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 were 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.

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.

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.

Chromosomal rearrangements and the first indication of an ♀X1 X1 X2 X2 /♂X1 X2 Y sex chromosome system in Rineloricaria fishes (Teleostei: Siluriformes).

Rineloricaria is the most diverse genus within the freshwater fish subfamily Loricariinae, and it is widely distributed in the Neotropical region. Despite limited cytogenetic data, records from southern and south-eastern Brazil suggest a high rate of chromosomal rearrangements in this genus, mirrored in remarkable inter- and intraspecific karyotype variability. In the present work, we investigated the karyotype features of Rineloricaria teffeana, an endemic representative from northern Brazil, using both conventional and molecular cytogenetic techniques. We revealed different diploid chromosome numbers (2n) between sexes (33♂/34♀), which suggests the presence of an ♀X1 X1 X2 X2 /♂X1 X2 Y multiple sex chromosome system. The male-limited Y chromosome was the largest and the only biarmed element in the karyotype, implying Y-autosome fusion as the most probable mechanism behind its origination. C-banding revealed low amounts of constitutive heterochromatin, mostly confined to the (peri)centromeric regions of most chromosomes (including the X2 and the Y) but also occupying the distal regions of a few chromosomal pairs. The chromosomal localization of the 18S ribosomal DNA (rDNA) clusters revealed a single site on chromosome pair 4, which was adjacent to the 5S rDNA cluster. Additional 5S rDNA loci were present on the autosome pair 8, X1 chromosome, and in the presumed fusion point on the Y chromosome. The probe for telomeric repeat motif (TTAGGG)n revealed signals of variable intensities at the ends of all chromosomes except for the Y chromosome, where no detectable signals were evidenced. Male-to-female comparative genomic hybridization revealed no sex-specific or sex-biased repetitive DNA accumulations, suggesting a presumably low level of neo-Y chromosome differentiation. We provide evidence that rDNA sites might have played a role in the formation of this putative multiple sex chromosome system and that chromosome fusions originate through different mechanisms among different Rineloricaria species.

Chromosomal Evolution of Suboscines: Karyotype Diversity and Evolutionary Trends in Ovenbirds (Passeriformes, Furnariidae).

Furnariidae (ovenbirds) is one of the most diversified families in the Passeriformes order and Suboscines suborder. Despite the great diversity of species, cytogenetic research is still in its early stages, restricting our knowledge of their karyotype evolution. We combined traditional and molecular cytogenetic analyses in three representative species, Synallaxis frontalis, Syndactyla rufosuperciliata, and Cranioleuca obsoleta, to examine the chromosomal structure and evolution of ovenbirds. Our findings revealed that all the species studied had the same diploid number (2n = 82). Differences in chromosomal morphology of some macrochromosomes indicate the presence of intrachromosomal rearrangements. Although the three species only had the 18S rDNA on one microchromosome pair, chromosomal mapping of six simple short repeats revealed a varied pattern of chromosome distribution among them, suggesting that each species underwent different repetitive DNA accumulation upon their divergence. The interspecific comparative genomic hybridization experiment revealed that the Furnariidae species investigated carry centromeric regions enriched in similar repetitive sequences, bolstering the Furnariidae family's karyotype conservation. Nonetheless, the outgroup species Turdus rufiventris (Turdidae) demonstrated an advanced stage of sequence divergence with hybridization signals that were almost entirely limited to a few microchromosomes. Overall, the findings imply that Furnariidae species have a high degree of chromosomal conservation, and we could also observe a differentiation of repetitive sequences in both Passeriformes suborders (Suboscines and Oscines).

Evolutionary breakpoint regions and chromosomal remodeling in Harttia (Siluriformes: Loricariidae) species diversification.

