A simple technique for demonstrating centromeric heterochromatin

Evolution of ZW Sex Chromosomes in Ptyas Snakes (Reptilia, Colubridae): New Insights from a Molecular Cytogenetic Perspective

Snakes are cytogenetically dynamic, characterized by largely conserved diploid chromosome numbers although displaying varied variable evolutionary stages of their sex chromosomes. This study examined four snakes, with a special focus on the genus Ptyas, to provide evolutionary insights into the evolution of ZW sex chromosomes. We performed an extensive karyotype characterization using conventional and molecular cytogenetic approaches, described for the first time the karyotype of Ptyas korros, and revisited the karyotype descriptions of P. mucosa, Chrysopelea ornata, and Fowlea flavipunctatus. We found that all species except F. flavipunctatus have highly heterochromatic W chromosomes enriched in satDNAs or microsatellite repeats. Repetitive sequences accumulate with the heterochromatinization of the W chromosome but are not necessarily associated with this process, demonstrating the dynamic makeup of snake sex chromosomes. Autosomal locus-specific and sex chromosome probes from Pogona vitticeps and Varanus acanthurus did not show hybridization signals in Ptyas snakes, suggesting divergent evolutionary pathways. This finding highlighted the dynamic nature of sex chromosome evolution in snakes, which occurred independently in lizards.

Cytogenetic insights into Sosippinae (Araneae, Lycosidae) reveal pronounced diploid number reduction in Aglaoctenus and elevated number of rDNA loci in two unrelated species

Spiders represent a fascinating group for studying chromosomal evolution due to their dynamic karyotypes, which reveal significant differences even between closely related taxa. Lycosidae, one of the most species-rich families of spiders, has its major relationships well stablished, though minor interspecific relationships remain poorly understood. Here, we analyzed chromosomal data from four species belonging to Aglaoctenus and Diapontia, two genera within the subfamily Sosippinae, to discuss the evolution of chromosomal traits within this lineage. For karyological analysis, we employed Giemsa staining, C-banding, Ag-NOR staining, and 28S rDNA FISH to identify key chromosomal characteristics and the distribution of repetitive elements. Both A. oblongus and D. uruguayensis exhibited 2n♂=28, X1X2, with acro/telocentric morphology, hypothesized to represent the ancestral condition for Lycosoidea. However, regarding the 28S rDNA chromosome mapping, these species revealed an unusually high number of loci with eight chromosome clusters in A. oblongus and a polymorphic condition in D. uruguayensis (10-14 signals), underscoring the utility of additional techniques for detecting specific chromosomal regions. Interestingly, A. castaneus and A. lagotis displayed a more derived karyotype, characterized by 2 n♂= 14, X1X2 and acro/telocentric morphology, with the sex chromosomes (X1 and X2) smaller than the autosomes. Taken together, these data suggest that, following the diversification of Aglaoctenus, a significant reduction in diploid number occurred, affecting only the autosomes. These findings encourage further cytogenetic research within Sosippinae and support the use of these data in future phylogenetic studies.

Small Fishes, Big Issues: Species Delimitation in Hemigrammus Marginatus, Gill, 1958 (Acestrorhamphidae: Pristellinae) from Brazilian Coastal Basins Based on Integrative Genetics

The small characins represent a systematic puzzle in the Neotropical ichthyofauna as a result of independent miniaturization processes, adaptive convergence and lack of diagnostic characters for several genera. In order to diminish the taxonomic uncertainties and the evolutionary pathways in Hemigrammus, we carried out an integrative genetic analysis in the putatively widespread Hemigrammus marginatus Ellis, 1958 by combining cytogenetic and molecular data based on the mitochondrial Cytochrome C Oxidase subunit I (COI). Specimens of H. marginatus from the type locality in Itapicuru River basin and other two populations from coastal rivers in northeastern Brazil were analyzed and compared with the available data from other regions in South America. Conspicuous macro and microkaryotypic differences were detected between the samples from northeastern and southern Brazil (Upper Paraná River basin). Likewise, the DNA barcoding and species delimitation analyses recovered distinct Molecular Operational Taxonomical Units within H. marginatus. Therefore, the population from the type locality should be referred to as H. marginatus stricto sensu, representing a restricted characin taxon from coastal drainages (including the São Francisco River basin) along northeastern Brazil, while other populations of this small characin fish need to be taxonomically revised and managed as unique lineages.

The role of dispersal of repetitive DNAs in the diversification of bristlenose plecos (Loricariidae, Hypostominae, Ancistrus) from South Atlantic Coastal drainages

Sea-level changes during the Pleistocene and the geomorphological history have largely molded the intricate shaping of coastal drainages in Eastern South America. Therefore, freshwater fishes from this region are promising models to infer how riverine isolation and reconnections affected their genetic diversification and geographic distribution. In the present study, we provided a detailed cytogenomic analysis of Ancistrus multispinis and Ancistrus brevipinnis, including the physical mapping of repetitive DNA classes, to verify whether chromosome differentiation would be related to the split between two major watersheds in Southern Brazil. Both species of Ancistrus shared the same modal diploid number (2n=52) and karyotype formulae (14 metacentric, 8 submetacentric and 30 subtelo/acrocentric chromosomes), besides single and terminal 18S ribosomal cistrons, (CGG)10 microsatellite sequences interspersed with heterochromatin in nucleolar organizer regions and a dispersed content of (AC)15 and (GT)15 microsatellites. In turn, the patterns of heterochromatin distribution, number of (GAG)10 microsatellites and 5S rDNA clusters diverged between both taxa. Most likely, these microstructural differences were determined by independent evolutionary processes, strongly associated to the geographic isolation between watersheds. Furthermore, the mapping of repetitive DNAs revealed a dynamic reorganization of genomes of Ancistrus, being useful for the taxonomic disambiguation in this complex group of Neotropical fish.

Repetitive DNAs and differentiation of the ZZ/ZW sex chromosome system in the combtail fish Belontia hasselti (Perciformes: Osphronemidae)

BACKGROUND

Java combtail fish Belontia hasselti (Cuvier, 1831), a member of the Osphronemidae family, inhabits lakes and rivers throughout Southeast Asia and Sri Lanka. Previous cytogenetic research revealed it possesses a diploid chromosome number of 48 chromosomes with a female-heterogametic ZZ/ZW sex chromosome system, where the W chromosome is distinguishable as the only metacentric element in the complement. Female-heterogametic sex chromosome systems seem to be otherwise surprisingly rare in the highly diverse order Perciformes and, therefore, B. hasselti provides an important comparative model to evolutionary studies in this teleost lineage. To examine the level of sex chromosome differentiation in B. hasselti and the contribution of repetitive DNAs to this process we combined bioinformatic analyses with chromosomal mapping of selected repetitive DNA classes, and comparative genomic hybridization.

RESULTS

By providing the first satellitome study in Perciformes, we herein identified 13 satellite DNA monomers in B. hasselti, suggesting a very low diversity of satDNA in this fish species. Using fluorescence in situ hybridization, we revealed detectable clusters on chromosomes only for four satellite DNA monomers. Together with the two mapped microsatellite motifs, the repeats primarily accumulated on autosomes, with no distinct clusters located on the sex chromosomes. Comparative genomic hybridization showed no region with accumulated female-specific or enriched repeats on the W chromosome. Telomeric repeats terminated all chromosomes, and no additional interstitial sites were detected.

CONCLUSION

These data collectively indicate a low degree of sex chromosome differentiation in B. hasselti despite their considerable heteromorphy. Possible mechanisms that may underlie this pattern are discussed.

Repetitive DNA Mapping Reveals Multiple Sex Chromosomes X1X1X2X2/X1X2Y in Pseudotylosurus microps (Günther 1866) (Beloniformes, Teleostei) from the Amazon

INTRODUCTION

Needlefish (Belonidae family) comprises 44 known species distributed worldwide. These species are predominantly marine but include estuarine representatives and 12 freshwater species. Among the recognized species, 8 are endemic to South American rivers. Cytogenetic studies of Belonidae are scarce and mostly limited to describing the diploid chromosome number (2n) and karyotypic structure.

METHODS

We used classical and molecular cytogenetic markers to karyotypically characterize Pseudotylosurus microps to understand the evolutionary processes of Belonidae species in the Amazon basin.

RESULTS

P. microps exhibited different diploid numbers between males (2n = 47, 3m + 3sm + 41st/a FN = 53) and females (2n = 48, 4m + 4sm + 40st/a FN = 56). Our study revealed the first case of multiple sex chromosomes in the Belonidae family.

CONCLUSION

These findings describe a multiple sex chromosome system of the type X1X1X2X2/X1X2Y. The C-banding pattern and 5S rDNA mapping suggest that this system likely resulted from a tandem fusion between a homolog of pair 1 and a homolog of pair 3, producing a large acrocentric Y chromosome. We propose that karyotypic changes due to internal chromosomal rearrangements, as observed in P. microps, can lead to species diversification and, in some cases, the emergence of a heteromorphic and multiple sex chromosome system.

