Sexual reproduction is the primary mode of reproduction in eukaryotes, but some organisms have evolved deviations from classical sex and switched to asexuality. These asexual lineages have sometimes been viewed as evolutionary dead ends, but recent research has revealed their importance in many areas of general biology. Our review explores the understudied, yet important mechanisms by which sperm-dependent asexuals that produce non-recombined gametes but rely on their fertilization, can have a significant impact on the evolution of coexisting sexual species and ecosystems. These impacts are concentrated around three major fields. Firstly, sperm-dependent asexuals can potentially impact the gene pool of coexisting sexual species by either restricting their population sizes or by providing bridges for interspecific gene flow whose type and consequences substantially differ from gene flow mechanisms expected under sexual reproduction. Secondly, they may impact on sexuals' diversification rates either directly, by serving as stepping-stones in speciation, or indirectly, by promoting the formation of pre- and postzygotic reproduction barriers among nascent species. Thirdly, they can potentially impact on spatial distribution of species, via direct or indirect (apparent) types of competition and Allee effects. For each such mechanism, we provide empirical examples of how natural sperm-dependent asexuals impact the evolution of their sexual counterparts. In particular, we highlight that these broad effects may last beyond the tenure of the individual asexual lineages causing them, which challenges the traditional perception that asexual lineages are short-lived evolutionary dead ends and minor sideshows. Our review also proposes new research directions to incorporate the aforementioned impacts of sperm-dependent asexuals. These research directions will ultimately enhance our understanding of the evolution of genomes and biological interactions in general.

• Klíčová slova
• apparent competition, hybridization, meiosis, population dynamics, speciation,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Hybridization and genome duplication have played crucial roles in the evolution of many animal and plant taxa. The subgenomes of parental species undergo considerable changes in hybrids and polyploids, which often selectively eliminate segments of one subgenome. However, the mechanisms underlying these changes are not well understood, particularly when the hybridization is linked with asexual reproduction that opens up unexpected evolutionary pathways. To elucidate this problem, we compared published cytogenetic and RNAseq data with exome sequences of asexual diploid and polyploid hybrids between three fish species; Cobitis elongatoides, C. taenia, and C. tanaitica. Clonal genomes remained generally static at chromosome-scale levels but their heterozygosity gradually deteriorated at the level of individual genes owing to allelic deletions and conversions. Interestingly, the impact of both processes varies among animals and genomic regions depending on ploidy level and the properties of affected genes. Namely, polyploids were more tolerant to deletions than diploid asexuals where conversions prevailed, and genomic restructuring events accumulated preferentially in genes characterized by high transcription levels and GC-content, strong purifying selection and specific functions like interacting with intracellular membranes. Although hybrids were phenotypically more similar to C. taenia, we found that they preferentially retained C. elongatoides alleles. This demonstrates that favored subgenome is not necessarily the transcriptionally dominant one. This study demonstrated that subgenomes in asexual hybrids and polyploids evolve under a complex interplay of selection and several molecular mechanisms whose efficiency depends on the organism's ploidy level, as well as functional properties and parental ancestry of the genomic region.

• Klíčová slova
• asexual reproduction, gene conversions, hemizygous deletions, hybridization, loss of heterozygosity, polyploidy,
• MeSH
• diploidie MeSH
• genom rostlinný MeSH
• hybridizace genetická MeSH
• máloostní * genetika   MeSH
• molekulární evoluce MeSH
• polyploidie * MeSH
• ztráta heterozygozity MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Despite its inherent costs, sexual reproduction is ubiquitous in nature, and the mechanisms to protect it from a competitive displacement by asexuality remain unclear. Popular mutation-based explanations, like the Muller's ratchet and the Kondrashov's hatchet, assume that purifying selection may not halt the accumulation of deleterious mutations in the nonrecombining genomes, ultimately leading to their degeneration. However, empirical evidence is scarce and it remains particularly unclear whether mutational degradation proceeds fast enough to ensure the decay of clonal organisms and to prevent them from outcompeting their sexual counterparts. To test this hypothesis, we jointly analysed the exome sequences and the fitness-related phenotypic traits of the sexually reproducing fish species and their clonal hybrids, whose evolutionary ages ranged from F1 generations to 300 ky. As expected, mutations tended to accumulate in the clonal genomes in a time-dependent manner. However, contrary to the predictions, we found no trend towards increased nonsynonymity of mutations acquired by clones, nor higher radicality of their amino acid substitutions. Moreover, there was no evidence for fitness degeneration in the old clones compared with that in the younger ones. In summary, although an efficacy of purifying selection may still be reduced in the asexual genomes, our data indicate that its efficiency is not drastically decreased. Even the oldest investigated clone was found to be too young to suffer fitness consequences from a mutation accumulation. This suggests that mechanisms other than mutation accumulation may be needed to explain the competitive advantage of sex in the short term.

