Karyotypic Differences Research Articles

A High-Quality Assembly of the Nine-Spined Stickleback (Pungitius pungitius) Genome.

The Gasterosteidae fish family hosts several species that are important models for eco-evolutionary, genetic, and genomic research. In particular, a wealth of genetic and genomic data has been generated for the three-spined stickleback (Gasterosteus aculeatus), the “ecology’s supermodel,” whereas the genomic resources for the nine-spined stickleback (Pungitius pungitius) have remained relatively scarce. Here, we report a high-quality chromosome-level genome assembly of P. pungitius consisting of 5,303 contigs (N50 = 1.2 Mbp) with a total size of 521 Mbp. These contigs were mapped to 21 linkage groups using a high-density linkage map, yielding a final assembly with 98.5% BUSCO completeness. A total of 25,062 protein-coding genes were annotated, and about 23% of the assembly was found to consist of repetitive elements. A comprehensive analysis of repetitive elements uncovered centromere-specific tandem repeats and provided insights into the evolution of retrotransposons. A multigene phylogenetic analysis inferred a divergence time of about 26 million years ago (Ma) between nine- and three-spined sticklebacks, which is far older than the commonly assumed estimate of 13 Ma. Compared with the three-spined stickleback, we identified an additional duplication of several genes in the hemoglobin cluster. Sequencing data from populations adapted to different environments indicated potential copy number variations in hemoglobin genes. Furthermore, genome-wide synteny comparisons between three- and nine-spined sticklebacks identified chromosomal rearrangements underlying the karyotypic differences between the two species. The high-quality chromosome-scale assembly of the nine-spined stickleback genome obtained with long-read sequencing technology provides a crucial resource for comparative and population genomic investigations of stickleback fishes and teleosts.

Widespread sex dimorphism in aging and age-related diseases.

Although aging is a conserved phenomenon across evolutionary distant species, aspects of the aging process have been found to differ between males and females of the same species. Indeed, observations across mammalian studies have revealed the existence of longevity and health disparities between sexes, including in humans (i.e. with a female or male advantage). However, the underlying mechanisms for these sex differences in health and lifespan remain poorly understood, and it is unclear which aspects of this dimorphism stem from hormonal differences (i.e. predominance of estrogens vs. androgens) or from karyotypic differences (i.e. XX vs. XY sex chromosome complement). In this review, we discuss the state of the knowledge in terms of sex dimorphism in various aspects of aging and in human age-related diseases. Where the interplay between sex differences and age-related differences has not been explored fully, we present the state of the field to highlight important future research directions. We also discuss various dietary, drug or genetic interventions that were shown to improve longevity in a sex-dimorphic fashion. Finally, emerging tools and models that can be leveraged to decipher the mechanisms underlying sex differences in aging are also briefly discussed.

Differences in Karyotype and Fluorochrome Banding Patterns among Variations of <i>Trichosanthes cucumerina</i> with Different Fruit Size

Differences in Karyotype and Fluorochrome Banding Patterns among Variations of <i>Trichosanthes cucumerina</i> with Different Fruit Size

Karyotyping and Molecular Sexing in Brycinus nurse (Characiformes, Alestidae) from Nile River in Egypt

The present study aimed to investigate the karyotype and molecular sex differences in Brycinus nurse. Analysis of 430 metaphases spreads from 12 specimens revealed that the diploid chromosome number is 44 chromosomes and the proposed karyotype formula is n = 3 M + 3 SM + 16 A, FN = 56. No morphologically differentiated heteromorphic sex chromosomes were observed. On the other hand, 29 primers of three molecular markers (RAPD, SCoT and ISSR) were tested to differentiate between males and females of B. nurse. From all tested primers only two primers (OPI-18 and SCoT-18) successfully generated female specific bands in the bulked DNA samples which further confirmed using individual DNA samples. According to molecular analysis result in this study it seems that females of B. nurse are the heterogametic gender (ZW) and males of B. nurse are the homogametic gender (ZZ). In the future, SCoT marker can be used as suitable and powerful marker in genetic analysis studies in fish.

