Karyotype Differentiation Research Articles

Karyotype diversity of four species of the incertae sedis group (Characidae) from different hydrographic basins: analysis of AgNORs, CMA3 and 18S rDNA

A large number of genera in the tropical fish family Characidae are incertae sedis. Cytogenetic analysis was made of four of these species: Astyanax eigenmanniorum, Deuterodon stigmaturus, Hyphessobrycon luetkenii, and H. anisitsi, collected from various hydrographic basins: hydrographic system from Laguna dos Patos/RS, Tramandaí basin/RS and Tibagi River basin/PR. The first two species were collected in their type locality in the State of Rio Grande do Sul. The 2n = 48 karyotype was observed only in A. eigenmanniorum, while the other species had 2n = 50 chromosomes, with different karyotypic formulas. There was weak heterochromatin staining in the pericentromeric region of A. eigenmanniorum, D. stigmaturus and H. luetkenni chromosomes. In H. anisitsi, heterochromatin appeared to be more abundant and distributed in the pericentromeric and terminal regions of the chromosomes; three pairs showed more evident heterochromatic blocks. There were multiple Ag-NORs in all populations, visualized by FISH with an 18S rDNA probe. While D. stigmaturus and H. luetkenii had conserved AgNOR, CMA3 and 18S rDNA sites, the other two species showed intra- and interindividual variation at these sites. The karyotype variability was high, as is common in this group of fish. Different species arising from isolated hydrographic basins maintain an elevated level of karyotype differentiation, mainly with respect to chromosome structure, heterochromatin distribution and rDNA localization. This is the first report with cytogenetic data for D. stigmaturus and H. luetkenii.

Population Diversity and Polyploidy Incidence in 3 <i>Silene</i> Species. A Cytological Approach

Cytological studies were performed in 20 populations of 3 Silene species of the section Auriculatae L., Silene gynodiocia Ghazanfar, S. crispans Litw., S. indeprensa Schischk. The populations studied had 2n=2x=24, 2n=4x=48 and 2n=8x=96 chromosome number, showing 2 polyploidy levels for S. indeprensa and S. gynodiocia. The chromosomes were mostly metacentric and submetacentric but 1 pair of teloentric chromosome was observed in the octaploid Dargaz population of S. indeprensa. The ANOVA test showed no significant difference among populations of S. indeprensa and populations of S. gynodiocia for size of the chromosomes, mean chromosome length, A1 and A2 indices as well as TF value. This indicates that no significant chromatin loss or gain has occurred in the process of karyotype differentiation in these populations, and in the case of octaploid and tetraploid populations, still the mean value of chromosomes are maintained. However, the species differed significantly for CV value, indicating that during species diversification a change has occurred in the size of chromosomes within a karyotype due to structural changes of the chromosomes. Meiosis analysis showed that the chromosomes mainly form bivalents and univalents in the metaphase of meiosis I, although some amounts of quadrivalents were observed in all populations including diploids due to heterozygote translocations. T-test analysis showed significant difference in the relative values of total and terminal chiasmata as well as a number of ring bivalents between the populations having 2n=24 and 2n=48 chromosome number indicating that with an increase in polyploidy level, significant change has occurred in the number of genes controlling chiasma frequency. The occurrence of unreduced pollen grains indicates the role of this phenomenon in polyploidy incidence in the species studied.

Comparative cytogenetic analysis of two grasshopper species of the tribe Abracrini (Ommatolampinae, Acrididae)

The grasshopper species Orthoscapheus rufipes and Eujivarus fusiformis were analyzed using several cytogenetic techniques. The karyotype of O. rufipes, described here for the first time, had a diploid number of 2n = 23, whereas E. fusiformis had a karyotype with 2n = 21. The two species showed the same mechanism of sex determination (XO type) but differed in chromosome morphology. Pericentromeric blocks of constitutive heterochromatin (CH) were detected in the chromosome complement of both species. CMA3/DA/DAPI staining revealed CMA3-positive blocks in CH regions in four autosomal bivalents of O. rufipes and in two of E. fusiformis. The location of active NORs differed between the two species, occurring in bivalents M6 and S9 of O. rufipes and M6 and M7 of E. fusiformsi. The rDNA sites revealed by FISH coincided with the number and position of the active NORs detected by AgNO3 staining. The variability in chromosomal markers accounted for the karyotype differentiation observed in the tribe Abracrini.