Clinal variation in autosomal satellite DNA clusters across a contact zone in Barker Frogs

Contact zones between genetically divergent lineages offer a unique opportunity to explore gene flow and speciation dynamics. Because satellite DNAs (satDNAs) have high evolutionary rates, they may be useful for comparing related taxa and assessing contact zones. Here, we analysed the distribution of chromosomal clusters of PcP190 satDNA across a contact zone between two distinct genetic lineages of a Neotropical species complex of frogs. The parental lineages, Physalaemus ephippifer and lineage 1B (L1B), exhibited pronounced divergence in the number of PcP190 clusters. We further expanded the geographic scope of this species complex by including two additional Brazilian localities in previously available cytogenetic and mitochondrial DNA datasets. The contact zone exhibited remarkable variation in the chromosomal distribution of PcP190 clusters among the autosomes; the only fixed autosomal site was found on chromosome 3. The highest numbers of PcP190 clusters were observed in specimens collected at sites near (approximately 320 km from) the distribution of L1B, whereas specimens from Dom Eliseu, which is near (approximately 330 km from) the distribution of P. ephippifer, had the lowest numbers of such clusters. Mitochondrial haplotypes also exhibited geographical variation across sites. Our findings expand the known contact zone of these Physalaemus lineages from 1,500 km2 to over 6,200 km2, demonstrating its extensive area, and emphasize the usefulness of satDNAs in studying contact zones.

A variant W chromosome in Centromochlus heckelii (Siluriformes, Auchenipteridae) and the role of repeated DNA in its heteromorphism

Centromochlus heckelii has the lowest diploid chromosome number (2n = 46) and the only described heteromorphic sex chromosome system in Auchenipteridae. This study presents a population of C. heckelii from the Central Amazon basin with subtle variations in the karyotype composition and a variant W chromosome with distinct morphology and increased C-positive heterochromatin content. In this population, the W chromosome is subtelocentric, whereas the only previous study on C. heckelii reported a metacentric W chromosome. Constitutive heterochromatin (CH) and accumulation of microsatellite motifs have significantly contributed to this W chromosome enlargement. Notably, this population exhibits numerous interstitial telomeric sites (ITSs). Some of these ITSs might represent genuine chromosomal fusion points due to the reduced 2n; however, additional mechanisms, such as chromosomal inversions, translocations, transpositions, or association with satellite DNA, are likely responsible for this unusual pattern. The 18S rDNA sites were found in both the Z and W chromosomes of all individuals. However, two individuals exhibited an additional 18S rDNA site in a single homologous of the chromosome pair 20, characterizing an intrapopulation polymorphism. The 5S rDNA sites were found in two chromosome pairs, distinguishing this population from other Centromochlinae species and further supporting it as one of the most efficient cytotaxonomic markers within the subfamily.

Evolutionary dynamics of the B chromosomes in the fish species Prochiloduslineatus Valenciennes, 1837 of the Paraná River Basin

The fish species Prochiloduslineatus has an interesting B chromosome system, with three morphological types as acrocentric, metacentric, and submetacentric. However, most cytogenetic studies on this species are restricted to the natural population of the Mogi Guaçu River. Given this, the present work aimed to study the structure karyotypic profile as well as the occurrence of supernumeraries in P.lineatus in several localities in the Paraná River basin, where this species is abundant. The results obtained showed a predominantly conserved karyotypic macrostructure and the presence of B chromosomes in all the seven localities studied, with the exception of the Apa River. Additionally, new variants of morphological characteristics were found in the population of the Batalha River (Reginópolis). These results allow us to infer that there is a large occurrence of B chromosomes in this species, with important differences in B chromosome frequency between the populations, especially in acrocentric and submetacentric B variants. Considering the possible origin and evolution of B chromosomes in P.lineatus, our results allow us to describe the dispersion of metacentric B variants, in contrast with the elimination observed in acrocentric and submetacentric variants.

Cytogenomics of Frieseomelitta varia (Hymenoptera: Apidae) and the Sharing of a Satellite DNA Family in Several Neotropical Meliponini Genera

BACKGROUND/OBJECTIVES

A striking feature of the karyotypes of stingless bees is the large amount of heterochromatin present in most species. Cytogenomic studies performed in some Meliponini species have suggested that evolutionary events related to the diversification and amplification of satellite DNA families in the heterochromatin may reflect the structuring of phylogenetic clades in this tribe. In this study, we performed a genomic analysis in Frieseomelitta varia to characterize different satDNA families in its genome. We also investigated the presence of the most abundant satDNA family of F. varia in its own chromosomes, in two other Frieseomelitta species, and in other Meliponini genera encompassing the three main clades of Neotropical Meliponini, according to the available molecular phylogeny.

METHODS

Genomic analyses were performed using RepeatExplorer2 on the Galaxy platform, and chromosomal investigations were conducted using fluorescent in situ hybridization.

RESULTS

Seven satDNA families were recovered, which together totaled an abundance of 11.223% of the analyzed F. varia genomic fraction. The most abundant satDNA family, FvarSat01-306, predominates in the analyzed repetitive fraction (representing around 89%) and was recently amplified and homogenized in almost all the heterochromatin of F. varia. In addition, the data revealed an unprecedented sharing of this satDNA family in the centromeric/pericentromeric heterochromatin among different Meliponini genera, with independent amplifications and loss of this sequence in some taxa.

CONCLUSIONS

One family of satellite DNA makes up most of the heterochromatin in this species and is shared with other Meliponini.

Chromosome homologies and polymorphisms in a Neotropical species complex of frogs revealed by the U2 snRNA gene

The Physalaemus cuvieri-Physalaemus ephippifer species complex is a Neotropical frog group that encompasses seven well-supported major clades. Although very similar morphologically, the five lineages previously karyotyped show notorious cytogenetic signatures. There is also evidence of ancient secondary contact between P. ephippifer, which has heteromorphic sex chromosomes, and the lineage known as L1B, which lacks sex chromosome heteromorphism. Here, to aid comparative analysis within this complex, we mapped the U2 small nuclear RNA (snRNA) gene using fluorescent in situ hybridization (FISH). All samples presented a U2 snRNA gene cluster terminally in the short arm of chromosome 6. Additional small FISH signals were also revealed, particularly in one lineage with previously noted polymorphism of nucleolar organizer regions. Moreover, one additional site contributed for the analysis of sex chromosomes, since the Z chromosome of P. ephippifer harbors a small FISH signal, which is absent in the W chromosome. In lineage L1B, chromosome 9-which is homologous to the sex chromosomes of P. ephippifer-is polymorphic for a small FISH signal, as did the Z chromosome in the group derived from the contact between these lineages. Finally, nucleotide sequence analysis revealed some truncated gene sequences, suggesting the presence of pseudogenes of the U2 snRNA gene in these frogs.

Karyotype evolution of suliformes and description of a ♂Z1Z1Z2Z2/♀Z1Z2W multiple sex chromosome system in boobies (Sula spp.)

Our comprehension of avian karyotypes still needs to be improved, especially for Suliform birds. To enhance understanding of chromosomal evolution in this order, we conducted conventional and molecular cytogenetic analysis in five species, named Sula dactylatra, Sula leucogaster, Sula sula (Sulidae), Fregata magnificens (Fregatidae), and Nannopterum brasilianum (Phalacrocoracidae). The diploid chromosome number for S. dactylatra and S. leucogaster was established as 2n = 76 in males, and 2n = 75 in females, but S. sula displayed a karyotype of 2n = 76 chromosomes in males. The disparity in diploid chromosome numbers between male and female Sula is due to a multiple sex chromosome system of the Z1Z1Z2Z2/Z1Z2W type. We propose that the emergence of this multiple-sex chromosome system resulted from a Robertsonian translocation involving the W chromosome and the smallest microchromosome. Fregata magnificens exhibited a diploid number 76 (2n = 76), while N. brasilianum displayed a diploid number of 74 (2n = 74) in both sexes. The ribosomal cluster was located in one microchromosome pair in S. dactylatra, S. leucogaster, S. sula, and F. magnificens and in four pairs in N. brasilianum. Our findings provide evidence of a conserved multiple-sex chromosome system within the Sula genus, shedding light on the high karyotype diversity in Suliformes.

Chromosomal and molecular perspectives on Potamotrygon motoro (Müller & Henle, 1841) from central Amazon

Cytogenetic studies on Potamotrygon motoro (Müller & Henle, 1841) are limited to classical cytogenetic techniques, but they do reveal great karyotypic variation. The main differences are related to the karyotypic formula and the absence/presence of sex chromosome systems. Thus, this study aimed to expand knowledge of the karyotypic composition of Potamotrygon motoro from different locations of the Central Amazon using Fluorescence in situ Hybridization to investigate the distribution of ribosomal DNAs (rDNA) and microsatellites sequences (SSRs). In addition, we used the mitochondrial DNA cytochrome oxidase subunit I (mtDNA COI) to perform neighbor-joining analysis to investigate the relationships among the individuals sampled. In our study, Potamotrygon motoro presented 2n = 66 chromosomes, with 18m + 12sm + 10st + 26a and heterochromatic blocks on centromeric region of all chromosomes. The 18S rDNA is present in three chromosomal pairs and 5S rDNA is located in the pair 16, which is a feature shared among freshwater stingray species. Regarding the mapping of SSRs, dinucleotide sequences showed a greater number of sites, usually on terminal regions of chromosomal pairs, with an accumulation throughout the long arms of the pair 17. Our molecular analyses did not reveal differences between the sequences used. In general, the karyotypic differences previously reported for Potamotrygon motoro indicate the presence of different cytotypes within the species.

