Karyotypic Variation Research Articles

Repeat competition and ecological shifts drive the evolution of the mobilome in Rhynchospora Vahl. (Cyperaceae), the holocentric beaksedges.

Genomic changes triggered by polyploidy, chromosomal rearrangements, and/ or environmental stress are among factors that affect the activity of mobile elements, particularly Long Terminal Repeats Retrotransposons (LTR-RTs) and DNA transposons. Because these elements can proliferate and move throughout host genomes, altering the genetic, epigenetic and nucleotypic landscape, they have been recognized as a relevant evolutionary force. Beaksedges (Rhynchospora) stand out for their wide cosmopolitan distribution, high diversity (~400 spp.) and holocentric chromosomes related to high karyotypic diversity and a centromere-specific satDNA Tyba. This makes the genus an interesting model to investigate the interactions between repetitive elements, phylogenetic relationships, and ecological variables. Here, we used comparative phylogenetic methods to investigate the forces driving the evolution of the entire set of mobile elements (mobilome) in the holocentric genus Rhynchospora. We statistically tested the impact of phylogenetic relationships, abundance of holocentromeric satDNA Tyba, diversity of repeatome composition, ecological variables, and chromosome number in mobile element diversification. Tyba abundance was found to be inversely correlated with LTR-RT content. Decrease of LTR abundance and diversity was also related to increase in chromosome number (likely due to fission events), and colonization of dry environments in the northern hemisphere. In contrast, we found constant LTR insertions throughout time in species with lower chromosome numbers in rainier environments in South America. A multivariate model showed that different traits drive LTR abundance, especially repeat diversity and Tyba abundance. Other mobile elements, such as non-LTR RTs and DNA transposons had insufficient abundance to be included in our models. Our findings suggest that LTR evolution is strongly impacted by the holocentric characteristics of Rhynchospora chromosomes, correlating with species diversification and biome shifts, and supporting a holokinetic drive model of evolution and a competitive scenario with Tyba. Altogether, our results present evidence of multi-trait influence on LTR-RT dynamics and provide a broader understanding of TE evolution in a macroevolutionary context.

From Micro to Macro: Avian Chromosome Evolution is Dominated by Natural Selection.

Birds display striking variation in chromosome number, defying the traditional view of highly conserved avian karyotypes. However, the evolutionary drivers of this variability remain unclear. To address this, we fit probabilistic models of chromosome number evolution across birds, enabling us to estimate rates of evolution for total chromosome number and the number of microchromosomes and macrochromosomes while simultaneously accounting for the impact of other evolving traits. Our analyses revealed higher rates of chromosome fusion than fission across all bird lineages. Notably, much of this signal was driven by Passeriformes, where migratory species showed a particularly strong bias towards fusions compared to sedentary counterparts. Furthermore, a robust correlation between the rearrangement rates of microchromosomes and macrochromosomes suggests that genome-wide processes drive rates of structural evolution. Additionally, we found that lineages with larger population sizes exhibited higher rates of both fusion and fission, indicating that positive selection plays a dominant role in driving divergence in chromosome number. Our findings illuminate the evolutionary dynamics of avian karyotypes and highlight that, while the fitness effects of random structural mutations are often deleterious, beneficial mutations may dominate karyotype divergence in some clades.

Recombination landscape and karyotypic variations revealed by linkage mapping in the grapevine downy mildew pathogen Plasmopara viticola.

Plasmopara viticola, the causal agent of grapevine downy mildew, is a biotrophic oomycete engaged in a tight coevolutionary relationship with its host. Rapid adaptation of the pathogen is favored by annual sexual reproduction that generates genotypic diversity. With the aim of studying the recombination landscape across the P. viticola genome, we generated 2 half-sibling F1 progenies (N = 189 and 162). Using targeted SNP sequencing, between 1,405 and 1,894 markers were included in parental linkage maps, and a consensus map was obtained by integrating 4,509 markers. The reference genome could be assembled into 17 pseudochromosomes, anchoring 88% of its physical length. We observed a strong collinearity between parental genomes and extensive synteny with the downy mildew Peronospora effusa. In the consensus map, the median recombination rate was 13.8 cM/Mb. The local recombination rate was highly variable along chromosomes, and recombination was suppressed in putative centromeric regions. Recombination rate was found negatively correlated with repeats' coverage and positively correlated with gene coverage. However, genes encoding secreted proteins and putative effectors were underrepresented in highly recombining regions. In both progenies, about 5% of the individuals presented karyotypic anomalies. Aneuploidies and triploidies almost exclusively originated from the male-transmitted chromosomes. Triploids resulted from fertilization by diploid gametes, but also from dispermy. Obligatory sexual reproduction each year may explain the lower level of karyotypic variation in P. viticola compared to other oomycetes. The linkage maps will be useful to guide future de novo chromosome-scale assemblies of P. viticola genomes and to perform forward genetics.

