An extraordinarily stable karyotype of the woody Populus species revealed by chromosome painting

The karyotype represents the basic genetic make‐up of a eukaryotic species. Comparative cytogenetic analysis of related species based on individually identified chromosomes has been conducted in only a few plant groups and not yet in woody plants. We have developed a complete set of 19 chromosome painting probes based on the reference genome of the model woody plant Populus trichocarpa. Using sequential fluorescence in situ hybridization we were able to identify all poplar chromosomes in the same metaphase cells, which led to the development of poplar karyotypes based on individually identified chromosomes. We demonstrate that five Populus species, belonging to five different sections within Populus, have maintained a remarkably conserved karyotype. No inter‐chromosomal structural rearrangements were observed on any of the 19 chromosomes among the five species. Thus, the chromosomal synteny in Populus has been remarkably maintained after nearly 14 million years of divergence. We propose that the karyotypes of woody species are more stable than those of herbaceous plants since it may take a longer period of time for woody plants to fix chromosome number or structural variants in natural populations.     

CYTOLOGICAL STUDIES OF PATERCULUS ELATUS (YANG) (HEMIPTERA:PENTATOMIDAE)

Abstract The karyotype of a Chinese pentatomid species Paterculus elatus (Yang) was studied in male germ cells prepared on air-dried slides stained with Giemsa. Karyotype analyses using specific software were made and model karyotype chart was presented. P. elatus (Yang ) has 16 chromosomes on mitosis metaphase plate and a X-Y sex chromosomal mechanism. The cytogenetic analysis has revealed the presence of a pair of m-chromosomes and a supernumerary chromosome.     

卷蝽Paterculus elatus(Yang)的细胞学研究(半翅目:蝽科)(英文)

本文研究了中国蝽科昆虫──卷蝽 Ｐａｔｅｒｃｕｌｕｓ ｅｌａｔｕｓ（Ｙａｎｇ）的核型并采用核型分析软件对第一次减数分裂终变期的染色体进行了该型分析。结果表明：卷蝽的２ｎ＝１６,具有ＸＹ性别决定机制,具有一对ｍ－染色体,在有些细胞中出现一个超量染色体。     

Evidence for chromosome number reduction and chromosomal homosequentiality in the 24-chromosome Korean frog Rana dybowskii and related species

The karyotype of the Korean frog Rana dybowskii with its pattern of C-band heterochromatin distribution was numerically analyzed. There are 2n = 24 chromosomes in the karyotype representing a reduction in number from the typical 2n = 26 chromosome karyotype of Rana. The karyotype shows other evidence of reorganization relative to 26-chromosome species. The chromosomes grade smoothly in size from largest to smallest without the two size classes that are characteristic for 26-chromosome species. In contrast to many 26-chromosome species, there are few centromeric C-bands but many interstitial ones. C-bands for each homologous chromosome pair are distinctive. A prominent secondary constriction is located on one of the smallest chromosomes, chromosome 11, in a position similar to that seen in most 26-chromosome species. The karyotype of R. dybowskii is compared to those of other species of Rana known to have 2n = 24 chromosomes; it is most similar to that of R. chensinensis, less so that of R. ornativentris and less still to that of R. arvalis in terms of the positions of centromeres and secondary constrictions. C-bands as well as secondary constrictions in the karyotypes of these frogs show evidence of chromosomal homosequentiality. The process and possible consequences of chromosome number reduction from an ancestral 26-chromosome karyotype is also evident in the karyotypes of these closely allied palearctic frogs. Pericentric inversions followed by fusion of two small elements apparently produced a new chromosome, chromosome 6, occurring originally among northeast Asian populations.     

滇蜀豹子花核型及其变异研究

本文详细报道了滇蜀豹子花的核型,发现居群中存在两种细胞型,即A型和B型。A型参考核型为2n = 24＝2m(2SAT)+2sm+8st(4SAT)+12t(2SAT),其第3号两条同源染色体长臂均无居间随体：B型参考核型为2n=24＝2m(2SAT)+2sm+8st(2SAT)+12t(3SAT)+0—1b,其第3号一条同源染色体长臂紧靠着丝点处有一大而明显的居间随体,而另一条同源染色体则无,构成明显的3号染色体的结构杂合性。统计表明,居群中二者的比例近似为1A;2B。研究还发现了大量的体细胞染色体结构变异核型,表明滇蜀豹子花核型尚未趋于稳定,还处于强烈分化之中,高频率的体细胞染色体结构变异是其种内分化不可忽视的一种进化要素。     