A Detailed Karyological Investigation of three Endemic Cobitis Linnaeus, 1758 Species (Teleostei, Cobitidae) in Anatolia, Türkiye

INTRODUCTION

Comparative cytogenetics is a vital approach for diagnosing chromosome abnormalities and identifying species-specific patterns. In this study, chromosomal analysis of three Anatolian endemic Cobitis species was performed: Cobitis bilseli, C. fahireae, and C. turcica.

METHODS

Conventional cytogenetic techniques such as Giemsa staining, C-banding, and Ag-NOR staining were applied, followed by measurements of chromosome arm lengths including analysis of the measured data.

RESULTS

The diploid chromosome number, 2n = 50, was determined for all three species. The karyotype formulas were as follows: four pairs of metacentric, 5 pairs of submetacentric, and 16 pairs of subtelo-telocentric chromosomes in C. bilseli; 11 pairs of metacentric, 7 pairs of submetacentric, and 7 pairs of subtelo-telocentric chromosomes in C. fahireae; and 4 pairs of metacentric, 4 pairs of submetacentric, and 17 pairs of subtelo-telocentric chromosomes in C. turcica. Dark C-bands were observed on the pericentromeres of nearly all chromosomes in C. bilseli and C. turcica, whereas light C-bands appeared on the pericentromeres of some chromosomes in C. fahireae. Silver-stained metaphases revealed signals on the short arm of a submetacentric chromosome pair in C. fahireae (each homologous chromosome carries one signal), while in C. bilseli and C. turcica, Ag-NOR signals were detected on the long arm of a single metacentric chromosome (only one homologous chromosome carries the signal, and the signal-carrying chromosome is the largest chromosome in the karyotype).

CONCLUSION

This study provides new cytogenetic data consistent with the phylogenetic distances between the studied species, indicating that pericentric inversions and/or translocations govern the formation of Cobitis karyotypes.

INTRODUCTION

Comparative cytogenetics is a vital approach for diagnosing chromosome abnormalities and identifying species-specific patterns. In this study, chromosomal analysis of three Anatolian endemic Cobitis species was performed: Cobitis bilseli, C. fahireae, and C. turcica.

METHODS

Conventional cytogenetic techniques such as Giemsa staining, C-banding, and Ag-NOR staining were applied, followed by measurements of chromosome arm lengths including analysis of the measured data.

RESULTS

The diploid chromosome number, 2n = 50, was determined for all three species. The karyotype formulas were as follows: four pairs of metacentric, 5 pairs of submetacentric, and 16 pairs of subtelo-telocentric chromosomes in C. bilseli; 11 pairs of metacentric, 7 pairs of submetacentric, and 7 pairs of subtelo-telocentric chromosomes in C. fahireae; and 4 pairs of metacentric, 4 pairs of submetacentric, and 17 pairs of subtelo-telocentric chromosomes in C. turcica. Dark C-bands were observed on the pericentromeres of nearly all chromosomes in C. bilseli and C. turcica, whereas light C-bands appeared on the pericentromeres of some chromosomes in C. fahireae. Silver-stained metaphases revealed signals on the short arm of a submetacentric chromosome pair in C. fahireae (each homologous chromosome carries one signal), while in C. bilseli and C. turcica, Ag-NOR signals were detected on the long arm of a single metacentric chromosome (only one homologous chromosome carries the signal, and the signal-carrying chromosome is the largest chromosome in the karyotype).

CONCLUSION

This study provides new cytogenetic data consistent with the phylogenetic distances between the studied species, indicating that pericentric inversions and/or translocations govern the formation of Cobitis karyotypes.

Supernumerary Chromosomes Enhance Karyotypic Diversification of Narrow-Headed Voles of the Subgenus Stenocranius (Rodentia, Mammalia)

The subgenus Stenocranius contains two cryptic species: Lasiopodomys gregalis (subdivided into three allopatrically distributed and genetically well-isolated lineages A, B, and C) and Lasiopodomys raddei. To identify karyotype characteristics of this poorly studied cryptic species complex, we used comparative cytogenetic analysis of 138 individuals from 41 localities in South Siberia and Mongolia. A detailed description of the L. raddei karyotype and of the L. gregalis lineage С karyotype is presented for the first time. The A chromosome complement of all examined narrow-headed voles consisted of 2n = 36 and a fundamental number of autosomal arms (FNa) of 50. Between species, patterns of differential staining were similar, though additional C-heterochromatic blocks were found in L. gregalis lineages; Ag-positive nucleolar organizers and ribosomal DNA (rDNA) clusters are located on eight and nine acrocentric pairs, respectively. No B chromosomes (Bs) were found in the Early Pleistocene relic L. raddei, while one to five small heterochromatic acrocentric Bs were detected in all L. gregalis lineages; the number and frequency of Bs varied considerably within lineages, but no intraindividual variation was observed. In both species, telomeric repeats were visualized at termini of all chromosomes, including Bs. The number and localization of rDNA clusters on Bs varied among B-carriers. Immunodetection of several meiotic proteins indicated that meio-Bs are transcriptionally inactive and have a pattern of meiotic behavior similar to that of sex chromosomes (some homology of Bs to sex chromosomes is supposed). The nature, mechanisms of inheritance and stability of Bs in L. gregalis require further investigation.

Detailed cytogenetic analysis of three duck species (the northern pintail, mallard, and common goldeneye) and karyotype evolution in the family Anatidae (Anseriformes, Aves)

Galliformes and Anseriformes are two branches of the Galloanserae group, basal to other Neognathae. In contrast to Galliformes, Anseriformes have not been thoroughly researched by cytogenetic methods. This report is focused on representatives of Anseriformes and the evolution of their chromosome sets. Detailed cytogenetic analysis (G-banding, C- banding, and fluorescence in situ hybridization) was performed on three duck species: the northern pintail (Anas acuta, 2n = 80), the mallard (A. platyrhynchos, 2n = 80), and the common goldeneye (Bucephala clangula, 2n = 80). Using stone curlew (Burhinus oedicnemus, 2n = 42, Charadriiformes) chromosome painting probes, we created homology maps covering macrochromosomes and some microchromosomes. The results indicated a high level of syntenic group conservation among the duck genomes. The two Anas species share their macrochromosome number, whereas in B. clangula, this number is increased due to fissions of two ancestral elements. Additionally, in this species, the presence of massive heterochromatic blocks in most macroautosomes and sex chromosomes was discovered. Localization of clusters of ribosomal DNA and telomere repeats revealed that the duck karyotypes contain some microchromosomes that bear ribosomal RNA genes and/or are enriched for telomere repeats and constitutive heterochromatin. Dot plot (D-GENIES) analysis confirmed the established view about the high level of syntenic group conservation among Anatidae genomes. The new data about the three Anatidae species add knowledge about the transformation of macro- and sex chromosomes of Anseriformes during evolution.

Karyotypes and Chromosomal Mapping of Some Repetitive DNAs in Two Stingless Bee Species (Apidae: Meliponini), with the Description of a B Chromosome in Plebeia Genus

INTRODUCTION

Cytogenetic studies on stingless bees have significantly contributed to our understanding of karyotypic evolution and the composition of euchromatin and heterochromatin regions, including repetitive sequences.

METHODS

In this study, we performed classical cytogenetics, chromosomal banding, and mapping of some repetitive sequences in two stingless bee species, Frieseomelitta trichocerata and Plebeia poecilochroa.

RESULTS

The species exhibit the typical diploid chromosome number of each genera, 2n = 30 for Frieseomelitta and 2n = 34 for Plebeia. Additionally, some individuals of P. poecilochroa presented a small heterochromatic B chromosome, showing a numeric variation of n = 17-18 in males and 2n = 34-35 in females. In both species, heterochromatin is primarily distributed in the short arm and centromeric regions. Centromeric regions were found to be AT-rich in both species, while subterminal/terminal regions of the short arms of one and six chromosomes presented GC-rich sites in P. poecilochroa and F. trichocerata, respectively. The rDNA clusters were mapped on two chromosomes in F. trichocerata, and in only one chromosome pair in P. poecilochroa. Microsatellites (GA)n, (GAG)n, and (CAA)n were predominantly mapped in euchromatic regions, while the telomeric motif (TTAGG)n mapped to the ends of most chromosomes, including the B chromosome of P. poecilochroa. The other repetitive probes used, including the rDNA clusters, do not label the B chromosome of P. poecilochroa.

CONCLUSIONS

Our cytogenetic data highlight both similarities and differences when compared to other congeneric species, expanding the chromosomal data for both genera.

Chromosomal analysis of two Acanthodoras species (Doradidae, Siluriformes): Insights into the oldest thorny catfish clade and its karyotype evolution

The Doradidae fishes constitute one of the most diverse groups of Neotropical freshwater environments. Acanthodoradinae is the oldest lineage and the sister group to all other thorny catfishes, and it includes only the genus Acanthodoras. The diversity of Acanthodoras remains underestimated, and the use of complementary approaches, including genetic studies, is an important step to better characterize this diversity and the relationships among the species within the genus. Therefore, we conducted a comprehensive analysis using conventional cytogenetic techniques and physical mapping of three multigene families (18S and 5S ribosomal DNA [rDNA], U2 small nuclear DNA [snDNA]) and four microsatellite motifs, namely (AC)n, (AT)n, (GA)n, and (GATA)n, in two sympatric species from the Negro River: Acanthodoras cataphractus and Acanthodoras cf. polygrammus. We found significant differences in constitutive heterochromatin (CH) content, distribution of the microsatellite (AT)n, and the number of 5S rDNA and U2 snDNA sites. These differences may result from chromosome rearrangements and repetitive DNA dispersal mechanisms. Furthermore, the characterization of the diploid number (2n) of these Acanthodoras species enables us to propose 2n = 58 chromosomes as the plesiomorphic 2n state in Doradidae based on ancestral state reconstruction. Acanthodoradinae is the oldest lineage of the thorny catfishes, and knowledge about its cytogenetic patterns is crucial for disentangling the karyotype evolution of the whole group. Thus, this study contributes to the understanding of the mechanisms behind chromosome diversification of Doradidae and highlights the importance of Acanthodoradinae in the evolutionary history of thorny catfishes.

