Karyotypic characterization of representatives from Melolonthinae (Coleoptera: Scarabaeidae): karyotypic analysis, banding and fluorescent in situ hybridization (FISH)

A new continuous cell line from the pest insect, Anomala cuprea (Coleoptera; Scarabaeidae): emergence of contractile cells

Insect contractile cells frequently appear at an early phase of cell culture, but in most cases, they disappear before a continuous cell line is established, so the cell line ceases to contract. Continuous contractile insect cell lines are currently available from only one species each of Hymenoptera and Diptera. Here, we obtained a new cell line that contracted long after being established as a continuous cell line. The cell line contracted for a short period at an early phase of insect cell culture before a continuous cell line was established, but then did not contract again for several years. After this cell line entered the continuous growth phase, it produced spontaneously contractile tissues for about 4 mo but stopped contracting again. This is the first instance of a cell line that contracted after its establishment as a non-contractile continuous cell line. It is unclear whether the contractile cells survive or die after contraction ceases at an early phase of cell culture, and our results indicate that potential contractile cells survive for years after they stop to contract. The cells of this line sometimes produced complex contractile structures, such as sheet-like tissues. Only a few continuous cell lines have been derived from scarabaeid beetles. The new continuous cell line was derived from the culture of the fat bodies of the scarab beetle Anomala cuprea, which is a pest in the agriculture and forestry of Japan. The population doubling time of the new cell line was 2.5 d and thus it grows very rapidly among coleopteran continuous cell lines. Our new cell line will facilitate research on the physiology and pathology of Coleoptera, including scarab beetles, and may also contribute to research on invertebrate muscles.

Comparative cytogenetics and derived phylogenic relationship among Sitophilus grain weevils (Coleoptera, Curculionidae, Dryophthorinae)

Cytogenetic characteristics and genome size are powerful tools for species characterization and identification of cryptic species, providing critical insights into phylogenetic and evolutionary relationships. Sitophilus Linnaeus, 1758 grain weevils can benefit from such tools as key pest species of stored products and also as sources of archeological information on human history and past urban environments. Moreover, the phylogenetic relationship among these weevil species remains controversial and is largely based on single DNA fragment analyses. Therefore, cytogenetic analyses and genome size determinations were performed for four Sitophilus grain weevil species, namely the granary weevil Sitophilus granarius (Linnaeus, 1758), the tamarind weevil S. linearis (Herbst, 1797), the rice weevil S. oryzae (Linnaeus, 1763), and the maize weevil S. zeamais Motschulsky, 1855. Both maize and rice weevils exhibited the same chromosome number (2n=22; 10 A + Xyp). In contrast, the granary and tamarind weevils exhibited higher chromosome number (2n=24; 11 A + Xyp and 11 A + neo-XY, respectively). The nuclear DNA content of these species was not proportionally related to either chromosome number or heterochromatin amount. Maize and rice weevils exhibited similar and larger genome sizes (0.730±0.003 pg and 0.786±0.003 pg, respectively), followed by the granary weevil (0.553±0.003 pg), and the tamarind weevil (0.440±0.001 pg). Parsimony phylogenetic analysis of the insect karyotypes indicate that S. zeamais and S. oryzae were phylogenetically closer than S. granarius and S. linearis, which were more closely related and share a more recent ancestral relationship.

Interstitial NORs, Fragile Sites, and Chromosome Evolution: A Not So Simple Relationship - The Example of Melolontha melolontha and Genus Protaetia (Coleoptera: Scarabaeidae)