Karyotype analysis of Eucinostomus argenteus, E. gula, E. harengulus, and Eugerres plumieri (Teleostei, Gerreidae) from Florida and Puerto Rico

The karyotypes of four gerreids of the western Atlantic Ocean are documented. A diploid chromosome complement of 48 telocentric chromosomes was found in the four species (2N=48t, fundamental number FN=48). No differences were detected either in the number of chromosomes of the standard karyotype, in their karyotype size, or between the karyotypes derived from male or female specimens of any of the species. Chromosome length decreased progressively and slightly from pair 1 to pair 24. The Ag–NOR karyotypes of E. argenteus and E. harengulus were characterized by the position of the nucleolar organizer regions next to the centromere in chromosome pair 1, whereas in E. gula and E. plumieri Ag–NORs were detected in pair 4. The other 46 chromosomes showed a light staining of the centromere with no terminal or intermediate heterochromatic blocks. All Eucinostomus species showed Ag–NORs of similar size, while Eugerres plumieri showed Ag–NORs 10–20% larger than Eucinostomus species. A combination of size and position of the Ag–NORs identified E. gula, while size alone identified E. plumieri. However, the ancestral state for size and position of Ag–NORs could not be established. There was no differential staining of the chromosomes by G-banding. The karyotype of the gerreids appears similar to the hypothetical ancestral karyotype of fish. The phylogenetic relationships among these species could not be established because of the lack of chromosome G-bands. Most likely this indicates a homogeneous distribution of GC nucleotides in the chromosomes.     

Microdissection and molecular manipulation of single chromosomes in woody fruit trees with small chromosomes using pomelo (<Emphasis Type="Italic">Citrus grandis</Emphasis>) as a model. I. Construction of single chromosomal DNA libraries

Construction of single chromosomal DNA libraries by means of chromosome microdissection and microcloning will be useful for genomic research, especially for those species that have not been extensively studied genetically. Application of the technology of microdissection and microcloning to woody fruit plants has not been reported hitherto, largely due to the generally small sizes of metaphase chromosomes and the difficulty of chromosome preparation. The present study was performed to establish a method for single chromosome microdissection and microcloning in woody fruit species using pomelo as a model. The standard karyotype of a pomelo cultivar (Citrus grandis cv. Guanxi) was established based on 20 prometaphase photomicrographs. According to the standard karyotype, chromosome 1 was identified and isolated with fine glass microneedles controlled by a micromanipulator. DNA fragments ranging from 0.3 kb to 2 kb were acquired from the isolated single chromosome 1 via two rounds of PCR mediated by Sau3A linker adaptors and then cloned into T-easy vectors to generate a DNA library of chromosome 1. Approximately 30,000 recombinant clones were obtained. Evaluation based on 108 randomly selected clones showed that the sizes of the cloned inserts varied from 0.5 kb to 1.5 kb with an average of 860 bp. Our research suggests that microdissection and microcloning of single small chromosomes in woody plants is feasible.Communicated by P. Langridge     

The bat genome: GC-biased small chromosomes associated with reduction in genome size

Bats are distinct from other mammals in their small genome size as well as their high metabolic rate, possibly related to flight ability. Although the genome sequence has been published in two species, the data lack cytogenetic information. In this study, the size and GC content of each chromosome are measured from the flow karyotype of the mouse-eared bat, Myotis myotis (MMY). The smaller chromosomes are GC-rich compared to the larger chromosomes, and the relative proportions of homologous segments between MMY and human differ among the MMY chromosomes. The MMY genome size calculated from the sum of the chromosome sizes is 2.25 Gb, and the total GC content is 42.3 %, compared to human and dog with 41.0 and 41.2 %, respectively. The GC-rich small MMY genome is characterised by GC-biased smaller chromosomes resulting from preferential loss of AT-rich sequences. Although the association between GC-rich small chromosomes and small genome size has been reported only in birds so far, we show in this paper, for the first time, that the same phenomenon is observed in at least one group of mammals, implying that this may be a mechanism common to genome evolution in general.     