The Neotropical armored catfish genus Harttia presents a wide variation of chromosomal rearrangements among its representatives. Studies indicate that translocation and Robertsonian rearrangements have triggered the karyotype evolution in the genus, including differentiation of sex chromosome systems. However, few studies used powerful tools, such as comparative whole chromosome painting, to clarify this highly diversified scenario. Here, we isolated probes from the X1 (a 5S rDNA carrier) and the X2 (a 45S rDNA carrier) chromosomes of Harttia punctata, which displays an X1X1X2X2/X1X2Y multiple sex chromosome system. Those probes were applied in other Harttia species to evidence homeologous chromosome blocks. The resulting data reinforce that translocation events played a role in the origin of the X1X2Y sex chromosome system in H. punctata. The repositioning of homologous chromosomal blocks carrying rDNA sites among ten Harttia species has also been demonstrated. Anchored to phylogenetic data it was possible to evidence some events of the karyotype diversification of the studied species and to prove an independent origin for the two types of multiple sex chromosomes, XX/XY1Y2 and X1X1X2X2/X1X2Y, that occur in Harttia species. The results point to evolutionary breakpoint regions in the genomes within or adjacent to rDNA sites that were widely reused in Harttia chromosome remodeling.

A new view on the scenario of karyotypic stasis in Epinephelidae fish: Cytogenetic, historical, and biogeographic approaches.

Epinephelidae (groupers) is an astonishingly diverse group of carnivorous fish widely distributed in reef environments around the world, with growing economic importance. The first chromosomal inferences suggested a conservative scenario for the family. However, to date, this has not been validated using biogeographic and phylogenetic approaches. Thus, to estimate karyotype diversification among groupers, eight species from the Atlantic and Indian oceans were investigated using conventional cytogenetic protocols and fluorescence in situ hybridization of repetitive sequences (rDNA, microsatellites, transposable elements). Despite the remarkable persistence of some symplesiomorphic karyotype patterns, such as all species sharing 2n=48 and most preserve a basal karyotype (2n=48 acrocentrics), the chromosomal diversification in the family revealed an unsuspected evolutionary dynamic, where about 40% of the species escape from the ancestral karyotype pattern. These karyotype changes showed a relation with the historical biogeography, likely as a byproduct of the progressive occupancy of new areas (huge diversity of adaptive and speciation conditions). In this context, oceanic regions harboring more recent clades such as those of the Indo-Pacific, exhibited a higher karyotype diversity. Therefore, the karyotype evolution of Epinephelidae fits well with the expansion and geographic contingencies of its clades, providing a more complex and diverse scenario than previously assumed.

Comparative chromosomal mapping of microsatellite repeats reveals divergent patterns of accumulation in 12 Siluridae (Teleostei: Siluriformes) species.

The freshwater family Siluridae occurs in Eurasia and is especially speciose in South and Southeast Asia, representing an important aquaculture and fishery targets. However, despite the restricted cytogenetic data, a high diploid number variation (from 2n=40 to 92) characterizes this fish group. Considering the large genomic divergence among its species, silurid genomes have experienced an enormous diversification throughout their evolutionary history. Here, we aim to investigate the chromosomal distribution of several microsatellite repeats in 12 Siluridae species and infer about their possible roles in the karyotype evolution that occurred in this group. Our results indicate divergent patterns of microsatellite distribution and accumulation among the analyzed species. Indeed, they are especially present in significant chromosome locations, such as the centromeric and telomeric regions, precisely the ones associated with several kinds of chromosomal rearrangements. Our data provide pieces of evidence that repetitive DNAs played a direct role in fostering the chromosomal differentiation and biodiversity in this fish family.

Chromosomes of Asian cyprinid fishes: Variable karyotype patterns and evolutionary trends in the genus Osteochilus (Cyprinidae, Labeoninae, "Osteochilini").

The Cyprinidae family is a highly diversified but demonstrably monophyletic lineage of cypriniform fishes. Among them, the genus Osteochilus contains 35 recognized valid species distributed from India, throughout Myanmar, Laos, Thailand, Malaysia, Indonesian archipelago to southern China. In this study, karyotypes and other chromosomal characteristics of five Osteochilus species occurring in Thailand, namely O. lini, O. melanopleura, O. microcephalus, O. vittatus and O. waandersii were examined using conventional and molecular cytogenetic protocols. Our results showed they possessed diploid chromosome number (2n) invariably 2n = 50, but the ratio of uni- and bi-armed chromosomes was highly variable among their karyotypes, indicating extensive chromosomal rearrangements. Only one chromosome pair bearing 5S rDNA sites occurred in most species, except O. melanopleura, where two sites were detected. In contrast, only one chromosomal pair bearing 18S rDNA sites were observed among their karyotypes, but in different positions. These cytogenetic patterns indicated that the cytogenomic divergence patterns of these Osteochilus species were largely corresponding to the inferred phylogenetic tree. Similarly, different patterns of the distributions of rDNAs and microsatellites across genomes of examined species as well as their different karyotype structures indicated significant evolutionary differentiation of Osteochilus genomes.

