CYTOTAXONOMY OF THE ELEOCHARIS TENUIS COMPLEX

Chromosome numbers of 2n = 20, 24, 36, and 38 were found in the various taxa comprising the Eleocharis tenuis complex in the United States. Eleocharis tenuis var. verrucosa, the only taxon in the complex with 2n = 20 is given the new status of a full species [E. verrucosa (Svens.) Harms] and seems most closely allied to two southern members of the subseries Truncatae which are not members of the tenuis complex s. s. Karyotypes and meiotic pairing in artificial hybrids indicate that the remainder of the taxa are derivatives of X = 6 with E. tenuis and one of two cytotypes of E. compressa with the lowest numbers of 2n = 24, although evidence is presented to indicate that they are of amphidiploid origin. A second cytotype of E. compressa with 2n = 36 is a segmental autoallohexaploid, whereas E. elliptica and E. elliptica var. pseudoptera (Svens.) Harms, comb. nov. with 2n = 38 are hyperploid derivatives of 2n = 36.     

Evidence for Emergence of Sex-Determining Gene(s) in a Centromeric Region in Vasconcellea parviflora

Sex chromosomes have been studied in many plant and animal species. However, few species are suitable as models to study the evolutionary histories of sex chromosomes. We previously demonstrated that papaya (Carica papaya) (2n = 2x = 18), a fruit tree in the family Caricaceae, contains recently emerged but cytologically heteromorphic X/Y chromosomes. We have been intrigued by the possible presence and evolution of sex chromosomes in other dioecious Caricaceae species. We selected a set of 22 bacterial artificial chromosome (BAC) clones that are distributed along the papaya X/Y chromosomes. These BACs were mapped to the meiotic pachytene chromosomes of Vasconcellea parviflora (2n = 2x = 18), a species that diverged from papaya ∼27 million years ago. We demonstrate that V. parviflora contains a pair of heteromorphic X/Y chromosomes that are homologous to the papaya X/Y chromosomes. The comparative mapping results revealed that the male-specific regions of the Y chromosomes (MSYs) probably initiated near the centromere of the Y chromosomes in both species. The two MSYs, however, shared only a small chromosomal domain near the centromere in otherwise rearranged chromosomes. The V. parviflora MSY expanded toward the short arm of the chromosome, whereas the papaya MSY expanded in the opposite direction. Most BACs mapped to papaya MSY were not located in V. parviflora MSY, revealing different DNA compositions in the two MSYs. These results suggest that mutation of gene(s) in the centromeric region may have triggered sex chromosome evolution in these plant species.     

Mitotic Microtubule Development and Histone H3 Phosphorylation in the Holocentric Chromosomes of Rhynchospora Tenuis (Cyperaceae)

In the present work we report the phosphorylation pattern of histone H3 and the development of microtubular structures using immunostaining techniques, in mitosis of Rhynchospora tenuis (2n = 4), a Cyperaceae with holocentric chromosomes. The main features of the holocentric chromosomes of R. tenuis coincide with those of other species namely: the absence of primary constriction in prometaphase and metaphase, and the parallel separation of sister chromatids at anaphase. Additionaly, we observed a highly conserved chromosome positioning at anaphase and early telophase sister nuclei. Four microtubule arrangements were distinguished during the root tip cell cycle. Interphase cells showed a cortical microtubule arrangement that progressively forms the characteristic pre-prophase band. At prometaphase the microtubules were homogeneously distributed around the nuclear envelope. Metaphase cells displayed the spindle arrangement with kinetochore microtubules attached throughout the entire chromosome extension. At anaphase kinetochoric microtubules become progressively shorter, whereas bundles of interzonal microtubules became increasingly broader and denser. At late telophase the microtubules were observed equatorially extended beyond the sister nuclei and reaching the cell wall. Immunolabelling with an antibody against phosphorylated histone H3 revealed the four chromosomes labelled throughout their entire extension at metaphase and anaphase. Apparently, the holocentric chromosomes of R. tenuis function as an extended centromeric region both in terms of cohesion and H3 phosphorylation.     