Meiotic drive shapes rates of karyotype evolution in mammals

Chromosome number is perhaps the most basic characteristic of a genome, yet generalizations that can explain the evolution of this trait across large clades have remained elusive. Using karyotype data from over 1000 mammals, we developed and applied a phylogenetic model of chromosome evolution that links chromosome number changes with karyotype morphology. Using our model, we infer that rates of chromosome number evolution are significantly lower in species with karyotypes that consist of either all bibrachial or all monobrachial chromosomes than in species with a mix of both types of morphologies. We suggest that species with homogeneous karyotypes may represent cases where meiotic drive acts to stabilize the karyotype, favoring the chromosome morphologies already present in the genome. In contrast, rapid bouts of chromosome number evolution in taxa with mixed karyotypes may indicate that a switch in the polarity of female meiotic drive favors changes in chromosome number. We do not find any evidence that karyotype morphology affects rates of speciation or extinction. Furthermore, we document that switches in meiotic drive polarity are likely common and have occurred in most major clades of mammals, and that rapid remodeling of karyotypes may be more common than once thought.     

Testing the generality of the ‘leafing intensity premium’ hypothesis in temperate broad-leaved forests: a survey of variation in leaf size within and between habitats

Because leaf size scales negatively and isometrically with leaf number per shoot size (leafing intensity) in woody species, and because most tree and shrub species have small leaves, Kleiman and Aarssen (J Ecol 95:376–382, 2007) recently proposed that natural selection favors high leafing intensity resulting in small leaves, i.e., the leafing-intensity-premium hypothesis. However, empirical evidence for or against this hypothesis is still lacking. In addition, this hypothesis has not been examined in the context of how leaf size varies among habitats. To fill this void, we investigated leaf size frequency distributions of woody species from temperate China and explored the relationships among leaf mass, leaf number, and stem mass of current-year shoots of 133 woody species at low and high altitudes of three mountain ranges. The scaling relationships between leaf size and leafing intensity (leaf number per stem mass) were determined using both standardized major axis regression analyses and phylogenetically independent comparative techniques. In light of the leafing-intensity-premium hypothesis, we made three predictions: (1) leaf size frequency distributions should be right-skewed for each local study area and for the entire study region, (2) leafing intensities at different altitudes at different sites should differ while leafing intensities at comparable altitudes should be similar baring large taxonomic differences among sites, and (3) that leafing intensity should be higher for any given leaf size in habitats with small-leaved species. Significant negative and isometric scaling relationships between leaf size and leafing intensity were found to be consistently conserved independent of habitat type, both across species and across correlated evolutionary divergences. Within each mountain range or across the entire study region, leaf size frequency distributions were right-skewed, in accordance with our prediction. However, leafing intensity was smaller for any given leaf size at the altitude with smaller leafed species than for altitudes characterized by large leafed species, i.e., altitudes characterized by species with small leaves did not have consistently higher leafing intensities than other altitudes on each mountain range. Our analyses therefore indicate the direct adaptive value of leaf size but not the selective advantage in high leafing intensity as posited by the leafing-intensity-premium hypothesis. We suggest that this hypothesis explains less about the variation of leaf size among different habitats as it does about variation within habitats, i.e., the relative importance of the adaptive significance of leafing intensity and leaf size can and does vary with habitats.     

中国西南地区鹿药属4种15居群核型研究

对产于中国西南部的鹿药属（Maianthemum）4种植物进行了细胞学研究,包括染色体数目,多倍化,非整倍性和随体染色体,以及核型不对称性和核型进化。结果表明：1）除了在云南丽江采集的Maianthemum tatsienensis染色体数目为2n=72之外,其余的居群全为2n=36;2）核型在居群间存在变异,特别是在具中部染色体和近中部染色体的数目以及随体染色体的数目和位置上。此外,M．nanchuanense和M．szechuanicum的核型是首次报道,B染色体也是首次在该属中发现。我们推测鹿药属的进化方式包括频繁的染色体畸变以及不同水平上的多倍化,而中国西南部是该属的分化中心。     