Phylogeny of Sphaerium solidum (Bivalvia) based on karyotype and sequences of 16S and ITS1 rDNA

Abstract The present work represents the first karyological and molecular characterisation of Sphaerium solidum, a rare European clam. Specimens of S. solidum were collected in Lithuania and Hungary. The modal diploid chromosome number found in both populations was 2n=30. Small, biarmed B chromosomes were found in 42.3% of cells studied in clams from Lithuania and in 11.8% of cells in clams from Hungary. Comparative analysis revealed no significant (P<0.05) interspecific differences in chromosome morphology of S. solidum and that of previously studied S. corneum. DNA sequence analyses of S. solidum showed no interpopulation differences in ITS1; moreover, only one site was different from ITS1 of S. corneum. However, differences in mitochondrial 16S sequence of S. solidum were revealed: two haplotypes in Lithuania and three in Hungary were identified. The genetic characteristics revealed in this study do not support ascription of S. solidum and S. corneum to different subgenus, Cyrenastrum and Sphaerium s. str., respectively. Comparative cytogenetic analysis disclosed that the chromosome morphology could be conserved in some sphaeriid species during speciation despite the fact that most other species in this family undergo radical karyotypic differentiation.

Chromosomal Homologies among Vampire Bats Revealed by Chromosome Painting (Phyllostomidae, Chiroptera)

Substantial effort has been made to elucidate karyotypic evolution of phyllostomid bats, mostly through comparisons of G-banding patterns. However, due to the limited number of G-bands in respective karyotypes and to the similarity of non-homologous bands, an accurate evolutionary history of chromosome segments remains questionable. This is the case for vampire bats (Desmodontinae). Despite several proposed homologies, banding data have not yet provided a detailed understanding of the chromosomal changes within vampire genera. We examined karyotype differentiation of the 3 species within this subfamily using whole chromosomal probes from Phyllostomus hastatus (Phyllostominae) and Carollia brevicauda (Carolliinae). Painting probes of P. hastatus respectively detected 22, 21 and 23 conserved segments in Diphylla ecaudata, Diaemus youngi, and Desmodus rotundus karyotypes, whereas 27, 27 and 28 were respectively detectedwith C. brevicauda paints. Based on the evolutionary relationships proposed by morphological and molecular data, we present probable chromosomal synapomorphies for vampire bats and propose chromosomes that were present in the common ancestor of the 5 genera analyzed. Karyotype comparisons allowed us to relate a number of conserved chromosomal segments among the 5 species, providing a broader database for understanding karyotype evolution in the family.

Physical mapping of 18S rDNA cistron in species of the Omophoita genus (Coleoptera, Alticinae) using fluorescent in situ hybridization

Alticinae has the greatest amount of biodiversity among the Chrysomelidae, with 40,000 described species, only 290 of which have been analyzed cytogenetically. The majority of studies refer to conventional staining and few species have been analyzed or have responded to differential staining methods. The aim of the present study was to describe an 18S rDNA probe for Alticinae and the location of this cluster in species of the Omophoita genus. The fragment of approximately 750 bp obtained through a PCR (Polymerase Chain Reaction) amplification reaction with specific oligonucleotides to 18S rDNA was cloned and denominated pTZ_Ooct_18Sp and then submitted to automatic sequencing. The alignment of the sequences obtained through the sequencing of the clones generated a consensus sequence of 722 bp for Omophoita octoguttata with 98% homology with other species of Alticinae. The analysis of mitotic cells of O. octoguttata and Omophoita magniguttis submitted to fluorescent in situ hybridization (FISH) with the 18S rDNA probe revealed that the ribosomal genes are located in 6th pair. O. magniguttis also has a second labeled pair. Omophoita personata exhibited nucleolar organizer regions associated to one autosome pair. The analysis of meiotic cells submitted to FISH revealed one labeled bivalent in metaphase I in O. octoguttata and O. personata and in one chromosome in metaphase II in O. octoguttata. FISH data suggest a conserved pattern in the species analyzed and an apomorphy of O. magniguttis karyotype. The rDNA 18S probe could be considered an important marker to evidence the karyotypic differentiation, not observed with conventional methodologies, in species considered karyotypically conserved and uniform.