Molecular Phylogenetics of Bradypus (Three-Toed Sloth, Pilosa: Bradypodidae, Mammalia) and Phylogeography of Bradypus variegatus (Brown-Throated Three-Toed Sloth) with Mitochondrial Gene Sequences

Xenarthra (sloths, anteaters, and armadillos) are the quintessential South American mammals. Among the xenarthrans, sloths constitute the most diverse paleontologically with almost 100 fossil genera recorded. However, this abundant sloth fauna in the Americas became extinct around 10,000 years ago. Only six species belonging to two genera, Bradypus (four three-toed sloth species) and Choloepus (two two-toed sloth species) are alive today in Central and South America. Bradypus variegatus is the sloth species with the widest geographical distribution in the Neotropics. Some regional population genetics have been reported, especially in Brazil, but with limited sample sizes. Herein, we sequenced 77 samples of Bradypys variegatus (Panama, Colombia, Venezuela, Peru, Bolivia, and Brazil; 65 new samples and 12 from GenBank), plus one B. tridactylus, one B. pygmaeus, and five B. torquatus (one new and four from GenBank) at the mitochondrial (mt) control region. Additionally, 25 of these samples, representing the four species, were sequenced for the entire mitochondrial genome. Our results indicate that there are at least six main genetically different haplogroups of B. variegatus. They are the trans-Andean, western Amazon (with some other internal groups), Tapajos River, Tocantins River, Negro River, and the Brazilian eastern Atlantic forest (with two recognizable sub-groups in northern and southern areas) ones, with the ancestor of the trans-Andean haplogroup the first to diverge. A very strong genetic heterogeneity and a striking spatial pattern were detected among these different geographical areas, with the trans-Andean, western Amazon, and Tocantins populations showing the highest levels of genetic diversity, meanwhile the Tapajos and the Brazilian eastern populations yielding lower levels of genetic diversity. The following conclusions were as follows: 1) B. torquatus should be considered as a different genus (Scaeopus) because of its extreme genetic differences from other Bradypus taxa as was previously claimed by other authors; 2) B. pygmaeus is not a recent species adapted to Holocene island environments from the Central America B. variegatus group; and 3) if we adopt a strict version of the Phylogenetic Species Concept (PSC), the highly significant monophyletic clade of the trans-Andean B. variegatus population should be defined as a valid and differentiated species of three-toed sloth. However, we are reluctant to define this population as a new species until new data shows possible strong karyotype differences and/or pre- or post-zygote reproductive barriers (Biological Species Concept, BSC) between the trans and the cis-Andean populations of the three-toed brown-throated sloth.

Rapid and extensive karyotype diversification in haploid clinical Candida auris isolates

Candida auris is a newly emerged pathogenic microbe, having been identified as a medically relevant fungus as recently as 2009. It is one of the most drug-resistant yeast species known to date and its emergence and population structure are unusual. Because of its recent emergence, we are largely ignorant about fundamental aspects of its general biology, life cycle, and population dynamics. Here, we report the karyotype variability of 26 C. auris strains representing the four main clades. We demonstrate that all strains are haploid and have a highly plastic karyotype containing five to seven chromosomes, which can undergo marked alterations within a short time frame when the fungus is put under genotoxic, heat, or osmotic stress. No simple correlation was found between karyotype pattern, drug resistance, and clade affiliation indicating that karyotype heterogeneity is rapidly evolving. As with other Candida species, these marked karyotype differences between isolates are likely to have an important impact on pathogenic traits of C. auris.

Chromosome-scale assemblies reveal the structural evolution of African cichlid genomes.

BackgroundAfrican cichlid fishes are well known for their rapid radiations and are a model system for studying evolutionary processes. Here we compare multiple, high-quality, chromosome-scale genome assemblies to elucidate the genetic mechanisms underlying cichlid diversification and study how genome structure evolves in rapidly radiating lineages.ResultsWe re-anchored our recent assembly of the Nile tilapia (Oreochromis niloticus) genome using a new high-density genetic map. We also developed a new de novo genome assembly of the Lake Malawi cichlid, Metriaclima zebra, using high-coverage Pacific Biosciences sequencing, and anchored contigs to linkage groups (LGs) using 4 different genetic maps. These new anchored assemblies allow the first chromosome-scale comparisons of African cichlid genomes. Large intra-chromosomal structural differences (∼2–28 megabase pairs) among species are common, while inter-chromosomal differences are rare (<10 megabase pairs total). Placement of the centromeres within the chromosome-scale assemblies identifies large structural differences that explain many of the karyotype differences among species. Structural differences are also associated with unique patterns of recombination on sex chromosomes. Structural differences on LG9, LG11, and LG20 are associated with reduced recombination, indicative of inversions between the rock- and sand-dwelling clades of Lake Malawi cichlids. M. zebra has a larger number of recent transposable element insertions compared with O. niloticus, suggesting that several transposable element families have a higher rate of insertion in the haplochromine cichlid lineage.ConclusionThis study identifies novel structural variation among East African cichlid genomes and provides a new set of genomic resources to support research on the mechanisms driving cichlid adaptation and speciation.