Phylogenomics resolves key relationships in Rumex and uncovers a dynamic history of independently evolving sex chromosomes

Abstract Sex chromosomes have evolved independently many times across eukaryotes. Despite a considerable body of literature on sex chromosome evolution, the causes and consequences of variation in their formation, degeneration, and turnover remain poorly understood. Chromosomal rearrangements are thought to play an important role in these processes by promoting or extending the suppression of recombination on sex chromosomes. Sex chromosome variation may also contribute to barriers to gene flow, limiting introgression among species. Comparative approaches in groups with sexual system variation can be valuable for understanding these questions. Rumex is a diverse genus of flowering plants harboring significant sexual system and karyotypic variation, including hermaphroditic and dioecious clades with XY (and XYY) sex chromosomes. Previous disagreement in the phylogenetic relationships among key species has rendered the history of sex chromosome evolution uncertain. Resolving this history is important for investigating the interplay of chromosomal rearrangements, introgression, and sex chromosome evolution in the genus. Here, we use new transcriptome assemblies from 11 species representing major clades in the genus, along with a whole-genome assembly generated for a key hermaphroditic species. Using phylogenomic approaches, we find evidence for the independent evolution of sex chromosomes across two major clades, and introgression from unsampled lineages likely predating the formation of sex chromosomes in the genus. Comparative genomic approaches revealed high rates of chromosomal rearrangement, especially in dioecious species, with evidence for a complex origin of the sex chromosomes through multiple chromosomal fusions. However, we found no evidence of elevated rates of fusion on the sex chromosomes in comparison with autosomes, providing no support for an adaptive hypothesis of sex chromosome expansion due to sexually antagonistic selection. Overall, our results highlight a complex history of karyotypic evolution in Rumex, raising questions about the role that chromosomal rearrangements might play in the evolution of large heteromorphic sex chromosomes.

Species limits in Wiedomys (Cricetidae: Sigmodontinae) reinforce the South American São Francisco River as a biogeographic barrier

Abstract Red-nosed mice (genus Wiedomys) are restricted to the Brazilian Cerrado and Caatinga biomes, distributed along the São Francisco River (SFR). Until recently, Wiedomys was considered monotypic, but 2 species with poorly defined geographic and morphological limits have been recognized: W. cerradensis and W. pyrrhorhinos. Our study used morphological, phylogenetic, and cytogenetic analyses to review and detail species limits within the genus and test whether the SFR could be associated with divergence between lineages. This integrative approach indicated that the SFR delineates the geographic boundaries between species, with W. pyrrhorhinos on the right bank and W. cerradensis on the left bank. The species are reciprocally monophyletic and diverge in cranial size, nasal morphology, and facial pelage color pattern. Karyotypic differences between and within W. pyrrhorhinos and W. cerradensis were also detected, and new chromosome complements (2n = 62, FN = 96 and 2n = 62, FN = 88, respectively) were found. Divergence time (0.339 to 0.025 Ma) is concordant with the timing of diversification of other co-distributed vertebrate taxa, and close to a younger estimate for the formation of SFR’s recent lower course to the east coast. Therefore, our study considerably expands knowledge of the geographic range of the genus, diagnoses of species, karyotypic variability between and within species, and reinforces the role of SFR as an important vicariant barrier in northeastern Brazil.

Unveiling genome plasticity as a mechanism of non-antifungal-induced antifungal resistance in Cryptococcus neoformans.

Cryptococcus neoformans, a critical priority pathogen designated by the World Health Organization, poses significant therapeutic challenges due to the limited availability of treatment options. The emergence of antifungal resistance, coupled with cross-resistance, further hampers treatment efficacy. Aneuploidy, known for its ability to induce diverse traits, including antifungal resistance, remains poorly understood in C. neoformans. We investigated the impact of tunicamycin, a well-established ER stress inducer, on aneuploidy formation in C. neoformans. Our findings show that both mild and severe ER stress induced by tunicamycin lead to the formation of aneuploid strains in C. neoformans. These aneuploid strains exhibit diverse karyotypes, with some conferring resistance or cross-resistance to antifungal drugs fluconazole and 5-flucytosine. Furthermore, these aneuploid strains display instability, spontaneously losing extra chromosomes in the absence of stress. Transcriptome analysis reveals the simultaneous upregulation of multiple drug resistance-associated genes in aneuploid strains. Our study reveals the genome plasticity of C. neoformans as a major mechanism contributing to non-antifungal-induced antifungal resistance.