In the present study, the origin of recurrent rearrangements involving chromosome 6 in 3.2% of cells of Melolontha melolontha (Coleoptera, Scarabaeidae) was investigated. Various chromosome staining techniques, including C-banding, Giemsa and silver staining, as well as fluorescence in situ hybridization with a human 28S rDNA probe, were applied to M. melolontha chromosome spreads. In addition, related species of the genera Melolontha and Protaetia were studied. On chromosome 6 of M. melolontha, there is a fragile site-like structure which corresponds to an interstitial nucleolus organizer region (NOR). Despite this instability, the NOR remains unique and interstitial in this species, as well as in the other species studied. It is proposed that the intercalary position of the NOR both facilitates the detection of its fragile site-like instability and correlates with its relative stability during evolution. We explain this apparent paradox by strong counter-selection for imbalances of the chromosome fragment distal to the interstitial NORs, which would recurrently occur in the progeny of translocation carriers. Thus, the frequent telomeric position of the NORs in most animal and plant taxa would have no functional rationale but would be the consequence of selection against the meiotic transmission of chromosome imbalances.

A new cell line derived from embryonic tissues of Holotrichia parallela (Coleoptera:Scarabaeidae)

Holotrichia parallela is an important agricultural underground insect pest and also an edible and medicinal insect. Establishing a new cell line of H. parallela will provide a rapid and convenient tool for the studies on its physiology, pathology, and gene functions. In this study, by using the embryonic tissue of H. parallela as the material, we established a new cell line named Hp-E-1. The microscopic observation of its morphological characteristics revealed that its cellular morphology was mainly in the spherical morphology with a mean cellular diameter of 17.71 ± 2.34 μm, accounting for 67% of the total cells. The spindle-shaped cells accounted for 33% of the total cells with a mean size of 23.51 ± 4.37 × 13.98 ± 2.05 μm. The chromosomal number varied from 7 to 40, with about 50% of the cells having a diploid chromosome number of 2n = 20. Random amplified polymorphic DNA (RAPD) analysis indicated that the profiles of PCR-amplified fragments of this cell line were basically similar to those of the embryonic tissues of H. parallela but were obviously different from those of cell line BTI-Tn5B1-4 of Trichoplusia ni and cell line Sf-9 of Spodoptera frugiperda. The DNA fragment encoding mitochondrial cytochrome C oxidase subunit I (COI) gene of this cell line shared 99.7% homology with that of the embryonic tissue of H. parallela, confirming that this cell line is indeed derived from H. parallela. The results of growth curve measurement indicated that the population doubling time of this cell line was 136.7 h. Cell line Hp-E-1 could not be infected by three viruses Autographa californica multiple nucleopolyhedrovirus (AcMNPV), Bombyx mori nucleopolyhedrovirus (BmNPV), and Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV).

Establishment and characterization of three new cell lines from the embryonic tissue of Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae)

The establishment of new insect cell lines plays important roles in the researches of insect pathology, insect toxicology, insecticide screening and activity assay, etc. Using embryos of Holotrichia oblita Faldermann (Coleoptera: Scarabaeidae) as materials, this study describes the establishment of three cell lines designated as QAU-Ho-E-3 (Ho-3), QAU-Ho-E-4 (Ho-4), and QAU-Ho-E-6 (Ho-6), respectively. Currently, the three cell lines have been passaged more than 50 times in the TNM-FH insect cell medium containing 10% fetal bovine serum (FBS). All of them showed adherent growth. The majority of Ho-3 cells are spindle-shaped, with a size of 24.35 ± 5.29 × 11.56 ± 1.67 μm. The Ho-4 cells were either spindle-shaped or oblong, with a size of 38.07 ± 8.57 × 17.62 ± 2.48 μm. The Ho-6 cells were primarily round in shape with a diameter of 14.54 ± 1.96 μm. The Ho-3 and Ho-4 cell lines contained 20 chromosomes (i.e., diploid, 2n = 20) at passages 14 and 45. The Ho-6 cell line contained 20 chromosomes (i.e., diploid, 2n = 20) at passage 14 but 40 chromosomes (i.e., polyploidy, 4n = 40) at passage 45. The results of random amplified polymorphic DNA (RAPD) analysis showed that the RAPD fingerprint of the three cell lines was consistent with that of H. oblita eggs, but clearly different from that of BTI-Tn5B1-4 and Sf-9 cells, demonstrating that the three cell lines Ho-3, Ho-4, and Ho-6 are H. oblita cell lines. The results of the growth curve test showed that the population doubling times of Ho-3, Ho-4, and Ho-6 were 101.1, 105.2, and 83.6 h, respectively. The viral infection assay indicated that these H. oblita cell lines were not permissive to infection by Autographa californica multiple nucleopolyhedrovirus (AcMNPV) or Bombyx mori nucleopolyhedrovirus (BmNPV).

