Search Results (39)

Woodcreepers (Dendrocolaptinae) constitute a subfamily of Neotropical passerines currently recognized as a monophyletic group within Furnariidae. Although Furnariidae is one of the most diverse avian families in the Neotropics, cytogenetic data remain scarce. In this study, we present the first cytogenetic analysis of Lepidocolaptes falcinellus using conventional (Ag-NOR, C-banding) and molecular (hybridization in situ fluorescence—FISH with telomeric and 18S rDNA probes) approaches. The species exhibits a karyotype with 2n = 80 chromosomes, predominantly acrocentric macrochromosomes, and heterochromatin restricted to centromeric regions. Telomeric repeats were confined to terminal regions, and 18S rDNA sites (NORs) were detected on the short arm of chromosome pair 1. This pattern, also observed in other Dendrocolaptinae species, contrasts with the ancestral avian condition of NORs on microchromosomes, suggesting a derived, lineage-specific chromosomal signature. These results support the cytogenetic cohesion of Dendrocolaptinae and reinforce the potential of NOR localization as a phylogenetic marker within the group. Our findings contribute novel cytotaxonomic data that enhance the understanding of chromosomal evolution and systematics in Furnariidae. Full article

Chromosome rearrangements during plant evolution can lead to alterations in genome structure and gene function, thereby influencing species adaptation and evolutionary processes. Gymnosperms, as an ancient group of plants, offer valuable insights into the morphological, physiological, and ecological characteristics of early terrestrial flora. The reconstruction of ancestral karyotypes in gymnosperms may provide critical clues for understanding their evolutionary history. In this study, we inferred the ancestral gymnosperm karyotype (AGK), which comprises 12 chromosomes, and conducted a collinearity analysis with existing gymnosperm genomes. Our findings indicate that chromosome numbers have remained remarkably stable throughout the evolution of gymnosperms. For species with multiplied chromosome numbers, such as gnetophytes, weak collinearities with the AGK were observed. Comparisons between the AGK and gnetophyte genomes revealed a biased pattern regarding retained duplication blocks. Furthermore, our analysis of transposable elements in Welwitschia mirabilis identified enriched regions containing LINE-1 retrotransposons within the syntenic blocks. Syntenic analysis between the AGK and angiosperms also demonstrated a biased distribution across chromosomes. These results provide a fundamental resource for further characterization of chromosomal evolution in gymnosperms. Full article

Background/Objectives: Arachnids are a megadiverse arthropod group. The present study investigated the chromosomes of pedipalpid tetrapulmonates (orders Amblypygi, Thelyphonida, Schizomida) and two arachnid orders of uncertain phylogenetic placement, Ricinulei and Solifugae, to reconstruct their karyotype evolution. Except for amblypygids, the cytogenetics of these arachnid orders was almost unknown prior to the present study. Methods: Chromosomes were investigated using methods of standard (Giemsa-stained preparations, banding techniques) and molecular cytogenetics (fluorescence in situ hybridization, comparative genomic hybridization). Results and Conclusions: New data for 38 species, combined with previously published data, suggest that ancestral arachnids possessed low to moderate 2n (22–40), monocentric chromosomes, one nucleolus organizer region (NOR), low levels of heterochromatin and recombinations, and no or homomorphic sex chromosomes. Karyotypes of Pedipalpi and Solifugae diversified via centric fusions, pericentric inversions, and changes in the pattern of NORs and, in solifuges, also through tandem fusions. Some solifuges display an enormous amount of constitutive heterochromatin and high NOR number. It is hypothesized that the common ancestor of amblypygids, thelyphonids, and spiders exhibited a homomorphic XY system, and that telomeric heterochromatin and NORs were involved in the evolution of amblypygid sex chromosomes. The new findings support the Cephalosomata clade (acariforms, palpigrades, and solifuges). Hypotheses concerning the origin of acariform holocentric chromosomes are presented. Unlike current phylogenetic hypotheses, the results suggest a sister relationship between Schizomida and a clade comprising other tetrapulmonates as well as a polyploidization in the common ancestor of the clade comprising Araneae, Amblypygi, and Thelyphonida. Full article