Shifts in Chromosome Evolution Rates Shape the Karyotype Patterns of Leafcutting Ants.

Trait evolution has become a central focus in evolutionary biology, with phylogenetic comparative methods offering a framework to study how and why traits vary among species. Identifying variations in trait evolution rates within phylogenies is important for uncovering the mechanisms behind these differences. Karyotype variation, which is substantial across eukaryotic organisms, plays an essential role in species diversification. This study investigates karyotype variation within the leafcutting ant clade, focusing on chromosome number and morphology. We aim to determine whether karyotypic traits are phylogenetically dependent and how different evolutionary models explain karyotype diversity. Previous models have been insufficient in explaining these variations. To address these gaps, we employ modern phylogenetic methods to assess the impact of chromosomal fissions and fusions on karyotype evolution. By evaluating various evolutionary models-particularly the Brownian motion model, which suggests neutral chromosomal changes-we pursue for the further understanding the mode and tempo of karyotype evolution in ants. Our research examines how shifts in chromosomal change rates contribute to divergence among leafcutting ant species and assesses the role of chromosomal changes in the clade's evolutionary trajectory. Comparative analysis of leafcutting ant ideograms suggests that shared karyotype traits are strongly related to species relationships. This implies that karyotype diversification in leafcutting ants follows a phylogenetic trajectory at varying rates, with differences in karyotype traits reflecting the evolutionary distance between lineages. Particularly, the increase in the chromosome number of Acromyrmex is likely due to fission rearrangements rather than demi or polyploidization. We discuss and provide insights into the mechanisms driving karyotype variation and its implications for leafcutting ant diversification.

Comparative satellite DNA mapping in species of the genus Prochilodus (Teleostei, Characiformes) and its evolutionary implications.

Satellite DNA (satDNA) sequences are dynamic components of the eukaryotic genome, that can play significant roles in species diversification. The Prochilodontidae family, which includes 21 Neotropical fish species, is characterized by a conserved karyotype of 2n = 54 biarmed chromosomes, with variation in some species and populations regarding the presence or absence of B chromosomes. This study aimed to investigate whether the chromosomal distribution of specific satDNA sequences is conserved among three Prochilodus species (P. lineatus, P. costatus, and P. argenteus) regarding organization and number of loci, and to compare their genomes using comparative genomic hybridization (CGH). Our results demonstrated that most satDNA sequences share a similar distribution pattern across the three species, and CGH analysis corroborated that their karyotypes are very similar in terms of repetitive DNA distribution. We also identified a potential CENP-B box sequence within PliSat01, a satDNA located in the pericentromeric region of all analyzed species. In contrast, PliSat04 and PliSat14 displayed differential locations and variations in the number of loci per genome, underscoring the dynamic nature of repetitive sequences even in species with otherwise highly conserved genomes. These findings represent the first evidence of karyotype diversification in Prochilodus, highlighting the evolutionary dynamism of satDNA sequences.

The burst of satellite DNA in Leptidea wood white butterflies and their putative role in karyotype evolution.

Satellite DNAs (satDNAs) are abundant components of eukaryotic genomes, playing pivotal roles in chromosomal organization, genome stability, and evolution. Here, we combined cytogenetic and genomic methods to characterize the satDNAs in the genomes of Leptidea butterflies. Leptidea is characterized by the presence of a high heterochromatin content, large genomes, and extensive chromosomal reshuffling as well as the occurrence of cryptic species. We show that, in contrast to other Lepidoptera, satDNAs constitute a considerable proportion of Leptidea genomes, ranging between 4.11% and 11.05%. This amplification of satDNAs, together with the hyperactivity of transposable elements, contributes to the substantial genome expansion in Leptidea. Using chromosomal mapping, we show that, particularly LepSat01-100 and LepSat03-167 satDNAs, are preferentially localized in heterochromatin exhibiting variable distribution that may have contributed to the highly diverse karyotypes within the genus. The satDNAs also exhibit W-chromosome accumulation, suggesting their involvement in sex chromosome evolution. Our results provide insights into the dynamics of satDNAs in Lepidoptera genomes and highlight their role in genome expansion and chromosomal organization, which could influence the speciation process. The high proportion of repetitive DNAs in the genomes of Leptidea underscores the complex evolutionary dynamics revealing the interplay between repetitive DNAs and genomic architecture in the genus.