A CYTOTAXOXOMIC SURVEY OF MELAMPODIUM (COMPOSITAE-HELIANTHEAE)

Turner , B. L.. and R. M. King . (U. Texas, Austin.) A cytotaxonomic survey of Melampodium (Compositae-Heliantheae). Amer. Jour. Bot. 49(3): 233–26. Illus. 1962.—Chromosome counts are reported for individuals from 89 populations of Melampodium representing 26 species The genus is multibasic with x = 9, 10, 11, 12, 16 and 23. Chromosome numbers on a base of x = 10 characterize the section Melampodium while basic numbers of x = 23, 16, 12, 11 and 9 occur in the section Zarabellia. Melampodium camphoratum (n = 16) differs from all other species examined in having relatively small meiotic chromosomes. Only 6 of the 23 species are polyploid or have polyploid races. Melampodium leucanthum and M. cinereum have both diploid and tetraploid populations; the latter occur without any apparent morphological or geographical correlation and are probably autoploid in origin. A survey of the basic chromosome numbers known for other genera of the subtribe Melampodinae (12 of 22 genera) is presented. and it is suggested that x = 10 is the most probable basic number of the genus and subtribe.     

Chromosomes of five artiodactyl mammals

Somatic chromosomes of six specimens belonging to the following five species of artiodactyls (Artiodactyla: Mammalia) are described: A female nilgai (Boselaphus tragocamelus), 2n=46; male baresingha (Rucervus duvauceli), two specimens, 2n=56; a female Himalayan tahr (Hemitragus jemlahicus), 2n=48; a female Kirk's dik-dik (Rhynchotragus kirki), 2n=46; and a male sambar (Cervus unicolor), 2n=58. In the baresingha and the sambar, one or more acrocentric chromosomes carried satellites on their long arms. ³H-thymidine radioautographs of cultured cells of the Himalayan tahr showed a long acrocentric chromosome to be late-replicating, suggesting that it is an X chromosome.     

Karyological observations on Turbellaria Proseriata: karyometric analysis ofMonocelis fusca,M. lineata (Monocelididae) andParotoplana macrostyla (Otoplanidae)

A karyometric analysis of the chromosome set of the marine turbellariansMonocelis fusca, M. lineata andParotoplana macrostyla has been carried out. The karyotype of the twoMonocelis species investigated (2n=6) is formed by three pairs of small and similarly sized chromosomes: InM. fusca, chromosome 1 is metacentric, chromosome 2 acrocentric and chromosome 3 is subtelocentric.M. lineata also presents one pair of metacentric chromosomes (chromosome 2), while chromosomes 1 and 3 are submetacentric.P. macrostyla (2n=12) reveals two pairs of large metacentric and four pairs of small chromosomes, three of which are metacentric, whereas the last is subtelocentric.     

Stable versus unstable orientations of sex chromosomes in two grasshopper species

The structural basis of orientation stability was investigated. The stable unipolar orientation of the Melanoplus sanguinipes X-chromosome univalent is unique in that it is stable without tension created by forces towards opposite poles; tension is thought to be the principle component in stabilizing kinetochore orientations to a pole. Stable orientation of the X chromosome in Melanoplus sanguinipes was compared with unstable X orientation in Melanoplus differentialis. Ten cells (five of each species) were studied, firstly in living cultures where chromosome behavior was followed, then by serial-section electron microscopy where the structural basis for chromosome behavior was examined. Microtubules other than kinetochore microtubules were observed impinging on the X chromosomes. One end of these microtubules was buried in chromatin, while the other ran towards a pole. The X chromosomes of M. sanguinipes had more of these microtubules than did M. differentialis X chromosomes. It is suggested that M. sanguinipes X chromosomes are less condensed than M. differentialis X chromosomes and so allow more microtubules to penetrate the chromosome. The extra microtubules impinging on the M. sanguinipes X chromosome probably prevent reorientation by inhibiting the turning of the chromosome towards the opposite pole, i.e., more force is needed to turn a kinetochore towards the opposite pole than can be generated and attempts at reorientation fail. This may be analogous to the effect that tension has on the orientation stability of bivalents.     