Integrative Taxonomy Suggests Resurrection of Species of the Astyanax bimaculatus Group (Characiformes, Characidae)

Using integrative tools can be effective for species identification, especially in complex groups like Astyanax. Astyanax bimaculatus group is composed of six valid species, including A. lacustris. "A. altiparanae", "A. asuncionensis", and "A. jacuhiensis" are considered as junior synonyms of A. lacustris. Seeking to test the operational taxonomic unit (OTU) status of the junior synonyms of A. lacustris ("A. altiparanae", "A. asuncionensis", and "A. jacuhiensis"), we used analyses through mitochondrial DNA (COI and Cytb), cytogenetic markers (classical and molecular), and morphometry ("truss network"). Analysis of mitochondrial DNA sequences separated A. lacustris from the other synonymized species. The cytogenetic and morphometric analyses did not corroborate the synonymization and suggest that besides A. lacustris, the OTUs A. altiparanae, A. asuncionensis, and A. jacuhiensis are valid species. The analysis of different characters proposed by the integrative taxonomy used on the same individuals could provide greater reliability and minimize the underestimation of biodiversity.

New Insights on Chromosome Diversification in Malagasy Chameleons

In this work, we performed a preliminary molecular analysis and a comparative cytogenetic study on 5 different species of Malagasy chameleons of the genus Brookesia (B. superciliaris) and Furcifer (F. balteautus, F. petteri, F. major and F. minor). A DNA barcoding analysis was first carried out on the study samples using a fragment of the mitochondrial gene coding for the cytochrome oxidase subunit 1 (COI) in order to assess the taxonomic identity of the available biological material. Subsequently, we performed on the studied individuals a chromosome analysis with standard karyotyping (5% Giemsa solution at pH 7) and sequential C-banding + Giemsa, + CMA3, and + DAPI. The results obtained indicate that the studied species are characterized by a different chromosome number and a variable heterochromatin content and distribution, with or without differentiated sex chromosomes. In particular, B. superciliaris (2n = 36) and F. balteatus (2n = 34) showed a similar karyotype with 6 macro- and 12-11 microchromosome pairs, without differentiated sex chromosomes. In turn, F. petteri, F. major, and F. minor showed a karyotype with a reduced chromosome number (2n = 22-24) and a differentiated sex chromosome system with female heterogamety (ZZ/ZW). Adding our newly generated data to those available from the literature, we highlight that the remarkable chromosomal diversification of the genus Furcifer was likely driven by non-homologous chromosome fusions, including autosome-autosome, Z-autosome, and W-autosome fusions. The results of this process resulted in a progressive reduction in the chromosome number and partially homologous sex chromosomes of different shapes and sizes.

Selecting reference genes for RT-qPCR studies involving the presence of B chromosomes in Psalidodon (Characiformes, Characidae)

BACKGROUND

B chromosomes are extra non-essential elements present in several eukaryotes. Unlike A chromosomes which are essential and present in all individuals of a species, B chromosomes are not necessary for normal functioning of an organism. Formerly regarded as genetically inactive, B chromosomes have been discovered to not only express their own genes, but also to exert influence on gene expression in A chromosomes. Recent studies have shown that, in some Psalidodon (Characiformes, Characidae) species, B chromosomes might be associated with phenotypic effects, such as changes in the reproductive cycle and gene expression.

METHODS AND RESULTS

In this study, we aimed to establish stable reference genes for RT-qPCR experiments conducted on gonads of three fish species within Psalidodon genus, both in the presence and absence of B chromosomes. The stability of five selected reference genes was assessed using NormFinder, geNorm, BestKeeper, and RefFinder algorithms. We determined ppiaa and pgk1 as the most stable genes in P. fasciatus, whereas ppiaa and hmbsa showed the highest stability in P. bockmanni. For P. paranae, tbp and hprt1 were the most stable genes in females, and ppiaa and hprt1 were the most stable in males.

CONCLUSIONS

We determined the most stable reference genes in gonads of three Psalidodon species considering the presence of B chromosomes. This is the first report of reference gene stability in the genus and provides valuable tools to better understand the effects of B chromosomes at gene expression level.

Satellitome analysis on the pale-breasted thrush Turdus leucomelas (Passeriformes; Turdidae) uncovers the putative co-evolution of sex chromosomes and satellite DNAs

Do all birds' sex chromosomes follow the same canonical one-way direction of evolution? We combined cytogenetic and genomic approaches to analyze the process of the W chromosomal differentiation in two selected Passeriform species, named the Pale-breasted Thrush Turdus leucomelas and the Rufous-bellied thrush T. rufiventris. We characterized the full catalog of satellite DNAs (satellitome) of T. leucomelas, and the 10 TleSatDNA classes obtained together with 16 microsatellite motifs were in situ mapped in both species. Additionally, using Comparative Genomic Hybridization (CGH) assays, we investigated their intragenomic variations. The W chromosomes of both species did not accumulate higher amounts of both heterochromatin and repetitive sequences. However, while T. leucomelas showed a heterochromatin-poor W chromosome with a very complex evolutionary history, T. rufiventris showed a small and partially heterochromatic W chromosome that represents a differentiated version of its original autosomal complement (Z chromosome). The combined approach of CGH and sequential satDNA mapping suggest the occurrence of a former W-autosomal translocation event in T. leucomelas, which had an impact on the W chromosome in terms of sequence gains and losses. At the same time, an autosome, which is present in both males and females in a polymorphic state, lost sequences and integrated previously W-specific ones. This putative W-autosomal translocation, however, did not result in the emergence of a multiple-sex chromosome system. Instead, the generation of a neo-W chromosome suggests an unexpected evolutionary trajectory that deviates from the standard canonical model of sex chromosome evolution.

Chromosomal and genomic analysis suggests single origin and high molecular differentiation of the B chromosome of Abracris flavolineata

Supernumerary chromosomes (B chromosomes) have been an intriguing subject of study. Our understanding of the molecular differentiation of B chromosomes from an interpopulation perspective remains limited, with most analyses involving chromosome banding and mapping of a few sequences. To gain insights into the molecular composition, origin, and evolution of B chromosomes, we conducted cytogenetic and next-generation sequencing analysis of the repeatome in the grasshopper Abracris flavolineata across various populations. Our results unveiled the presence of B chromosomes in two newly investigated populations and described new satellite DNA sequences. While we observed some degree of genetic connection among A. flavolineata populations, our comparative analysis of genomes with and without B chromosomes provided evidence of two new B chromosome variants. These variants exhibited distinct compositions of various repeat classes, including transposable elements and satellite DNAs. Based on shared repeats, their chromosomal location, and the C-positive heterochromatin content on the B chromosome, these variants likely share a common origin but have undergone distinct molecular differentiation processes, resulting in varying degrees of heterochromatinization. Our data serve as a detailed example of the dynamic and differentiated nature of B chromosome molecular content at the interpopulation level, even when they share a common origin.

Satellitome Analysis of Adalia bipunctata (Coleoptera): Revealing Centromeric Turnover and Potential Chromosome Rearrangements in a Comparative Interspecific Study

Eukaryotic genomes exhibit a dynamic interplay between single-copy sequences and repetitive DNA elements, with satellite DNA (satDNA) representing a substantial portion, mainly situated at telomeric and centromeric chromosomal regions. We utilized Illumina next-generation sequencing data from Adalia bipunctata to investigate its satellitome. Cytogenetic mapping via fluorescence in situ hybridization was performed for the most abundant satDNA families. In silico localization of satDNAs was carried out using the CHRISMAPP (Chromosome In Silico Mapping) pipeline on the high-fidelity chromosome-level assembly already available for this species, enabling a meticulous characterization and localization of multiple satDNA families. Additionally, we analyzed the conservation of the satellitome at an interspecific scale. Specifically, we employed the CHRISMAPP pipeline to map the satDNAs of A. bipunctata onto the genome of Adalia decempunctata, which has also been sequenced and assembled at the chromosome level. This analysis, along with the creation of a synteny map between the two species, suggests a rapid turnover of centromeric satDNA between these species and the potential occurrence of chromosomal rearrangements, despite the considerable conservation of their satellitomes. Specific satDNA families in the sex chromosomes of both species suggest a role in sex chromosome differentiation. Our interspecific comparative study can provide a significant advance in the understanding of the repeat genome organization and evolution in beetles.

