Cytotypes of Andropogon gerardii Vitman (Poaceae): fertility and reproduction of aneuploids

In many North American prairies, populations of Andropogon gerardii Vitman (Poaceae) are composed of hexaploid and enneaploid cytotypes (2 n  = 60, 90), with intermediates occurring occasionally. Under controlled pollination, the two common cytotypes can be crossed, producing progeny with a range of chromosome numbers. In an investigation of fertility and compatibilities of intermediate cytotypes, individuals with chromosome numbers between 60 and 90 were crossed with each other, with the 2 n  = 60 and 90 cytotypes, and with South American Andropogon species having 60 chromosomes. Regardless of cytotype, all A. gerardii plants had some fertility and virtually all crosses produced seeds. Cytotype is only partially predictive of fertility. Inter-specific hybrids between A. gerardii and South American hexaploid species were vigorous but sterile. Gene flow in natural A. gerardii populations of mixed cytotype probably involves plants of all cytotypes.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 95–103.     

Tetraploids inLuzula multiflora (Juncaceae) in Ireland: Karyology and meiotic behaviour

Populations ofLuzula multiflora s.l. in Ireland were examined karyologically. Plants from 14 populations were invariably tetraploid with 2n=24. Chromosomes of the tetraploid are of AL type (true tetraploidy). Meiosis of the tetraploids is of the same type as described for otherLuzula taxa in the literature. In meiosis, 12 bivalents are regularly formed. A hypothesis based on the morphological and allozyme data, that the tetraploids are of alloploid origin, is supported by the present results. Meiosis in an artificial hybrid between the presumed parental taxa,L. campestris andL. pallidula, was studied; a certain tendency towards chromosome doubling was observed. The geographical distribution of theL. multiflora cytotypes is also discussed.     

Ploidy dimorphism and reproductive biology in Stenodrepanum bergii (Leguminosae), a rare South American endemism

This is the first report on chromosome numbers and the reproductive behaviour in Stenodrepanum Harms, a rare endemic and monotypic legume genus from the arid and salty areas of central-western Argentina. Sixty individuals belonging to two populations from two salty areas ("salinas") were surveyed and included mostly triploid (2n = 3x = 36) and only two diploid (2n = 2x = 24) plants. Meiosis in diploids is regular, with bivalent pairing and uniform and viable pollen. In contrast, meiosis in triploids is characterized by high trivalent pairing, with irregularly shaped pollen and variation in cytoplasm content and stainability, which is in agreement with an unbalanced segregation occurring in anaphases I and II. However, different triploid plants/individuals showed various degrees of pollen fertility, which may be attributed to particular genotypes. Research on reproductive biology events indicates sexual cross-pollinated reproduction enhanced by protogyny in both cytotypes. All plants produced seeds, but seedlings were only recovered from diploid plants pollinated with triploids, and even those eventually perished. Chromosome counts in these seedlings revealed aneuploid chromosome numbers owing to the combination of unbalanced gametes.     

CYTOGENETIC ANALYSIS OF CHROMOSOMAL INTERMEDIATES FROM A HYBRID ZONE BETWEEN TWO CHROMOSOME RACES OF THE SCELOPORUS GRAMMICUS COMPLEX (SAURIA,PHRYNOSOMATIDAE)

Underdominance for chromosomal rearrangements is the central assumption of several models of chromosomally based speciation including the cascade model, proposed for the Sceloporus grammicus complex. Several cytotypes of the S. grammicus complex hybridize at localities in central México. A hybrid zone between two of the most chromosomally divergent races (= cytotypes) of S. grammicus (F5, 2n = 34 and FM2, 2n = 44–46) was examined to assess the meiotic effects of heterozygosity at multiple chromosomes. Meiosis was examined in males heterozygous for “simple” Robertsonian fissions at chromosomes 1, 3, 4, and 6 and/or a pericentric inversion at chromosome 4. Analysis of synaptonemal complexes and chromosomal configurations at diakinesis showed trivalent formation in fission heterozygotes and heterosynapsis (lack of reverse-loop formation) in an inversion heterozygote. Analysis of metaphase II configurations revealed primarily balanced segregation and low levels of nondisjunction regardless of chromosomal background. The lack of underdominance associated with “simple” fission heterozygosity in this narrow hybrid zone contradicts the key premise of most chromosomally based models of speciation.     