三种食肉目动物的核型分析

本文报道了产于我国华北地区的艾鼬、貉和果子狸的核型。其中艾鼬2n=36。组型由20条双臂染色体、14条单臂染色体和一对性染色体组成。貉2n=65,它与wuster等报道过的貉的2n=42的核型表现出同种动物核型间的多态现象。果子狸2n=44,其c带带型中具有一对带有较大异染色质的中部着丝点染色体。     

A fascinating island: 2n = 4

Abstract

Among Angiosperms, only six species are known to possess the lowest identified chromosome number, i.e. 2n = 4. These plants are the monocotyledons Zingeria biebersteiniana, Colpodium versicolor, Ornithogalum tenuifolium and Rhynchospora tenuis, and the dicotyledons Haplopappus gracilis and Brachyscome dichromosomatica. The low chromosome number may be cytogenetically derived from a different ancestral basic number, characteristic of each genus, by different processes, including tandem fusion or unequal reciprocal translocations with loss of centric fragments. All these plants possess low nuclear 4C DNA contents, ranging from 1.56 pg (R. tenuis) to 8.20 pg (H. gracilis), and they generally display a similar chromosome size and a similar position of the nucleolus organising region (NOR), that is often located in the terminal or subterminal region of the small chromosome pair. All these characteristics could be a consequence of common adaptative mechanisms. Peculiar characteristics within these karyotypes are the holocentric chromosomes of R. tenuis and the presence of B chromosomes in B. dichromosomatica. Plants with a very low chromosome number may be considered to constitute a fascinating “island of interest”; moreover, they represent simple systems helpful for the examination of the structural organisation and evolution of Angiosperm chromosomes.     

Karyological notes on another eight species of Achillea (Asteraceae) from Turkey

The chromosome number and morphology in eight species of the sections Ptarmica (Mill.) W. D. J. Koch, Anthemoideae (DC.) Heimerl, Arthrolepis Boiss., Santolinoideae (DC.) Heimerl and Achillea of the genus Achillea L. (Asteraceae) were investigated using karyological techniques. Sample plants and seeds of A. biserrata M. Bieb., A. fraasii var. troiana Aschers. & Heimerl, A. multifida (DC.) Boiss., A. brachyphylla Boiss. & Hausskn., A. pseudaleppica Hub.-Mor., A. cretica L., A. latiloba Ledeb. ex Nordm., and A. kotschyi Boiss. subsp. kotschyi) were collected from natural habitats in 2003 and 2004. The chromosome number found in seven species was 2n = 18, while only A. kotschyi had 2n = 36. All chromosomes had median point (M), median region (m), and submedian (sm) centromers. In addition, only A. biserrata species had one subterminal (st) chromosome. An increase in asymmetry was not observed in the karyotypes of the species studied. None of the studied species had any B chromosomes.     

THE ORIGIN OF AGROPYRON SMITHII

The hypothesis that North American octoploid Agropyron smithii Rydb., 2n = 56, originated by hybridization between tetraploid Agropyron and Elymus species, followed by chromosome doubling, was tested by observing chromosome pairing in hybrids of A. smithii with an induced amphiploid, 2n = 56, derived from E. canadensis L., 2n = 28, X E. dasystachys Trin., 2n = 28, F₁'s. Chromosome pairing in A. smithii averaged 0.52^I, 27.70^II, 0.01^III, and 0.01^IV in 184 metaphase-I cells; and the amphiploid averaged 1.13^I and 27.44^II in 195 cells. Chromosome pairing in A. smithii X amphiploid hybrids averaged 8.20^I, 23.38^II, 0.34^III, and 0.05^IV in 101 metaphase-I cells. It was concluded that A. smithii was genomically similar to the E. canadensis-E. dasystachys amphiploid. The basic genome formula of the amphiploid is SSHHJJXX, with the SSHH genomes coming from E. canadensis and the JJXX genomes coming from E. dasystachys. Consideration of the morphological, ecological, and reproductive characteristics of all North American species that contain the basic SSHH and JJXX genomes led to the conclusion that A. dasystachyum (Hook.) Scribn., SSHH, and E. triticoides Buckl., JJXX, are the probable progenitors of A. smithii.     

