Intra- and inter-individual chromosome variation in Hoplerythrinus unitaeniatus (Pisces, Erythrinidae): a population from the Brazilian São Francisco river basin

Chromosomal studies were carried out on a population of the fish Hoplerythrinus unitaeniatus (jeju) from Prata river in the São Francisco river basin, Minas Gerais, Brazil using conventional Giemsa staining, C-banding, silver nitrate nucleolar organizer region (Ag-NOR) staining and fluorescent in situ hybridization (FISH) with 18S and 5S rDNA probes. We found a high degree of inter- and intra-individual variability with the identification of 2n = 50, 2n = 51 and 2n = 52 karyotypes at nearly the same frequency within the population. Intra-individual variation in chromosomal morphology and, consequently, karyotype formulae was also observed, chiefly in the specimens with 2n = 50 and 2n = 52 chromosomes. Ag-NORs and 18S rDNA sites also showed numerical and chromosomal variation similar to that found for the 5S rDNA sites. Some putative hypotheses are considered in order to explain these results

Preferential accumulation of sex and Bs chromosomes in biarmed karyotypes by meiotic drive and rates of chromosomal changes in fishes

Mechanisms of accumulation based on typical centromeric drive or of chromosomes carrying pericentric inversions are adjusted to the general karyotype differentiation in the principal Actinopterygii orders. Here, we show that meiotic drive in fish is also supported by preferential establishment of sex chromosome systems and B chromosomes in orders with predominantly bi-brachial chromosomes. The mosaic of trends acting at an infra-familiar level in fish could be explained as the interaction of the directional process of meiotic drive as background, modulated on a smaller scale by adaptive factors or specific karyotypic properties of each group, as proposed for the orthoselection model

Molecular cytogenetic analysis in freshwater prawns of the genus macrobrachium (Crustacea:Decapoda: Palaemonidae)

Freshwater prawns of the genus Macrobrachium are one of the important components of circumtropical marine, estuarine, and freshwater environments. They have been extensively exploited for human consumption for many years. More than 250 species reflect the evolutionary success of this highly diversified group, with a complex and challenging taxonomy due to morphological variations and vast geographical distribution. Although genetic approaches have been used to clarify phylogenetic and taxonomic aspects of Macrobrachium species, cytogenetic information is still very scarce and mostly focused on chromosome number and morphology. Here, we present chromosome data for three species from the Neotropical region, M. carcinus, M. acanthurus, and M. amazonicum, and one species from the Oriental region, M. rosenbergii. Using conventional cytogenetic approaches and chromosome mapping of repetitive DNAs by fluorescence in situ hybridization (FISH), we identified numerical diversification of the diploid set, within and between both zoogeographic regions. These included M. acanthurus and M. amazonicum sharing diploid chromosomes of 98, while M. carcinus has 94, and M. rosenbergii has 118 chromosomes. Argentophilic sites are also variable in number, but they occur in a much higher number than 18S rDNA, representing two to 10 sites within the study species. Microsatellites repeat motifs are also abundant in the chromosomes, with a co-localization and uniform distribution along the chromosome arms, but completely absent in the AT-rich centromeric regions. As a whole, our study suggests that the 2n divergence was followed by a considerable rDNA diversification. The abundance of the exceptional amount of microsatellite sequences in the chromosomes also suggests that they are essential components of the Macrobrachium genome and, therefore, maintained as a shared feature by the species, the reason for which is yet unknown

Integrating Cytogenetics and Population Genomics:Allopatry and Neo-Sex Chromosomes May Have Shaped the Genetic Divergence in the Erythrinus erythrinus Species Complex (Teleostei, Characiformes)

SIMPLE SUMMARY: Fish present astonishing diversity, comprising more species than the combined total of all other vertebrates. Here, we integrated cytogenetic and genomic data to investigate how the evolution of multiple sex chromosomes together with allopatry is linked to genetic diversity and speciation in the fish species Erythrinus erythrinus. We hypothesized that the presence of multiple sex chromosomes has contributed to the genetic differentiation of populations, which could have potentially accelerated speciation. ABSTRACT: Diversity found in Neotropical freshwater fish is remarkable. It can even hinder a proper delimitation of many species, with the wolf fish Erythrinus erythrinus (Teleostei, Characiformes) being a notable example. This nominal species shows remarkable intra-specific variation, with extensive karyotype diversity found among populations in terms of different diploid chromosome numbers (2n), karyotype compositions and sex chromosome systems. Here, we analyzed three distinct populations (one of them cytogenetically investigated for the first time) that differed in terms of their chromosomal features (termed karyomorphs) and by the presence or absence of heteromorphic sex chromosomes. We combined cytogenetics with genomic approaches to investigate how the evolution of multiple sex chromosomes together with allopatry is linked to genetic diversity and speciation. The results indicated the presence of high genetic differentiation among populations both from cytogenetic and genomic aspects, with long-distance allopatry potentially being the main agent of genetic divergence. One population showed a neo-X(1)X(2)Y sexual chromosome system and we hypothesize that this system is associated with enhanced inter-population genetic differentiation which could have potentially accelerated speciation compared to the effect of allopatry alone