Comparison of common cytotypesof Andropogon gerardii(Andropogoneae,Poaceae)

Many plant species contain populations with more than one polyploid cytotype, but little is known of the mechanisms maintaining several cytotypes in a population. Andropogon gerardii cytotypes were compared to evaluate different models of autopolyploid cytotype coexistence. The enneaploid (90 chromosome, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different. The two cytotypes are not exomorphologically separable in the field because of great plasticity in response to environmental variation and wide variation within each cytotype. These data suggest cytotypic variation is maintained by natural selection.     

Meiotic pairing as an indicator of genome composition in polyploid prairie cordgrass (<Emphasis Type="Italic">Spartina pectinata</Emphasis> Link)

The existence of neopolyploidy in prairie cordgrass (Spartina pectinata Link) has been documented. The neohexaploid was discovered coexisting with tetraploids in central Illinois, and has been reported to exhibit competitiveness in the natural environment. It is hypothesized that the natural tetraploid cytotype produced the hexaploid cytotype via production of unreduced gametes. Meiosis I chromosome pairing was observed in tetraploid (2n?=?4x?=?40), hexaploid (2n?=?6x?=?60), and octoploid (2n?=?8x?=?80) accessions and the percentage of meiotic abnormality was determined. Significant differences in meiotic abnormality exist between tetraploid, hexaploid, and octoploid cytotypes. An elevated incidence of abnormal, predominantly trivalent pairing in the neohexaploid suggests that it may possess homologous chromosomes in sets of three, in contrast to the tetraploid and octoploid cytotypes, which likely possess homologous chromosomes in sets of two. Abnormal chromosome pairing in the hexaploid may result in unequal allocation of chromosomes to daughter cells during later stages of meiosis. Chromosome pairing patterns in tetraploid, hexaploid, and octoploid cytotypes indicate genome compositions of AABB, AAABBB, and AABBA′A′B′B′, respectively.     

Chromosome numbers,characterization of chromosomal pairing during meiosis,origin and natural propagation in polyploid cytotypes (4x, 5x and 6x) of Agrimonia eupatoria L. (Rosaceae) in northwest Himalayas (India)

Despite the presence of intraspecific polyploidy (2x, 4x, 5x and 6x) in Agrimonia eupatoria, origin of these cytotypes has never been addressed adequately. The aim of the present study was to record the original chromosome counts and characterize chromosomal pairing during meiosis and microsporogenesis in the 5x cytotype, and discussing the hypothesis regarding the possible origin of polyploid cytotypes (4x, 5x and 6x) in the species. The geographical distribution pattern of cytotypes in the Indian Himalayas and elsewhere has also been analyzed. The present meiotic analysis revealed three chromosomes counts, the tetraploid (2n?=?4x?=?56), the pentaploid (2n?=?5x?=?70) and the hexaploid (2n?=?6x?=?84) cytotypes based on x?=?14. Meiotic course was perfectly normal in the 4x and 6x cytotypes resulting into high pollen fertility (94–100 %). Meiotic course in the imbalanced 5x cytotype has been found to be irregular characterized by the presence of high frequency of univalents at diakinesis and metaphase-I. Abnormal meiotic course contributed towards high pollen sterility (74–88 %). Even the apparently fertile/stained pollen grains were of irregular shape and of heterogeneous sizes. Meiotic behaviour of the 5x cytotype is like typical of allopolyploid. Individuals of 5x cytotype did not produce seeds and propagate vegetatively (root suckers) while 4x and 6x cytotypes exploited sexual (seeds) as well as vegetative means for propagation. Chromosomal pairing in pentaploid cytotype is like typical of an allopolyploid and we assume that it might have originated owing to natural inter-cytotype hybridization between 4x and 6x cytotypes in a mixed population. Analysis of geographical distribution pattern of cytotypes shows that Indian Himalayas represent the most cytotype-diverse region for A. eupatoria with the existence of all the four cytotypes (2x, 4x, 5x, 6x). This shows the dynamic nature of the species at chromosomal level in this part of the world.     