Evolution of diploid chromosome number,sex‐determining systems,and heterochromatin in Western Mediterranean and Canarian species of the genus Pimelia (Coleoptera: Tenebrionidae)

A compilation of the diploid chromosome numbers and karyotype formulae of 30 species of the genus Pimelia from Morocco, Iberian Peninsula, Balearic and Canary Islands is presented. All species show a conservation of diploid numbers and karyotype formulae 2n = 18 (8 + Xy_p) except for Pimelia cribra, Pimelia elevata, and Pimelia interjecta 2n = 20 (9 + Xy_p) and Pimelia sparsa sparsa 2n = 18 (8 + neoXY). The ancestral state for the genus Pimelia is suggested to be 2n = 18 (8 + Xy_p) in accordance with a previously described phylogeny of these species based on mitochondrial and nuclear DNA. The derived state 2n = 20 (9 + Xy_p) is present in a monophyletic clade, which originated about 2.5–5 Mya. The male meiotic formula 8 + neoXY found in P. sparsa sparsa seems to have originated by the reorganization of the Xy_p pair resulting in two homomorphic sexual chromosomes and the lost of most of the heterochromatin from the former X chromosome. In all chromosomes C‐banding revealed conspicuous pericentromeric heterochromatic blocks, except in the Y chromosome in most of the species, and in situ hybridization of satellite DNA probes revealed the correspondence between heterochromatin and satellite DNA. Finally, the possible role of heterochromatin and satellite DNA is discussed in relation to the uniformity of the Tenebrionidae α‐karyology.     

BIOSYSTEMATIC STUDIES IN THE BOUTELOUA CURTIPENDULA COMPLEX. III. POLLEN SIZE AS RELATED TO CHROMOSOME NUMBERS

Pollen size statistics are presented for 10 closely related species of Bouteloua and relationships between pollen size and chromosome numbers are presented for 13 populations of 5 species and 3 varieties. With 1 exception, all populations of all taxa conformed to a general pattern of pollen size dependent upon chromosome number. Chromosome numbers varied from 2n = 20 to 2n = ca. 103, with several independent aneuploid series. Statistical analyses were made of pollen size as related to chromosome number in the 3 varieties of B. curtipendula. These data showed that tetraploids (2n = 40) of var. tenuis had significantly greater pollen size and coefficient of variation than diploids (2n = 20) of the same variety. Similarly, aneuploids of var. curtipendula with 2n = 45 to 2n = 64 chromosomes had significantly larger and more variable pollen than tetraploids (2n = 40) of the same variety. Highly significant positive regression coefficients were obtained from analyses of chromosome numbers and mean pollen size, and chromosome numbers and coefficient of variation, for var. curtipendula. Regression coefficients for var. caespitosa populations with chromosome numbers over the hexaploid (2n = 60) level were not significant.     

Comparative karyotype analysis in Haplopappus Cass. and Grindelia Willd. (Asteraceae) by double FISH with rRNA specific genes

