Stable karyotypes: a general rule for the fish of the family Prochilodontidae?

Cytogenetic studies involving the family Prochilodontidae have shown that these fish can be characterized by a constant diploid number and a conserved karyotypic macrostructure. This study focused on comparative physical chromosomal mapping using 18S and 5S rDNA to compare the species Semaprochilodus insignis and S. taeniurus. Our results indicated the conservation of large number of conventional chromosomal markers. The molecular cytogenetic analyses of the location of the 18S rDNA indicated the maintenance of a chromosome pair bearing these sites in both species analyzed, and it appears to be a conserved character among the majority of the species of this family. The stability of the number of 5S ribosomal DNA sites and their chromosomal localization as has been reported for the Prochilodontidae was not, however, confirmed for S. insignis and S. taeniurus, as these species showed multiple specific rDNA 5S sites. As such, and in spite of the fact that a number of studies indicate that the family Prochilodontidae has a conserved karyotypic structure, the utilization of molecular tools that use chromosomal segments as markers revealed that this presumed stability cannot be extended to the genome level for the species S. insignis and S. taeniurus.     

Karyotypic evolution and phylogeny of Mexican Passalidae (Coleoptera: Polyphaga: Scarabaeoidea)

The chromosomes of 26 taxa from Mexico of the tribes Passalini (three species) and Proculini (23 species) have been studied, increasing the karyotypically known species of the family Passalidae to 56. Karyotypic dynamism is high since the diploid number varies from 18 to 44 in the tribe Proculini. and from 25 to 31 in the tribe Passalini. In addition, supernumerary chromosomes, chromosome heteromorphism, translocations and possible sex multivalents have been found. These results contrast with the numerical conservatism found in related families of the superfamily Scarabaeoidea. However, both tribes are conservative with regard to sex determination, as all species of Proculini have male XY chromosomes whereas species of the Passalini have male XO chromosomes. It is postulated that differences in patterns shown by these two tribes are mainly due to population structure, because many species of Proculini are endemic to restricted areas of Meso and South America, favouring the settlement of karyotypic changes, whereas species of Passalini are distributed over large areas in the lowlands. It is also postulated that the ancestral karyotypic formula of the family is close to 12–14 pairs of autosomes although the ancestral male sex determination may be either XY or XO. At present only a weak relationship between morphological and karyotypic evolution has been found, which together with the marked numerical variability found within and between genera make it difficult to obtain phylogenetic conclusions from karyotypic results.     

A simple parameter of dispersion index that serves as an adjunct to karyotype asymmetry

In order to refine the measure of karyotype asymmetry a new chromosomal parameter of dispersion index is proposed that has the potential to decipher even the minor karyotypic variations, thus permitting further evolutionary gradations to the karyotype asymmetry classes of Stebbins. The higher the dispersion index, the more specialized would be the karyotype. The dispersion index takes into account the variance lor gradual change in chromosome size within a complementvis-a-vis variance for the position of centromere in a karyotypic totality. The dispersion index is calculated as the proportionate measure of centromeric gradient to the coefficient of variation for chromosome length; wherin centromeric gradient = length of median short arm — length of median chromosome. Thus, the three most important karyotypic criteriaviz., differences in: absolute chromosome size, position of centromere and relative chromosome size, are all covered in the proposed parameter. The effectiveness of dispersion index has been tested on a plant taxa,Papaver L., where karyomorphological details, nuclear DNA content, and morphotaxonomic parameters have been amply elucidated from an evolutionary stand point. It is hoped that dispersion index would find immense utility in delimiting species interrelationships particularly in the closely related taxa, when applied in conjunction with other systematic parameters.     

Karyotypes of parasitic Hymenoptera: Diversity, evolution and taxonomic significance

Haploid chromosome numbers (n) of parasitic Hymenoptera (= traditional Parasitica + Chrysidoidea) vary from 2 to 23. However, this range can be subdivided into three intervals with n= 14–23 (less derived parasitic wasps, e.g., some Ichneumonidae and Braconidae as well as Gasteruptiidae), 8–13 (many other parasitic Hymenoptera) and 2–7 (Dryinidae, the majority of Chalcidoidea and some advanced Braconidae, e.g. Aphidiinae). The symmetric karyotype with a relatively high chromosome number (n= 14–17) and the prevalence of biarmed chromosomes must be considered as a groundplan feature of parasitic Hymenoptera. Independent reductions of chromosome numbers (n≤ 10–11) occurred in some groups of the superfamily Ichneumonoidea as well as in the common ancestor of the Proctotrupoidea sensu lato, Ceraphronoidea, Cynipoidea and Chalcidoidea. Further multiple decreases in chromosome numbers (n≤ 4–6) took place in some Braconidae, various lineages of the superfamily Chalcidoidea as well as in the family Dryinidae. Two main trends prevailed in the karyotype evolution of parasitic wasps: the reduction of chromosome numbers (mainly due to tandem fusions and less frequently due to centric ones) and karyotypic dissymmetrization (through an increase in size differentiation of chromosomes and/or in the share of acrocentrics in a chromosome set). Although karyotypic features of parasitic Hymenoptera can be used for solving taxonomic problems at various levels, this method is the most effective at the species level.     