Revisiting the karyotypes of alligators and caimans (Crocodylia, alligatoridae) after a half-century delay:Bridging the gap in the chromosomal evolution of reptiles

Although crocodilians have attracted enormous attention in other research fields, from the cytogenetic point of view, this group remains understudied. Here, we analyzed the karyotypes of eight species formally described from the Alligatoridae family using differential staining, fluorescence in situ hybridization with rDNA and repetitive motifs as a probe, whole chromosome painting (WCP), and comparative genome hybridization. All Caimaninae species have a diploid chromosome number (2n) 42 and karyotypes dominated by acrocentric chromosomes, in contrast to both species of Alligatorinae, which have 2n = 32 and karyotypes that are predominantly metacentric, suggesting fusion/fission rearrangements. Our WCP results supported this scenario by revealing the homeology of the largest metacentric pair present in both Alligator spp. with two smaller pairs of acrocentrics in Caimaninae species. The clusters of 18S rDNA were found on one chromosome pair in all species, except for Paleosuchus spp., which possessed three chromosome pairs bearing these sites. Similarly, comparative genomic hybridization demonstrated an advanced stage of sequence divergence among the caiman genomes, with Paleosuchus standing out as the most divergent. Thus, although Alligatoridae exhibited rather low species diversity and some level of karyotype stasis, their genomic content indicates that they are not as conserved as previously thought. These new data deepen the discussion of cytotaxonomy in this family

Comparative cytogenetic survey of the giant bonytongue arapaima fish (Osteoglossiformes:Arapaimidae), across different Amazonian and Tocantins/Araguaia River Basins

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (401962/2016–4 and 302449/2018–3 to MBC); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (2018/22033–1 to MBC; and 2017/10240–0 to MFP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)/Alexander von Humboldt Foundation (88881.136128/2017–01 to MBC). project EXCELLENCE (CZ.02.1.01/0.0/0.0/ 15_003/0000460 OP).Universidade Federal de São Carlos. Departamento de Genética e Evolução. São Carlos, SP, Brazil / Secretaria de Estado de Educação de Mato Grosso. Cuiabá, MT, Brazil.Universidade Federal de São Carlos. Departamento de Genética e Evolução. São Carlos, SP, Brazil.Universidade Federal de São Carlos. Departamento de Genética e Evolução. São Carlos, SP, Brazil.Universidade Federal de São Carlos. Departamento de Genética e Evolução. São Carlos, SP, Brazil.Czech Academy of Sciences. Institute of Animal Physiology and Genetics. Laboratory of Fish Genetics. Czech Republic.University of Canberra. Instituto for Applied Ecology. Canberra, ACT, Australia.Universidade Federal de São Carlos. Departamento de Genética e Evolução. São Carlos, SP, Brazil.Instituto Nacional de Pesquisas da Amazônia. Coordenação de Biodiversidade. Laboratório de Genética Animal. Petrópolis, AM, Brazil.Instituto Nacional de Pesquisas da Amazônia. Coordenação de Biodiversidade. Laboratório de Genética Animal. Petrópolis, AM, Brazil.Ministério da Saúde. Secretaria de Vigilância em Saúde. Instituto Evandro Chagas. Laboratório de Cultura de Tecidos e Citogenética. Ananindeua, PA, Brasil.Universidade Federal de São Carlos. Departamento de Genética e Evolução. São Carlos, SP, Brazil.The South American giant fishes of the genus Arapaima, commonly known as pirarucu, are one of the most iconic among Osteoglossiformes. Previously cytogenetic studies have identified their karyotype characteristics; however, characterization of cytotaxonomic differentiation across their distribution range remains unknown. In this study, we compared chromosomal characteristics using conventional and molecular cytogenetic protocols in pirarucu populations from the Amazon and Tocantins-Araguaia river basins to verify if there is differentiation among representatives of this genus. Our data revealed that individuals from all populations present the same diploid chromosome number 2n=56 and karyotype composed of 14 pairs of meta-to submetacentric and 14 pairs of subtelo-to acrocentric chromosomes. The minor and major rDNA sites are in separate chromosomal pairs, in which major rDNA sites corresponds to large heterochromatic blocks. Comparative genomic hybridizations (CGH) showed that the genome of these populations shared a great portion of repetitive elements, due to a lack of substantial specific signals. Our comparative cytogenetic data analysis of pirarucu suggested that, although significant genetic differences occur among populations, their general karyotype patterns remain conserved