Hybrid Zone between the Sok and Serov Chromosomal Races of the Common Shrew Sorex araneus (Lipotyphla, Mammalia) in European Russia

Analysis of the frequencies of karyotypic variants in the hybrid zone between the Sok and Serov chromosomal races of the common shrew Sorex araneus revealed that the zone has a complex configuration. A large part of the contact zone is located in a monotonous mid taiga zone, where there are no significant barriers to limit dispersion of shrews. Another part of the zone runs along the Pechora River (Komi Republic). Analysis of distribution of the diagnostic chromosomes on a transect along the Pechora River showed that the hybrid zone could be described by opposing metacentric clines. Individuals of both pure Sok and Serov races, as well as F1 hybrids, were found only on the left bank of the Pechora River. The right bank was occupied only by the Serov race, and F1 hybrids were rare there. The observed number of interracial hybrids in the center of the zone does not differ from that expected in the case of random breeding. This allows us to define this zone as unimodal. The standard width of the zone is about 40 km. This is considerably higher than all known cases of hybrid zones with the same level of karyotypic differences between parental races: two pairs of diagnostic metacentric chromosomes with monobrachial homology. We discuss possible causes of this phenomenon.

Karyoevolution of Crenicichla heckel 1840 (Cichlidae, Perciformes): a process mediated by inversions.

ABSTRACTCrenicichla (Cichliformes, Cichlidae) present a highly conserved diploid number 2n=48 with fundamental numbers varying between 52 and 62. We analyzed four species in order to investigate the role of repetitive DNA in chromosome evolution in the genus. Crenicichla johanna, Crenicichla cf. saxatilis and Crenicichla cf. regani have 2n=48 (8 m/sm and 40st/a) and FN=56, while Crenicichla sp. ‘Xingu I’ has 2n=48 (48 st/a) and FN=48. Different patterns of constitutive heterochromatin distribution were observed including pericentric, interstitial and whole arm C bands. A single chromosome bears 18S rDNA clusters in most species, except C. johanna, where population variation exists in terms of the quantity and distribution of clusters and their association with interstitial telomeric sequences. All species showed hybridization of 5S rDNA sequences in an interstitial region on an acrocentric chromosome pair. The karyotypic differences and maintenance of the diploid number supports chromosome evolution mediated by inversions in Crenicichla. The telomeric and 18S rDNA sequence association in various chromosomes of C. johanna are proposed to represent hotspots for breakage, favoring intra-chromosomal rearrangements. The results suggest that repetitive sequences can contribute to microstructural cytogenetic diversity in Crenicichla.

Differences in Karyotypes between Two Populations of &lt;i&gt;Crotalaria incana&lt;/i&gt; from Mexico

Differences in Karyotypes between Two Populations of &lt;i&gt;Crotalaria incana&lt;/i&gt; from Mexico

Cytogenetic Diversity of Korean Hexaploid Wheat (Triticum aestivum L.) with Simple Sequence Repeats (SSRs) by Fluorescence In Situ Hybridization