THE CYTO-ECOLOGY OF FOUR SPECIES OF TRILLIUM FROM WESTERN NORTH CAROLINA

The major center of variability in the genus Trillium occurs in the southern Appalachian mountains of the eastern United States. The karyotypic variation existing within T. cuneatum Raf., T. grandiflorum (Michx.) Salisb., T. erectum L., and T. gleasoni Fern., the four most abundant Trillium species in western North Carolina, was analyzed and compared with the variation in gross morphology and the ecological associations of the respective species. The number of types of each kind of chromosome (A-E), as exhibited following “nucleic acid starvation” by cold treatment, varied widely from species to species. Chromosome types varied within each species and within populations in the numbers, sizes, and positions of euchromatic and heterochromatic segments. No 10-chromosome karyotype and only one 5-chromosome complement was found to be duplicated in any two plants which belonged to different species. Trillium cuneatum with eight chromosome types was morphologically stable and occurred in a limited geographic area. Trillium gleasoni, characteristically adapted to elevations near 2,000 feet, contained 32 chromosome types and exhibited a high morphological variability. Trillium erectum (25 types) and T. grandiflorum (23 types) were also intermediate in morphological variability. These two species had the widest geographical range. Karyotypes were analyzed from pure stands of each of the four species and for each species from mixed stands of two or more of the species growing in close association. These Trillium species are maintaining a high level of karyotypic and gross morphological variability within comparatively limited geographical areas. None of the observed karyotypes in any species is likely to have arisen by recent interspecific hybridization. The composite karyotype of each species could be used as an aid to classification in the genus Trillium.     

Redescription of the karyotype of five species of the family Bufonidae (Amphibia: Anura) from central area of Argentina

In this study karyotypic features of the five species of the family Bufonidae from the central area of Argentina are described. The species are Rhinella achalensis, Rhinella arenarum, Rhinella fernandezae, Rhinella schneideri and Melanophryniscus stelzneri. The metaphases were obtained from intestinal and testis cells, using conventional techniques. Twenty metaphasic figures per individual were analyzed and the total length of each chromosome and the length of the four arms were measured. The obtained measurements were processed using Excel 2000 to obtain the average length of the arms p and q, the arm ratio, the centromeric index, the relative chromosome length and the relative arm length. All species showed karyotype 2n = 22, and karyotype formula of 6: 5. Pairs one to six were large, with a relative chromosome length between 18.64–7.59%; pairs seven to eleven were small, with a relative chromosome length between 7.18–2.42%. In all species the chromosome morphology was metacentric or submetacentric. Karyotype and ideograms were made for all species, based on morphometric parameters of the chromosome complement. Finally, discriminant analysis was used to separate the five species analyzed, with a highly significant classification rate of 80% and P < 0.0001. These results agree, in general, with those presented by other authors, however, in M. stelzneri detailed karyological studied have not been made so far, thus this work represents a significant contribution to the karyotypic decryption features of this species and the Rhinellla species from central area of Argentina.     

Genome size evolution in Sapindaceae at subfamily level: a case study of independence in relation to karyological and palynological traits

Sapindaceae s.l. is a moderately large family of trees, shrubs and lianas. Current knowledge on genome size and how it varies in this family is scarce. This research aims to characterize the DNA content in 39 species of Sapindaceae, mainly in tribe Paullinieae s.s., by the analysis of the variation in genome size relative to karyotypic and palynological features. Nuclear DNA amount was measured by flow cytometry, and linear regression analyses were conducted to analyse the relationship between genome size variation and various karyotypic and palynological features. Genome size varied nine‐fold among species, ranging from 1C = 0.305 pg (Lophostigma plumosum) to 2.710 pg (Cardiospermum heringeri). The low regression coefficients obtained suggest that genome size mainly varies independently of karyotypic and palynological features. With regard to karyotype evolution, the constant chromosome number but variable genome size in Houssayanthus, Paullinia and Serjania suggest that structural changes mainly caused by changes in the amounts of repetitive DNA are more important than numerical change. In contrast, in Cardiospermum and Urvillea, variation in chromosome number and genome size supports the suggestion that numerical and structural changes are important in the karyotype evolution of these genera. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174 , 589–600.     