Chromosome studies in Hippeastrum (Amaryllidaceae): variation in genome size

This paper presents the karyotype and DNA content of 12 diploid species of Hippeastrum from South America. The variation in genome size is compared with the karyotype and DNA content of Amaryllis belladonna from South Africa. The Hippeastrum species present a uniform and bimodal basic karyotype formula, but significant differences are found in the total chromosome volume (TCV) and nuclear DNA content. A positive correlation between the DNA content and TCV is also observed. The karyotype's constancy is a product of changes in DNA content occurring in the whole chromosome complement. The DNA addition to the long and short sets of chromosomes varies independently. In species with higher DNA contents, the short chromosomes add equal DNA amounts to both arms, maintaining their metacentric morphology, whereas the long chromosomes add DNA only to the short arm, increasing the chromosome symmetry. These data show that the evolutionary changes in DNA amount are proportional to chromosome length, maintaining the karyotypic uniformity. A. belladonna has a larger DNA content and possesses a karyotype different from that of Hippeastrum spp., supporting the distinction between the two genera and upholding the name Amaryllis for the South African entity against Hippeastrum for the South American genus.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 171–178.     

兰州鲇染色体组型

本研究的目的在于认识兰州鲇(Silurus lanzhouensis)染色体组特征,为兰州鲇的细胞遗传学和人工育种研究提供基础参考资料。以兰州鲇培养肾细胞为材料,采用空气干燥法制备染色体玻片标本,分析了兰州鲇的染色体组型。兰州鲇的染色体数2n=58,核型公式为2n=20m+18sm+16st+4t,染色体总臂数(NF)为96。通过比较分析认为,兰州鲇在鲇属鱼类中属于较为原始的类群。     

The distribution of B chromosomes across species

In this review we look at the broad picture of how B chromosomes are distributed across a wide range of species. We review recent studies of the factors associated with the presence of Bs across species, and provide new analyses with updated data and additional variables. The major obstacle facing comparative studies of B chromosome distribution is variation among species in the intensity of cytogenetic study. Because Bs are, by definition, not present in all individuals of a species, they may often be overlooked in species that are rarely studied. We give examples of corrections for differences in study effort, and show that after a variety of such corrections, strong correlations remain. Several major biological factors are associated with the presence of B chromosomes. Among flowering plants, Bs are more likely to occur in outcrossing than in inbred species, and their presence is also positively correlated with genome size and negatively with chromosome number. They are no more frequent in polyploids than in diploids, nor in species with multiple ploidies. Among mammals, Bs are more likely to occur in species with karyotypes consisting of mostly acrocentric chromosomes. We find no evidence for an association with chromosome number or genome size in mammals, although the sample for genome size is small. The associations with breeding system and acrocentric chromosomes were both predicted in advance, but those with genome size and chromosome number were discovered empirically and we can offer only tentative explanations for the very strong associations we have uncovered. Our understanding of why B chromosomes are present in some species and absent in others is still in its infancy, and we suggest several potential avenues for future research.     

Variation in the electrophoretic karyotype analysed by the assignment of DNA probes in Candida albicans

By using pulsed-field gel electrophoresis, we have separated the entire chromosome bands and examined the electrophoretic karyotypes of 27 strains of Candida albicans. The electrophoretic karyotype varied widely among these strains. Their chromosomal DNAs were resolved into 7-12 bands ranging in size from 0.42 to 3.0 Mb. Most of the separated chromosomal bands were assigned by eight cloned C. albicans DNA probes. These results suggest that the haploid number of C. albicans chromosomes is eight. Each of the probes hybridized specifically to one or two bands of similar size in most strains. With the exception of the MGL1 probe, when two bands were detected by one probe, the size of one of them was very conserved whilst the other was of fairly variable size. The sizes of the chromosome bands assigned by the MGL1 probe were much more variable. As C. albicans is considered to be a diploid organism, it is inferred that the karyotype polymorphism between strains is mainly derived from wide size heterogeneity in one of the homologous chromosomes. Furthermore, we have confirmed species-specific and strain-specific variation in medically important Candida species (C. stellatoidea, C. tropicalis, C. parapsilosis, C. krusei, C. guilliermondii, C. kefyr and C. glabrata). Electrophoretic karyotype analysis is thus useful for species assignation. The TUB2 probe, encoding C. albicans beta-tubulin, hybridized to the chromosomal DNA of all the Candida species examined, but four C. albicans probes exhibited cross-species hybridization with C. stellatoidea only. The karyotype of C. stellatoidea seems to be within the range of the intraspecies variation observed in C. albicans.     