Chromosomes in a hybrid zone of Israeli mole rars (Spalax, Rodentia)

Chromosomal novelties and the level of meiotic and mitotic abnormalities were studied in a hybrid zone between two chromosomally differentiated Spalax cytotypes of 2n = 58 and 2n = 52. These cytotypes differ by five Rb fusions, four centromeric shifts accompanied by heterochromatin deletion, one paracentric inversion, and the Y-chromosome reorganization. Among 149 specimens studied, 82 were hybrids with 64 different karyotypes ranging in diploid numbers from 2n = 50 to 2n = 60. Nine hybrid specimens were mosaics for the chromosome numbers due to occurrence of cell lines with different Robertsonian chromosome arrangements, and six specimens possessed variable number of B-chromosomes. Mosaicism of B-chromosomes was found also in meiotic cells however chromatid breaks and abnormal chromosome pairing during meiosis occurred very rarely. All these results imply some local genomic instability resulting in the spontaneous process of reversible Rb fusions.     

Ecological, morphological and allozymic differentiation between diploid and tetraploid knapweeds (Centaurea jacea) from a contact zone in the Belgian Ardennes

In the northeastern part of Belgium, the Centaurea jacea complex shows extensive morphological variation and is represented by a diploid (2 n = 22) and a tetraploid (2 n = 44) cytotype. Polysomic inheritance of allozyme markers in the tetraploids, suggesting autopolyploidy, is here demonstrated for the first time. In order to test whether the two cytotypes occupy distinct habitats and possess different gene pools, patterns of allozymic and morphological variation were investigated in relation to ploidy level and site characteristics in 26 populations from the Belgian Ardennes. The two cytotypes showed a parapatric distribution, the diploids occurring at higher elevations (mostly above 500 m) than the tetraploids (mostly below 500 m). Three mixed populations were found near the contact zone of the two cytotypes. Within the mixed populations no triploid plant and no evidence for gene flow between cytotypes were found, despite widely overlapping flowering periods. The two cytotypes can be distinguished on the basis of morphological traits and enzymatic gene pools. The congruence of morphological and allozymic variation with chromosome numbers suggests a secondary contact between the two cytotypes with limited gene flow between them. The origin and persistence of the parapatric distribution are discussed.     

Chromosomes in a hybrid zone of Israeli mole rars (Spalax, Radentia)

Chromosomal novelties and the level of meiotic and mitotic abnormalities were studied in a hybrid zone between two chromosomally differentiated Spalax cytotypes of 2n = 58 and 2n = 52. These cytotypes differ by five Rb fusions, four centromeric shifts accompanied by heterochromatin deletion, one paracentric inversion, and the Y-chromosome reorganization. Among 149 specimens studied, 82 were hybrids with 64 different karyotypes ranging in diploid numbers from 2n = 50 to 2n = 60. Nine hybrid specimens were mosaics for the chromosome numbers due to occurrence of cell lines with different Robertsonian chromosome arrangements, and six specimens possessed variable number of B-chromosomes. Mosaicism of B-chromosomes was found also in meiotic cells however chromatid breaks and abnormal chromosome pairing during meiosis occurred very rarely. All these results imply some local genomic instability resulting in the spontaneous process of reversible Rb fusions.     

Genetic diversity among Korean bermudagrass (Cynodon spp.) ecotypes characterized by morphological, cytological and molecular approaches

The genus Cynodon comprises ten species. The objective of this study was to evaluate the genetic diversity of Korean bermudagrasses at the morphological, cytological and molecular levels. Morphological parameters, the nuclear DNA content and ploidy levels were observed in 43 bermudagrass ecotypes. AFLP markers were evaluated to define the genetic diversity, and chromosome counts were made to confirm the inferred cytotypes. Nuclear DNA contents were in the ranges 1.42-1.56, 1.94-2.19, 2.54, and 2.77-2.85 pg/2C for the triploid, tetraploid, pentaploid, and hexaploid accessions, respectively. The inferred cytotypes were triploid (2n = 3x = 27), tetraploid (2n = 4x = 36), pentaploid (2n = 5x = 45), and hexaploid (2n = 6x = 54), but the majority of the collections were tetraploid (81%). Mitotic chromosome counts verified the corresponding ploidy levels. The fast growing fine-textured ecotypes had lower ploidy levels, while the pentaploids and hexaploids were coarse types. The genetic similarity ranged from 0.42 to 0.94 with an average of 0.64. UPGMA cluster analysis and principle coordinate analysis separated the ecotypes into 6 distinct groups. The genetic similarity suggests natural hybridization between the different cytotypes, which could be useful resources for future breeding and genetic studies.     

