Genetic system relationships inTrifolium

Examination of species of Trifolium in the Kentucky collection revealed that annual species generally have simple tap roots, low chromosome numbers (2n = 10?32), are usually self-pollinating and many were introduced from a Mediterranean type climate. Perennial species generally are tap-rooted, stoloniferous, or rhizomatous, possess higher chromosome numbers than annuals (2n = 12? 130), are mostly cross-pollinating and do not have specific climate-habitat relationships. Species introduced from Eurasia are more numerous and more diverse in base chromosome number (n = 5?8) than from other origins. Only species with diploid chromosome numbers of 16 or higher are stoloniferous or rhizomatous. Rhizomatous species, mostly cross-pollinated, were introduced from Eurasia, North and South America, but not from Africa, and not often from Mediterranean climates. Self- and cross-pollinated species occur in all origins. Different flower colors and leafmarks are not associated with origins, climates, and other morphological and physiological characteristics.     

Physical localization of rRNA genes by fluorescence in situ hybridization (FISH) and analysis of spacer length variants of 45S rRNA (slvs) genes in some species of genus Sesbania

The somatic chromosome numbers 2n = 12 in S. macrantha, S. coerulescens and 2n = 24 in S. simplicuscula were determined, additionally the contradictory chromosome numbers of S. bispinosa (2n = 12, 13, 14, 24) and S. pachycarpa (2n 12, 14) were determined as 2n = 24 and 2n = 14, respectively. The number of 5S rDNA sites in chromosome pair 1 was highly conserved in all the diploid and tetraploid species studied irrespective of their geographic distribution, suggesting that all diploid and tetraploid species/cytotypes of Sesbania analyzed in the present study are in close proximity. Cytogenetic mapping of the 45S multi-gene family was also carried out using fluorescence in situ hybridization. 45S rDNA was consistently located on short or long arms of two sub-metacentric chromosome pairs except on one chromosome pair in S. macrantha and on three chromosome pairs in S. bispinosa and S. cannabina. Out of these nine species, we observed the homogenization of intergenic spacer in six species and find only one spacer length variant (slv) located on one to three chromosome loci. However, three of the species were observed to have two slvs located on two different chromosomes. The species were grouped as per their evolutionary relationship on the basis of the results of the present study.     

Intranuclear destruction of heterochromatin in two species of armored scale insects

Spermatogenesis is described in two species of armored scale insects,Parlatoria proteus andParlatoria ziziphus. In the males of both species, a haploid set of four chromosomes becomes heterochromatic during early embryogeny. The heterochromatic chromosomes are lost later by two different mechanisms during spermatogenesis. Just before meiosis begins one or more heterochromatic chromosomes disappear from each primary spermatocyte as a consequence of a rapid intranuclear chromosome destruction. Meiosis consists of a single achiasmatic division. At prophase four euchromatic and from one to three heterochromatic chromosomes are present in each cell. Although both the euchromatic and remaining heterochromatic chromosomes divide, the heterochromatic chromosomes are later eliminated by posttelophase ejection; the eliminated chromosomes then disintegrate slowly in the cytoplasm. Each of the two species displays a species specific level of heterochromatin retention and both differ in this regard from the previously describedParlatoria oleae. The evolution of a chromosome system involving intranuclear chromosome destruction is discussed.     

Maximum likelihood inference implies a high, not a low, ancestral haploid chromosome number in Araceae, with a critique of the bias introduced by 'x'

Background and Aims

For 84 years, botanists have relied on calculating the highest common factor for series of haploid chromosome numbers to arrive at a so-called basic number, x. This was done without consistent (reproducible) reference to species relationships and frequencies of different numbers in a clade. Likelihood models that treat polyploidy, chromosome fusion and fission as events with particular probabilities now allow reconstruction of ancestral chromosome numbers in an explicit framework. We have used a modelling approach to reconstruct chromosome number change in the large monocot family Araceae and to test earlier hypotheses about basic numbers in the family.

Methods

Using a maximum likelihood approach and chromosome counts for 26 % of the 3300 species of Araceae and representative numbers for each of the other 13 families of Alismatales, polyploidization events and single chromosome changes were inferred on a genus-level phylogenetic tree for 113 of the 117 genera of Araceae.