Tracking the evolutionary pathway of sex chromosomes among fishes: characterizing the unique XX/XY1Y2 system in Hoplias malabaricus (Teleostei, Characiformes).

The Neotropical fish, Hoplias malabaricus, is one of the most cytogenetically studied fish taxon with seven distinct karyomorphs (A-G) comprising varying degrees of sex chromosome differentiation, ranging from homomorphic to highly differentiated simple and multiple sex chromosomes. Therefore, this fish offers a unique opportunity to track evolutionary mechanisms standing behind the sex chromosome evolution and differentiation. Here, we focused on a high-resolution cytogenetic characterization of the unique XX/XY1Y2 multiple sex chromosome system found in one of its karyomorphs (G). For this, we applied a suite of conventional (Giemsa-staining, C-banding) and molecular cytogenetic approaches, including fluorescence in situ hybridization FISH (with 5S and 18S rDNAs, 10 microsatellite motifs and telomeric (TTAGGG) n sequences as probes), comparative genomic hybridization (CGH), and whole chromosome painting (WCP). In addition, we performed comparative analyses with other Erythrinidae species to discover the evolutionary origin of this unique karyomorph G-specific XY1Y2 multiple sex chromosome system. WCP experiments confirmed the homology between these multiple sex chromosomes and the nascent XX/XY sex system found in the karyomorph F, but disproved a homology with those of karyomorphs A-D and other closely related species. Besides, the putative origin of such XY1Y2 system by rearrangements of several chromosome pairs from an ancestral karyotype was also highlighted. In addition, clear identification of a male-specific region on the Y1 chromosome suggested a differential pattern of repetitive sequences accumulation. The present data suggested the origin of this unique XY1Y2 sex system, revealing evidences for the high level of plasticity of sex chromosome differentiation within the Erythrinidae.

Chromosome Microdissection on Semi-Archived Material.

Glass needle-based chromosome microdissection (midi) is a standard approach developed in the 1980s and remains more frequently applied in testing than the comparable technique using laser-based platforms. As the amount of DNA extracted by this technique is minimal and often in the range of picograms, the isolated DNA must be further amplified prior to use; the isolated amplified product can be readily utilized in multiple molecular research and diagnostic investigation. DNA libraries created by midi are either chromosome- or chromosome-region-specific. However, a critical component to this process is the need for timely chromosome preparation via the air-drying method not to exceed a ~2-3 h before midi is performed. Failure of this time-sensitive step often results in the chromosomes drying out after dropping, and upon initiation of the midi technique, the dissected material can jump away while touching by the needle, and collection of a suitable sample is inhibited. Herein, we demonstrate with a simple adaptation of the standard procedure, midi can be performed on semi-archived material stored for longer periods at -20°C. Thus, the critical step to obtain well-spread chromosome preparations can be completed under established conditions, for example, in the primary laboratory, stored at -20°C, and sent directly to specialized reference laboratories offering midi. In our study, we were able to obtain high-quality DNA libraries, as verified by gel electrophoreses and reverse fluorescence in situ hybridization, via midi extracted chromosome spreads derived from human, fish, snake, lampbrush, and insect stored for up to 6 months. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Deciphering the Origin and Evolution of the X1X2Y System in Two Closely-Related Oplegnathus Species (Oplegnathidae and Centrarchiformes).