Chromosomes of Korean hexaploid wheat were investigated to compare the chromosomal karyotype for cytogenetic diversity. Chromosomal karyotyping was done with in situ hybridization using two types of simple sequence repeats (SSR)s, (AAG)5 and (AAC)5 labeled with tetramethyl-rhodamine-5-dUTP and fluorescein-12-dUPT as a fluorescence, respectively. The two SSRs as cytogenetic markers revealed that the cytogenetic characteristics of the wheat chromosomes were remarkably a B genome. In this study, the chromosomal karyotype of Keumkang, a Korean hexaploid wheat cultivar, was the A, B, and D genomes used as a cytogenetic reference. The expressed signals from the two SSRs showed a difference in the chromosomal karyotype of chromosome 1B among the Korean hexaploid wheat. The distribution pattern and the degree of condensation for the (AAG)5 and (AAC)5 signals on the short arm of chromosome 1B were different in the Korean hexaploid wheat shown in descending order: Keumkang > Joeun > Johan > Olgeuru. Olgeuru had a lower level of distribution and condensation for the two SSRs signals compared to the other Korean hexaploid wheat. In the A genome, chromosome 7A showed an unbalanced expression of the (AAG)5 signal on the distal region of the short and long arms in several Korean hexaploid wheat while Joeun, a Korean hexaploid wheat, showed a definite (AAG)5 signal on the distal region of each arm of chromosome 7A. Among the Korean hexaploid wheat, Shinmichal1, a Korean hexaploid waxy wheat, had a chromosome with a unique expression pattern for (AAG)5 and (AAC)5 compared the other Korean hexaploid wheat. Those cytogenetic differences identified in this study are useful as an indicator to improve the cytogenetic diversity in the Korean wheat breeding program.

BRCA1 & BRCA2 Germline Variants Are Enriched in MDS/AML and Portend Higher Average Mutational Burden

The homologous DNA repair pathway genes BRCA1 and BRCA2 are classically associated with increased susceptibility to hereditary breast and ovarian cancer due to increased vulnerability to double stranded DNA breaks (mutator phenotype). In addition to their role in breast/ovarian cancer, defects in these genes may predispose to myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). For example, in large populations of breast cancer patients, those with inherited defects in homologous repair (HR) showed a propensity to therapy-related MDS and AML; however, a relationship between BRCA gene variants and spontaneous myeloid neoplasms has yet to be elucidated. Moreover, analyses are complicated by the large number of clinically uncharacterized single nucleotide variants (SNV) in BRCA gene loci.We thus evaluated the relationship between germline BRCA variants (GLVs) and the risk of adult MDS or AML. We applied next generation sequencing to a large cohort of patients (N =463) presenting with MDS (402) and AML (61). In these analyses, all mutations with a variant allele frequency of less than 30% were considered somatic. We then identified alterations known to be linked with breast/ovarian cancer development by linkage analyses. These mutations (n=2), along with missense mutations with an allele frequency <.001% and previously unknown mutations with a CADD score >10, were considered Tier-1 mutations (n=37). Tier 2 mutations were defined as missense mutations with a population frequency >.01% or mutations in patients with incomplete clinical or sequencing data. After excluding Tier-2 variants, 39 of 88 GLVs were further analyzed.BRCA Tier-1 GLV were significantly over-represented in the MDS/AML cohort compared to the general population, estimated via publically available exome aggregation databases (ExAC, 8% vs 0.1% p<.001). No biallelic mutations were detected. We compared the pattern of somatic mutation and cytogenetic alteration in patients with Tier-1 GLVs to those without these mutations. Patients carrying Tier-1 GLVs exhibited a significantly higher average mutational burden compared to those without GLVs, measured by an NGS panel including 186 genes (1.2 vs. 0.4, p<.005). The most common co-occurring mutations in BRCA GLV carriers affected DNMT3A(4), ASXL1(3), SF3B1(3), TET2(3), and TP53(3). Among these mutations, TP53 alterations were significantly enriched in BRCA GLV carriers (OR = 6.8, p = 0.003, Figure 1). There was no difference in complex karyotype, del5q, and del7 alterations in BRCA GLV carriers when compared to other MDS/AML patients. BRCA GLV carriers had a higher burden of familial cancer (41% vs. 19%, p<.001). There was no difference in gender, age-at-diagnosis of MDS/AML, or 10-year survival in carriers of BRCA 1/2 GLVs in comparison to the broader cohort (Figure 2).BRCA GLVs (Tier-1) are over-represented in MDS/AML patients as compared to the general population, and linked with a higher rate of somatic point mutations but not common MDS/AML-associated cytogenetic abnormalities. This suggests the possibility that defects in HDR may facilitate the evolution of apparently spontaneous MDS/AML that is actually germline predisposed. As with breast and ovarian cancers, another possibility is that such variants could have implications in treatment selection, especially in the context of the evolution of PARP inhibition as a therapeutic modality in MDS/AML. [Display omitted] DisclosuresSaunthararajah:Novo Nordisk, A/S: Patents & Royalties; EpiDestiny, LLC: Patents & Royalties. Carraway:Jazz: Speakers Bureau; FibroGen: Consultancy; Balaxa: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Speakers Bureau; Agios: Consultancy, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Membership on an entity's Board of Directors or advisory committees. Nazha:MEI: Consultancy. Sekeres:Opsona: Membership on an entity's Board of Directors or advisory committees; Opsona: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Maciejewski:Alexion Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Apellis Pharmaceuticals: Consultancy; Apellis Pharmaceuticals: Consultancy; Ra Pharmaceuticals, Inc: Consultancy; Alexion Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Ra Pharmaceuticals, Inc: Consultancy.