Chromosomal diversification of diploid number, heterochromatin and rDNAs in two species of Phanaeus beetles (Scarabaeidae, Scarabaeinae)

The genus Phanaeus is included in the tribe Phanaeini, one of the most diverse tribes within the subfamily Scarabaeinae in terms of chromosomal characteristics. However, so far the species of this genus were not studied with differential cytogenetic techniques, limiting any inference of the probable mechanisms responsible for this diversity. In this work, several techniques were applied with the aim of cytogenetically characterizing two Phanaeus species. The karyotype found for Phanaeus (Notiophanaeus) chalcomelas was 2n = 12, neo-XY, and that of P. (N.) splendidulus was 2n = 20, Xy_p, considered primitive for the family Scarabaeidae. The chromosomes of both species showed a high amount of constitutive heterochromatin (CH), with blocks rich in base pairs GC (CMA₃⁺). Moreover, in P. (N.) chalcomelas the marks revealed by C-banding and fluorochrome staining were different in size, showing CH variability. Sites of 18S ribosomal DNA (rDNA) were identified in one autosomal pair of P. (N.) chalcomelas and in five autosomal pairs of P. (N.) splendidulus. On the other hand, only one autosomal pair exhibited 5S rDNA sequences in these species. The results suggest that the karyotype differentiation of the Phanaeus species studied here involved pericentric inversions and centric fusions, as well as mechanisms related to amplification and dispersion of CH and rDNA sequences.

Cytogenetic analysis of Lagria villosa (Coleoptera, Tenebrionidae): emphasis on the mechanism of association of the Xy(p) sex chromosomes

The Xy(p) sex determination mechanism is the system most frequent and ancestral to Coleoptera. Moreover, the presence of argyrophilous material associated with the sex bivalent is described as being responsible for the maintenance and association of these chromosomes. There are no karyotype data available regarding the genus Lagria and no consensus in the literature regarding the argyrophilous material present in the lumen of sex bivalent. Therefore, the aim of this work was to investigate the mechanism of sex chromosome bivalent association in Lagria villosa by analyzing the argyrophilous nature of the material present in the Xy(p) lumen. It was also intended to characterize L. villosa cytogenetically. The analysis of meiotic cells showed 2n = 18 = 16+Xy(p) for males and 2n = 18 = 16+XX in females and the meiotic formula was 2n = 8(II)+Xy(p). The C-banding showed blocks of pericentromeric heterochromatin in all chromosomes except in the y(p) chromosome. In these regions, the use of fluorochromes revealed the presence of heterochromatin containing GC rich DNA sequences. The study of synaptonemal complex showed a gradual increase in the electron-density of the axial elements of the sex chromosomes and their association with strongly electron-dense material. The pepsin pretreatment revealed that the material impregnated by silver is protein.

Cytogenetics of the darkling beetles Zophobas aff. confusus and Nyctobates gigas (Coleoptera, Tenebrionidae)

Males of Zophobas aff. confusus and Nyctobates gigas (Tenebrionidae) collected in the State of Pernambuco, Brazil, were studied through conventional staining, C-banding, silver nitrate impregnation (AgNO₃), and the base specific fluorochromes CMA₃ and DAPI. Z. aff. confusus was found to have 2n = 20 (9+Xyp) while N. gigas exhibited 2n = 18 (8+neoXY). Large pericentromeric blocks of constitutive heterochromatin (CH) were detected throughout the autosomal complement of the two species, except in one autosomal pair of N. gigas in which no heterochromatic block was observed. The sex chromosomes of both species were almost totally heterochromatic. Double staining with CMA₃/DA (distamycin) and DAPI/DA marked CH in Z. aff. confusus. However, DAPI staining was more intense. N. gigas was found to possess blocks of CH-positive CMA₃ and homogeneous DAPI. AgNO₃ staining also revealed differences between the two species. In Z. confusus an NOR was observed in the sexual bivalent Xyp and N. gigas was found to have an autosomal NOR.