Geographical distribution of Allium oleraceum cytotypes in Finland and Sweden

Chromosome numbers from a total number of 226 populations of Allium oleraceum were determined in Finland, Sweden and seven other countries. Two different chromosome numbers or cytotypes were found, tetraploids (2n = 32) and pentaploids (2n = 40). In Finland, samples were collected for chromosome counts from a total of 190 populations, which fairly well covers the distribution area of the species in Finland. The majority of the populations of A. oleraceum in Finland contained only one of the two cytotypes. A clear pattern in the geographical distribution of the cytotypes could be distinguished. The pentaploid cytotype predominates in the Åland Islands and in the archipelago of Regio aboënsis. The tetraploid cytotype predominates on the mainland of the Regio aboënsis and along the coast of the Nylandia. In south Häme, all studied native populations were of the tetraploid cytotype. Of all the studied populations in Finland 43.7% were tetraploid and 51.6% pentaploid. A few mixed populations with both tetraploid and pentaploid plants occurring in the same population were also found (4.7%). The chromosome numbers of 19 populations of A. oleraceum from the southern part of Sweden were pentaploids, with the exception of one tetraploid population. It seems that the pentaploid cytotype is predominant in Sweden, but no conclusions about a geographical pattern between the two cytotypes could be drawn. Based on the occurrence of the cytotypes, it is suggested that the pentaploid cytotype might have spread to Finland from the Swedish east coast via the Åland Islands to Kaland on the Finnish west coast and along the coast of Nyland to the archipelagos of Kotka and Hamina in Karelia australis. The tetraploid populations in south Häme are clearly connected to Iron Age activity and to old inland trade routes, and may be of eastern origin.     

Cytogenetics and karyosystematics of South American oryzomyine rodents (Cricetidae: Sigmodontinae). IV. Karyotypes of Venezuelan, Trinidadian, and Argentinian water rats of the genus Nectomys.

Bone marrow chromosomes were studied in South American water rats of the genus Nectomys from Venezuela, Trinidad, and Argentina. Specimens of N. squamipes from western and southern Venezuela showed a 2n = 52-53 karyotype, whereas a 2n = 56-57 karyotype was found in specimens from northeastern Argentina. In both cases, odd karyotypes can be explained by the presence of a supernumerary chromosome. In contrast, water rats from northeastern Venezuela and Trinidad showed a strikingly reduced 2n = 16-17 polymorphic chromosome complement. Six different karyomorphs were found among the latter, which may have resulted from a combination of pericentric inversions in two pairs of autosomes and a centromeric fusion in another autosomal pair. It is proposed that the new 2n = 16-17 cytotypes belong to a species of its own, for which the name N. palmipes is suggested.     

Activation of the anaphase-promoting complex and degradation of cyclin B is not required for progression from Meiosis I to II in Xenopus oocytes.

Sister chromatid separation and cyclin degradation in mitosis depend on the association of the anaphase-promoting complex (APC) with the Fizzy protein (Cdc20), leading to the metaphase/anaphase transition and exit from mitosis [1--3]. In Xenopus, after metaphase of the first meiotic division, only partial cyclin degradation occurs, and chromosome segregation during anaphase I proceeds without sister chromatid separation [4--7]. We investigated the role of xFizzy during meiosis using an antisense depletion approach. xFizzy accumulates to high levels in Meiosis I, and injection of antisense oligonucleotides to xFizzy blocks nearly all APC-mediated cyclin B degradation and Cdc2/cyclin B (MPF) inactivation between Meiosis I and II. However, even without APC activation, xFizzy-ablated oocytes progress to Meiosis II as shown by cyclin E synthesis, further accumulation of cyclin B, and evolution of the metaphase I spindle to a metaphase II spindle via a disc-shaped aggregate of microtubules known to follow anaphase I [8]. Inhibition of the MAPK pathway by U0126 in antisense-injected oocytes prevents cyclin B accumulation beyond the level that is present at metaphase I. Full synthesis and accumulation can be restored in the presence of U0126 by the expression of a constitutively active form of the MAPK target, p90(Rsk). Thus, p90(Rsk) is sufficient not only to partially inhibit APC activity [7], but also to stimulate cyclin B synthesis in Meiosis II.     