The intraspecies and interspecies Comparative Genomic Hybridization (CGH) between the closely related Cebidae species, capuchin monkeys (Cebus capucinus, Sapajus apella), and the tamarins (Saguinus mystax, Leontocebus fuscicollis) was performed to analyze their genomes. In particular, this approach determines balanced and unbalanced repetitive DNA sequence distribution and reveals dynamics during evolution. Capuchin monkeys are considered the most ancestral group with conserved syntenies compared to the hypothetical ancestral New World monkeys’ karyotype. Also, more derived karyotypes of phylogenetically distant species from the Saguinus and Leontocebus genera are analyzed here. The distribution of repetitive sequences has been traditionally studied through classical staining methods of cytogenetics. It has been hypothesized that repeats are species-specific and their conservation across closely related species are also common; their role in the genome has been extensively studied even though its role in speciation is not well studied and understood. The CGH shows bright signals with balanced and imbalanced DNA involving different genome regions: such as predominantly repetitive DNA at centromeric positions, and interstitial distribution with extended blocks. Cross-species CGH demonstrated the origin of some heterochromatic regions and identified apomorphic heterochromatin expansion events. The uncovered distribution of repetitive sequences is analyzed from an evolutionary perspective to elucidate the genomic dynamics of the repetitive sequences at the level of chromosomal organization. Full article

Currently, clusters of 45S and 5S ribosomal DNA (rDNA) have been studied in about 1000 and 100 species of the class Insecta, respectively. Although the number of insect species with known 45S rDNA clusters (also referred to as nucleolus-organizing regions, or NORs) constitutes less than 0.1 percent of the described members of this enormous group, certain conclusions can already be drawn. Since haploid karyotypes with single 45S and 5S rDNA clusters predominate in both basal and derived insect groups, this character state is apparently ancestral for the class Insecta in general. Nevertheless, the number, chromosomal location, and other characteristics of both 45S and 5S rDNA sites substantially vary across different species, and sometimes even within the same species. There are several main factors and molecular mechanisms that either maintain these parameters or alter them on the short-term and/or long-term scale. Chromosome structure (i.e., monocentric vs. holokinetic chromosomes), excessive numbers of rRNA gene copies per cluster, interactions with transposable elements, pseudogenization, and meiotic recombination are perhaps the most important among them. Full article

The detection of cryptic species in complexes that have undergone recent speciation is often difficult, since many standard nuclear markers have not yet accumulated differences between closely related taxa, and differences in mitochondrial markers can be leveled out due to mitochondrial introgressions. In these cases, the use of derived chromosomal characters such as non-ancestral chromosomal numbers and/or unusual karyotype features may be a solution to the species delimitation problem. However, non-ancestral but similar karyotypes may arise secondarily as a result of homoplastic evolution, and their interpretation as homologies may lead to incorrect taxonomic conclusions. In our study, we show that the combined use of mitochondrial DNA barcodes and karyotypes helps to solve this problem and identifies cryptic species in situations where each of these markers does not work individually. Using this approach, we show that the fauna of Armenia and adjacent Iran includes the following cryptic taxa of the Polyommatus ripartii species complex (haploid chromosome number, n in parentheses): P. ripartii paralcestis (n = 90), P. ripartii kalashiani, subsp. nov (n close to 90), P. emmeli, sp. nov. (n = 77–79), P. keleybaricus, sp. nov. (n = 86), P. demavendi belovi (n = 73–75), P. demavendi antonius, subsp. nov. (n = 71–73), P. admetus anatoliensis (n = 79) and P. eriwanensis (n = 29–34). Polyommatus admetus yeranyani is synonymized with P. admetus anatoliensis. Full article

It is argued that carcinogenesis and speciation are evolutionary events which are based on changes in the ‘karyotypic code’ through a phase of ‘genome instability’, followed by a bottleneck of selection for the viability and adaptability of the initial cells. Genomic (i.e., chromosomal) instability is caused by (massive) DNA breakage and the subsequent mis-repair of DNA double-strand breaks (DSBs) resulting in various chromosome rearrangements. Potential tumor cells are selected for rapid somatic proliferation. Cells eventually yielding a novel species need not only to be viable and proliferation proficient, but also to have a balanced genome which, after passing meiosis as another bottleneck and fusing with an identical gamete, can result in a well-adapted organism. Such new organisms should be genetically or geographically isolated from the ancestral population and possess or develop an at least partial sexual barrier. Full article

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. Full article

The plecos (Loricariidae) fish represent a great model for cytogenetic investigations due to their variety of karyotypes, including diploid and polyploid genomes, and different types of sex chromosomes. In this study we investigate Transancistrus santarosensis a rare loricariid endemic to Ecuador, integrating cytogenetic methods with specimens’ molecular identification by mtDNA, to describe the the species karyotype. We aim to verify whether sex chromosomes are cytologically identifiable and if they are associated with the accumulation of repetitive sequences present in other species of the family. The analysis of the karyotype (2n = 54 chromosomes) excludes recent centric fusion and pericentromeric inversion and suggests the presence of a ZZ/ZW sex chromosome system at an early stage of differentiation: the W chromosome is degenerated but is not characterized by the presence of differential sex-specific repetitive DNAs. Data indicate that although T. santarosensis has retained the ancestral diploid number of Loricariidae, it accumulated heterochromatin and shows non-syntenic ribosomal genes localization, chromosomal traits considered apomorphic in the family. Full article