Power law fitness landscapes and their ability to predict fitness

Whether or not evolution by natural selection is predictable depends on the existence of general patterns shaping the way mutations interact with the genetic background. This interaction, also known as epistasis, has been observed during adaptation (macroscopic epistasis) and in individual mutations (microscopic epistasis). Interestingly, a consistent negative correlation between the fitness effect of beneficial mutations and background fitness (known as diminishing returns epistasis) has been observed across different species and conditions. We tested whether the adaptation pattern of an additional species, Schizosaccharomyces pombe, followed the same trend. We used strains that differed by the presence of large karyotype differences and observed the same pattern of fitness convergence. Using these data along with published datasets, we measured the ability of different models to describe adaptation rates. We found that a phenotype-fitness landscape shaped like a power law is able to correctly predict adaptation dynamics in a variety of species and conditions. Furthermore we show that this model can provide a link between the observed macroscopic and microscopic epistasis. It may be very useful in the development of algorithms able to predict the adaptation of microorganisms from measures of the current phenotypes. Overall, our results suggest that even though adaptation quickly slows down, populations adapting to lab conditions may be quite far from a fitness peak.

Comparative cytogenetic analysis in Erythrolamprus snakes (Serpentes: Dipsadidae) from Argentina

We described the karyotypes of five snake taxa from Argentina: Erythrolamprus almadensis, E. ceii, E. poecilogyrus caesius, E. p. schotti and E. p. sublineatus, and also intergrading individuals between the last two subspecies by conventional staining, chromosome bandings and fluorescent in situ hybridization (FISH) with 28S ribosomal DNA probes. Erythrolamprus ceii and E. almadensis share a diploid chromosome number of 2n= 28, whereas in E. poecilogyrus intraspecific variations were observed: E. p. caesius has 2n= 28, E. p. schotti and E. p. sublineatus as well as in the intergrading individuals have 2n= 32. In E. almadensis and E. p. caesius, the 2nd and 6th chromosome pairs respectively are heteromorphic by size, morphology and C-banding pattern. These results allow us to suggest that these chromosome pairs might be considered as the ZW sex chromosomes in these species. The present comparative cytogenetic analyzes contributes to the already remarkable karyotypic variability in Erythrolamprus genus and propose a hypothesis about potential mechanisms involved in the chromosome evolution among taxa analyzed. Furthermore, the karyotypic differences observed between E. p. caesius (2n= 28) and E. p. schotti and E. p. sublineatus (2n= 32) might play a causal role in speciation.

Dynamics of tandemly repeated DNA sequences during evolution of diploid and tetraploid botiid loaches (Teleostei: Cobitoidea: Botiidae).