Cytotypes of Kirk's dik-dik (Madoqua kirkii,Bovidae) show multiple tandem fusions

Madoqua kirkii, a miniature African antelope, is noted for extensive chromosomal variation that has been categorized in four distinct cytotypes (A-D). In this investigation, we analyzed the A cytotype (2n = 46, FN = 48) using a suite of molecular cytogenetic approaches that entailed (i) whole chromosome and subchromosomal painting by fluorescence in situ hybridization (FISH), (ii) the study of Madoqua centromeric-specific DNA derived from pooled DNA obtained from the centromeric regions of the acrocentric chromosomes, and (iii) DNA from the telomere:centromere junctions of tandemly fused chromosomes. DNA from these sources was used to probe for the persistence of interstitial satellite DNA and residual centromeric sequences in the tandem and centric fusion junctions by PCR and FISH. The analyses show centromeric sequences at two of the six tandem fusion junctions. These data, and those of hybrid specimens (A × B cytotypes) in conjunction with published information permitted an interpretation of the probable sequence of chromosomal rearrangements among the M. kirkii cytotypes. We discuss the findings in the context of chromosomal evolution in these antelopes, and the implications that these hold for ex-situ breeding programs of the species.     

Cytogenetic analysis of the tamaraw (Bubalus mindorensis): a comparison of R-banded karyotype and chromosomal distribution of centromeric satellite DNAs, telomeric sequence, and 18S-28S rRNA genes with domestic water buffaloes

The karyotype of the tamaraw (Bubalus mindorensis, 2n = 46) was investigated by RBG-banding technique and compared with those of the river and the swamp cytotypes of domestic water buffalo (B. bubalis). The tamaraw karyotype consisted of 6 submetacentric and 16 acrocentric autosome pairs (NAA = 56), and X and Y chromosomes. The RBG-banded karyotype of the three taxa had a high degree of homology, and the tamaraw karyotype could be explained by a Robertsonian translocation between chromosomes 7 and 15 and by a telomere-centromere tandem fusion between chromosomes 4p and 12 of the standardized river buffalo cytotype (2n = 50, NAA = 58). The buffalo satellite I and II DNAs were localized to the centromeric regions of all the tamaraw chromosomes. The biarmed chromosome 2 of the tamaraw resulting from the fusion between chromosomes 7 and 15 of the standard contained much larger amounts of the satellite I DNA than the other biarmed chromosomes, suggesting that this chromosome was formed by a relatively recent Robertsonian fusion. The (TTAGGG)n telomeric sequence was specifically localized to the telomeric region of all the buffalo chromosomes. The 18S + 28S rDNA was localized to the telomeric regions of the chromosomes 5p, 7, 19, 21, and 22 of the tamaraw and of their homologous chromosomes in the river and swamp buffalo cytotypes.     

Cytogeography of the South American Turnera sidoides L. complex (Turneraceae, Leiocarpae)

New chromosome number determinations are presented for 48 populations of five subspecies of Turnera sidoides. Chromosome counts in sspp. carnea, holosericea, integrifolia and sidoides confirm previous data while, in ssp. pinnatifida , the numbers 2n=2x = 14 and 2n = 6x = 42 are reported for the first time. The results show that polyploidy is a very frequent phenomenon. Populations are primarily tetraploids (2n = 4x = 28), while diploids (2n = 2x = 14), hexaploids (2n = 6x =42) and octoploids (2rc = 8x = 56) are less frequent. Diploid, tetraploid and hexaploid cytotypes occur in sspp. carnea and pinnatifida , whereas tetraploids and hexaploids are known in ssp. holosericea. Turnera sidoides ssp. integrifolia shows a polyploid series with ploidy levels from 2x to 8x. The ssp. sidoides appears to be uniformly tetraploid, with the exception of an isolated pentaploid (2rc = 5x = 35). On the basis of these counts and previous reports the geographical distribution of the cytotypes has been determined and related to climatic and ecological factors.     