Karyotype evolution and speciation of European lilies from Lilium sect. Liriotypus

AbstractThe main purpose of this study was to clarify the speciation and taxonomic status of European representatives of Lilium sect. Liriotypus (Lilium albanicum, L. bosniacum, L. bulbiferum, L. candidum, L. carniolicum, L. chalcedonicum, L. jankae, L. pomponium, L. rhodopaeum, L. pyrenaicum) based on karyotype differentiation. Clear interspecific differentiation was revealed among karyotypes of these taxa using fluorochrome (chromomycin and DAPI) bandings, fluorescent in situ hybridization and silver staining. Differences were evident in the number and position of CMA and DAPI bands and in the number, position and activity of 18S‐26S and 5S rDNA genes. It is hypothesized that the type species of Lilium sect. Liriotypus, L. candidum, represents the ancestral species from which three evolutionary directions diverged: the first towards L. chalcedonicum, the second towards L. rhodopaeum, and the third towards L. albanicum. The radiation process expanded from L. albanicum, beyond the southeast to the central Dinaric Alps where L. bosniacum is strongly represented. Furthermore, L. carniolicum evolved from northwestern populations of L. bosniacum. According to this evolutionary hypothesis, L. pomponium and L. pyrenaicum would be the youngest species.

Comparative Cytogenetic Analysis of the Genus Symphysodon (Discus Fishes, Cichlidae): Chromosomal Characteristics of Retrotransposons and Minor Ribosomal DNA

As part of a genetic screening program for wild Discus fishes, we analyzed karyotypes and cytogenetic characteristics of Symphysodon aequifasciatus, S. discus and S. haraldi using C-banding and fluorescent in situ hybridization (FISH) with the Rex3 retrotransposon and 5S rDNA probes in mitotic and meiotic chromosomes. In the 3 species, diploid chromosome number was 2n = 60 and karyotypes contained predominantly meta-submetacentric chromosomes. C-banding showed blocks of constitutive heterochromatin mainly in the pericentromeric region. Physical mapping of repetitive 5S rDNA sequences and Rex3 retrotransposons in mitotic and meiotic chromosomes showed partial colocalization of constitutive heterochromatin and repetitive elements. Correlations among the accumulation of repetitive elements, heterochromatinization and chromosome rearrangements have been hypothesized to explain the karyotype differentiation in the Symphysodon genus. The role of repetitive elements in adaptation to highly diverse habitats, as well as in the generation of the phenotypic and genetic variability found in wild Discus populations, needs to be further investigated.

Karyotype differentiation in three species of Tripogandra Raf. (Commelinaceae) with different ploidy levels

Most species of the genus Tripogandra (Commelinaceae) are taxonomically poorly circumscribed, in spite of having a relatively stable basic number x = 8. Aiming to estimate the cytological variation among Tripogandra species carrying this base number, several structural karyotypic characters were investigated in the diploid T. glandulosa, the hexaploid T. serrulata, and the octoploid T. diuretica. A careful evaluation of chromosome size and morphology did not reveal clear chromosome homeologies among karyotypes. The mean chromosome size was strongly reduced in the octoploid species, but not in the hexaploid species. They also differed largely in the CMA+ banding pattern and in the number of 5S and 45S rDNA sites per monoploid chromosome complement. All three species showed proximal DAPI + heterochromatin, although in T. serrulata this kind of heterochromatin was only visible after FISH. Further, the meiosis in T. serrulata was highly irregular, suggesting that this species has a hybrid origin. The data indicate that, in spite of the conservation of the base number, these species are karyologically quite different from each other.