Polyploidization has played an important role in the evolution of vertebrates, particularly at the base of Teleostei–an enormously successful ray-finned fish group with additional genome doublings on lower taxonomic levels. The investigation of post-polyploid genome dynamics might provide important clues about the evolution and ecology of respective species and can help to decipher the role of polyploidy per se on speciation. Few studies have attempted to investigate the dynamics of repetitive DNA sequences in the post-polyploid genome using molecular cytogenetic tools in fishes, though recent efforts demonstrated their usefulness. The demonstrably monophyletic freshwater loach family Botiidae, branching to evolutionary diploid and tetraploid lineages separated >25 Mya, offers a suited model group for comparing the long-term repetitive DNA evolution. For this, we integrated phylogenetic analyses with cytogenetical survey involving Giemsa- and Chromomycin A3 (CMA3)/DAPI stainings and fluorescence in situ hybridization with 5S/45S rDNA, U2 snDNA and telomeric probes in representative sample of 12 botiid species.The karyotypes of all diploids were composed of 2n = 50 chromosomes, while majority of tetraploids had 2n = 4x = 100, with only subtle interspecific karyotype differences. The exceptional karyotype of Botia dario (2n = 4x = 96) suggested centric fusions behind the 2n reduction. Variable patterns of FISH signals revealed cases of intraspecific polymorphisms, rDNA amplification, variable degree of correspondence with CMA3+ sites and almost no phylogenetic signal. In tetraploids, either additivity or loci gain/loss was recorded. Despite absence of classical interstitial telomeric sites, large blocks of interspersed rDNA/telomeric regions were found in diploids only.We uncovered different molecular drives of studied repetitive DNA classes within botiid genomes as well as the advanced stage of the re-diploidization process in tetraploids. Our results may contribute to link genomic approach with molecular cytogenetic analyses in addressing the origin and mechanism of this polyploidization event.

Genome incompatibility between rainbow trout (Oncorhynchus mykiss) and sea trout (Salmo trutta) and induction of the interspecies gynogenesis.

Rainbow trout (Oncorhynchus mykiss Walbaum) and sea trout (Salmo trutta Linnaeus, 1758) show large karyotypic differences and their hybrid offspring is not viable due to unstable karyotype and chromosome fragmentation. However, gametes from these two species were used to induce gynogenetic development. Rainbow trout eggs activated by UV-irradiated sea trout sperm were subjected to high hydrostatic pressure (HHP) shock to prevent release of the 2nd polar body (early shock) or to inhibit the first cleavage (late shock) in order to produce diploid meiotic gynogenotes and gynogenetic doubled haploids (DHs), respectively. Cytogenetic analysis proved fish that development was induced by the sea trout spermatozoa were rainbow trout. In turn, molecular examination confirmed homozygosity of the gynogenetic DHs. Presumed appearance of the recessive alleles resulted in lower survival of the gynogenetic DH larvae (~25%) when compared to survival of the heterozygous (meiotic) gynogenotes (c. 50%). Our results proved that genomic incompatibilities between studied trout species result in the hybrid unviability. However, artificial gynogenesis including activation of rainbow trout eggs with UV-irradiated sea trout spermatozoa was successfully induced. As both species are unable to cross, application of the UV-irradiated sea trout spermatozoa to activate rainbow trout development assures only maternal inheritance with no contamination by the residues of the paternal chromosomes.

Lack of satellite DNA species-specific homogenization and relationship to chromosomal rearrangements in monitor lizards (Varanidae, Squamata)

BackgroundSatellite DNAs (stDNAs) are highly repeated sequences that constitute large portions of any genome. The evolutionary dynamics of stDNA (e.g. copy number, nucleotide sequence, location) can, therefore, provide an insight into genome organization and evolution. We investigated the evolutionary origin of VSAREP stDNA in 17 monitor lizards (seven Asian, five Australian, and five African) at molecular and cytogenetic level.ResultsResults revealed that VSAREP is conserved in the genome of Asian and Australian varanids, but not in African varanids, suggesting that these sequences are either differentiated or lost in the African varanids. Phylogenetic and arrangement network analyses revealed the existence of at least four VSAREP subfamilies. The similarity of each sequence unit within the same VSAREP subfamily from different species was higher than those of other VSAREP subfamilies belonging to the same species. Additionally, all VSAREP subfamilies isolated from the three Australian species (Varanus rosenbergi, V. gouldii, and V. acanthurus) were co-localized near the centromeric or pericentromeric regions of the macrochromosomes, except for chromosomes 3 and 4 in each Australian varanid. However, their chromosomal arrangements were different among species.ConclusionsThe VSAREP stDNA family lack homogenized species-specific nucleotide positions in varanid lineage. Most VSAREP sequences were shared among varanids within the four VSAREP subfamilies. This suggests that nucleotide substitutions in each varanid species accumulated more slowly than homogenization rates in each VSAREP subfamily, resulting in non-species-specific evolution of stDNA profiles. Moreover, changes in location of VSAREP stDNA in each Australian varanid suggests a correlation with chromosomal rearrangements, leading to karyotypic differences among these species.