Comparative molecular and conventional cytogenetic analyses of three species of Rhinella (Anura; Bufonidae)

The genus Rhinella corresponds to a group of anurans characterized by numerous taxonomic and systemic challenges, leading to their organization into species complexes. Cytogenetic data for this genus thus far are limited to the diploid number and chromosome morphology, which remain highly conserved among the species. In this study, we analyse the karyotypes of three species of the genus Rhinella (Rhinella granulosa, Rhinella margaritifera, and Rhinella marina) using both classical (conventional staining and C-banding) and molecular (FISH-fluorescence in situ hybridization with 18S rDNA, telomeric sequences, and microsatellite probes) cytogenetic approaches. The aim of this study is to provide data that can reveal variations in the distribution of repetitive sequences that can contribute to understanding karyotypic diversification in these species. The results revealed a conserved karyotype across the species, with 2n = 22 and FN = 44, with metacentric and submetacentric chromosomes. C-banding revealed heterochromatic blocks in the pericentromeric region for all species, with a proximal block on the long arms of pairs 3 and 6 in R. marina and on the short arms of pairs 4 and 6 in R. margaritifera. Additionally, 18S rDNA probes hybridized to pair 5 in R. granulosa, to pair 7 in R. marina, and to pair 10 in R. margaritifera. Telomeric sequence probes displayed signals exclusively in the distal region of the chromosomes, while microsatellite DNA probes showed species-specific patterns. These findings indicate that despite a conserved karyotypical macrostructure, chromosomal differences exist among the species due to the accumulation of repetitive sequences. This variation may be attributed to chromosome rearrangements or differential accumulation of these sequences, highlighting the dynamic role of repetitive sequences in the chromosomal evolution of Rhinella species. Ultimately, this study emphasizes the importance of the role of repetitive DNAs in chromosomal rearrangements to elucidate the evolutionary mechanisms leading to independent diversification in the distinct phylogenetic groups of Rhinella.

Chromosomal organization of different repetitive sequences in four wasp species of the genus Trypoxylon Latreille (Hymenoptera: Crabronidae) and insights into the composition of wasp telomeres

This study characterizes the chromosomal organization of DNA repetitive sequences and the karyotypic evolution in four representatives of the solitary wasp genus Trypoxylon using conventional and molecular cytogenetic techniques. Our findings present the first cytogenetic data for Trypoxylon rogenhoferi (2n = 30) and Trypoxylon albonigrum (2n = 32), while the karyotypes of Trypoxylon nitidum (2n = 30) and Trypoxylon lactitarse (2n = 30) were similar to those previously described. Fluorochrome staining and microsatellite distribution data revealed differences in the constitutive heterochromatin composition among species. Trypoxylon nitidum and T. albonigrum exhibited one major rDNA cluster, potentially representing an ancestral pattern for aculeate Hymenoptera, while T. rogenhoferi and T. lactitarse showed two pericentromeric rRNA gene sites, suggesting amplification events in their ancestral clade. The (TCAGG)n motif hybridized in the terminal regions of the chromosomes in all four Trypoxylon species, which may suggest that this sequence represents DNA telomeric repeat. Notably, the presence of this repetitive sequence in the centromeric regions of certain chromosome pairs in two species supports the hypothesis of chromosomal fusions or inversions in the ancestral karyotype of Trypoxylon. The study expands the chromosomal mapping data of repetitive sequences in wasps and offers insights into the dynamic evolutionary landscape of karyotypes in these insects.

Establishment and molecular characterization of HCB-541, a novel and aggressive human cutaneous squamous cell carcinoma cell line

Cutaneous squamous cell carcinoma (cSCC) is a common type of skin cancer that can result in significant morbidity, although it is usually well-managed and rarely metastasizes. However, the lack of commercially available cSCC cell lines hinders our understanding of this disease. This study aims to establish and characterize a new metastatic cSCC cell line derived from a Brazilian patient. A tumor biopsy was taken from a metastatic cSCC patient, immortalized, and named HCB-541 after several passages. The cytokeratin expression profile, karyotypic alterations, mutational analysis, mRNA and protein differential expression, tumorigenic capacity in xenograft models, and drug sensitivity were analyzed. The HCB-541 cell line showed a doubling time between 20 and 30 h and high tumorigenic capacity in the xenograft mouse model. The HCB-541 cell line showed hypodiploid and hypotetraploidy populations. We found pathogenic mutations in TP53 p.(Arg248Leu), HRAS (Gln61His) and TERT promoter (C228T) and high-level microsatellite instability (MSI-H) in both tumor and cell line. We observed 37 cancer-related genes differentially expressed when compared with HACAT control cells. The HCB-541 cells exhibited high phosphorylated levels of EGFR, AXL, Tie, FGFR, and ROR2, and high sensitivity to cisplatin, carboplatin, and EGFR inhibitors. Our study successfully established HCB-541, a new cSCC cell line that could be useful as a valuable biological model for understanding the biology and therapy of metastatic skin cancer.

Karyotype analysis of Quasipaaspinosa David, 1875 (Anura, Dicroglossidae) with conventional cytogenetic techniques

The current study analyzed the chromosomal karyotype of Quasipaaspinosa David, 1875 from Hunan Province, China. The karyotype, C-banding, BrdU-banding pattern were characterized using direct preparation of bone-marrow cells and hemocyte cultures. The findings indicated that Q.spinosa was a diploid species (2n = 26) that lacked heteromorphic chromosomes and secondary constrictions. C-banding analysis revealed an abundance of positive signals in the centromere regions, while the BrdU-banding pattern showed three phases in both male and female, occurring consistently and in chronological sequence during S-phase. Notably, there was no asynchronous replication in the late phase. This study enhanced our understanding of the karyotypic structure of Q.spinosa by conventional cytogenetic techniques, thus providing essential scientific insights into the cytogenetics of Q.spinosa.

Mapping of Repetitive Sequences in Brachyhypopomus brevirostris (Hypopomidae, Gymnotiformes) from the Brazilian Amazon

Brachyhypopomus (Hypopomidae, Gymnotiformes) is a monophyletic genus consisting of 28 formally described species. Karyotypic data are available for 12 species. The same karyotype is described for two species (B. brevirostris and B. hamiltoni), as well as different karyotypes for the same species from distinct locations (B. brevirostris). In this context, B. brevirostris may constitute a cryptic species complex. Thus, in the present study, we analyzed the karyotype of B. brevirostris, from Santarém, Pará, and Tefé, Amazonas, using classical cytogenetics (conventional staining and C-banding) and molecular techniques (fluorescence in situ hybridization using 18S rDNA, 5S rDNA, U2 snRNA, and telomeric probes). The results show that samples from both locations present 2n = 38, with all chromosomes being acrocentric (FC = 38a). In both populations, 18S rDNA sequences are present on only one pair of homologous chromosomes and telomeric sequences occur only at the ends of the chromosomes. In the Tefé sample, the 5S rDNA occurs in two pairs, and the U2 snRNA in three pairs. These results are the first descriptions of these sequences for B. brevirostris samples from the Tefé locality, as well as the first karyotypic description for the Santarém locality. Future cytotaxonomic studies of this genus can benefit from these results.

Comparative Cytogenetics of the Malagasy Ground Geckos of the Paroedura bastardi and Paroedura picta Species Groups

We present a comparative chromosome study of several taxa of the Malagasy ground geckos of the Paroedura bastardi and P. picta species groups. We employed a preliminary molecular analysis using a trait of the mitochondrial 16S rRNA gene (of about 570 bp) to assess the taxonomic status of the samples studied and a cytogenetic analysis with standard karyotyping (5% Giemsa solution), silver staining (Ag-NOR staining) and sequential C-banding (C-banding + Giemsa and + fluorochromes). Our results show that all the taxa studied of the P. bastardi group (P. ibityensis, P. rennerae and P. cf. guibeae) have a similar karyotype composed of 2n = 34 chromosomes, with two metacentric pairs (1 and 3) and all other pairs being acrocentric. Chromosome diversification in the P. bastardi group was mainly linked to the diversification of heteromorphic sex chromosome systems (ZZ/ZW) in P. ibityensis and P. rennerae, while no heteromorphic sex chromosome pair was found in P. cf. guibeae. The two taxa investigated of the P. picta species group (here named P. picta and P. cf. picta based on molecular data) showed the same chromosome number of 2n = 36, mostly acrocentric elements, but differed in the number of metacentric elements, probably as a result of an inversion at chromosome pair 2. We highlight that the genus Paroedura is characterized by the independent diversification of heterogametic sex chromosomes in different evolutionary lineages and, similarly to other phylogenetically related gecko genera, by a progressive formation of a biarmed element by means of tandem fusions and inversions of distinct pairs.

Initial Steps of XY Sex Chromosome Differentiation in the Armored Catfish Hypostomus albopunctatus (Siluriformes: Loricariidae) Revealed by Heterochromatin Accumulation

In fish species, heterochromatinization is one process that could trigger sex chromosome differentiation. The present article describes a nascent XX/XY sex chromosome system evidenced by heterochromatin accumulation and microsatellite (GATA)8 in Hypostomus albopunctatus from two populations of the Paraná River basin. The specimens of H. albopunctatus from the Campo and Bossi Rivers share the same karyotype. The species exhibits 74 chromosomes (8m+14sm +16st +36a, fundamental number = 112). The C-banding technique suggests male heterogamety in H. albopunctatus, where the Y-chromosome is morphologically like the X-chromosome but differs from it for having long arms that are entirely heterochromatic. Double fluorescence in situ hybridization (FISH) with 18S and 5S rDNA probes confirmed the Ag-nucleolus organizer region sites in a single pair for both populations, and minor rDNA clusters showed interpopulational variation. FISH with the microsatellite (GATA)8 probe showed a dispersed pattern in the karyotype, accumulating these sequences of sex chromosomes of both populations. FISH with microsatellite (CGC)10 probe showed interpopulational variation. The absence of differentiated sex chromosomes in H. albopunctatus is described previously, and a new variant is documented herein where XY chromosomes can be seen in an early stage of differentiation.