Key Results

The previously inferred basic numbers x = 14 and x = 7 are rejected. Instead, maximum likelihood optimization revealed an ancestral haploid chromosome number of n = 16, Bayesian inference of n = 18. Chromosome fusion (loss) is the predominant inferred event, whereas polyploidization events occurred less frequently and mainly towards the tips of the tree.

Conclusions

The bias towards low basic numbers (x) introduced by the algebraic approach to inferring chromosome number changes, prevalent among botanists, may have contributed to an unrealistic picture of ancestral chromosome numbers in many plant clades. The availability of robust quantitative methods for reconstructing ancestral chromosome numbers on molecular phylogenetic trees (with or without branch length information), with confidence statistics, makes the calculation of x an obsolete approach, at least when applied to large clades.     

Chromosomes ofLauxaniidae andChamaemyiidae (Diptera)

Chromosome numbers of 28 species ofLauxaniidae range from 2n=8 to 2n=12 with one having 2n=8, three having 2n=10 and 24 having 2n=12. Total complement length averaged 58.1 μ for 71 complements measured. The species studied in detail are classified according to chromosome number and morphology. The two Chamaemyiid species studied have 2n=6 and 2n=15, the latter including several microchromosomes. The karyotypical reorganizations have clearly involved inversions and translocations and a progressive reduction of chromosome numbers.     

Polyploidy in Ambrosia dumosa (Compositae: Ambrosieae)

Ambrosia dumosa (A. Gray ex Torr.) Payne is one of the most abundant shrubs of the Sonoran Desert. Allopatric and sympatric populations of this species frequently exhibit distinctive morphological features, particularly with regard to leaf-segment width, but also in blooming time and ecology. Chromosome numbers ofn = 18, 36, and 54 were frequently encountered in our preliminary investigations ofA. dumosa. Fifty-six chromosome number determinations have now accumulated for this taxon, and these additional counts confirm the existence of three major chromosome races withinA. dumosa. Diploids generally occur throughout the range of the species; hexaploids tend to be confined to the deserts of California; and tetraploids occur through most of the range of the species, with the exception of southern Baja California and Owens Valley, California. External morphology was found to be correlated with chromosome number only locally, but even in many local areas, morphological intergradation occurs between different chromosome races. It is therefore considered impractical to attempt a formal taxonomy which would recognize these chromosomal races.     

Chromosome numbers in some cacti Of western North America—II

Documented chromosome numbers and meiotic behavior are recorded for an additional 30 taxa representing 25 species of Cactaceae of southwestern United States and northern Mexico. Diploid and polyploid taxa including two triploids were observed, all of which indicate the same base number,x = 11. Trisomism and inversions are reported for the first time in cacti.     

Reproductive relationships between annual species ofCalendula (Compositae)

Breeding experiments were carried out inCalendula species. In the annuals, which are selfers, rarely some outcrossing was observed only in the most peripheral flowers. In experimental crosses fruit was produced in all combinations. Fertile F₁ and F₂ hybrids could be grown from crosses between parents with similar chromosome numbers:C. palaestina ×C. pachysperma and crosses of different morphological forms ofC. arvensis. In crosses of species with different chromosome numbers at least partly fertile F₁ hybrids were obtained fromC. tripterocarpa ×C. stellata andC. tripterocarpa ×C. arvensis and crosses of the latter withC. palaestina. Fertile F₂ plants were grown from the combination ofC. arvensis ×C. tripterocarpa. Considering this information and previously obtained data, a scheme is proposed for explaining speciation in the genusCalendula.     