Chromosomal Diversity of Three Species of Hypostomus Lacépède, 1803 (Siluriformes, Loricariidae), from the Paraná River Basin, Brazil: A Species Complex in Hypostomus ancistroides Reinforced by a ZZ/ZW Sex Chromosome System.

Hypostomus shows wide morphological patterns, corroborated by great chromosomal diversity that has suggested the existence of new species, especially from small tributaries. Cytogenetic analysis has contributed to estimate a cryptic diversity providing important data for taxonomic and evolutionary studies. Cytogenetic techniques were carried out on species from a small tributary of Ivaí River, Keller River (upper Paraná River basin): Hypostomus aff. ancistroides, Hypostomus topavae, and Hypostomus aff. hermanni that presented 2n = 68, 80, and 72 chromosomes, respectively. Each species showed the same diploid number from previous descriptions for other populations but different karyotype formulas, and Hypostomus aff. ancistroides had a ZZ/ZW sex chromosome system. Multiple NORs (nucleolar organizer regions) and pericentromeric heterochromatin blocks were found in the three species. Moreover, each of them showed species-specific heterochromatins. Multiple 5S rDNA sites were detected in Hypostomus aff. ancistroides and H. topavae, whereas Hypostomus aff. hermanni had only one pair bearing these sites. In addition to the divergence in the karyotype formulas, chromosomal markers used showed karyotype differences in the three species related to other respective populations studied. Furthermore, the first description of a ZZ/ZW system for Hypostomus aff. ancistroides reinforces the hypothesis that it may correspond to a species complex and yet, confirming an unknown cryptic diversity existent in small rivers.

Comparative analysis based on replication banding reveals the mechanism responsible for the difference in the karyotype constitution of treefrogs Ololygon and Scinax (Arboranae, Hylidae, Scinaxinae).

According to the recent taxonomic and phylogenetic revision of the family Hylidae, species of the former Scinax catharinae (Boulenger, 1888) clade were included in the resurrected genus Ololygon Fitzinger, 1843, while species of the Scinax ruber (Laurenti, 1768) clade were mostly included in the genus Scinax Wagler, 1830, and two were allocated to the newly created genus Julianus Duellman et al., 2016. Although all the species of the former Scinax genus shared a diploid number of 2n = 24 and the same fundamental number of chromosome arms of FN = 48, two karyotypic constitutions were unequivocally recognized, related mainly to the distinct size and morphology of the first two chromosome pairs. Some possible mechanisms for these differences had been suggested, but without any experimental evidence. In this paper, a comparison was carried out based on replication chromosome banding, obtained after DNA incorporation of 5-bromodeoxiuridine in chromosomes of Ololygon and Scinax. The obtained results revealed that the loss of repetitive segments in chromosome pairs 1 and 2 was the mechanism responsible for karyotype difference. The distinct localization of the nucleolus organizer regions in the species of both genera also differentiates the two karyotypic constitutions.

Comparative analysis based on replication banding reveals the mechanism responsible for the difference in the karyotype constitution of treefrogs Ololygon and Scinax (Arboranae, Hylidae, Scinaxinae)

According to the recent taxonomic and phylogenetic revision of the family Hylidae, species of the former Scinaxcatharinae (Boulenger, 1888) clade were included in the resurrected genus Ololygon Fitzinger, 1843, while species of the Scinaxruber (Laurenti, 1768) clade were mostly included in the genus Scinax Wagler, 1830, and two were allocated to the newly created genus JulianusDuellman et al., 2016. Although all the species of the former Scinax genus shared a diploid number of 2n = 24 and the same fundamental number of chromosome arms of FN = 48, two karyotypic constitutions were unequivocally recognized, related mainly to the distinct size and morphology of the first two chromosome pairs. Some possible mechanisms for these differences had been suggested, but without any experimental evidence. In this paper, a comparison was carried out based on replication chromosome banding, obtained after DNA incorporation of 5-bromodeoxiuridine in chromosomes of Ololygon and Scinax. The obtained results revealed that the loss of repetitive segments in chromosome pairs 1 and 2 was the mechanism responsible for karyotype difference. The distinct localization of the nucleolus organizer regions in the species of both genera also differentiates the two karyotypic constitutions.