Cyclocephala (Coleoptera: Scarabaeidae: Dynastinae) evolution in Lesser West Indies indicates a Northward colonization by C. tridentata

A dual cytogenetic and molecular analysis was performed in four species of Cyclocepala (Coleoptera: Scarabaeidae: Dynastinae) from Lesser Antilles (Martinique, Dominica and Guadeloupe). Two species/sub-species, C. mafaffa grandis and C. insulicola, are endemic to Guadeloupe. They have their own non-polymorphic karyotype and a fairly homogeneous haplotype of the COI gene. C. melanocephala rubiginosa has a distinct karyotype. Its COI haplotype is homogeneous in Guadeloupe and heterogeneous in Martinique. Finally, C. tridentata has highly different karyotypes and haplotypes in the three islands. In Martinique, its karyotype, composed of metacentrics, is monomorphic while its haplotype is fairly heterogeneous. Both are close to those of other Cyclocephala and Dynastinae species, thus fairly ancestral. In Guadeloupe, its karyotype is highly polymorphic, with many acrocentrics, and its haplotype fairly homogeneous. Both are highly derived. In Dominica, both the karyotype and the haplotype represent intermediate stages between those of Martinique and Guadeloupe. We conclude that several independent colonization episodes have occurred, which excludes that C. insulicola is a vicariant form of C. tridentata in Guadeloupe. Both chromosome and COI gene polymorphisms clearly indicate a recent colonization with a northward direction for C. tridentata.

Karyotype analysis of four jewel-beetle species (Coleoptera, Buprestidae) detected by standard staining, C-banding, AgNOR-banding and CMA3/DAPI staining

The male karyotypes of Acmaeodera pilosellae persica Mannerheim, 1837 with 2n=20 (18+neoXY), Sphenoptera scovitzii Faldermann, 1835 (2n=38-46), Dicerca aenea validiuscula Semenov, 1895 - 2n=20 (18+Xyp) and Sphaerobothris aghababiani Volkovitsh et Kalashian, 1998 - 2n=16 (14+Xyp) were studied using conventional staining and different chromosome banding techniques: C-banding, AgNOR-banding, as well as fluorochrome Chromomycin A3 (CMA3) and DAPI. It is shown that C-positive segments are weakly visible in all four species which indicates a small amount of constitutive heterochromatin (CH). There were no signals after DAPI staining and some positive signals were discovered using CMA3 staining demonstrating absence of AT-rich DNA and presence of GC-rich clusters of CH. Nucleolus organizing regions (NORs) were revealed using Ag-NOR technique; argentophilic material mostly coincides with positive signals obtained using CMA3 staining.

Chromosomal organization of the 18S and 5S rRNAs and histone H3 genes in Scarabaeinae coleopterans: insights into the evolutionary dynamics of multigene families and heterochromatin

BACKGROUND

Scarabaeinae beetles show a high level of macro-chromosomal variability, although the karyotypic organization of heterochromatin and multigene families (rDNAs and histone genes) is poorly understood in this group. To better understand the chromosomal organization and evolution in this group, we analyzed the karyotypes, heterochromatin distribution and chromosomal locations of the rRNAs and histone H3 genes in beetles belonging to eight tribes from the Scarabaeinae subfamily (Coleoptera, Scarabaeidae).