Genome characterization of Pyrenophora tritici-repentis isolates reveals high plasticity and independent chromosomal location of ToxA and ToxB

The fungus Pyrenophora tritici - repentis (Died.) causes tan spot, an important leaf disease of wheat worldwide. Isolates of this pathogen have been collected and characterized into eight races on the basis of their ability to produce three different host-selective toxins. The karyotype of 47 isolates was determined by pulsed field gel electrophoresis. The collection originated from different parts of the world and included genotypes from all races. A single isolate was characterized for each of races 3, 4 and 6, whereas fourteen, five, nine, five and eleven isolates were karyotyped for races 1, 2, 5, 7 and 8, respectively. The survey showed that the chromosome number of P. tritici-repentis was highly variable, with some isolates having as few as eight chromosomes, but others having 11 or more. Similarly, the genome size ranged from 25.5 to 48.0 Mb, and individual chromosome sizes ranged from 1.3 to more than 5.7 Mb. Considerable variation was observed in karyotype patterns among the P. tritici-repentis isolates tested. A total of 29 different karyotypes was identified among the 47 isolates. These chromosome level variations were as variable for isolates within a race as for isolates across races. Southern blot analysis of the 47 isolates with ToxA and ToxB probes revealed that the toxin genes were always located on different chromosomes. Furthermore, with six chromosome-specific single-copy probes, the ToxA -carrying chromosome was shown to be homologous among the Ptr ToxA-producing isolates, with a related chromosome in the non-ToxA-producing isolates, suggesting that the chromosome on which ToxA generally resides is of an essential nature. Interestingly, a molecular rearrangement involving a translocation of ToxA to a different chromosome was identified in one isolate.     

The generality of leaf size versus number trade-off in temperate woody species

Background and Aims

Trade-offs are fundamental to life-history theory, and the leaf size vs. number trade-off has recently been suggested to be of importance to our understanding leaf size evolution. The purpose of the present study was to test whether the isometric, negative relationship between leaf size and number found by Kleiman and Aarssen is conserved between plant functional types and between habitats.

Methods

Leaf mass, area and number, and stem mass and volume of current-year shoots were measured for 107 temperate broadleaved woody species at two altitudes on Gongga Mountain, south-west China. The scaling relationships of leaf size (leaf area and mass) vs. (mass- and volume-based) leafing intensity were analysed in relation to leaf habit, leaf form and habitat type. Trait relationships were determined with both a standardized major axis method and a phylogenetically independent comparative method.

Key Results

Significant negative, isometric scaling relationships between leaf size and leafing intensity were found to be consistently conserved across species independent of leaf habit, leaf form and habitat type. In particular, about 99 % of the variation in leaf mass across species could be accounted for by proportional variation in mass-based leafing intensity. The negative correlations between leaf size and leafing intensity were also observed across correlated evolutionary divergences. However, evergreen species had a lower y-intercept in the scaling relationships of leaf area vs. leafing intensity than deciduous species. This indicated that leaf area was smaller in the evergreen species at a given leafing intensity than in the deciduous species. The compound-leaved deciduous species were observed usually to have significant upper shifts along the common slopes relative to the simple-leaved species, which suggested that the compound-leaved species were larger in leaf size but smaller in leafing intensity than their simple counterparts. No significant difference was found in the scaling relationships between altitudes.

Conclusions

The negative, isometric scaling relationship between leaf size and number is largely conserved in plants, while the leaf size vs. number trade-off can be mediated by leaf properties. The isometry of the leaf size vs. number relationship may simply result from a biomass allocation trade-off, although a twig size constraint may provide an alternative mechanism.Key words: Allometry, trade-off, leafing intensity, leaf size, leaf habit, leaf form     

Chromosomal analysis of twelve species of Microhylidae (Anura) from Madagascar

The karyotypes of four species of Dyscophinae and eight species of Cophylinae were analyzed. The chromosome number was 2n=26 in all cases. Between the two subfamilies a difference in the form of the karyotype was observed; the chromosomes show a gradual decrease in length in the Dyscophinae, whereas in the Cophylinae the karyotype demonstrates a clear discontinuity of size between pairs 5 and 6.Chromosomal polymorphism was found in Plethodontohyla tuberata, the chromosomes of pair 4 were subtelocentric in the homozygous specimens, whereas this pair showed a subtelocentric and a submetacentric chromosome of equal length in the heterozygous one, suggesting a pericentric inversion. Although in the Cophylinae the chromosome number is constant, the number of chromosome arms is variable. Pericentric inversions seem to play an important role in the chromosomal evolution of the Cophylinae.