Cytogenetic mapping of the Muller F element genes in Drosophila willistoni group

Comparative genomics in Drosophila began in 1940, when Muller stated that the ancestral haploid karyotype of this genus is constituted by five acrocentric chromosomes and one dot chromosome, named A to F elements. In some species of the willistoni group such as Drosophila willistoni and D. insularis, the F element, instead of a dot chromosome, has been incorporated into the E element, forming chromosome III (E + F fusion). The aim of this study was to investigate the scope of the E + F fusion in the willistoni group, evaluating six other species. Fluorescent in situ hybridization was used to locate two genes of the F element previously studied—cubitus interruptus (ci) and eyeless (ey)—in species of the willistoni and bocainensis subgroups. Moreover, polytene chromosome photomaps corresponding to the F element (basal portion of chromosome III) were constructed for each species studied. In D. willistoni, D. paulistorum and D. equinoxialis, the ci gene was located in subSectction 78B and the ey gene in 78C. In D. tropicalis, ci was located in subSection 76B and ey in 76C. In species of the bocainensis subgroup, ci and ey were localized, respectively, at subsections 76B and 76C in D. nebulosa and D. capricorni, and 76A and 76C in D. fumipennis. Despite the differences in the subsection numbers, all species showed the same position for ci and ey. The results confirm the synteny of E + F fusion in willistoni and bocainensis subgroups, and allow estimating the occurrence of this event at 15 Mya, at least.     

Cytogenetics of ticks (Acari: Ixodoidea)

Chromosomes and sex determination of 9 species of Haemaphysalis assigned to 4 subgenera are described. H. (tAlloceraea) kitaokai possesses an XX∶XO sex chromosome system with 18 autosomes plus XX in females; 18 plus X in males. H. (Kaiseriana) hystricis has 18 +XX and 18 + XY in females and males, respectively, in most specimens, but a supernumerary chromosome is present in some individuals. A supernumerary chromosome was also observed in 1 male H. (Aborphysalis) formosensis. These two species are the second and third species of ticks reported to have supernumerary chromosomes. H. formosensis, H. (Kaiseriana) bispinosa, H. (Haemaphysalis) campanulata, H. (H.) flava, H. (H.) megaspinosa, H. (H.) japonica, and H. (H.) pentalagi possess 20 autosomes plus 2 sex chromosomes in females and 20+1 sex chromosomes in males. Phylogenetic relationships within the genus Haemaphysalis are briefly discussed.     

Chromosomal instabilities in callus tissue from haploid barley (Hordeum vulgare L.)

Callus culture was derived from haploid barley embryos after crossing withHordeum bulbosum. The callus tissue is cytologically heterogeneous, containing haploid, diploid and polyploid cells. Aneuploidy and karyokinetic irregularities were also observed. Some problems of chromosomal instabilities in plant tissue cultures are discussed.     

The karyograms of some Falconiformes and Strigiformes

The chromosome complements of cultured cells of the Falconidae are characterized by their low values: 2n=52 in Falco tinnunculus. 2n=68 in Buteo buteo, 64 in an unknown species (Accipiter nisus ?). The Strigidae have high chromosome numbers: 82 in Strix aluco and Athene noctua, 92 in Tyto alba. In some species the boundary between macro- and microchromosomes is obsolete and in Tyto alba all the chromosome pairs but one are acrocentric. — In all birds examined the female heterogametic sex has two heterochromosomes ZW. In two cases the Z is the fourth or fifth largest as in other birds, in three cases it is the biggest, but the percentual ratio between the length of the Z and that of the haploid set is rather constant. — In the subclass Carinatae. the distribution of the haploid number frequencies is not normal. It is postulated that there are some factors limiting the random scattering of the values.     

Cytological studies on three species of neotropical cassidines (Coleoptera,Chrysomelidae)

Chromosome numbers, meiosis and sex-determining mechanisms of three species of Chrysomelidae (Coleoptera) were studied. They belong to the tribe Stolaini of Neotropical Cassidinae. Stolas lacordairei and Botanochara sp. have high chromosome numbers (2n=30♂), the first with a primitive coleopteran sex chromosome system Xy _p and the other with a very complex one X _p ¹ X _p ² neo Xneo Y. Botanochara bonariensis shows an even higher chromosome number (2n=44♂) and multiple sex chromosomes as does B. sp. The possible tendencies in the karyological evolution of the Stolaine Cassidines are discussed.     