RESULTS

The number of 18S rRNA gene (a member of the 45S rDNA unit) sites varied from one to 16 and were located on the autosomes, sex chromosomes or both, although two clusters were most common. Comparison of the 45S rDNA cluster number and the diploid numbers revealed a low correlation value. However, a comparison between the number of 45S rDNA sites per genome and the quantity of heterochromatin revealed (i) species presenting heterochromatin restricted to the centromeric/pericentromeric region that contained few rDNA sites and (ii) species with a high quantity of heterochromatin and a higher number of rDNA sites. In contrast to the high variability for heterochromatin and 45S rDNA cluster, the presence of two clusters (one bivalent cluster) co-located on autosomal chromosomes with the 5S rRNA and histone H3 genes was highly conserved.

CONCLUSIONS

Our results indicate that the variability of the 45S rDNA chromosomal clusters is not associated with macro-chromosomal rearrangements but are instead related to the spread of heterochromatin. The data obtained also indicate that both heterochromatin and the 45S rDNA loci could be constrained by similar evolutionary forces regulating spreading in the distinct Scarabaeinae subfamily lineages. For the 5S rRNA and the histone H3 genes, a similar chromosomal organization could be attributed to their association/co-localization in the Scarabaeinae karyotypes. These data provide evidence that different evolutionary forces act at the heterochromatin and the 45S rDNA loci compared to the 5S rRNA and histone H3 genes during the evolution of the Scarabainae karyotypes.

Chromosomal organization of the 18S and 5S rRNAs and histone H3 genes in Scarabaeinae coleopterans: insights into the evolutionary dynamics of multigene families and heterochromatin

Background

Scarabaeinae beetles show a high level of macro-chromosomal variability, although the karyotypic organization of heterochromatin and multigene families (rDNAs and histone genes) is poorly understood in this group. To better understand the chromosomal organization and evolution in this group, we analyzed the karyotypes, heterochromatin distribution and chromosomal locations of the rRNAs and histone H3 genes in beetles belonging to eight tribes from the Scarabaeinae subfamily (Coleoptera, Scarabaeidae).

Results

The number of 18S rRNA gene (a member of the 45S rDNA unit) sites varied from one to 16 and were located on the autosomes, sex chromosomes or both, although two clusters were most common. Comparison of the 45S rDNA cluster number and the diploid numbers revealed a low correlation value. However, a comparison between the number of 45S rDNA sites per genome and the quantity of heterochromatin revealed (i) species presenting heterochromatin restricted to the centromeric/pericentromeric region that contained few rDNA sites and (ii) species with a high quantity of heterochromatin and a higher number of rDNA sites. In contrast to the high variability for heterochromatin and 45S rDNA cluster, the presence of two clusters (one bivalent cluster) co-located on autosomal chromosomes with the 5S rRNA and histone H3 genes was highly conserved.

Conclusions

Our results indicate that the variability of the 45S rDNA chromosomal clusters is not associated with macro-chromosomal rearrangements but are instead related to the spread of heterochromatin. The data obtained also indicate that both heterochromatin and the 45S rDNA loci could be constrained by similar evolutionary forces regulating spreading in the distinct Scarabaeinae subfamily lineages. For the 5S rRNA and the histone H3 genes, a similar chromosomal organization could be attributed to their association/co-localization in the Scarabaeinae karyotypes. These data provide evidence that different evolutionary forces act at the heterochromatin and the 45S rDNA loci compared to the 5S rRNA and histone H3 genes during the evolution of the Scarabainae karyotypes.

Evolution of European cockchafers (Melolonthinae: Scarabaeidae: Coleoptera): a morphological, molecular and chromosomal study of intra- and inter-specific variations

In cockchafers of the genus Melolontha, there is a marked intraspecific polymorphism for morphological characters, making some specimens of one species resemble another. A cytogenetic and molecular (mitochondrial COI gene sequence) study of typical and atypical forms of M. melolontha and M. hippocastani, captured at the same period and area, was performed. Karyotypes and haplotypes clearly characterize each taxon, placing atypical specimens in one or the other species unambiguously. This formally discards the role of hybridization in phenotypic resemblance, as usually proposed. Karyotypes and haplotypes were compared to those of M. pectoralis and Phyllophaga pleei, a more distantly related Melolonthinae, and some Dynastinae species, to reconstruct their ancestral karyotype. The karyotype of M. melolontha is the most derivative and that of P. pleei the most conserved among the Melolonthinae studied, which fits with the phylogeny established by COI gene analysis. Both karyotypes and COI haplotypes demonstrate the proximity of M. pectoralis and M. melolontha. The karyotype of M. melolontha is polymorphic, without relationship with morphological variations. Finally, the existence of similar morphological variations in different Melolontha species and chromosomal polymorphism in M. melolontha is discussed in relation with a network (reticulated) mode of speciation.