In recent years, the number of mole species with species status confirmed by genetic methods has been continuously increasing. Unfortunately, cytogenetic data are not yet available for all species. Here, for the first time, a GTG-banded karyotype of the small-toothed mole from Vietnam, Euroscaptor parvidens, a representative of the Eastern clade of the genus Euroscaptor, has been described. Through comparative analysis of available Euroscaptor (Euroscaptor parvidens, Euroscaptor klossi, and Euroscaptor malayana) and Oreoscaptor (Oreoscaptor mizura) karyotypes, we found cytogenetic signatures for each of the studied species. Zoo-FISH with sorted chromosomes of the Siberian mole (Talpa altaica) on chromosome sets of the small-toothed mole (E. parvidens), the small Japanese mole (Mogera imaizumii) from the closely related genus, and the Japanese shrew mole (Urotrichus talpoides) from the tribe Urotrichini made it possible to identify syntenic regions between these species. We propose a possible ancestral karyotype of the tribe and, based on it, traced the features of chromosomal rearrangements accompanying the divergence of moles. The low rates of chromosomal evolution within the species of the genus Talpa—T. altaica and T. europaea—and the high rates of karyotypic reshuffling within the Asian genera of the tribe were confirmed. The karyotype of the Japanese mountain mole O. mizura seems to be the most conserved among the Asian moles. The most frequently occurring types of chromosomal rearrangements in moles are the pericentric inversions and amplification of heterochromatin. The pericentric inversions on four pairs of autosomes are shared between the closely related genera Euroscaptor, Oreoscaptor, and Mogera, while many more apomorphic rearrangements have occurred in each lineage additionally. The highest rate of chromosomal changes, with five rearrangements occurring over approximately 7 million years, was recorded in the lineage of the small-toothed mole. Full article

Several cytogenetic studies have already been performed in Triatominae, such that different karyotypes could be characterized (ranging from 2n = 21 to 25 chromosomes), being the changes in the number of chromosomes related mainly to fusion and fission events. These changes have been associated with reproductive isolation and speciation events in other insect groups. Thus, we evaluated whether different karyotypes could act in the reproductive isolation of triatomines and we analyzed how the events of karyotypic evolution occurred along the diversification of these vectors. For this, experimental crosses were carried out between triatomine species with different karyotypes. Furthermore, based on a phylogeny with 88 triatomine taxa (developed with different molecular markers), a reconstruction of ancestral karyotypes and of anagenetic and cladogenetic events related to karyotypic alterations was performed through the ChromoSSE chromosomal evolution model. All crosses performed did not result in hybrids (prezygotic isolation in both directions). Our modeling results suggest that during Triatominae diversification, at least nine cladogenetic events may be associated with karyotype change. Thus, we emphasize that these alterations in the number of chromosomes can act as a prezygotic barrier in Triatominae (karyotypic isolation), being important evolutionary events during the diversification of the species of Chagas disease vectors. Full article

The Lygaeoidea comprise about 4660 species in 790 genera and 16 families. Using standard chromosome staining and FISH with 18S rDNA and telomeric (TTAGG)_n probes, we studied male karyotypes and meiosis in 10 species of Lygaeoidea belonging to eight genera of the families Blissidae, Cymidae, Heterogastridae, Lygaeidae, and Rhyparochromidae. Chromosome numbers were shown to range from 12 to 28, with 2n = 14 being predominant. All species have an XY system and all but one have a pair of m-chromosomes. The exception is Spilostethus saxatilis (Lygaeidae: Lygaeinae); in another species of Lygaeinae, Thunbergia floridulus, m-chromosomes were present, which represents the first finding for this subfamily. All species have an inverted sequence of sex chromosome divisions (“post-reduction”). The 18S rDNA loci were observed on one or both sex chromosomes in Kleidocerys resedae and Th. floridulus, respectively (Lygaeidae), while on an autosomal bivalent in all other species. The rDNA loci tended to be close to the end of the chromosome. Using (TTAGG)_n—FISH, we were able to show for the first time that the Lygaeoidea lack the canonical “insect” telomere motif (TTAGG)_n. We speculate that this ancestral motif is absent from the entire infraorder Pentatomomorpha being replaced by some other telomere repeat motif sequences. Full article