Sequence diversity of polysomal mRNAs in roots and shoots of etiolated and greened pea seedlings

The sequence complexity and abundance of polysomal mRNA populations of pea seedlings were measured using RNA excess hybridization to both single-copy DNA and complementary DNA. The estimated sequence complexity of the polysomal mRNA populations was 2.5·10⁷ nucleotides or 19,400 different mRNAs of average size. Since the haploid genome size of pea was found to be 4.0·10⁹ nucleotide pairs, only 0.62% of the total haploid genome of pea was transcribed into polysomal mRNA. The roots and shoots of 4-d etiolated and light-grown seedlings contained similar numbers of diverse mRNAs. The RNA excess hybridizations, using single-copy DNA enriched for sequences transcribed in either light-grown shoots or etiolated roots and single-copy DNA depleted of such sequences, indicated that at least 92% of the sequence complexity of polysomal mRNAs was identical in roots and shoots irrespective of the presence of a functional photosynthetic system. In contrast, RNA excess hybridization to complementary DNA revealed that 21% of the polysomal polyadenylated mRNA mass found in light-grown shoots was absent in etiolated roots. The kinetics of these hybridizations indicated that this was due to the appearance of a limited number of abundant mRNAs under conditions of illumination.     

Cytotaxonomy ofCalliphoridae (Diptera)

A modification of the general system of classification ofCalliphoridae is proposed in this report. Information about the chromosome complements of about 90 species is provided including references to the earlier literature on chromosomes of this family. With one exception all species studied by us or by earlier investigators have 2n=12. The total complement length of 556 complements from 83 species averaged 66.4 μ. Most species have a short heteromorphic sex pair but the size and morphology vary considerably and one species,Hemipyrellia fernandica, seems to have a quadrivalent sex-chromosome complex in a 2n=14 complement. The autosomal pairs vary in both length and arm ratios between the species but seem to be more stable than the sex chromosomes. Only minor variations were found between different collections of the same species except for two collections ofCalliphora croceipalpis. Although presently available data on the chromosomes of Diptera species suggest that increases in total complement length accompany evolutionary progress, no such general trends were obvious in either the total complement lengths or chromosome morphology, either within or between the tribes ofCalliphoridae. Thus the karyotypical reorganizations in the family have apparently not been directly associated with changes in the general morphological features of the adults which may have responded in these respects more extensively to genetic mutations.     

Plant and animal communities in brackish supra-littoral pools (‘dobben’) in the northern part of the Netherlands

Fifty brackish supra-littoral pools bordering the Waddenzee were studied. The structure of plant communities (Potamogeton pectinatus L., Ranunculus baudotii Godr. and Zannichellia pedunculata Rchb.) is discussed in relation to water level fluctuations, chlorinity and water transparency. Chlorinity tolerances of the macrophytes (7 species) are discussed. The macrofauna was studied semi-quantitatively. The aquatic Coleoptera had the greatest diversity (24 species). A distinct relationship between the number of Coleoptera species and the percentage of macrophyte coverage was found. The distribution patterns of the most frequent species with respect to chlorinity categories are shown in histograms. The number of aquatic Heteroptera species is also discussed in relation to chlorinity and vegetation coverage. Less important macrofaunal groups (the Crustacea, Mollusca and Odonata) occurred in low species numbers.     

Recent advances in anther culture of Hevea brasiliensis (Muell.-Arg.)

Summary The yield of pollen embryoids from cultured Hevea anthers was increased 4 fold by optimizing the proportion of ammonium nitrate to potassium nitrate in the dedifferentiation medium. For optimal differentiation of pollen embryoids, kinetin, 2,4-D and -naphtalene acetic acid are required. Anther culture for 50 days on the dedifferentiation medium is a prerequisite for the selective development of calli and embryoids from microspores.The determination of chromosome numbers in embryoids, plantlets and regenerated trees reveals that they originate from (poly)haploid pollen grains (n=2x=18). Aneuploid, triploid (3x=27) and tetraploid (4x=36) cells were encountered in increasing frequencies as the embryoids and plants developed. A few haploid cells with 9 chromosomes were consistently observed. Buds from shoots with mixoploid chromosome numbers can be grafted and the change in the chromosome constitution of the developing new shoots followed.