Chromosome-level genome assembly of the morabine grasshopper Vandiemenella viatica19

Morabine grasshoppers in the Vandiemenella viatica species group, which show karyotype diversity, have been studied for their ecological distribution and speciation in relation to their genetic and chromosomal diversity. They are good models for studying sex chromosome evolution as “old” and newly emerged sex chromosomes co-exist within the group. Here we present a reference genome for the viatica19 chromosomal race, that possesses the ancestral karyotype within the group. Using PacBio HiFi and Hi-C sequencing, we generated a chromosome-level assembly of 4.09 Gb in span, scaffold N50 of 429 Mb, and complete BUSCO score of 98.1%, containing 10 pseudo-chromosomes. We provide Illumina datasets of males and females, used to identify the X chromosome. The assembly contains 19,034 predicted protein-coding genes, and a total of 75.21% of repetitive DNA sequences. By leveraging HiFi reads, we mapped the genome-wide distribution of methylated bases (5mC and 6 mA). This comprehensive assembly offers a robust reference for morabine grasshoppers and supports further research into speciation and sex chromosome diversification within the group and its related species.

Exploring Chromosomal Polymorphism and Evolutionary Implications in Rineloricaria lanceolata (Günther, 1868) (Siluriformes: Loricariidae): Insights from Meiotic Behavior and Phylogenetic Analysis.

Chromosomal polymorphism is a significant aspect of population genetics, influencing the adaptation and evolution of species. In Rineloricaria lanceolata, a Neotropical fish species, chromosomal polymorphism has been observed, yet the underlying mechanisms and evolutionary implications remain poorly understood. This article aims to investigate the chromosomal polymorphism in Rineloricaria lanceolata, focusing on elucidating the meiotic behavior of karyotypic variants and tracing the phylogenetic origins of this polymorphism within the genus. By employing molecular markers and cytogenetic techniques, we aim to uncover the mechanisms driving chromosomal rearrangements and their potential role in speciation and adaptation. Understanding the genetic basis of chromosomal polymorphism in R. lanceolata not only contributes to our knowledge of species evolution but also holds implications for the conservation of genetic diversity within this vulnerable group of Neotropical fishes.

Earthworm (Oligochaeta, Lumbricidae) intraspecific genetic variation and polyploidy.

Earthworms are known for their intricate systematics and a diverse range of reproduction modes, including outcrossing, self-fertilization, parthenogenesis, and some other modes, which can occasionally coexist in a single species. Moreover, they exhibit considerable intraspecific karyotype diversity, with ploidy levels varying from di- to decaploid, as well as high genetic variation. In some cases, a single species may exhibit significant morphological variation, contain several races of different ploidy, and harbor multiple genetic lineages that display significant divergence in both nuclear and mitochondrial DNA. However, the relationship between ploidy races and genetic lineages in earthworms remains largely unexplored. To address this question, we conducted a comprehensive review of available data on earthworm genetic diversity and karyotypes. Our analysis revealed that in many cases, a single genetic lineage appears to encompass populations with different ploidy levels, indicating recent polyploidization. On the other hand, some other cases like Octolasion tyrtaeum and Dendrobaena schmidti/D. tellermanica demonstrate pronounced genetic boundaries between ploidy races, implying that they diverged long ago. Certain cases like the Eisenia nordenskioldi complex represent a complex picture with ancient divergence between lineages and both ancient and recent polyploidization. The comparison of phylogenetic and cytological data suggests that some ploidy races have arisen independently multiple times, which supports the early findings by T.S. Vsevolodova-Perel and T.V. Malinina. The key to such a complex picture is probably the plasticity of reproductive modes in earthworms, which encompass diverse modes of sexual and asexual reproduction; also, it has been demonstrated that even high-ploidy forms can retain amphimixis.

Karyotypic and phenotypic condensation in allotetraploid wheats accompanied with reproductive strategy transformation: from natural evolution to domestication.

