Sex chromosomes have evolved repeatedly across eukaryotes. The emergence of a sex-determining (SD) locus is expected to progressively restrict recombination, driving convergent molecular differentiation. However, evidence from taxa like teleost fishes, representing over half of vertebrate species with unmatched diversity in SD systems, challenges this model. Teleost sex chromosomes are often difficult to detect as they experience frequent turnovers, resetting the differentiation process. Nothobranchius killifishes, which include the XY system shared by N. furzeri and N. kadleci and X1X2Y systems in six other species, offer a valuable model to study sex chromosome turnovers. We characterised X1X2Y systems in five killifish species and found that sex chromosomes evolved at least four times independently. Sex-determining regions resided near centromeres or predicted chromosome rearrangement breakpoints in N. brieni and N. guentheri, suggesting recombination cold spots may facilitate sex chromosome evolution. Chromosomes representing the XY system in N. furzeri/N. kadleci were sex-linked also in the outgroup Fundulosoma thierryi, with several genes, including gdf6, residing in the region of differentiation. Although the X1X2Y systems of N. guentheri, N. lourensi (both Coastal clade), and N. brieni (Kalahari clade) involved different chromosomes, they shared a potential SD region. We uncovered two sex-linked evolutionary strata of distinct age in N. guentheri. However, its potential SD gene amhr2 was located in the younger stratum and is hence unlikely to be the ancestral SD gene in this lineage. Our findings suggest recombination landscapes shape sex chromosome turnover and that certain synteny blocks are repeatedly co-opted as sex chromosomes in killifishes.

• Klíčová slova
• bacterial artificial chromosome, chromosome fusion, pool‐seq, recombination suppression, sex chromosome differentiation, zoo‐FISH,
• MeSH
• Cyprinodontidae * genetika   MeSH
• fylogeneze MeSH
• molekulární evoluce * MeSH
• pohlavní chromozomy * genetika   MeSH
• procesy určující pohlaví * genetika   MeSH
• rekombinace genetická MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Eurasia has undergone substantial tectonic, geological, and climatic changes throughout the Cenozoic, primarily associated with tectonic plate collisions and a global cooling trend. The evolution of present-day biodiversity unfolded in this dynamic environment, characterised by intricate interactions of abiotic factors. However, comprehensive, large-scale reconstructions illustrating the extent of these influences are lacking. We reconstructed the evolutionary history of the freshwater fish family Nemacheilidae across Eurasia and spanning most of the Cenozoic on the base of 471 specimens representing 279 species and 37 genera plus outgroup samples. Molecular phylogeny using six genes uncovered six major clades within the family, along with numerous unresolved taxonomic issues. Dating of cladogenetic events and ancestral range estimation traced the origin of Nemacheilidae to Indochina around 48 mya. Subsequently, one branch of Nemacheilidae colonised eastern, central, and northern Asia, as well as Europe, while another branch expanded into the Burmese region, the Indian subcontinent, the Near East, and northeast Africa. These expansions were facilitated by tectonic connections, favourable climatic conditions, and orogenic processes. Conversely, aridification emerged as the primary cause of extinction events. Our study marks the first comprehensive reconstruction of the evolution of Eurasian freshwater biodiversity on a continental scale and across deep geological time.

Stone loaches, also known as Nemacheilidae, are a large family of fish commonly found in the streams and rivers of Europe and Asia, with a small number of species also inhabiting certain Ethiopian lakes. How these fish, which originated in Asia about 50 million years ago, made their way into European and African waters remains poorly understood. Major geological and climate changes took place throughout this period, from the formation of the Himalayas and other mountain ranges in eastern and western Asia to large drops in temperatures or rainfalls in certain regions. Šlechtová et al. studied the influence of these events on the spread and evolution of stone loaches. The team used a large dataset of 471 samples obtained from more than 250 species to reconstruct the evolutionary tree of the Nemacheilidae. The analysis uncovers six major groups (or clades) within the family, all stemming from a common ancestor living 48 million years ago in Indochina (current mainland Southeast Asia). Each clade has separate yet sometimes overlapping geographical distributions. They followed distinct routes to spread across Asia and Europe, which Šlechtová et al. were able to examine in the light of geological and climate changes. For instance, a major aridification event taking place in Central Asia between 34 to 23 million years ago created a geographical divide within an ancestral stone loach group, splitting it into two parts that evolved separately to form two of the six current clades. While the Himalayas also acted as a strong barrier, growing highlands in eastern and western Asia expanded the range of suitable habitats for the fish, allowing them to colonize central and northern Asia and, from there, Europe. Other major geological events played a strong role in the propagation of the Nemacheilidae. When a small tectonic plate known as West Burma Terrane first contacted Southeast Asia 33 million years ago and later northeast India around 30 million years ago, the ancestral fish family used the plate like a ferry boat to spread to these new territories, and from there, expand into the Near East, Southeast Europe and Northeast Africa. These findings build on prior work investigating how geological and climate events have shaped evolution. However, they are the first case study to show the complete evolution of an animal group over such a large area and long period. It is the first detailed example of its type and could be precious to inform future work on evolution.