Cytogenetic analysis of two Coprophanaeus species (Scarabaeidae) revealing wide constitutive heterochromatin variability and the largest number of 45S rDNA sites among Coleoptera

The Coleopterans of Scarabaeinae clade presents Coprophanaeus (Megaphanaeus) ensifer and C. (Coprophanaeus) cyanescens (Scarabaeidae) when they are studied cytogenetically by different techniques. The species present symmetric karyotypes, diploid number of 2n=20, and meta-submetacentric chromosomes. C. (M.) ensifer present an XY sex-determining mechanism and C. (C.) cyanescens an XY(p) parachute mechanism. Analysis of constitutive heterochromatin (CH) in the two species revealed the presence of diphasic autosomes, with log arm heterochromatics. Moreover, an additional heterochromatic block in four autosomal bivalents were observed in C. (M.) ensifer. CMA(3)/DA/DAPI fluorochrome staining detected CMA(3) positive heterochromatic blocks restricted to the sex chromosomes in C. (C.) cyanescens, whereas in C. (M.) ensifer CMA(3) positive pericentromeric blocks were present in all autosomes, in the Y chromosome and in the four additional heterochromatic blocks. DAPI staining was neutral in both species. Silver nitrate (AgNO(3)) staining was inefficient for the detection of the nucleolar organizer region (NORs), but showed affinity for the heterochromatic regions. Fluorescence in situ hybridization (FISH) revealed the presence of 45S rDNA sites in the terminal region of the three autosomal bivalents of C. (C.) cyanescens and in seven bivalents and the Y chromosome of C. (M.) ensifer. These results contribute to a better understanding of chromosome evolution in the genus Coprophanaeus, and demonstrate a wide CH variability and the largest number of ribosomal sites among Coleoptera.

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 750bp 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 722bp 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.

Cytogenetic analysis of Astylus antis (Perty, 1830) (Coleoptera, Melyridae): Karyotype, heterochromatin and location of ribosomal genes

Cytogenetic analysis of Astylus antis using mitotic and meiotic cells was performed to characterize the haploid and diploid numbers, sex determination system, chromosome morphology, constitutive heterochromatin distribution pattern and chromosomes carrying nucleolus organizer regions (NORs). Analysis of spermatogonial metaphase cells revealed the diploid number 2n = 18, with mostly metacentric chromosomes. Metaphase I cells exhibited 2n = 8II+Xyp and a parachute configuration of the sex chromosomes. Spermatogonial metaphase cells submitted to C-banding showed the presence of small dots of constitutive heterochromatin in the centromeric regions of nearly all the autosomes and on the short arm of the X chromosome (Xp), as well as an additional band on one of the arms of pair 1. Mitotic cells submitted to double staining with base-specific fluorochromes (DAPI-CMA(3) ) revealed no regions rich in A+T or G+C sequences. Analysis of spermatogonial mitotic cells after sequential Giemsa/AgNO (3) staining did not reveal any specific mark on the chromosomes. Meiotic metaphase I cells stained with silver nitrate revealed a strong impregnation associated to the sex chromosomes, and in situ hybridization with an 18S rDNA probe showed ribosomal cistrons in an autosomal bivalent.

