely related to species from other sections ofPelargonium that have the same basic chromosome number and small chromosome size, rather than to other species of sect.Eumorpha.     

蜘蛛抱蛋属植物的核型不对称性分析

报道了蜘蛛抱蛋属(Aspidistra)两种植物的染色体数目和核型,其中河口蜘蛛抱蛋(A.hekouensi)的染色体数目(2n=38)为首次报道,四川蜘蛛抱蛋(A.sichuanensis)染色体数目也为2n=38,但其核型与以往的报道有差别.使用染色体内不对称系数(A1)和染色体间不对称系数(A2)对该属34种植物核型的不对称性进行了分析,结果表明该属植物的核型似乎并没有向不对称性增强的方向演化.     

Karyomorphology of four species in Ancylostemon,Briggsiopsis and Lysionotus (Gesneriaceae)

Reported in the present paper are chromosome numbers and karyotypes of three genera of the Gesneriaceae, i.e. Ancylostemon Craib. , Briggsiopsis (Franch.) K. Y. Pan and Lysionotus D. Don. The former two genera are endemic to China. The karyotype of Ancylostemon aureus (Franch.) Burtt is formulated as 2n = 34 = 20m(1sat) + 14sm, with the same chromosome number as its allied species A. convexus Craib. This species is characterized by the interphase nucleus of complex chromocenter type and the proximal type of chromosomes in the mitotic prophase. The chromosome number of the monospecific genus Briggsiopsis is 2n = 34, the same as the lowest chromosome number reported in Briggsia. The karyotype of Briggsiopsis, which is formulated as 2n = 25m + 6sm + 3st, also seems to be primitive among the species of the two genera. Briggsiopsis is characterized by the interphase nucleus of simple-complex chromocenter type and the interstitial-gradient type of chromosomes in the mitotic prophase. The chromosome number of Lysionotus carnosus Hemsl. is the lowest reported in this genus. Its karyotype is formulated as 2n= 30 = 21m + 5sm + 3st + lt. Lysionotus serratus var. pterocaulis, with the karyotype being formulated as 2n= 32 = 2lm + 10sm + lt, has the same chromosome number as var. serratus. These two species show a remarkable differentiation of karyotypes and are characterized by the interphase nuclei of simple-complex chromocenter type and the gradient type of chromosomes in the mitotic prophase. _ .     

Chromosomes of sixteen European species ofLongitarsus flea-beetles (Coleoptera,Chrysomelidae)

Sixteen species ofLongitarsus have been chromosomally surveyed, showing a continuous range of even numbers from 2n=26 to 2n=32 chromosomes. Among the total of twenty-three known species, about 40% display a 14+Xy male karyotypic formula, the possible modal and most primitive one for the genus. The current taxonomy of species groupings is in good agreement with the chromosome numbers in some cases, but not in others. Also, there is no interrelationship between chromosome numbers and foodplant selection. The number of large bivalents at metaphase I is generally negatively correlated with the diploid value, suggesting the possible role of centric fusions coupled to shifts in the amount of chromatin as the main chromosomal changes in the evolution ofLongitarsus. The karyotypes of a few studied species are composed of metacentric chromosomes, some of them of rather large size, and a minute y-chromosome. A possible example of polymorphism for the chromosome number inL. nigrofasciatus is reported and briefly discussed.