A cytological study ofPelargonium sect.Eumorpha (Geraniaceae)

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

Differentiated evolutionary pathways in Haemulidae (Perciformes): karyotype stasis versus morphological differentiation

Extensive phenotypic diversity (size, colors and shapes) among species of Haemulidae is practically dissociated from the conservative cytogenetic pattern observed in this family. Detailed analyses indicate that karyotypic stasis is maintained even under the scrutiny of different chromosome investigation methods. Chromosomal banding patterns (endophenotype) of five Atlantic species are presented here: Conodon nobilis, Pomadasys corvinaeformis, Haemulon aurolineatum, H. plumierii and H. steindachneri, obtained by incorporating the base analog 5-BrdU, C-banding and staining with base-specific fluorochromes. Despite a few chromosomal specificities, relative karyotypic conservation was confirmed, corroborating earlier studies on this family. On the other hand, phenotypic patterns (exophenotype), identified by geometric morphometrics contrast visibly with the chromosomal conservation of this group. As such, the evolutionary rates of chromosomes and body morphology demonstrate clear asynchrony. Possible causes of karyotypic stasis in Haemulidae are discussed as well as the sharing of this condition with other Perciformes.     

Chromosomal evolution within the family Estrildidae (Aves) II. The Lonchurae

Thirteen species of estrildid finches belonging to the Lonchurae were examined cytogenetically by G- and C-banding. The major forms of karyotypic change, both within and between species, were pericentric inversions and changes in the amount of heterochromatin. It appears that the direction of chromosome change in this lineage is towards an entirely telocentric karyotype because inversions converting a biarmed chromosome into a telocentric one only occur when all the macrochromosomes of smaller size are also telocentric. A comparison of hybrid fertility data and karyotypic differences indicates that genic factors affecting gonadal development, and not chromosomal rearrangements, are the primary influence in determining hybrid fertility. The chromosomal data was also used to clarify systematic relationships within the Lonchurae and demonstrate that the genus Lonchura as presently construed is polyphyletic.     

Karyotype studies in thirty‐two species of Lilium (Liliaceae) from China1

Fifty‐two populations representing thirty‐two taxa of Lilium L. from China are karyologically analyzed. The results showed that all populations have the same basic chromosome number x=12, and all species are diploid except Lilium tigrinum, which is triploid with 2n=36. In addition, one population of L. sulphureum is aneuploid with 2n=23. The karyotype evolution in the genus Lilium is mainly in terms of alterations of the fine structure of the chromosomes, not in ploidy or basic chromosome number variation. When combining previous studies and our results, we consider the major driving forces for evolution of Lilium to be an increase in karyotypic asymmetry, and unequal translocation and formation of secondary constrictions. The existence of intercalary satellites on the two largest pairs of chromosomes is correlated with the geographic distribution pattern of Lilium across the world. The Hengduan Mountains is a modern diversity and differentiation center of Lilium and it also could be the center of origin for this genus. In addition, some taxonomic conclusions were verified on the subgenus level. Among the species investigated, the chromosome number and karyotypes of 13 taxa were documented for the first time.     

Karyomorphology and GC-rich heterochromatin pattern in Passiflora (Passifloraceae) wild species from Decaloba and Passiflora subgenera

Thirteen wild species of Passiflora were analyzed using conventional and CMA/DA/DAPI staining to evaluate the karyotype diversity between and within the subgenus Decaloba and Passiflora. The karyotypic features indicate that both subgenera have a conserved chromosome number, as reported before for several species. Submetacentric (sm) chromosomes were found in species from both subgenera, suggesting that sm chromosomes are not restricted to a particular subgenus. The analysis of the karyotypic heterogeneity enabled to distribute the species in three groups, but with no support to phylogenetic and taxonomic levels. The application of fluorochromes allowed for the visualization of CMA⁺/DAPI⁻ blocks, which in our studies always correlated with the occurrence of satellites, showing that occurrence of two chromosome pairs with satellites per cell is a characteristic shared by some species from both subgenera. This feature does not always have relationship with the basic chromosome number. The data found in this study will help to understand the phylogeny, cytotaxonomy, and evolution of the genus Passiflora showing that karyotypic variation can be seen between and within the subgenus Decaloba and Passiflora.     

Selected features of marsupial genetics

As a consequence of the ancient separation of the marsupial and eutherian lineages, comparative genetical studies of these two mammalian taxa can be particularly informative. The potential for marsupial genetical research has been enhanced by the development of laboratory colonies of three model species-Macropus eugenii, Monodelphis domestica andSminthopsis crassicaudata. In this paper two selected aspects of marsupial genetics are reviewed, one involving cytogenetics and the other linkage. Marsupials provide a spectacular example of karyotypic conservation. The so-called basic karyotype (2n=14) is probably ancestral in all extant marsupials. Karyotypes that do not conform to this basic arrangement are thought to have been derived from it. A notable feature of the basic karyotype is that it has been retained, possibly for as long as 150 million years, in morphologically, behaviourally and ecologically diverse species from at least five Australian and two American families; this suggests that selective forces, presently unknown, have acted to conserve the basic chromosome form and number in these species. With respect to genetic linkage, family studies inS. crassicaudata and more recentlyM. domestica have indicated extreme differences between the sexes with the recombination frequencies for linked loci being very much greater in males than in females, a situation that is strikingly different from that in eutherian mammals. These differences in linkage values are paralleled by differences in the number and distribution of chiasmata during male and female meiosis. Prospects for further research in marsupials, particularly research that builds upon the observations of karyotypic conservation and genetic linkage, are noted.     