The genera Grindelia Willd. and Haplopappus Cass. belong to the family Asteraceae - Astereae and are distributed in America and South America, respectively. Previous cytotaxonomic studies showed for South American species of Grindelia 2n=12 and for Haplopappus 2n=10 and 2n=12. Both Grindelia species (G. anethifolia, G. prunelloides), newly analyzed with molecular-cytological methods, exhibited symmetric karyotypes (AsI %=55.46 and 55.95) with metacentric chromosome sets (5m + 1m-sat) and 2n=12 chromosomes. The NOR was detected after fluorescence in situ hybridization (FISH) with 18/25S rDNA in the satellite chromosome 2. In contrast H. Happlopappus glutinosus, H. grindeloides and H. stolpii showed exclusively a higher asymmetric index (66.83%, 67.01% and 68.87%, respectively) with submetacentric chromosome sets (4sm + 1sm–sat). The sat-chromosomes 3 of H. glutinosus and H. grindelioides were both significantly different in their length from chromosomes 2 and 4. Furthermore in Grindelia the FISH with 5S rDNA could estimate signals in the short arms of chromosomes 3 or 4, that were not significantly differentiated in their length. Contrary to these findings in Grindelia, the position of 5S rDNA in Haplopappus was detected in the long arms of chromosome 1 (H. grindelioides and H. stolpii) and chromosome 2 (with two different loci) and chromosome 4 of H. glutinosus. The lengths of all measured chromosome arms with 5S rDNA were significantly different to those of the neighbours in the karyotypes. The two-color FISH of 5S and 18/25S rDNA had provided clear karyotypic markers for three (Haplopappus glutinosus) and two (H. grindelioides and H. stolpii) chromosomes. The number and position of rDNA signals were relatively highly conserved in the investigated five species without the double marked chromosome 2 of H. glutinosus, which shows an evolutionary dynamic of this 5S rRNA specific gene cluster. This investigation supports the assumption that the evolution of New World members of Grindelia and Haplopappus has not been accompanied by large karyotypic changes, but small chromosomal rearrangements have undoubtedly occurred (e.g. 5S rDNA localizations).     

Achiasmate Segregation of a B Chromosome from the X Chromosome in Two Species of Psyllids (Psylloidea, Homoptera)

The segregation of a B chromosome from the X chromosome was studied in male meiosis in two psyllid species, Rhinocola aceris (L.) and Psylla foersteri (Flor.) (Psylloidea, Homoptera). The frequency of segregation was determined from cells at metaphase II. In R. aceris, the B chromosome was mitotically stable and segregated quite regularly from the X chromosome in four geographically distant populations, while it showed less regular, but preferential segregation in one population. This was attributed to the presence of B chromosome variants that differ in their ability to interact with the X chromosome in segregation. In P. foersteri, the B chromosome was mitotically unstable and segregated preferentially from the X chromosome in spermatocyte cysts, which displayed one B chromosome in every cell. Behaviour of the B chromosome and X chromosome univalents during meiotic prophase and at metaphase I in R. aceris, and during anaphase I in P. foersteri suggested that the regular segregation resulted from the incorporation of B chromosomes in achiasmate segregation mechanisms with the X chromosome in the place occupied by the Y chromosome in species with XY system. The regular segregation of a B chromosome from the X chromosome may obscure the distinction of a B chromosome and an achiasmate Y chromosome in some cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

End-to-end chromosome attachments in mitotic interphase and their possible significance to meiotic chromosome pairing

Cytological studies on telophase and early prophase in roottip cells of several plant species (Allium cepa, 2n=16; four Crepis species, including Crepis capillaris, 2n=6; Callitriche hermaphroditica, 2n=6; Nigella arvensis, 2n=12; Secale cereale, 2n=14) revealed that chromosome ends are attached two by two forming chains of chromosomes (interphase associations). In these chains homologous chromosomes are presumably located adjacent to each other. In Crepis capillaris it was observed that the two nucleolar chromosomes form a separate ring one end attached to the ring of the four remaining chromosomes and the other end attached to the nucleolus. It is proposed that these end-to-end attachments have significance for chromosome pairing in meiosis. The adjacent location of homologous chromosomes in the interphase associations would facilitate rapid and regular synapsis.     