The genus Agave presents a bimodal karyotype with x = 30 (5L, large, +25S, small chromosomes). Bimodality within this genus is generally attributed to allopolyploidy in the ancestral form of Agavoideae. However, alternative mechanisms, such as the preferential accumulation of repetitive elements at the macrochromosomes, could also be important. Aiming to understand the role of repetitive DNA within the bimodal karyotype of Agave, genomic DNA from the commercial hybrid 11648 (2n = 2x = 60, 6.31 Gbp) was sequenced at low coverage, and the repetitive fraction was characterized. In silico analysis showed that ~67.6% of the genome is mainly composed of different LTR retrotransposon lineages and one satellite DNA family (AgSAT171). The satellite DNA localized at the centromeric regions of all chromosomes; however, stronger signals were observed for 20 of the macro- and microchromosomes. All transposable elements showed a dispersed distribution, but not uniform across the length of the chromosomes. Different distribution patterns were observed for different TE lineages, with larger accumulation at the macrochromosomes. The data indicate the differential accumulation of LTR retrotransposon lineages at the macrochromosomes, probably contributing to the bimodality. Nevertheless, the differential accumulation of the satDNA in one group of macro- and microchromosomes possibly reflects the hybrid origin of this Agave accession. Full article

Butterfly chromosomes are holocentric, i.e., lacking a localized centromere. Potentially, this can lead to rapid karyotypic evolution through chromosome fissions and fusions, since fragmented chromosomes retain kinetic activity, while fused chromosomes are not dicentric. However, the actual mechanisms of butterfly genome evolution are poorly understood. Here, we analyzed chromosome-scale genome assemblies to identify structural rearrangements between karyotypes of satyrine butterfly species. For the species pair Erebia ligea–Maniola jurtina, sharing the ancestral diploid karyotype 2n = 56 + ZW, we demonstrate a high level of chromosomal macrosynteny and nine inversions separating these species. We show that the formation of a karyotype with a low number of chromosomes (2n = 36 + ZW) in Erebia aethiops was based on ten fusions, including one autosome–sex chromosome fusion, resulting in a neo-Z chromosome. We also detected inversions on the Z sex chromosome that were differentially fixed between the species. We conclude that chromosomal evolution is dynamic in the satyrines, even in the lineage that preserves the ancestral chromosome number. We hypothesize that the exceptional role of Z chromosomes in speciation may be further enhanced by inversions and sex chromosome–autosome fusions. We argue that not only fusions/fissions but also inversions are drivers of the holocentromere-mediated mode of chromosomal speciation. Full article

Amongst the 460 karyotypes of Polyphagan Coleoptera that we studied, 50 (10.8%) were carriers of an X autosome rearrangement. In addition to mitotic metaphase analysis, the correct diagnosis was performed on meiotic cells, principally at the pachytene stage. The percentages of these inter-chromosomal rearrangements, principally fusions, varied in relation to the total diploid number of chromosomes: high (51%) below 19, null at 19, low (2.7%) at 20 (the ancestral and modal number), and slightly increasing from 7.1% to 16.7% from 22 to above 30. The involvement of the X in chromosome fusions appears to be more than seven-fold higher than expected for the average of the autosomes. Examples of karyotypes with X autosome rearrangements are shown, including insertion of the whole X in the autosome (ins(A;X)), which has never been reported before in animals. End-to-end fusions (Robertsonian translocations, terminal rearrangements, and pseudo-dicentrics) are the most frequent types of X autosome rearrangements. As in the 34 species with a 19,X formula, there was no trace of the Y chromosome in the 50 karyotypes with an X autosome rearrangement, which demonstrates the dispensability of this chromosome. In most instances, C-banded heterochromatin was present at the X autosome junction, which suggests that it insulates the gonosome from the autosome portions, whose genes are subjected to different levels of expression. Finally, it is proposed that the very preferential involvement of the X in inter-chromosome rearrangements is explained by: (1) the frequent acrocentric morphology of the X, thus the terminal position of constitutive heterochromatin, which can insulate the attached gonosomal and autosomal components; (2) the dispensability of the Y chromosome, which considerably minimizes the deleterious consequences of the heterozygous status in male meiosis, (3) following the rapid loss of the useless Y chromosome, the correct segregation of the X autosome–autosome trivalent, which ipso facto is ensured by a chiasma in its autosomal portion. Full article