• Klíčová slova
• Cypriniformes, Nemacheilidae, Teleostei, ecology, evolutionary biology,
• MeSH
• biodiverzita MeSH
• biologická evoluce * MeSH
• fylogeneze * MeSH
• sladká voda MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Asie MeSH
• Evropa MeSH

Satellite DNA (satDNA) is a rapidly evolving class of tandem repeats, with some monomers being involved in centromere organization and function. To identify repeats associated with (peri)centromeric regions, we investigated satDNA across Southern and Coastal clades of African annual killifishes of the genus Nothobranchius. Molecular cytogenetic and bioinformatic analyses revealed that two previously identified satellites, designated here as NkadSat01-77 and NfurSat01-348, are associated with (peri)centromeres only in one lineage of the Southern clade. NfurSat01-348 was, however, additionally detected outside centromeres in three members of the Coastal clade. We also identified a novel satDNA, NrubSat01-48, associated with (peri)centromeres in N. foerschi, N. guentheri, and N. rubripinnis. Our findings revealed fast turnover of satDNA associated with (peri)centromeres and different trends in their evolution in two clades of the genus Nothobranchius.

• Klíčová slova
• Centromere drive, Constitutive heterochromatin, RepeatExplorer, Repetitive sequences, satDNA,
• MeSH
• centromera genetika   MeSH
• Cyprinodontidae * genetika   MeSH
• Fundulidae * genetika   MeSH
• molekulární evoluce MeSH
• satelitní DNA MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• satelitní DNA MeSH

To approach the taxonomy of large and complex animal groups it is of advantage to focus on species groups with shared derived character state. We investigate the composition, morphological characteristics and relationships of and within the Schistura cincticauda species group, whose members are small freshwater fishes that inhabit streams and rivers in eastern Myanmar and western and southern Thailand. A phylogenetic analysis using molecular genetic markers demonstrated the monophyly of this group; a combined genetic and morphological analysis revealed the inclusion of at least twelve species. They share the presence of a pair of black marks on the lower lip, one on each side of the median interruption (these marks may be reduced to few melanophores or even missing in some individuals). Additionally, all species share a small body size (max. 60 mm SL), an incomplete lateral line reaching at most to vertical through anal-fin base, and the absence of sexual dimorphism. Each of the 12 species is diagnosed by a unique combination of character states in fin ray numbers, anus position, presence/absence of an axillary pelvic lobe, and colour pattern. The distribution areas of several species overlap and five cases of syntopic occurrence are known. Five unnamed species are described herein.

• MeSH
• fylogeneze MeSH
• lidé MeSH
• máloostní * MeSH
• pohlavní dimorfismus MeSH
• řeky MeSH
• velikost těla MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The representatives of cyprinid lineage 'Poropuntiinae' with 16 recognized genera and around 100 species form a significant part of Southeast Asian ichthyofauna. Cytogenetics are valuable when studying fish evolution, especially the dynamics of repetitive DNAs, such as ribosomal DNAs (5S and 18S) and microsatellites, that can vary between species. Here, karyotypes of seven 'poropuntiin' species, namely Cosmochilus harmandi, Cyclocheilichthys apogon, Hypsibarbus malcomi, H. wetmorei, Mystacoleucus chilopterus, M. ectypus, and Puntioplties proctozysron occurring in Thailand were examined using conventional and molecular cytogenetic protocols. Variable numbers of uni- and bi-armed chromosomes indicated widespread chromosome rearrangements with a stable diploid chromosome number (2n) of 50. Examination with fluorescence in situ hybridization using major and minor ribosomal probes showed that Cosmochilus harmandi, Cyclocheilichthys apogon, and Puntioplites proctozystron all had one chromosomal pair with 5S rDNA sites. However, more than two sites were found in Hypsibarbus malcolmi, H. wetmorei, Mystacoleucus chilopterus, and M. ectypus. The number of chromosomes with 18S rDNA sites varied amongst their karyotypes from one to three; additionally, comparative genomic hybridization and microsatellite patterns varied among species. Our results reinforce the trend of chromosomal evolution in cyprinifom fishes, with major chromosomal rearrangements, while conserving their 2n.