NUCLEAR DNA CONTENT VARIATION WITHIN THE ROSACEAE

Nuclear DNA content has been estimated using flow cytometry for 17 species and eight cultivars of Malus and for 44 species of 29 other genera within the Rosaceae. Compared to other angiosperms, diploid genome sizes vary little within the family Rosaceae and within the genus Malus. C-values of genera within the subfamilies Spiraeoideae and Rosoideae are among the smallest of flowering plants thus far reported. In general, the Maloideae have the largest diploid genomes of the family, consistent with their higher chromosome numbers and presumed polyploid origin.     

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

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

Comparative cytogenetic analysis of hexaploid <Emphasis Type="Italic">Avena</Emphasis> L. species

Using C-banding method and in situ hybridizatiion with the 45S and 5S rRNA gene probes, six hexaploid species of the genus Avena L. with the ACD genome constitution were studied to reveal evolutionary karyotypic changes. Similarity in the C-banding patterns of chromosomal patterns and in the patterns of distribution of the rRNA gene families suggests a common origin of all hexaploid species. Avena fatua is characterized by the broadest intraspecific variation of the karyotype; this species displays chromosomal variants typical of other hexaploid species of Avena. For instance, a translocation with the involvement of chromosome 5C marking A. occidentalis was discovered in many A. fatua accessions, whereas in other representatives of this species this chromosome is highly similar to the chromosome of A. sterilis. Only A. fatua and A. sativa show slight changes in the morphology and in the C-banding pattern of patterns of chromosome 2C. These results can be explained either by a hybrid origin of A. fatua or by the fact that this species is an intermediate evolutionary form of hexaploid oats. The 7C–17 translocation was identified in all studied accessions of wild and weedy species (A. sterilis, A. fatua, A. ludoviciana, and A. occidentalis) and in most A. sativa cultivars, but it was absent in A. byzantina and in two accessions of A. sativa. The origin and evolution of the Avena hexaploid species are discussed in context of the results.     

从细胞学资料看金松属的系统位置

本文比较了金松(属)和杉科其他各属植物的核型,它的染色体数目(2n=20)和基数(x=10)较低,其核型最为对称。细胞学资料支持金松属从杉科分出另立金松科SciadopityaceaeHayata,它的系统位置则很可能比杉科来得原始。这也得到古植物学的支持。     

Chromosome studies in the mammalian subfamily Antilopinae

The karyology was studied in nine species of Antilopinae and evaluated with regard to cytotaxonomic relations within the subfamily. Karyotypes of three of these species were previously undescribed. Chromosomes were examined by conventional staining methods, G-, C-, and T-banding techniques, and by autoradiography. Evolutionary differentiation of karyotypes in this group is characterized by extensive Robertsonian fusions and a particular translocation between the X chromosome and an autosome. With comparison of Giemsa-banding patterns a taxonomy has been constructed which differs most markedly from the classical taxonomy in two aspects: the blackbuck, Antilope cervicapra, shows a strong karyotypic affinity to gazelles of the subgenus Nanger; Thomson's gazelle, Gazella thomsoni, lacks the numerous Robertsonian fusions and the X-autosome translocation common to other members of Gazella studied to date. Cases of intraspecific polymorphism of chromosome morphology and number are presented.     

Relative DNA content of somatic nuclei and chromosomal studies in three genera,Tilapia, Sarotherodon,andOreochromis of the tribe Tilapiini (Pisces,Cichlidae)

Seven Tilapiine species from three generaTilapia, Sarotherodon, andOreochromis were cytogenetically studied for chromosome number, chromosome morphology, and DNA content. The chromosome number 2n=44 was the same in all seven species. Arm number (NF) differences indicate the possible role of pericentric invasions in the karyotypic evolution of these species. C-banding of metaphase chromosomes shows that heterochromatin is localised around the centromere in all species ofOreochromis and Sarotherodon butT. zillii has more heterochromatin with six chromosomes having completely C-positive short arms. DNA values vary between 0.84 pq forO. macrochir and 1.21 pq forO. aureus. No heteromorphic sex chromosome pair could be found in any species. These findings suggest that karyotypic evolution has occurred but does not appear to be associated with speciation in this group.