NOR Dispersion, Telomeric Sequence Detection in Centromeric Regions and Meiotic Multivalent Configurations in Species of the Aplastodiscus albofrenatus Group (Anura, Hylidae)

In the present study, we examined the chromosome number and morphology, heterochromatin pattern, and location of the nucleolar organizer region (NOR) and telomeric sequences in Aplastodiscus albofrenatus, A. arildae, A. ehrhardti and A. eugenioi in order to cytogenetically characterize the Aplastodiscus albofrenatus group. The 4 species analyzed in this study had diploid numbers of 2n = 22 and very similar chromosome morphology. These species could be differentiated based on the distribution and amount of heterochromatin and the location of the nucleolar organizer region (NOR). Six of the 8 A. albofrenatus individuals had an NOR polymorphism previously unknown in anurans since only one of the homologs of pairs 1 and 7 was stained. In the other 2 specimens, the NOR occurred on both homologs of pair 7. In A. ehrhardti, pairs 6 and 10 were stained by the AgNOR technique, but only pair 6 was confirmed by in situ hybridization. The NOR was located on pair 10 in A. arildae and on pair 7 in A. eugenioi. In A. albofrenatus and A. arildae, multivalent rings involving NOR-containing chromosomes were observed during prophase I of meiosis. The telomeric probe identified the telomeres in all species and also centromeric regions in the chromosomes of A. albofrenatus and A. arildae, which were coincident with centromeric heterochromatin. The conserved chromosomal morphology seen mainly in the first 7 pairs among species of the A. albofrenatus group suggests that all of these species probably originated from a common ancestral karyotype and that chromosomal rearrangements resulted in karyotype differentiation, with changes in NOR location, as well as telomeric and heterochromatin dispersal.

Cytogenetic analysis of two related Deltochilum (Coleoptera, Scarabaeidae) species: Diploid number reduction, extensive heterochromatin addition and differentiation

Male mitotic and meiotic chromosomes of two species of the genus Deltochilum (Scarabaeidae) were analyzed through conventional staining, C-banding, base-specific fluorochromes, silver nitrate staining (AgNO 3) and FISH (45S rDNA). The two species possessed karyotypes with 2 n = 14, neo-XY and meta-submetacentric chromosomes. The analysis of constitutive heterochromatin (CH) revealed mainly diphasic chromosomes in the two species, showing heterochromatic long arms. Silver nitrate staining labeled the blocks corresponding to CH in D. ( Deltohyboma) aff morbillosum while in D. ( Deltohyboma) calcaratum, AgNO 3 staining revealed only the CH blocks of the diphasic autosomes. The fluorochrome staining revealed in D. ( D.) calcaratum the diphasic autosomes and the sex chromosomes with CMA 3 + blocks, and in D. ( D.) aff morbillosum, the GC-rich sequences were restricted to the terminal regions of the long arms of the pairs 1 and 2 and the X. The FISH revealed 45S rDNA sites in two autosomic pairs and in the X chromosome. The analyses performed allowed for the identification of cytogenetic markers and the discussion of possible chromosome rearrangements that have been involved in the karyotypic differentiation of these species mainly related to the repetitive genome.

Amplification of repetitive DNA and origin of a rare chromosomal sex bivalent in Deltochilum (Calhyboma) verruciferum (Coleoptera, Scarabaeidae)

The most intriguing karyotypic variation in the Coleoptera involves variation in sex chromosome structure, origin and behavior. In this report we describe chromosomal characteristics of Deltochilum (Calhyboma) verruciferum (Coleoptera, Scarabaeidae) using conventional and differential cytogenetic techniques, with emphasis on the description of a rare sex bivalent in the Coleoptera and dispersion of repetitive DNA. This species shows 2n = 20,XY(p) with biarmed chromosomes. Analysis of constitutive heterochromatin through C-banding revealed mainly diphasic autosomes with short heterochromatic arms, while the X was completely heterochromatic and the Y was heterochromatic in the long arm. This pattern was confirmed through the use of CMA(3) fluorochrome that stained all heterochromatic regions. Silver nitrate staining marked all heterochromatic regions and the lumen of the sex bivalent in metaphase I. These results indicated that karyotypic differentiation in D. (C.) verruciferum involved autosomal amplification and dispersion of repetitive DNA and the origin of unusual sex chromosomes (XY(p)), generating a unique karyotype in this species.

Mechanisms of karyotype differentiation in Cassidinae sensu lato (Coleoptera, Polyphaga, Chrysomelidae) based on seven species of the Brazilian fauna and an overview of the cytogenetic data

Among the subfamilies of Chrysomelidae, Cassidinae sensu lato ( s.l.) includes 6000 species distributed in 43 tribes. Approximately 100 of these species were cytogenetically analyzed and most of them presented 2 n = 18 = 16 + Xy p, which was smaller than 2 n = 20 = 18 + Xy p considered basal for Polyphaga. However, some groups of species presented maintenance of the basal diploid number and others showed increase in this number. Certain species of the latter group also exhibited variation in the type of sex chromosome system (SCS). Considering the recent taxonomic revision accomplished for the Cassidinae s.l. species, the existence of phylogenetic relationship for some species of this subfamily, the high diversity of species of this group in the Neotropical region, and the low number of Cassidinae s.l. species karyotyped so far, the aim of the present work was to establish the main mechanisms involved in the karyotype evolution of this subfamily through the study of seven species of the Brazilian fauna and overview of the cytogenetic data. The individuals were collected in southeast and south of Brazil. The chromosomal preparations obtained from embryo and testes of adult males were stained with Giemsa solution. The species Agroiconota inedita (2 n = 42 = 40 + Xy p), Charidotella ( s.str.) immaculata (2 n = 22 = 20 + Xy p), Charidotella ( s.str.) sexpunctata (2 n = 22 = 20 + Xy p), and Stolas chalybaea (2 n = 24 = 22 + Xy p) revealed diploid number higher than that established as basal for Polyphaga and biarmed chromosomes. The karyotype of Cteisella confusa, Deloyala cruciata, and Metriona elatior showed the chromosomal formulae 2 n = 18 = 16 + Xy p considered modal for Cassidinae s.l. and biarmed chromosomes. The seven species exhibited easily identified sex chromosomes due to their size and/or morphology. The analysis of meiotic cells of all the species showed pachytenes with a positively heteropycnotic block probably corresponding to the sex chromosomes; diplotenes with a high number of bivalents with two chiasmata and sex chromosomes in a parachute configuration, and metaphases II that confirmed the chromosomal morphology, the type of SCS, and the regular segregation of all chromosomes. The data regarding to the number and morphology of the chromosomes, their behaviour during meiosis, and type of SCS were inedit for the majority of these species. In relation to the all Cassidinae s.l. species that presented SCS of the Xy p type, A. inedita was that with the highest diploid number. Furthermore, this work reported for the first time the cytogenetic information of representatives of the genera Cteisella and Metriona. Taking into account the phylogenetic and cytogenetic data of Cassidinae s.l. species, the karyotype differentiation of this group seems to have occurred from the basal karyotype of Polyphaga by decrease in the chromosome number and subsequent increase in this number. Pericentric inversion, centric fusion and fission seem to have been the main mechanisms that promoted the evolution of the autosomes. However, in the sex chromosome evolution, the mechanisms involved were centric fission and/or chromosomal translocation.

Cytotaxonomical study in Brazilian species of Solanum, Lycianthes and Vassobia (Solanaceae)

Solanum comprises about 1,400 species of shrubs, trees and vines. This group is cytogenetically interesting because it possesses karyotypes apparently conserved in chromosome number and shape, but with diversity in the repetitive DNA. The objective of this study is to characterize 16 species of Solanum and two species of closely related genera (Lycianthes australe and Vassobia breviflora) using cytogenetic parameters. All the species presented 2n = 24, confirming previous chromosome counting. Additionally, nonreticulated nuclei, proximal condensation in prophase-metaphase and little variation in the karyotype symmetry were observed. Solanum corymbiflorum exhibited chromosomes approximately three times bigger in relation to the other species. GC-rich heterochromatin was preferentially located at terminal regions and AT-rich blocks always appear in the centromeric regions. The 45S rDNA sites were coincident with C/CMA3 + regions (satellites) and found in just one pair, except in S. corymbiflorum which presented two pairs. FISH with 5S rDNA showed signals in the paracentromeric region of one chromosome pair, except in S. trachytrichium and S. gemellum which showed two hybridization signals. The results point out to different ways of karyotype differentiation in Solanum and closely related genera and bring important issues on the value of the cytogenetical information for taxonomic studies.