• Klíčová slova
• Ag-NOR, comparative genomic hybridization, repetitive DNAs, ribosomal DNA,
• Publikační typ
• časopisecké články MeSH

Miniature refers to species with extraordinarily small adult body size when adult and can be found within all major metazoan groups. It is considered that miniature species have experienced severe alteration of numerous morphological traits during evolution. For a variety of reasons, including severe labor concerns during collecting, chromosomal acquisition, and taxonomic issues, miniature fishes are neglected and understudied. Since some available studies indicate possible relationship between diploid chromosome number (2n) and body size in fishes, we aimed to study one of the smallest Neotropical fish Nannostomus anduzei (Teleostei, Characiformes, Lebiasinidae), using both conventional (Giemsa staining, C-banding) and molecular cytogenetic methods (FISH mapping of rDNAs, microsatellites, and telomeric sequences). Our research revealed that N. anduzei possesses one of the lowest diploid chromosome numbers (2n = 22) among teleost fishes, and its karyotype is entirely composed of large metacentric chromosomes. All chromosomes, except for pair number 11, showed an 18S rDNA signal in the pericentromeric region. 5S rDNA signals were detected in the pericentromeric regions of chromosome pair number 1 and 6, displaying synteny to 18S rDNA signals. Interstitial telomeric sites (ITS) were identified in the centromeric region of pairs 6 and 8, indicating that centric fusions played a significant role in karyotype evolution of studied species. Our study provides further evidence supporting the trend of diploid chromosome number reduction along with miniaturization of adult body size in fishes.

• Klíčová slova
• 2n reduction, chromosomal rearrangements, karyotype, neotropical fishes,
• MeSH
• Characiformes * genetika   MeSH
• karyotyp MeSH
• karyotypizace MeSH
• ribozomální DNA genetika   MeSH
• telomery genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ribozomální DNA MeSH

Large animal families with unresolved taxonomy are notoriously difficult to handle with respect to their biodiversity, systematics, and evolutionary history. We approach a large and taxonomically unresolved family of freshwater fishes (Nemacheilidae, >600 species) by proposing, on the basis of morphologic data, a species group within the family and study its phylogeny with conclusions regarding its diversity, taxonomy, and biogeographic history. Phylogenetic analyses of two mitochondrial and three nuclear genes of 139 specimens, representing about 46 species (17 candidate species from the proposed species-group, plus 29 comparative species), revealed that the proposed species group does not form a distinct monophyletic lineage, but that the candidate and comparative species mixed in three different lineages. However, the results revealed more than 20% of undescribed species within the ingroup and showed that species do not cluster according to the presently recognised genera. At least one of the genetic clades shows signs of an eastward range expansion during the second half of Miocene from north India via Myanmar into Laos, western China, and western Thailand. We conclude that the approach of picking monophyletic lineages to study biodiversity, systematics, and evolutionary history helps to open the door to large animal families.

• Klíčová slova
• biodiversity, evolutionary history, freshwater fish, molecular marker, pigmentation pattern, systematics,
• Publikační typ
• časopisecké články MeSH