Understanding the chromosomal evolution in cuckoos (Aves, Cuculiformes): a journey through unusual rearrangements

The Cuculiformes are a family of over 150 species that live in a range of habitats, such as forests, savannas, and deserts. Here, bacterial artificial chromosome (BAC) probes (75 from chicken and 14 from zebra finch macrochromosomes 1-10 +ZW and for microchromosomes 11-28 (except 16)) were used to investigate chromosome homologies between chicken and the squirrel cuckoo (Piaya cayana). In addition, repetitive DNA probes were applied to characterize the chromosome organization and to explore the role of these sequences in the karyotype evolution of P. cayana. We also applied BAC probes for chicken chromosome 17 and Z to the guira cuckoo (Guira guira) to test whether this species has an unusual Robertsonian translocation between a microchromosome and the Z chromosome, recently described in the smooth-billed ani (Crotophaga ani). Our results revealed extensive chromosome reorganization with inter- and intrachromosomal rearrangements in P. cayana, including a conspicuous chromosome size and heterochromatin polymorphism on chromosome pair 20. Furthermore, we confirmed that the Z-autosome Robertsonian translocation found in C. ani is also found in G. guira, not P. cayana. These findings suggest that this translocation occurred prior to the divergence between C. ani and G. guira, but after the divergence with P. cayana.

First Karyotypic Insights into Potamotrygon schroederi Fernández-Yépez, 1958: Association of Different Classes of Repetitive DNA

INTRODUCTION

Currently, there are 38 valid species of freshwater stingrays, and these belong to the subfamily Potamotrygoninae. However, cytogenetic information about this group is limited, with studies mainly using classical techniques, Giemsa, and C-banding.

METHODS

In this study, we used classical and molecular cytogenetic techniques - mapping of 18S and 5S rDNA and simple sequence repeats (SSRs) - in order to investigate the karyotypic composition of Potamotrygon schroederi and reveal the karyoevolutionary trends of this group.

RESULTS

The species presented 2n = 66 chromosomes with 18m + 12sm + 16st + 20a, heterochromatic blocks distributed in the centromeric regions of all the chromosomes, and terminal blocks in the q arm of pairs 2 and 3. Mapping of 18S rDNA regions revealed multiple clusters on pairs 2 and 7 and a homolog of pair 24. The 5S rDNA region was found in the pericentromeric portion of the subtelocentric pair 16. Furthermore, dinucleotide SSRs sequences were found in the centromeric and terminal regions of different chromosomal pairs, with preferential accumulation in pair 17. In addition, we identified conspicuous blocks of (GATA)n and (GACA)n sequences colocalized with the 5S rDNA (pair 16).

CONCLUSION

In general, this study corroborates the general trend of a reduction in 2n in the species of Potamotrygoninae subfamily. Moreover, we found that the location of rDNA regions is very similar among Potamotrygon species, and the SSRs accumulation in the second subtelocentric pair (17) seems to be a common trait in this genus.

Differentiated sex chromosomes, karyotype evolution, and spontaneous triploidy in carphodactylid geckos

Geckos exhibit derived karyotypes without a clear distinction between macrochromosomes and microchromosomes and intriguing diversity in sex determination mechanisms. We conducted cytogenetic analyses in six species from the genera Nephrurus, Phyllurus, and Saltuarius of the gecko family Carphodactylidae. We confirmed the presence of a female heterogametic system with markedly differentiated and heteromorphic sex chromosomes in all examined species, typically with the W chromosome notably larger than the Z chromosome. One species, Nephrurus cinctus, possesses unusual multiple Z1Z1Z2Z2/Z1Z2W sex chromosomes. The morphology of the sex chromosomes, along with repetitive DNA content, suggests that the differentiation or emergence of sex chromosomes occurred independently in the genus Phyllurus. Furthermore, our study unveils a case of spontaneous triploidy in a fully grown individual of Saltuarius cornutus (3n = 57) and explores its implications for reproduction in carphodactylid geckos. We revealed that most carphodactylids retain the putative ancestral gekkotan karyotype of 2n = 38, characterized by predominantly acrocentric chromosomes that gradually decrease in size. If present, biarmed chromosomes emerge through pericentric inversions, maintaining the chromosome (and centromere) numbers. However, Phyllurus platurus is a notable exception, with a karyotype of 2n = 22 chromosomes. Its eight pairs of biarmed chromosomes were probably formed by Robertsonian fusions of acrocentric chromosomes. The family underscores a remarkable instance of evolutionary stability in chromosome numbers, followed by a profound transformation through parallel interchromosomal rearrangements. Our study highlights the need to continue generating cytogenetic data in order to test long-standing ideas about reproductive biology and the evolution of genome and sex determination.

Conventional cytogenetics and microsatellite chromosomal distribution in social wasp Mischocyttarus cassununga (Ihering, 1903) (Vespidae, Polistinae, Mischocyttarini)

Cytogenetics has allowed the investigation of chromosomal diversity and repetitive genomic content in wasps. In this study, we characterized the karyotype of the social wasp Mischocyttarus cassununga using conventional cytogenetics and chromosomal mapping of repetitive sequences. This study was undertaken to extend our understanding of the genomic organization of repetitive DNA in social wasps and is the first molecular cytogenetic insight into the genus Mischocyttarus. The karyotype of M. cassununga had a chromosome number of 2n = 64 for females and n = 32 for males. Constitutive heterochromatin exhibited three distribution patterns: centromeric and pericentromeric regions along the smaller arms and extending almost the entire chromosome. The major ribosomal DNA sites were located on chromosome pair in females and one chromosome in males. Positive signals for the microsatellite probes (GA)n and (GAG)n were observed in the euchromatic regions of all chromosomes. The microsatellites, (CGG)n, (TAT)n, (TTAGG)n, and (TCAGG)n were not observed in any region of the chromosomes. Our results contrast with those previously obtained for Polybia fastidiosuscula, which showed that the microsatellites (GAG)n, (CGG)n, (TAT)n, (TTAGG)n, and (TCAGG)n are located predominantly in constitutive heterochromatin. This suggests variations in the diversity and chromosomal organization of repetitive sequences in the genomes of social wasps.

Evolution of bird sex chromosomes: a cytogenomic approach in Palaeognathae species

BACKGROUND

Different patterns of sex chromosome differentiation are seen in Palaeognathae birds, a lineage that includes the ratites (Struthioniformes, Rheiformes, Apterygiformes, Casuariiformes, and the sister group Tinamiformes). While some Tinamiform species have well-differentiated W chromosomes, both Z and W of all the flightless ratites are still morphologically undifferentiated. Here, we conducted a comprehensive analysis of the ZW differentiation in birds using a combination of cytogenetic, genomic, and bioinformatic approaches. The whole set of satDNAs from the emu (Dromaius novaehollandiae) was described and characterized. Furthermore, we examined the in situ locations of these satDNAs alongside several microsatellite repeats and carried out Comparative Genomic Hybridizations in two related species: the greater rhea (Rhea americana) and the tataupa tinamou (Crypturellus tataupa).

RESULTS

From the 24 satDNA families identified (which represent the greatest diversity of satDNAs ever uncovered in any bird species), only three of them were found to accumulate on the emu's sex chromosomes, with no discernible accumulation observed on the W chromosome. The W chromosomes of both the greater rhea and the emu did not exhibit a significant buildup of either C-positive heterochromatin or repetitive DNAs, indicating their large undifferentiation both at morphological and molecular levels. In contrast, the tataupa tinamou has a highly differentiated W chromosome that accumulates several DNA repeats.

CONCLUSION

The findings provide new information on the architecture of the avian genome and an inside look at the starting points of sex chromosome differentiation in birds.

Karyotypic changes and diversification time in Epinephelidae groupers (Perciformes). Implications on reproductive isolation

Groupers (Epinephelidae and Serranidae) have attracted special attention to fish farming, and their species offer good opportunities for successful hybridizations. Cytogenetic data allow a better understanding of the role of karyotypic diversification in the acquisition of post-zygotic reproductive isolation (RI). Thus, chromosomal analyses were performed on E. striatus (Caribbean Sea), E. coioides and E. tauvina (Indo-Pacific Region), using standard procedures and mapping of six repetitive DNA classes by the in situ hybridization. The three species have 2n=48 chromosomes. The karyotypes of E. coioides and E. striatus are composed only of acrocentric chromosomes (FN=48), while E. tauvina has 8 submetacentric chromosomes (FN=56). Heterochromatin has a preferential centromeric distribution, and the microsatellite repeats are dispersed throughout the chromosomes of all species. The 18S and 5S rDNA sites are unique but show a colocalization arrangement in E. tauvina and E. striatus. The chromosomal organization suggests that the three species still maintain a significant amount of syntenic regions. The range of the karyotype divergence and the RI levels showed low, but goes turn proportionally greater in relation to the divergence time between the parental species. The slow acquisition of postzygotic RI is consistent with the high karyotype homogeneity presented by Epinephelidae family.