Oplegnathus fasciatus and O. punctatus (Teleostei: Centrarchiformes: Oplegnathidae), are commercially important rocky reef fishes, endemic to East Asia. Both species present an X1X2Y sex chromosome system. Here, we investigated the evolutionary forces behind the origin and differentiation of these sex chromosomes, with the aim to elucidate whether they had a single or convergent origin. To achieve this, conventional and molecular cytogenetic protocols, involving the mapping of repetitive DNA markers, comparative genomic hybridization (CGH), and whole chromosome painting (WCP) were applied. Both species presented similar 2n, karyotype structure and hybridization patterns of repetitive DNA classes. 5S rDNA loci, besides being placed on the autosomal pair 22, resided in the terminal region of the long arms of both X1 chromosomes in females, and on the X1 and Y chromosomes in males. Furthermore, WCP experiments with a probe derived from the Y chromosome of O. fasciatus (OFAS-Y) entirely painted the X1 and X2 chromosomes in females and the X1, X2, and Y chromosomes in males of both species. CGH failed to reveal any sign of sequence differentiation on the Y chromosome in both species, thereby suggesting the shared early stage of neo-Y chromosome differentiation. Altogether, the present findings confirmed the origin of the X1X2Y sex chromosomes via Y-autosome centric fusion and strongly suggested their common origin.

Chromosomal Evolution and Evolutionary Relationships of Lebiasina Species (Characiformes, Lebiasinidae).

We present the first cytogenetic data for Lebiasina bimaculata and L. melanoguttata with the aim of (1) investigating evolutionary events within Lebiasina and their relationships with other Lebiasinidae genera and (2) checking the evolutionary relationships between Lebiasinidae and Ctenoluciidae. Both species have a diploid number 2n = 36 with similar karyotypes and microsatellite distribution patterns but present contrasting C-positive heterochromatin and CMA3+ banding patterns. The remarkable interstitial series of C-positive heterochromatin occurring in L. melanoguttata is absent in L. bimaculata. Accordingly, L. bimaculata shows the ribosomal DNA sites as the only GC-rich (CMA3+) regions, while L. melanoguttata shows evidence of a clear intercalated CMA3+ banding pattern. In addition, the multiple 5S and 18S rDNA sites in L. melanogutatta contrast with single sites present in L. bimaculata. Comparative genomic hybridization (CGH) experiments also revealed a high level of genomic differentiation between both species. A polymorphic state of a conspicuous C-positive, CMA3+, and (CGG)n band was found only to occur in L. bimaculata females, and its possible relationship with a nascent sex chromosome system is discussed. Whole chromosome painting (WCP) and CGH experiments indicate that the Lebiasina species examined and Boulengerella maculata share similar chromosomal sequences, thus supporting the relatedness between them and the evolutionary relationships between the Lebiasinidae and Ctenoluciidae families.

Deciphering the Evolutionary History of Arowana Fishes (Teleostei, Osteoglossiformes, Osteoglossidae): Insight from Comparative Cytogenomics.

Arowanas (Osteoglossinae) are charismatic freshwater fishes with six species and two genera (Osteoglossum and Scleropages) distributed in South America, Asia, and Australia. In an attempt to provide a better assessment of the processes shaping their evolution, we employed a set of cytogenetic and genomic approaches, including i) molecular cytogenetic analyses using C- and CMA3/DAPI staining, repetitive DNA mapping, comparative genomic hybridization (CGH), and Zoo-FISH, along with ii) the genotypic analyses of single nucleotide polymorphisms (SNPs) generated by diversity array technology sequencing (DArTseq). We observed diploid chromosome numbers of 2n = 56 and 54 in O. bicirrhosum and O. ferreirai, respectively, and 2n = 50 in S. formosus, while S. jardinii and S. leichardti presented 2n = 48 and 44, respectively. A time-calibrated phylogenetic tree revealed that Osteoglossum and Scleropages divergence occurred approximately 50 million years ago (MYA), at the time of the final separation of Australia and South America (with Antarctica). Asian S. formosus and Australian Scleropages diverged about 35.5 MYA, substantially after the latest terrestrial connection between Australia and Southeast Asia through the Indian plate movement. Our combined data provided a comprehensive perspective of the cytogenomic diversity and evolution of arowana species on a timescale.