Teleost fishes exhibit a breath-taking diversity of sex determination and differentiation mechanisms. They encompass at least nine sex chromosome systems with often low degree of differentiation, high rate of inter- and intra-specific variability, and frequent turnovers. Nevertheless, several mainly female heterogametic systems at an advanced stage of genetic differentiation and high evolutionary stability have been also found across teleosts, especially among Neotropical characiforms. In this study, we aim to characterize the ZZ/ZW sex chromosome system in representatives of the Triportheidae family (Triportheus auritus, Agoniates halecinus, and the basal-most species Lignobrycon myersi) and its sister clade Gasteropelecidae (Carnegiella strigata, Gasteropelecus levis, and Thoracocharax stellatus). We applied both conventional and molecular cytogenetic approaches including chromosomal mapping of 5S and 18S ribosomal DNA clusters, cross-species chromosome painting (Zoo-FISH) with sex chromosome-derived probes and comparative genomic hybridization (CGH). We identified the ZW sex chromosome system for the first time in A. halecinus and G. levis and also in C. strigata formerly reported to lack sex chromosomes. We also brought evidence for possible mechanisms underlying the sex chromosome differentiation, including inversions, repetitive DNA accumulation, and exchange of genetic material. Our Zoo-FISH experiments further strongly indicated that the ZW sex chromosomes of Triportheidae and Gasteropelecidae are homeologous, suggesting their origin before the split of these lineages (approx. 40-70 million years ago). Such extent of sex chromosome stability is almost exceptional in teleosts, and hence, these lineages afford a special opportunity to scrutinize unique evolutionary forces and pressures shaping sex chromosome evolution in fishes and vertebrates in general.

• Klíčová slova
• CGH, Zoo-FISH, chromosome rearrangements, rDNA, sex chromosome evolution,
• MeSH
• Characiformes * genetika   MeSH
• lidé MeSH
• malování chromozomů MeSH
• mapování chromozomů MeSH
• molekulární evoluce MeSH
• pohlavní chromozomy genetika   MeSH
• srovnávací genomová hybridizace MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Sex chromosomes are generally derived from a pair of classical type-A chromosomes, and relatively few alternative models have been proposed up to now.1,2 B chromosomes (Bs) are supernumerary and dispensable chromosomes with non-Mendelian inheritance found in many plant and animal species3,4 that have often been considered as selfish genetic elements that behave as genome parasites.5,6 The observation that in some species Bs can be either restricted or predominant in one sex7-14 raised the interesting hypothesis that Bs could play a role in sex determination.15 The characterization of putative B master sex-determining (MSD) genes, however, has not yet been provided to support this hypothesis. Here, in Astyanax mexicanus cavefish originating from Pachón cave, we show that Bs are strongly male predominant. Based on a high-quality genome assembly of a B-carrying male, we characterized the Pachón cavefish B sequence and found that it contains two duplicated loci of the putative MSD gene growth differentiation factor 6b (gdf6b). Supporting its role as an MSD gene, we found that the Pachón cavefish gdf6b gene is expressed specifically in differentiating male gonads, and that its knockout induces male-to-female sex reversal in B-carrying males. This demonstrates that gdf6b is necessary for triggering male sex determination in Pachón cavefish. Altogether these results bring multiple and independent lines of evidence supporting the conclusion that the Pachón cavefish B is a "B-sex" chromosome that contains duplicated copies of the gdf6b gene, which can promote male sex determination in this species.

• Klíčová slova
• B chromosome, cavefish, gdf6, genome, sex chromosomes, sex determination, sex differentiation, gonads,
• MeSH
• biologická evoluce MeSH
• Characidae * genetika   MeSH
• jeskyně MeSH
• pohlavní chromozomy genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH

Despite decades of cytogenetic and genomic research of dynamic sex chromosome evolution in teleost fishes, multiple sex chromosomes have been largely neglected. In this review, we compiled available data on teleost multiple sex chromosomes, identified major trends in their evolution and suggest further trajectories in their investigation. In a compiled dataset of 440 verified records of fish sex chromosomes, we counted 75 multiple sex chromosome systems with 60 estimated independent origins. We showed that male-heterogametic systems created by Y-autosome fusion predominate and that multiple sex chromosomes are over-represented in the order Perciformes. We documented a striking difference in patterns of differentiation of sex chromosomes between male and female heterogamety and hypothesize that faster W sex chromosome differentiation may constrain sex chromosome turnover in female-heterogametic systems. We also found no significant association between the mechanism of multiple sex chromosome formation and percentage of uni-armed chromosomes in teleost karyotypes. Last but not least, we hypothesized that interaction between fish populations, which differ in their sex chromosomes, can drive the evolution of multiple sex chromosomes in fishes. This underlines the importance of broader inter-population sampling in studies of fish sex chromosomes. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)'.

• Klíčová slova
• chromosome rearrangements, fish, repetitive DNA accumulation, sex chromosome differentiation, sex chromosome turnover,
• MeSH
• biologická evoluce * MeSH
• cytogenetika MeSH
• pohlavní chromozomy genetika   MeSH
• ryby genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH