Chromosomal rearrangements act as barriers to gene flow and can thus promote speciation. In moths and butterflies (Lepidoptera), which possess holocentric chromosomes facilitating karyotype changes, chromosome fusions are more common than fissions. Yet, limited evidence suggests that when speciation involves chromosomal rearrangements, it is most often linked to fissions. Notable karyotypic variation is observed in three clades of the subfamily Polyommatinae (Lycaenidae), with chromosome numbers ranging from n = 10 to 225. We investigated genome sizes and karyotypes in several species of the genera Polyommatus and Lysandra with modal and derived high chromosome numbers. Our findings showed no support for polyploidy, confirming previous conclusions about karyotypic diversification via chromosome fragmentation in this butterfly family. Species with high chromosome numbers have slightly larger genomes, which indicate a potential role of repetitive sequences but contradict the hypothesis of holocentric drive. Ends of fragmented chromosomes were healed with telomeres synthesized de novo, which were significantly larger than those of species with modal karyotype. No interstitial telomeric sequences were detected on autosomes. Internal telomeric signals on sex chromosomes, however, revealed multiple sex chromosome systems in Polyommatus (Plebicula) dorylas and Polyommatus icarus, with two karyotype races differing in sex chromosome constitution in the latter. Notably, the W chromosome resisted fragmentation, presumably due to its epigenetic silencing.

• Klíčová slova
• Polyommatus, butterfly, fission, fusion, sex chromosomes, telomere,
• MeSH
• chromozomy hmyzu MeSH
• karyotyp MeSH
• motýli * genetika   MeSH
• pohlavní chromozomy * genetika   MeSH
• polyploidie MeSH
• telomery * genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

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

Sex chromosomes play an outsized role in adaptation and speciation, and thus deserve particular attention in evolutionary genomics. In particular, fusions between sex chromosomes and autosomes can produce neo-sex chromosomes, which offer important insights into the evolutionary dynamics of sex chromosomes. Here, we investigate the evolutionary origin of the previously reported Danaus neo-sex chromosome within the tribe Danaini. We assembled and annotated genomes of Tirumala septentrionis (subtribe Danaina), Ideopsis similis (Amaurina), Idea leuconoe (Euploeina) and Lycorea halia (Itunina) and identified their Z-linked scaffolds. We found that the Danaus neo-sex chromosome resulting from the fusion between a Z chromosome and an autosome corresponding to the Melitaea cinxia chromosome (McChr) 21 arose in a common ancestor of Danaina, Amaurina and Euploina. We also identified two additional fusions as the W chromosome further fused with the synteny block McChr31 in I. similis and independent fusion occurred between ancestral Z chromosome and McChr12 in L. halia. We further tested a possible role of sexually antagonistic selection in sex chromosome turnover by analysing the genomic distribution of sex-biased genes in I. leuconoe and L. halia. The autosomes corresponding to McChr21 and McChr31 involved in the fusions are significantly enriched in female- and male-biased genes, respectively, which could have hypothetically facilitated fixation of the neo-sex chromosomes. This suggests a role of sexual antagonism in sex chromosome turnover in Lepidoptera. The neo-Z chromosomes of both I. leuconoe and L. halia appear fully compensated in somatic tissues, but the extent of dosage compensation for the ancestral Z varies across tissues and species.

• Klíčová slova
• butterflies, dosage compensation, fusions, sex chromosomes, sexual antagonism, sex‐biased genes,
• MeSH
• fylogeneze MeSH
• molekulární evoluce MeSH
• motýli * genetika   MeSH
• pohlavní chromozomy * genetika   MeSH
• syntenie MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

Multiple sex chromosomes usually arise from chromosomal rearrangements which involve ancestral sex chromosomes. There is a fundamental condition to be met for their long-term fixation: the meiosis must function, leading to the stability of the emerged system, mainly concerning the segregation of the sex multivalent. Here, we sought to analyze the degree of differentiation and meiotic pairing properties in the selected fish multiple sex chromosome system present in the wolf-fish Hoplias malabaricus (HMA). This species complex encompasses seven known karyotype forms (karyomorphs) where the karyomorph C (HMA-C) exhibits a nascent XY sex chromosomes from which the multiple X1X2Y system evolved in karyomorph HMA-D via a Y-autosome fusion. We combined genomic and cytogenetic approaches to analyze the satellite DNA (satDNA) content in the genome of HMA-D karyomorph and to investigate its potential contribution to X1X2Y sex chromosome differentiation. We revealed 56 satDNA monomers of which the majority was AT-rich and with repeat units longer than 100 bp. Seven out of 18 satDNA families chosen for chromosomal mapping by fluorescence in situ hybridization (FISH) formed detectable accumulation in at least one of the three sex chromosomes (X1, X2 and neo-Y). Nine satDNA monomers showed only two hybridization signals limited to HMA-D autosomes, and the two remaining ones provided no visible FISH signals. Out of seven satDNAs located on the HMA-D sex chromosomes, five mapped also to XY chromosomes of HMA-C. We showed that after the autosome-Y fusion event, the neo-Y chromosome has not substantially accumulated or eliminated satDNA sequences except for minor changes in the centromere-proximal region. Finally, based on the obtained FISHpatterns, we speculate on the possible contribution of satDNA to sex trivalent pairing and segregation.

• Klíčová slova
• FISH, Meiosis, Multiple sex chromosomes, Satellitome, Sex trivalent,
• MeSH
• Characiformes * genetika   MeSH
• chromozom Y genetika   MeSH
• hybridizace in situ fluorescenční * MeSH
• karyotyp MeSH
• meióza genetika   MeSH
• molekulární evoluce MeSH
• pohlavní chromozomy * genetika   MeSH
• satelitní DNA * genetika   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• satelitní DNA * MeSH