Correction to: Whole chromosome painting reveals independent origin of sex chromosomes in closely related forms of a fish species.

ere, we report that a paragraph from the "Discussion" section of Cioffi et al. (2011; p. 1070, 4th paragraph of column 1) was transcribed (with only minor edits) from an introductory paragraph previously published in Chromosome Research by O'Meally et al.

Early Stages of XY Sex Chromosomes Differentiation in the Fish Hoplias malabaricus (Characiformes, Erythrinidae) Revealed by DNA Repeats Accumulation.

BACKGROUND: Species with 'young' or nascent sex chromosomes provide unique opportunities to understand early evolutionary mechanisms (e.g. accumulation of repetitive sequences, cessation of recombination and gene loss) that drive the evolution of sex chromosomes. Among vertebrates, fishes exhibit highly diverse and a wide spectrum of sex-determining mechanisms and sex chromosomes, ranging from cryptic to highly differentiated ones, as well as, from simple to multiple sex chromosome systems. Such variability in sex chromosome morphology and composition not only exists within closely related taxa, but often within races/populations of the same species. Inside this context, the wolf fish Hoplias malabaricus offers opportunity to investigate the evolution of morphologically variable sex chromosomes within a species complex, as homomorphic to highly differentiated sex chromosome systems occur among its different karyomorphs. MATERIALS & METHODS: To discover various evolutionary stages of sex chromosomes and to compare their sequence composition among the wolf fish´s karyomorphs, we applied multipronged molecular cytogenetic approaches, including C-banding, repetitive DNAs mapping, Comparative Genomic Hybridization (CGH) and Whole Chromosomal Painting (WCP). Our study was able to characterize a cryptically differentiated XX/XY sex chromosome system in the karyomorph F of this species. CONCLUSION: The Y chromosome was clearly identified by an interstitial heterochromatic block on the short arms, primarily composed of microsatellite motifs and retrotransposons. Additionally, CGH also identified a male specific chromosome region in the same chromosomal location, implying that the accumulation of these repeats may have initiated the Y chromosome differentiation, as well as played a critical role towards the evolution and differentiation of sex chromosomes in various karyomorphs of this species.

Chromosome mapping of repetitive DNAs in sergeant major fishes (Abudefdufinae, Pomacentridae): a general view on the chromosomal conservatism of the genus.

Species of the Abudefduf genus (sergeant-majors) are widely distributed in the Indian, Pacific and Atlantic oceans, with large schools inhabiting rocky coastal regions and coral reefs. This genus consists of twenty recognized species are of generalist habit, showing typical characteristics of colonizers. Some populations maintain gene flow between large oceanic areas, a condition that may influence their cytogenetic features. A number of species have been shown to be invaders and able to hybridize with local species. However, cytogenetic data in this genus are restricted to few species. In this way, the present study includes the chromosomal investigation, using conventional (Giemsa staining, Ag-NOR and C-banding) and molecular (in situ mapping of six different repetitive DNA classes) approaches in four Abudefduf species from different oceanic regions (A. bengalensis and A. sexfasciatus from the Indo-Pacific, A. vaigiensis from the Indian and A. saxatilis from the Atlantic oceans, respectively), to investigate the evolutionary events associated with the chromosomal diversification in this group. All species share a similar karyotype (2n = 48; NF = 52), except A. sexfasciatus (2n = 48; NF = 50), which possesses a characteristic pericentric inversion in the NOR-bearing chromosomal pair. Mapping of repetitive sequences suggests a chromosomal conservatism in this genus. The high karyotypic similarity between allopatric species of Abudefduf may be related to the success of natural viable hybrids among species with recent secondary contact.

W Chromosome Dynamics in Triportheus Species (Characiformes, Triportheidae): An Ongoing Process Narrated by Repetitive Sequences.