NORTHERN AND SOUTHERN HEMISPHERE HYBRIDS OF MACROCYSTIS (PHAEOPHYCEAE)1

All combinations of individuals of Macrocystis pyrifera (L.) C. Agardh, M. integrifolia Bory, and M. angustifolia Bory hybridized. Gametophyte isolates obtained from 18 individuals were used, including M. pyrifera and M. integrifolia from the extremes of their Northern Hemisphere ranges along the Pacific Coast of North America and M. pyrifera and M. angustifolia from Tasmania, Australia. All combinations of gametophytes produced sporophytes of normal morphology, with the exception of crosses involving three gametophyte isolates. One female (M. integrifolia) and two male (M. pyrifera and M. angustifolia)gametophyte isolates were unable to produce normal sporophytes in combination with gametophytes of the opposite sex. Some cultures of female gametophytes produced abnormally shaped parthenogenetic sporophytes. Gametophytes and sporangia of M. pyrifera had n= 16 chromosomes. The M. integrifolia female gametophyte that was unable to produce normal sporophytes had n = ca. 32 chromosomes. These results show that these species of Macrocystis have not become reproductively isolated. Although these species may be considered conspecific according to the biological species concept, we recommend that they continue to be recognized as separate species based on morphological differences.     

Chromosome complements of the genus Xenopus

The oytogenetic analysis of the genus Xenopus shows that X. laevis laevis, X. laevis petersi, X. laevis victorianus, X. (laevis) borealis, X. gilli, X. muelleri, and X. fraseri have chromosome numbers 2n=36; X. tropicalis has 20 (2n), X. (laevis) bunyoniensis 72 and X. ruwenzoriensis 108. This heterogeneity of the chromosome numbers is interesting as it represents new examples of polyploidy among Anurans. There are no big morphological differences among the karyotypes of the divers species, only the chromosomes with secondary constrictions vary considerably.     

Reclassification of North American Haplopappus (Compositae: Astereae) completed: Rayjacksonia gen. nov.

Rayjacksonia R. L. Hartman & M. A. Lane, gen. nov. (Compositae: Astereae), is named to accommodate the “phyllocephalus complex,” formerly of Haplopappus Cass. sect. Blepharodon DC. The new combinations are R. phyllocephalus (DC.) R. L. Hartman & M. A. Lane, R. annua (Rydb.) R. L. Hartman & M. A. Lane, and R. aurea (A. Gray) R. L. Hartman & M. A. Lane. This transfer completes the reclassification of the North American species of Haplopappus sensu Hall, leaving that genus exclusively South American. Rayjacksonia has a base chromosome number of x = 6. Furthermore, it shares abruptly ampliate disk corollas, deltate disk style-branch appendages, and corolla epidermal cell type, among other features, with Grindelia, Isocoma, Olivaea, Prionopsis, Stephanodoria, and Xanthocephalum. Phylogenetic analyses of morphological and chloroplast DNA restriction site data, taken together, demonstrate that these genera are closely related but distinct.     

Chromosomal diversity and evolution in the ground beetle genus Bembidion and related taxa (Coleoptera: Carabidae: Trechitae)

Chromosome numbers and sex chromosome systems of 154 previously unstudied Bembidion species are described. The genus is nearly uniform: males of 176 of 205 species are 2n=22+XY. Karyotypes are presented for 30 species. There is some variation among species in size of Y and size of autosomes. Within most species autosomes are subequal in size, and metacentric or submetacentric. Subterminal secondary constrictions and B chromosomes are reported from several species.The supertribe Trechitae (Zolini + Trechini + Pogonini + Bembidiini) is hypothesized to be primitively male 2n=22+X or 24+X, and the ancestral Bembidion stock 2n=22+XY. Conclusions are based on the most parsimonious hypothesis of ancestral state given an inferred phylogeny of the group, rather than the widespread-is-primitive arguments used previously. Evolution within Bembidion away from the presumably-primitive 2n=22+XY is discussed. Six lineages have lost Y chromosomes; seven have undergone changes in autosome number. It is not known why such changes are so scarce, nor what particular rearrangements led to the observed diversity. Nonetheless, the cytogenetic data can be used to infer a monophyletic origin of groups possessing derived chromosome numbers or sex chromosomes, and to help resolve species limits.