Cytogenetic characterization of Eurysternus caribaeus (Coleoptera: Scarabaeidae): evidence of sex-autosome fusion and diploid number reduction prior to species dispersion

Mitotic and meiotic chromosomes of several populations of Eurysternus caribaeus (Coleoptera: Scarabaeidae) were analysed through conventional staining, C-banding, base-specific fluorochromes, silver nitrate staining and fluorescent in situ hybridization (FISH). All specimens showed 2n = 8 in their karyotypes, with a neo-XY sex system (Y is a submetacentric and X a metacentric) and three pairs of submetacentric autosomes. The analysis of constitutive heterochromatin (CH) revealed small blocks located in the centromeric region of all chromosomes which do not present positive staining under the fluorochromes CMA3 and DAPI. Silver nitrate staining revealed that the nucleolar organizer region (NORs) is associated with the sex chromosomes. The FISH technique revealed that rDNA sites in the X and Y are different in size. Data from different populations indicate that the diploid number reduction (2n = 8) observed in E. caribaeus is established and presumably has preceded the dispersion of this species. Moreover, this reduction occasioned the translocation of rDNA sites to the sex chromosomes, X and Y, an uncommon pattern in Scarabaeidae that was observed for the first time by the FISH in this work.

Comparative cytogenetics of three species of Dichotomius (Coleoptera, Scarabaeidae)

Meiotic and mitotic chromosomes of Dichotomius nisus, D. semisquamosus and D. sericeus were analyzed after conventional staining, C-banding and silver nitrate staining. In addition, Dichotomius nisus and D. semisquamosus chromosomes were also analyzed after fluorescent in situ hybridization (FISH) with an rDNA probe. The species analyzed had an asymmetrical karyotype with 2n = 18 and meta-submetacentric chromosomes. The sex determination mechanism was of the Xy_p type in D. nisus and D. semisquamosus and of the Xy _r type in D. sericeus. C-banding revealed the presence of pericentromeric blocks of constitutive heterochromatin (CH) in all the chromosomes of the three species. After silver staining, the nucleolar organizer regions (NORs) were located in autosomes of D. semisquamosus and D. sericeus and in the sexual bivalent of D. nisus. FISH with an rDNA probe confirmed NORs location in D. semisquamosus and in D. nisus. Our results suggest that chromosome inversions and fusions occurred during the evolution of the group.

Comparative analysis of rDNA location in five Neotropical gomphocerine grasshopper species

We report here, for the first time, the chromosome complement, number and location of the nucleolar organizer regions (NORs) revealed by silver staining (AgNO(3)) and fluorescent in situ hybridization (FISH) in five Neotropical gomphocerine species: Rhammatocerus brasiliensis, R. brunneri, R. palustris, R. pictus and Amblytropidia sp. The objective of this study was to summarize available data and propose a model of chromosome evolution in Neotropical gomphocerines. All five species studied showed chromosome numbers consisting of 2n = 23,X0 in males and 2n = 24,XX in females. Amblytropidia sp. was the only species showing a bivalent (M(8)) with megameric behavior during meiosis. The rDNA sites were restricted to autosomal pairs, i.e. the pericentromeric region of the S(9) chromosome, the consensus NOR location in all five species. R. brasiliensis was the only species showing additional NORs on M(4) and M(6) pairs which, likewise the S(9) NOR, were active in all cells analyzed. Comparison of these results with those reported previously in Palearctic gomphocerine species suggests higher resemblance of Neotropical species with the Old World species also possessing 23/24 chromosomes. Evolutionary mechanisms responsible for the observed interspecific variation in NOR location in this group are discussed.

Evolution of sexual dimorphism and male dimorphism in the expression of beetle horns: phylogenetic evidence for modularity, evolutionary lability, and constraint

Beetle horns are enlarged outgrowths of the head or thorax that are used as weapons in contests over access to mates. Horn development is typically confined to males (sexual dimorphism) and often only to the largest males (male dimorphism). Both types of dimorphism result from endocrine threshold mechanisms that coordinate cell proliferation near the end of the larval period. Here, we map the presence/absence of each type of dimorphism onto a recent phylogeny for the genus Onthophagus (Coleoptera: Scarabaeidae) to explore how horn development has changed over time. Our results provide empirical support for several recent predictions regarding the evolutionary lability of developmental thresholds, including uncoupled evolution of alternative phenotypes and repeated fixation of phenotypes. We also report striking evidence of a possible developmental constraint. We show that male dimorphism and sexual dimorphism map together on the phylogeny; whenever small males have horns, females also have horns (and vice versa). We raise the possibility that correlated evolution of these two phenomena results from a shared element in their endocrine regulatory mechanisms rather than a history of common selection pressures. These results illustrate the type of insight that can be gained only from the integration of developmental and evolutionary perspectives.