The role of U-type exchanges in the differentiation of karyotypes in Najas marina

Spontaneous bridge and fragment formation was observed at the first and second meiotic division, in root tip, premeiotic and pollen mitoses of both chromosomal races of Najas murina, a dioecious and annual species. The frequency of disturbed divisions ranged from 0.9 to 6.5 per cent. Since no reverse loop pairing was observed at pachytene, and the aberrations observed were incompatible with inversion polymorphism, the most probable source of the disturbances was considered to be U-type exchanges. Aberrations in mitotic divisions were also presumed to be formed by U-type reunion of sister chromatid exchanges. All Ihe fragment size classes can be explained on the basis of a breakage and reunion in the centromeric heterochromatin and in the allocyclic regions. However. some break points outside these regions were actually seen. Hence additional 'weak points' are believed to be present in the brightly fluorescent distal parts of the chromosomes. A model is presented of the rearrangements leading from karyotype B to A. Spontaneous breakage and reunion produce continuously new combinations of chromosome segments in N. marina, and hence have been of evolutionary significance in the differentiation of the two karyotypes.

Karyotype differentiation of four Cestrum species (Solanaceae) revealed by fluorescent chromosome banding and FISH

The karyotypes of four South American species of Cestrum (C. capsulare,C. corymbosum,C. laevigatum and C. megalophylum) were studied using conventional staining, C-CMA/DAPI chromosome banding and FISH with 45S and 5S rDNA probes. The karyotypes showed a chromosome number of 2n = 2x = 16, with metacentric chromosomes, except for the eighth submeta- to acrocentric pair. Several types of heterochromatin were detected, which varied in size, number, distribution and base composition. The C-CMA+ bands and 45S rDNA were located predominantly in terminal regions. The C-CMA + /DAPI + bands appeared in interstitial and terminal regions, and the C-DAPI + bands were found in all chromosome regions. The 5S rDNA sites were observed on the long arm of pair 8 in all species except C. capsulare, where they were found in the paracentromeric region of the long arm of pair 4. The differences in band patterns among the species studied here, along with data from other nine species reported in the literature, suggest that the bands are dispersed in an equilocal and non-equilocal manner and that structural rearrangements can be responsible for internal karyotype diversification. However, it is important to point out that the structural changes involving repetitive segments did not culminate in substantial changes in the general karyotype structure concerning chromosome size and morphology.

Chromosome reduction in Eleocharis maculosa (Cyperaceae)

Chromosome numbers in Cyperaceae lower than the typical basic number x = 5 have been described for only three species: Rhynchospora tenuis (n = 2), Fimbristylis umbellaris (n = 3) and Eleocharis subarticulata (n = 3). Eleocharis maculosa is recorded here as the fourth species of Cyperaceae that has a chromosome number lower than 2n = 10, with 2n = 8, 7 and 6. The karyotype differentiation in E. maculosa was studied using conventional staining (mitosis and meiosis), FISH with 45S and 5S rDNA and telomere probes. The results allow us to determine which chromosomes of the chromosome race with 2n = 10 fused to form the remaining reduced numbers, as well as to understand how the symploidy and translocation mechanisms were important in karyotype differentiation and the formation of chromosome races in Eleocharis.