Satellite DNAs, heterochromatin, and sex chromosomes of the wattled jacana (Charadriiformes; Jacanidae): a species with highly rearranged karyotype

Charadriiformes, which comprises shorebirds and their relatives, is one of the most diverse avian orders, with over 390 species showing a wide range of karyotypes. Here, we isolated and characterized the whole collection of satellite DNAs (satDNAs) at both molecular and cytogenetic levels of one of its representative species, named the wattled jacana (Jacana jacana), a species that contains a typical ZZ/ZW sex chromosome system and a highly rearranged karyotype. In addition, we also investigate the in situ location of telomeric and microsatellite repeats. A small catalog of 11 satDNAs was identified that typically accumulated on microchromosomes and on the W chromosome. The latter also showed a significant accumulation of telomeric signals, being (GA)10 the only microsatellite with positive hybridization signals among all the 16 tested ones. These current findings contribute to our understanding of the genomic organization of repetitive DNAs in a bird species with high degree of chromosomal reorganization contrary to the majority of bird species that have stable karyotypes.

Comparative Cytogenetics in Tyrannidae (Aves, Passeriformes): High Genetic Diversity despite Conserved Karyotype Organization

INTRODUCTION

Passeriformes has the greatest species diversity among Neoaves, and the Tyrannidae is the richest in this order with about 600 valid species. The diploid number of this family remains constant, ranging from 2n = 76 to 84, but the chromosomal morphology varies, indicating the occurrence of different chromosomal rearrangements. Cytogenetic studies of the Tyrannidae remain limited, with approximately 20 species having been karyotyped thus far. This study aimed to describe the karyotypes of two species from this family, Myiopagis viridicata and Sirystes sibilator.

METHODS

Skin biopsies were taken from each individual to establish fibroblast cell cultures and to obtain chromosomal preparations using the standard methodology. The chromosomal distribution of constitutive heterochromatin was investigated by C-banding, while the location of simple repetitive sequences (SSRs), 18S rDNA, and telomeric sequences was found through fluorescence in situ hybridization.

RESULTS

The karyotypes of both species are composed of 2n = 80. The 18S rDNA probes hybridized into two pairs of microchromosomes in M. viridicata, but only a single pair in S. sibilator. Only the telomeric portions of each chromosome in both species were hybridized by the telomere sequence probes. Most of the SSRs were found accumulated in the centromeric and telomeric regions of several macro- and microchromosomes in both species, which likely correspond to the heterochromatin-rich regions.

CONCLUSION

Although both species analyzed showed a conserved karyotype organization (2n = 80), our study revealed significant differences in their chromosomal architecture, rDNA distribution, and SSR accumulation. These findings were discussed in the context of the evolution of Tyrannidae karyotypes.

Cytogenetic Analysis of Satellitome of Madagascar Leaf-Tailed Geckos

Satellite DNA (satDNA) consists of sequences of DNA that form tandem repetitions across the genome, and it is notorious for its diversity and fast evolutionary rate. Despite its importance, satDNA has been only sporadically studied in reptile lineages. Here, we sequenced genomic DNA and PCR-amplified microdissected W chromosomes on the Illumina platform in order to characterize the monomers of satDNA from the Henkel's leaf-tailed gecko U. henkeli and to compare their topology by in situ hybridization in the karyotypes of the closely related Günther's flat-tail gecko U. guentheri and gold dust day gecko P. laticauda. We identified seventeen different satDNAs; twelve of them seem to accumulate in centromeres, telomeres and/or the W chromosome. Notably, centromeric and telomeric regions seem to share similar types of satDNAs, and we found two that seem to accumulate at both edges of all chromosomes in all three species. We speculate that the long-term stability of all-acrocentric karyotypes in geckos might be explained from the presence of specific satDNAs at the centromeric regions that are strong meiotic drivers, a hypothesis that should be further tested.

Karyotypic characterization of Centromochlus schultzi Rössel 1962 (Auchenipteridae, Centromochlinae) from the Xingu River basin: New inferences on chromosomal evolution in Centromochlus

Centromochlinae is a widely diverse subfamily with more than 50 species and several taxonomic conflicts due to morphological similarity between Tatia and Centromochlus species. However, cytogenetic studies on this group have been limited to only four species so far. Therefore, here we present the karyotype of Centromochlus schultzi from the Xingu River in Brazil using classic cytogenetic techniques, physical mapping of the 5S and 18S rDNAs, and telomeric sequences (TTAGGG)n. The species had 58 chromosomes, simple NORs and 18S rDNA sites. Heterochromatic regions were detected on the terminal position of most chromosomes, including pericentromeric and centromeric blocks that correspond to interstitial telomeric sites. The 5S rDNA had multiple sites, including a synteny with the 18S rDNA in the pair 24st, which is an ancestral feature for Doradidae, sister group of Auchenipteridae, but appears to be a homoplastic trait in this species. So far, C. schultzi is only the second species within Centromochlus to be karyotyped, but it has already presented characteristics with great potential to assist in future discussions on taxonomic issues in the subfamily Centromochlinae, including the first synteny between rDNAs in Auchenipteridae and also the presence of heterochromatic ITSs that could represent remnants of ancient chromosomal fusions.

Heterochromatin Is Not the Only Place for satDNAs: The High Diversity of satDNAs in the Euchromatin of the Beetle Chrysolina americana (Coleoptera, Chrysomelidae)

The satellitome of the beetle Chrysolina americana Linneo, 1758 has been characterized through chromosomal analysis, genomic sequencing, and bioinformatics tools. C-banding reveals the presence of constitutive heterochromatin blocks enriched in A+T content, primarily located in pericentromeric regions. Furthermore, a comprehensive satellitome analysis unveils the extensive diversity of satellite DNA families within the genome of C. americana. Using fluorescence in situ hybridization techniques and the innovative CHRISMAPP approach, we precisely map the localization of satDNA families on assembled chromosomes, providing insights into their organization and distribution patterns. Among the 165 identified satDNA families, only three of them exhibit a remarkable amplification and accumulation, forming large blocks predominantly in pericentromeric regions. In contrast, the remaining, less abundant satDNA families are dispersed throughout euchromatic regions, challenging the traditional association of satDNA with heterochromatin. Overall, our findings underscore the complexity of repetitive DNA elements in the genome of C. americana and emphasize the need for further exploration to elucidate their functional significance and evolutionary implications.

Multiple Transitions between Y Chromosome and Autosome in Tago's Brown Frog Species Complex

Sex chromosome turnover is the transition between sex chromosomes and autosomes. Although many cases have been reported in poikilothermic vertebrates, their evolutionary causes and genetic mechanisms remain unclear. In this study, we report multiple transitions between the Y chromosome and autosome in the Japanese Tago's brown frog complex. Using chromosome banding and molecular analyses (sex-linked and autosomal single nucleotide polymorphisms, SNPs, from the nuclear genome), we investigated the frogs of geographic populations ranging from northern to southern Japan of two species, Rana tagoi and Rana sakuraii (2n = 26). Particularly, the Chiba populations of East Japan and Akita populations of North Japan in R. tagoi have been, for the first time, investigated here. As a result, we identified three different sex chromosomes, namely chromosomes 3, 7, and 13, in the populations of the two species. Furthermore, we found that the transition between the Y chromosome (chromosome 7) and autosome was repeated through hybridization between two or three different populations belonging to the two species, followed by restricted chromosome introgression. These dynamic sex chromosome turnovers represent the first such findings in vertebrates and imply that speciation associated with inter- or intraspecific hybridization plays an important role in sex chromosome turnover in frogs.

New Karyotype Information for Ctenomys (Rodentia: Ctenomyidae) from Midwest and Northern Brazil

INTRODUCTION

Its wide karyotypic variation characterizes the genus Ctenomys, and in Brazil, the genus is distributed in the country's southern, Midwest, and northern regions. Recently, populations of Ctenomys have been found in the Midwest and northern Brazil, with two new lineages named C. sp. "xingu" and C. sp. "central."

METHODS

This work combines classical cytogenetic and molecular analyses to provide new chromosomal information on the boliviensis group distributed in northern and Midwestern Brazil. This includes the validation of the karyotype of C. bicolor and C. nattereri and the description of the karyotype of C. sp. "xingu" and C. sp. "central."

RESULTS

We found three different karyotypes: 2n = 40 for C. bicolor; 2n = 36 for C. nattereri, and specimens from a locality belonging to C. sp. "central"; 2n = 34 for the lineage C. sp. "xingu" and specimens from a locality belonging to C. sp. "central." Furthermore, GTG banding revealed homologous chromosomes between species/lineages and allowed the identification of the rearrangements that occurred, which proved the occurrence of fissions.

CONCLUSION

Considering our results on the variation of 2n in the boliviensis group, we found two possibilities: the first, deduced by parsimony, is that 2n = 36 appeared initially, and two fissions produced gave rise to 2n = 40, and an independent fusion gave rise to 2n = 34 from 2n = 36; moreover, the second explanation is that all karyotypes arose independently.

Satellitome Analysis in the Southern Lapwing (Vanellus chilensis) Genome: Implications for SatDNA Evolution in Charadriiform Birds

Vanellus (Charadriidae; Charadriiformes) comprises around 20 species commonly referred to as lapwings. In this study, by integrating cytogenetic and genomic approaches, we assessed the satellite DNA (satDNA) composition of one typical species, Vanellus chilensis, with a highly conserved karyotype. We additionally underlined its role in the evolution, structure, and differentiation process of the present ZW sex chromosome system. Seven distinct satellite DNA families were identified within its genome, accumulating on the centromeres, microchromosomes, and the W chromosome. However, these identified satellite DNA families were not found in two other Charadriiformes members, namely Jacana jacana and Calidris canutus. The hybridization of microsatellite sequences revealed the presence of a few repetitive sequences in V. chilensis, with only two out of sixteen displaying positive hybridization signals. Overall, our results contribute to understanding the genomic organization and satDNA evolution in Charadriiform birds.