Allotetraploid wheat reflects evolutionary divergence and domestication convergence in the karyotypic and phenotypic evolution, accompanied with the transformation from r- strategy to K- strategy in reproductive fitness. Allotetraploid wheat, the progenitor of hexaploidy bread wheat, has undergone 300,000years of natural evolution and 10,000years of domestication. The variations in karyotype and phenotype as well as fertility fitness have not been systematically linked. Here, by combining fluorescent in situ hybridization with the quantification of phenotypic and reproductive traits, we compared the karyotype, vegetative growth phenotype and reproductive fitness among synthesized, wild and domesticated accessions of allotetraploid wheat. We detected that the wild accessions showed dramatically high frequencies of homologous recombination and copy number variations of simple sequence repeats (SSR) comparing with synthetic and domesticated accessions. The phenotypic traits reflected significant differences among the populations shaped by distinct evolutionary processes. The diversity observed in wild accessions was significantly greater than that in domesticated ones, particularly in traits associated with vegetative growth and spike morphology. We found that the active pollen of domesticated accessions exhibited greater potential of germination, despite a lower rate of active pollen compared with the wild accessions, indicating a transformation in reproductive fitness strategy for pollen development in domesticated accessions compared to the wild accessions, from r-strategy to K-strategy. Our results demonstrate the condensation of karyotype and phenotype from natural wild accessions to domesticated accessions in allotetraploid wheats. Ecological strategy transformation should be seriously considered from evolution to domestication in polyploid plants, especially crops, which may provide a perspective on the adaptive evolution of polyploid plants.

Centromeric transposable elements and epigenetic status drive karyotypic variation in the eastern hoolock gibbon.

Great apes have maintained a stable karyotype with few large-scale rearrangements; in contrast, gibbons have undergone a high rate of chromosomal rearrangements coincident with rapid centromere turnover. Here we characterize assembled centromeres in the Eastern hoolock gibbon, Hoolock leuconedys (HLE), finding a diverse group of transposable elements (TEs) that differ from the canonical alpha satellites found across centromeres of other apes. We find that HLE centromeres contain a CpG methylation centromere dip region, providing evidence this epigenetic feature is conserved in the absence of satellite arrays; nevertheless, we report a variety of atypical centromeric features, including protein-coding genes and mismatched replication timing. Further, large structural variations define HLE centromeres and distinguish them from other gibbons. Combined with differentially methylated TEs, topologically associated domain boundaries, and segmental duplications at chromosomal breakpoints, we propose that a "perfect storm" of multiple genomic attributes with propensities for chromosome instability shaped gibbon centromere evolution.

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

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

Integrating Genetic and Cytogenetic Data: A Diversity Study of Astyanax and Psalidodon (Characidae) Species from the Paraná River Basin.

Astyanax is one of the most specious fish groups in the Neotropical region, with many cryptic species, which represents a challenge for correct identification through traditional taxonomic methods. Psalidodon is a recently resurrected genus group of species previously belonging to Astyanax, specifically those with extensive chromosomal variation of the A. scabripinnis and fasciatus complexes. In the present study, the mitochondrial genes cytochrome c oxidase subunit 1 (COI), mitochondrial ATP synthase 6 and 8 (ATPase 6/8), and NADH dehydrogenase subunit 2 (ND2) were used in conjunction with chromosomal data to characterize molecularly and cytogenetically populations of Astyanax and Psalidodon from rivers and streams of the Ivaí River Basin (Paraná Basin). The results demonstrated the effectiveness of the integrative use of molecular and cytogenetic techniques, with the confirmation of at least three species for the sampled sites: A. lacustris, P. paranae, and P. fasciatus, which showed inter- and intrapopulation karyotype variations. In addition, extensive haplotypic variation can be observed for these species within the Ivaí River Basin and throughout the Paraná River Basin. The data demonstrate a hidden diversity among the species analyzed, enrich the ichthyofaunistic knowledge of small rivers and streams, and contribute to future conservation projects in these areas.