Taxonomy of the Genus Isophya (Orthoptera, Phaneropteridae, Barbitistinae): Comparison of Karyological and Morphological Data

The genus Isophya represents one of the largest orthopteran genera with about 45 species occurring in Europe. All over its range the genus includes groups of sibling species, the recognition of which is hampered by their morphological similarity. In part, some species were grouped according to their morphology: the Isophya straubei-group, the I. amplipennis-group and the I. major-group. Nevertheless, many species have not been studied using new methods. This is particularly true for 15 taxa described from the Balkans, more or less resembling I. modesta, known mostly from old, unsatisfactorily informative descriptions. Chromosomal analysis of 25 species/subspecies of the genus Isophya showed the karyotypic evolution among species. The karyotype of 18 species/subspecies was investigated for the first time. The most remarkable changes in the sex chromosomes were the ancient acrocentric X chromosome inversions in 19 species and an X chromosome/autosome mutual tandem translocation, from which the sex determination system neo-XY originated in I. hemiptera. Karyotype differentiation has been less rapid in autosomes than in sex chromosomes, in this case interspecific autosomal differentiation has involved the distribution and quantity of C-heterochromatin as well as the number of NORs. Cytogenetic analysis revealed some changes reflecting the level of genomic organization, and the results suggest some association of related taxa from biogeographic regions.

Karyotype differentiation patterns in species of the subfamily Scarabaeinae (Scarabaeidae, Coleoptera)

The aim of this study was to describe the karyotype of species belonging to the subfamily Scarabaeinae (Coleoptera, Scarabaeidae) and to compile the conventional cytogenetic data available in the literature for this group. The karyotypes of ten species belonging to the tribes Canthonini, Coprini, Onthophagini and Phanaeini were analyzed by conventional staining. Eight of these species were described for the first time ( Canthon aff carbonarius, Canthon chalybaeus, Coprophanaeus dardanus, Deltochilum aff amazonicum, Dichotomius geminatus, Oxysternon silenus, Phanaeus chalcomelas and Malagoniella aff astyanax) and two were redescribed ( Diabroctis mimas and Digitonthophagus gazella) since their karyotypes differed from those previously published in the literature. Four species studied showed a diploid number of 2n = 20 and a parachute type sex determining system and the karyotype was 2n = 20,Xy in two species and 2n = 18,Xy p, 2n = 19,X0, 2n = 12,XY and 2n = 14,neoXY in one each. The chromosome morphology of the different species varied, with the observation of metacentric, submetacentric, subacrocentric and acrocentric chromosomes. The X chromosome was predominantly meta or submetacentric in the species analyzed, whereas the y chromosome presented two arms or was punctiform. In conclusion, the subfamily Scarabaeinae comprises 120 species analyzed cytogenetically, and are observed the occurrence of five chromosome rearrangements (autosome–autosome and X-autosome fusions, pericentric inversions, fissions and loss of the y chromosome) that are related to the chromosome variability and evolution in the group.

Karyotype Diversification and Evolution in Diploid and Polyploid South American Hypochaeris (Asteraceae) Inferred from rDNA Localization and Genetic Fingerprint Data

Changes in chromosome structure and number play an important role in plant evolution. A system well-suited to studying different modes of chromosome evolution is the genus Hypochaeris (Asteraceae) with its centre of species' diversity in South America. All South American species uniformly have a chromosome base number of x = 4 combined with variation in rDNA number and distribution, and a high frequency of polyploidy. The aim of this paper is to assess directions and mechanisms of karyotype evolution in South American species by interpreting both newly obtained and previous data concerning rDNA localization in a phylogenetic context. Eleven Hypochaeris species from 18 populations were studied using fluorescence in situ hybridization (FISH) with 35S and 5S rDNA probes. A phylogenetic framework was established from neighbour-net analysis of amplified fragment length polymorphism (AFLP) fingerprint data. A single 5S rDNA locus is invariably found on the short arm of chromosome 2. Using 35S rDNA loci, based on number (one or two) and localization (interstitial on the long arm of chromosome 2, but sometimes lacking, and terminal or interstitial on the short arm of chromosome 3, only very rarely lacking), seven karyotype groups can be distinguished; five of these include polyploids. Karyotype groups with more than one species do not form monophyletic groups. Early evolution of Hypochaeris in South America was characterized by considerable karyotype differentiation resulting from independent derivations from an ancestral karyotype. There was marked diversification with respect to the position and evolution of the 35S rDNA locus on chromosome 3, probably involving inversions and/or transpositions, and on chromosome 2 (rarely 3) concerning inactivation and loss. Among these different karyotype assemblages, the apargioides group and its derivatives constitute by far the majority of species.