Repetitive DNA Mapping in Five Genera of Tree Frogs (Amphibia: Anura) from the Atlantic Forest: New Highlights on Genomic Organization in Hylidae

INTRODUCTION

The tribes Cophomantini, Scinaxini, and Dendropsophini are anurans that belong to Hylidae, with wide distribution in tropical and subtropical regions around the world. The taxonomy and systematics of this family remain in a state of ongoing revision. Previous cytogenetic analyses of genera Boana, Bokermannohyla, Ololygon, Scinax, and Dendropsophus described some karyotypic characters such as conventional staining, C-banding and NORs, and FISH with specific probes.

METHODS

This study describes for the first time the karyotypes of four species: Bokermannohyla ibitipoca, Ololygon luizotavioi, Dendropsophus bipunctatus, and Dendropsophus ruschii. Furthermore, we map CA(15) and CAT(10) microsatellite sites for the aforementioned species and six more species from the same genera for insight into the chromosomal evolution within the subfamily Hyalinae.

RESULTS

B. ibitipoca and O. luizotavioi had 2n = 24 and karyotypic formulas 18m + 4sm + 2st and 8m + 12sm + 4st, while D. bipunctatus and D. ruschii showed 2n = 30 and karyotypic formulas 12m + 12sm + 4st + 2t and 10m + 10sm + 6st + 4t, respectively. The diploid numbers and karyotypic formulas revealed here follow the previously reported trend for Hylidae, except B. ibitipoca has a particularity of eight metacentric chromosomes, more than what is commonly found in species of this genus. The microsatellites probes CA(15) and CAT(10) had markings accumulated in blocks in the centromeric, pericentromeric, and terminal regions that were more specific for some species, as well as markings scattered along the chromosomes. We present a comprehensive review table of current data on cytogenetics of these genera.

CONCLUSION

Our findings showed that the karyotypes of the hylids studied here majority fit the postulated conserved diploid number (2n = 24) and morphological chromosome patterns, while the mapping of the microsatellites enabled us to detect differences between species that share similar chromosomal morphologies.

New insights into the chromosomes of stoneflies: I. Karyotype, C-banding and localization of ribosomal and telomeric DNA markers in Skwalacompacta (McLachlan, 1872) (Polyneoptera, Plecoptera, Perlodidae) from Siberia

This study provides data on chromosome number (2n♂♀=26), sex determination mechanism (XY♂/XX♀), C-banding pattern, distribution of clusters of telomeric TTAGG repeats and 18S ribosomal DNA in the karyotype of the stonefly Skwalacompacta (McLachlan, 1872). For the first time in the history of stoneflies cytogenetics, we provide photos of the chromosomes of the Plecoptera insects. The karyotype of males and females of S.compacta consists of 12 pairs of autosomes. Three pairs of large autosomes and four pairs of medium-sized autosomes are subacrocentric. The remaining pairs of autosomes are small, with unclear morphology. Pericentromeric C-bands were revealed in all autosomes. The sex chromosomes are also subacrocentric. The short arms of X and Y chromosomes are entirely heterochromatic and are rich in ribosomal DNA sequences. In the X chromosome this arm is larger than in the Y chromosome. It is likely that this arm associated with the nucleolar organizer (NOR). Telomeric DNA (TTAGG)n repeats were detected in the terminal regions of all chromosomes.

First Cytogenetic Analysis of Hemidactylus mercatorius Gray, 1842 Provides Insights on Interspecific Chromosomal Diversification in the Genus Hemidactylus (Squamata: Gekkonidae)

This contribution provides the first karyotype description of Hemidactylus mercatorius and discusses the interspecific chromosome diversification in the genus. Chromosomal analysis was performed on samples from different Malagasy populations using standard karyotyping, Ag-NOR staining, and banding methods (sequential C-banding + Giemsa, + Chromomycin A3, +4',6-diamidino-2-phenylindole). Irrespective of sex or sampling locality, H. mercatorius shows a karyotype of 2n = 42 with metacentric (1, 18-21), submetacentric (4), subtelocentric (5, 11), and acrocentric pairs (all the remaining pairs). There was no heteromorphic chromosome pair and no clear distinction between macro- and microchromosomes. NORs were localised close to the centromeres of a medium acrocentric pair (14). Heterochromatic blocks were identified on the telomeric and centromeric regions of most chromosome pairs. A comparison with the karyotype of H. mabouia highlights that the different morphology of several chromosome pairs clearly distinguishes the two species, contrasting the previously proposed synonymy. The differences between the karyotypes of H. mercatorius and H. mabouia concern the number of biarmed and acrocentric elements, suggesting the occurrence of several chromosome inversions. Considering all the available karyotype data on Hemidactylus and its sister genus Cyrtodactylus, it is possible to advance an evolutionary hypothesis on their chromosomal evolution, starting from a common ancestor with 2n = 48 and all acrocentric elements. From this ancestral condition, the karyotype diversification in the two genera has been prevalently characterised by a progressive accumulation of fusions and inversions which have reduced the total chromosome count and increased the number of biarmed chromosomes.

Chromosomal rearrangements played an important role in the speciation of rice rats of genus Cerradomys (Rodentia, Sigmodontinae, Oryzomyini)

Rodents of the genus Cerradomys belong to tribe Oryzomyini, one of the most diverse and speciose groups in Sigmodontinae (Rodentia, Cricetidae). The speciation process in Cerradomys is associated with chromosomal rearrangements and biogeographic dynamics in South America during the Pleistocene era. As the morphological, molecular and karyotypic aspects of Myomorpha rodents do not evolve at the same rate, we strategically employed karyotypic characters for the construction of chromosomal phylogeny to investigate whether phylogenetic relationships using chromosomal data corroborate the radiation of Cerradomys taxa recovered by molecular phylogeny. Comparative chromosome painting using Hylaeamys megacephalus (HME) whole chromosome probes in C. langguthi (CLA), Cerradomys scotii (CSC), C. subflavus (CSU) and C. vivoi (CVI) shows that karyotypic variability is due to 16 fusion events, 2 fission events, 10 pericentric inversions and 1 centromeric repositioning, plus amplification of constitutive heterochromatin in the short arms of the X chromosomes of CSC and CLA. The chromosomal phylogeny obtained by Maximum Parsimony analysis retrieved Cerradomys as a monophyletic group with 97% support (bootstrap), with CSC as the sister to the other species, followed by a ramification into two clades (69% of branch support), the first comprising CLA and the other branch including CVI and CSU. We integrated the chromosome painting analysis of Eumuroida rodents investigated by HME and Mus musculus (MMU) probes and identified several syntenic blocks shared among representatives of Cricetidae and Muridae. The Cerradomys genus underwent an extensive karyotypic evolutionary process, with multiple rearrangements that shaped extant karyotypes. The chromosomal phylogeny corroborates the phylogenetic relationships proposed by molecular analysis and indicates that karyotypic diversity is associated with species radiation. Three syntenic blocks were identified as part of the ancestral Eumuroida karyotype (AEK): MMU 7/19 (AEK 1), MMU 14 (AEK 10) and MMU 12 (AEK 11). Besides, MMU 5/10 (HME 18/2/24) and MMU 8/13 (HME 22/5/11) should be considered as signatures for Cricetidae, while MMU 5/9/14, 5/7/19, 5 and 8/17 for Sigmodontinae.

De novo assembly and characterization of a highly degenerated ZW sex chromosome in the fish Megaleporinus macrocephalus

BACKGROUND

Megaleporinus macrocephalus (piauçu) is a Neotropical fish within Characoidei that presents a well-established heteromorphic ZZ/ZW sex determination system and thus constitutes a good model for studying W and Z chromosomes in fishes. We used PacBio reads and Hi-C to assemble a chromosome-level reference genome for M. macrocephalus. We generated family segregation information to construct a genetic map, pool sequencing of males and females to characterize its sex system, and RNA sequencing to highlight candidate genes of M. macrocephalus sex determination.

RESULTS

The reference genome of M. macrocephalus is 1,282,030,339 bp in length and has a contig and scaffold N50 of 5.0 Mb and 45.03 Mb, respectively. In the sex chromosome, based on patterns of recombination suppression, coverage, FST, and sex-specific SNPs, we distinguished a putative W-specific region that is highly differentiated, a region where Z and W still share some similarities and is undergoing degeneration, and the PAR. The sex chromosome gene repertoire includes genes from the TGF-β family (amhr2, bmp7) and the Wnt/β-catenin pathway (wnt4, wnt7a), some of which are differentially expressed.

CONCLUSIONS

The chromosome-level genome of piauçu exhibits high quality, establishing a valuable resource for advancing research within the group. Our discoveries offer insights into the evolutionary dynamics of Z and W sex chromosomes in fish, emphasizing ongoing degenerative processes and indicating complex interactions between Z and W sequences in specific genomic regions. Notably, amhr2 and bmp7 are potential candidate genes for sex determination in M. macrocephalus.