Plasticity of the mitotic spindle in response to karyotype variation

Karyotypes, composed of chromosomes, must be accurately partitioned by the mitotic spindle for optimal cell health. However, it is unknown how underlying characteristics of karyotypes, such as chromosome number and size, govern the scaling of the mitotic spindle to ensure accurate chromosome segregation and cell proliferation. We utilize budding yeast strains engineered with fewer chromosomes, including just two "mega chromosomes," to study how spindle size and function are responsive to, and scaled by, karyotype. We determined that deletion and overexpression of spindle-related genes are detrimental to the growth of strains with two chromosomes, suggesting that mega chromosomes exert altered demands on the spindle. Using confocal microscopy, we demonstrate that cells with fewer but longer chromosomes have smaller spindle pole bodies, fewer microtubules, and longer spindles. Moreover, using electron tomography and confocal imaging, we observe elongated, bent anaphase spindles with fewer core microtubules in strains with mega chromosomes. Cells harboring mega chromosomes grow more slowly, are delayed in mitosis, and a subset struggle to complete chromosome segregation. We propose that the karyotype of the cell dictates the microtubule number, type, spindle pole body size, and spindle length, subsequently influencing the dynamics of mitosis, such as the rate of spindle elongation and the velocity of pole separation. Taken together, our results suggest that mitotic spindles are highly plastic ultrastructures that can accommodate and adjust to a variety of karyotypes, even within a species.

Multiple karyotype differences between populations of the Hoplias malabaricus (Teleostei; Characiformes), a species complex in the gray area of the speciation process.

Neotropical fishes exhibit remarkable karyotype diversity, whose evolution is poorly understood. Here, we studied genetic differences in 60 individuals, from 11 localities of one species, the wolf fish Hoplias malabaricus, from populations that include six different "karyomorphs". These differ in Y-X chromosome differentiation, and, in several cases, by fusions with autosomes that have resulted in multiple sex chromosomes. Other differences are also observed in diploid chromosome numbers and morphologies. In an attempt to start understanding how this diversity was generated, we analyzed within- and between-population differences in a genome-wide sequence data set. We detect clear genotype differences between karyomorphs. Even in sympatry, samples with different karyomorphs differ more in sequence than samples from allopatric populations of the same karyomorph, suggesting that they represent populations that are to some degree reproductively isolated. However, sequence divergence between populations with different karyomorphs is remarkably low, suggesting that chromosome rearrangements may have evolved during a brief evolutionary time. We suggest that the karyotypic differences probably evolved in allopatry, in small populations that would have allowed rapid fixation of rearrangements, and that they became sympatric after their differentiation. Further studies are needed to test whether the karyotype differences contribute to reproductive isolation detected between some H. malabaricus karyomorphs.

Mapping of SINEs in the genome of Proechimys (Mammalia: Rodentia)

This study aimed to analyze the distribution of short interspersed elements (SINEs) in the chromosomes of five species of rodents of the genus Proechimys and in a variant karyotype of P. guyannensis. Molecular cytogenetic techniques were used to characterize the sequences of the B1, B4, MAR and THER SINEs, which were used as probes for hybridization in metaphase chromosomes. A wide distribution of SINEs was observed in the chromosomes of the Proechimys species examined, thus indicating differentiation of these retroelements. The signal of the B4 SINE was more evident than that of the B1 SINE, especially in P. echinothrix, P. longicaudatus, and P. cuvieri. Although the signal of the MAR SINE was more explosive than that of the THER SINE, in the species P. echinothrix, P. guyannensis (2n = 46) and P. longicaudatus, its distribution in the karyotypes was similar. The signals of these retroelements occurred at specific heterochromatic sites and were centromeric/pericentromeric and at the terminal regions in most chromosomes. This appears to be a typical distribution pattern of the SINEs and may indicate involvement with rearrangements during karyotypic diversification in Proechimys. The variation of the SINEs in the genome of Proechimys species demonstrates that these elements are distributed in a specific way in this genus and the preference for some sites, considered hotspots for chromosomal breakage, allows us to propose that these elements are related to the karyotypic evolution of Proechimys.

A case of cryptic diversity in the bat Hsunycteris thomasi (Lonchophyllinae, Chiroptera): New insights into unrecognized species

AbstractIntegrating different lines of evidence is currently recognized as the most robust approach to investigating taxonomic questions, particularly those concerning cryptic diversity. In recent years, different sources of evidence have pointed to new cryptic taxa for bats, with the genus Hsunycteris being an excellent study group because of its large karyotypic variability and high genetic divergence revealed by the latest taxonomic and systematic reviews. This study tests the cryptic diversity hypothesis for the Hsunycteris thomasi complex through an integrative approach using species delimitation, phylogenetic analysis, chromosome painting, and linear morphometry. Our results suggest the existence of three lineages for H. thomasi that are morphologically indistinguishable, confirming the two previously described lineages in the literature and adding a third. We argue that the paraphyly in H. thomasi, as reported by previous studies, should be treated as independent species since they have unique evolutionary histories. Finally, we demonstrate that chromosomal and molecular methods are indispensable for recognizing and confirming groups that include cryptic species or species with confusing and controversial taxonomy.