Studies on the Asian Eupatorias

Analysis of 265 plants derived from 13 sites in the Rokko Mountains shows that the widely distributed eastern AsianEupatorium chinense var.simplicifolium consists of seven cytotypes. These polymorphic karyotypes comprise four levels of ploidy based on X=10 and partial deficiency, occurring either alone or in combination. The polyploid cytotypes exhibit anomalous meiosis and highly variable pollen stainability in contrast to the nearly-normal behaviour of the diploid. The polyploid cytotypes were revealed as being agamospermous. They are readily distinguishable from the diploid cytotypes by several morphological characters and by growth habits closely related to their respective niches. Two or more cytotypes occurred in all sites examined, the most common being the coexistence of triploid and tetraploid cytotypes. The frequencies of occurrence of the pentaploid plants and the cytotypes involving a deficient chromosome were relatively low. While the diploid cytotype is restricted to fragile gravitational slopes and rocky areas which are poor in species and lack tall competitors, the polyploids occur widely in the grasslands, the roadsides or the forest-margins, closely associated with tall grasses and forbs such asMiscanthus sinensis. Based on these data, theE. chinense var.simplicifolium complex is divided into two distinct groups: the diploid cytotype and the polyploid cytotypes.     

Cytotaxonomy and geographic distribution of cytotypes of species of the South American genus Chrysolaena (Vernonieae,Asteraceae)

Understanding speciation and biodiversity patterns in plants requires knowledge of the general role of climate in allowing polyploids to escape competition and persist with their diploid progenitors. This is a particularly interesting issue in widespread species that present multiple ploidy levels and occur across a heterogeneous environment. Chrysolaena (Vernonieae, Asteraceae) is a cytogenetically very diverse genus, with significant interspecific and intraspecific ploidy level variation and with continuous distribution across South America. No previous studies have summarized chromosome count data of Chrysolaena or addressed the cytogeography of the genus. Ploidy level of Chrysolaena species was determined by chromosome counting during mitosis and/or meiosis; the geographic distribution of cytotypes was examined and the correlations between the distribution of particular cytotypes and current ecological conditions were evaluated. A total of 43 new chromosome counts and five ploidy levels (2x, 4x, 6x, 7x, 8x) were reported. The chromosome number of C. cordifolia (2n = 7x = 70) and a new cytotype for C. propinqua var. canescens (2n = 4x = 40) are reported for the first time. Three geographic areas with high diversity of cytotypes and species were detected. The results obtained do not suggest a clear distribution pattern that depends on climatic factors for Chrysolaena populations. However, a geographic pattern was identified in the distribution of ploidy levels, with diploid species presenting a more restricted distribution than polyploid species.     

Occurrence of two cytotypes in <Emphasis Type="Italic">Bryconamericus</Emphasis> aff. <Emphasis Type="Italic">iheringii</Emphasis> (Characidae): karyotype analysis by C- and G-banding and replication bands

Cytogenetic analyses of Bryconamericus aff. iheringii specimens from the upper Paraná River basin (State of Paraná, Brazil) are provided. They had 2n = 52 chromosomes and two cytotypes with variations in their karyotypic formulae: cytotype I with 12 metacentric, 18 submetacentric, 8 subtelocentric and 14 acrocentric chromosomes with a fundamental number (FN) of 90; cytotype II with 8 metacentric, 28 submetacentric, 6 subtelocentric and 10 acrocentric chromosomes with a fundamental number (FN) of 94. Differences in C- and G-band patterns between the cytotypes, distinguishing marker chromosomes for each karyotype, were reported. The R-band pattern by 5-bromodeoxyuridine incorporation was obtained in chromosomes of the cytotype II sample. In some metaphases, the second pair of submetacentric chromosomes is distinctive: its short arm is heterochromatic (positive C-band), corresponding to a late replication region. In the same cytotype, a G- and R-band size heteromorphism w as recorded in the long arm of pair 9 (submetacentric). These methodologies revealed an actual karyotypic differentiation in the B. aff. iheringii population analyzed. Morphometrical comparative analyses and a discussion of evolutionary aspects of chromosome diversification in species of this genus are provided as well.