Nucleolus and chromosome relationships at pachynema in four Scarabaeoidea (Coleoptera) species with various combinations of NOR and sex chromosomes

Nucleolus organizer regions (NORs) and nucleolus locations were studied after silver staining in spermatocytes at pachynema from four beetle species selected for their various combinations of sex chromosomes. Their karyotypic formulae were: 18,neoXY (Dorcus parallelipipedus); 25,X (Passalus unicornis) and 20,Xyp (Cetonia aurata and Protaecia (Potosia) opaca). NORs were located in the short arms of a unique acrocentric autosome pair in the first three and in intercalary position in a sub-metacentric autosome pair in the last species. Silver staining gave remarkably more consistent results in pachytene than in mitotic spreads, enabling the detection of both NORs and nucleoli, and also better results in embryo than in spermatogonial metaphases. At pachynema the NORs were elongated, roughly in proportion to the number of nucleoli, which always remained associated with NOR. Nucleoli were not recurrently associated with sex chromosomes, except in P. unicornis, at late pachynema. In C. aurata and P. opaca the sex body was recurrently associated with acrocentric short arms and metacentric telomeres, respectively. Even in these simple situations, with NORs located in a single autosome pair, the number of nucleoli and their relationships with sex chromosomes varied strongly from species to species. These variations appear to be largely determined by the chromosome rearrangements which have occurred during evolution, which makes extrapolations and generalizations quite hazardous. In D. parallelipipedus pachytene cells a quasi-systematic and transient fusion between the terminal heterochromatin of two sub-metacentrics was detected. Other chromosome bivalents could also be occasionally associated, but not the NOR carrier one. A strong enhancement of DAPI or quinacrine mustard staining was observed at the fusion point.

Karyotype characterization of Eurysternus caribaeus: the smallest diploid number among Scarabaeidae (Coleoptera: Scarabaeoidea)

Eurysternus caribaeus was analyzed cytologically by conventional chromosomal staining. The species presents a diploid number of 2n=8, chromosomes with two arms and an XY sex determining mechanism. This is the first karyotype described for the genus Eurysternus and the tribe Eurysternini, and is also the smallest diploid number observed in the family Scarabaeidae and superfamily Scarabaeoidea.

Heterochromatin of the scarab beetle, Bubas bison (Coleoptera: Scarabaeidae) II. Evidence for AT-rich compartmentalization and a high amount of rDNA copies

An unexpected result arising from a previous characterization of the scarab beetle Bubas bison (Coleoptera: Scarabaeidae) heterochromatin was its unusual homogeneous reaction to different staining methods. In particular, silver stainability of heterochromatic ends of all chromosomes prevented identification of the number of rDNA transcriptionally active regions. Data formerly obtained using silver impregnation (Ag-NOR), C- G- and DAPI banding are here improved and completed by application of CMA(3) staining and rDNA FISH with the aim to investigate heterochromatin base composition and locate rDNA regions with respect to NOR-associated heterochromatin. Our results show that B. bison has a high amount of heterochromatin (almost 50%) and that--as revealed by rDNA FISH--major rRNA genes are spread over the heterochromatic telomeric regions of eight chromosomes, thus suggesting that only a portion, although consistent, of total heterochromatin is associated with ribosomal clusters. Moreover, DAPI-positive (AT-specific) and CMA(3)-negative (GC-specific) reactions of heterochromatic DNA confirm its AT-rich composition. Finally, possible explanations for the bright DAPI-fluorescence of both heterochromatin and rDNA sequences are discussed.