Characterizing the abundance and genomic distribution of repetitive DNAs provides information on genome evolution, especially regarding the origin and differentiation of sex chromosomes. Triportheus fishes offer a useful model to explore the evolution of sex chromosomes, since they represent a monophyletic group in which all species share a ZZ/ZW sex chromosome system. In this study, we analyzed the distribution of 13 classes of repetitive DNA sequences by FISH, including microsatellites, rDNAs, and transposable elements in 6 Triportheus species, in order to investigate the fate of the sex-specific chromosome among them. These findings show the dynamic differentiation process of the W chromosome concerning changes in the repetitive DNA fraction of the heterochromatin. The differential accumulation of the same class of repeats on this chromosome, in both nearby and distant species, reflects the inherent dynamism of the microsatellites, as well as the plasticity that shapes the evolutionary history of the sex chromosomes, even among closely related species sharing a same sex chromosome system.

The Evolutionary Dynamics of Ribosomal Genes, Histone H3, and Transposable Rex Elements in the Genome of Atlantic Snappers.

Lutjanidae is a family of primarily marine and carnivorous fishes distributed in the Atlantic, Indian, and Pacific oceans, with enormous economic and ecological importance. In order to better clarify the conservative chromosomal evolution of Lutjanidae, we analyzed the evolutionary dynamics of 5 repetitive DNA classes in 5 Lutjanus and in 1 Ocyurus species from the Western Atlantic. The ribosomal 18S sites were generally located in a single chromosome pair, except for L. jocu and L. alexandrei where they are found in 2 pairs. In turn, the 5S rDNA sites are unique, terminal and nonsyntenic with the 18S rDNA sites. In 3 species analyzed, H3 hisDNA genes were found in 1 chromosomal pair. However, while L. jocu presented 2 H3 sites, O. chrysurus showed a noteworthy dispersion of this gene in almost all chromosomes of the karyotype. Retrotransposons Rex1 and Rex3 do not exhibit any association with the explosive distribution of H3 sequences in O. chrysurus. The low compartmentalization of Rex elements, in addition to the general nondynamic distribution of ribosomal and H3 genes, corroborate the karyotype conservatism in Lutjanidae species, also at the microstructural level. However, some "disturbing evolutionary waves" can break down this conservative scenario, as evidenced by the massive random dispersion of H3 hisDNA in the genome of O. chrysurus. The implication of the genomic expansion of H3 histone genes and their functionality remain unknown, although suggesting that they have higher evolutionary dynamics than previously thought.

Chromosomes of Asian cyprinid fishes: Novel insight into the chromosomal evolution of Labeoninae (Teleostei, Cyprinidae).

The Labeoninae subfamily is a highly diversified but demonstrably monophyletic lineage of cyprinid fishes comprising five tribes and six incertae sedis genera. This widely distributed assemblage contains some 48 genera and around 480 recognized species distributed in freshwaters of Africa and Asia. In this study, the karyotypes and other chromosomal properties of five Labeoninae species found in Thailand Labeo chrysophekadion (Labeonini) and Epalzeorhynchos bicolor, Epalzeorhynchos munense, Henicorhynchus siamensis, Thynnichthys thynnoides (´Osteochilini´) were examined using conventional and molecular cytogenetic protocols. Our results confirmed a diploid chromosome number (2n) invariably 2n = 50, but the ratio of uni- and bi-armed chromosomes was highly variable among their karyotypes, indicating extensive structural chromosomal rearrangements. Karyotype of L. chrysophekadion contained 10m+6sm+20st+14a, 32m+10sm+8st for H. siamensis, 20m+12sm+10st+8a in E. bicolor, 20m+8sm+8st+14a in E. munense, and 18m+24sm+8st in T. thynnoides. Except for H. siamensis, which had four sites of 5S rDNA sites, other species under study had only one chromosome pair with those sites. In contrast, only one pair containing 18S rDNA sites were found in the karyotypes of three species, whereas two sites were found in that of E. bicolor. These cytogenetic patterns indicated that the cytogenomic divergence patterns of these labeonine species largely corresponded to the inferred phylogenetic tree. In spite of the 2n stability, diverse patterns of rDNA and microsatellite distribution as well as their various karyotype structures demonstrated significant evolutionary differentiation of Labeoninae genomes as exemplified in examined species. Labeoninae offers a traditional point of view on the evolutionary forces fostering biological diversity, and the recent findings add new pieces to comprehend the function of structural chromosomal rearrangements in adaption and speciation.