• Klíčová slova
• Muller’s ratchet, asexuality, clonal decay, exome capture, fitness, mutation load,
• MeSH
• biologická evoluce * MeSH
• emoce MeSH
• genom MeSH
• modely genetické MeSH
• mutace MeSH
• nepohlavní rozmnožování genetika   MeSH
• rozmnožování * genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Interspecific hybridization is a powerful evolutionary force. However, the investigation of hybrids requires the application of methodologies that provide efficient and indubitable identification of both parental subgenomes in hybrid individuals. Repetitive DNA, and especially the satellite DNA sequences (satDNA), can rapidly diverge even between closely related species, hence providing a useful tool for cytogenetic investigations of hybrids. Recent progress in whole-genome sequencing (WGS) offers unprecedented possibilities for the development of new tools for species determination, including identification of species-specific satDNA markers. In this study, we focused on spined loaches (Cobitis, Teleostei), a group of fishes with frequent interspecific hybridization. Using the WGS of one species, C. elongatoides, we identified seven satDNA markers, which were mapped by fluorescence in situ hybridization on mitotic and lampbrush chromosomes of C. elongatoides, C. taenia and their triploid hybrids (C. elongatoides × 2C. taenia). Two of these markers were chromosome-specific in both species, one had centromeric localization in multiple chromosomes and four had variable patterns between tested species. Our study provided a novel set of cytogenetic markers for Cobitis species and demonstrated that NGS-based development of satDNA cytogenetic markers may provide a very efficient and easy tool for the investigation of hybrid genomes, cell ploidy, and karyotype evolution.

• Klíčová slova
• FISH, clonal vertebrates, hybridization, mitotic and lampbrush chromosomes, satellite DNA,
• MeSH
• druhová specificita MeSH
• hybridizace genetická MeSH
• hybridizace in situ fluorescenční MeSH
• karyotyp MeSH
• karyotypizace MeSH
• klonální evoluce genetika   MeSH
• máloostní genetika   MeSH
• nepohlavní rozmnožování genetika   MeSH
• satelitní DNA genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• satelitní DNA MeSH

Interspecific competition is a fundamental process affecting community structure and evolution of interacting species. Besides direct competition, this process is also mediated by shared enemies, which can change the outcome of competition dramatically. However, previous studies investigating interactions between competing species and their parasites (parasite-mediated competition) completely overlooked the effect of 'sperm' parasites (i.e. sperm-dependent parthenogens or pseudogams) on competition. These organisms originate by interspecific hybridization, produce clonal gametes, but exploit parental species for their own reproduction, being therefore analogous to classical parasites. Here we use the reaction-diffusion model and show that pseudogams alter the outcome of interspecific competition significantly. They may either slow down competitive exclusion of the inferior competitor or even turn the outcome of competition between the species. Asexual organisms may thus have unexpectedly strong impact on community structure, and have more significant evolutionary potential than was previously thought.

• MeSH
• biologická evoluce * MeSH
• biologické modely MeSH
• interakce hostitele a parazita genetika   MeSH
• kompetitivní chování fyziologie   MeSH
• rozmnožování genetika   MeSH
• sexuální chování fyziologie   MeSH
• spermie růst a vývoj   mikrobiologie   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

BACKGROUND: Anthropogenic factors can have a major impact on the contemporary distribution of intraspecific genetic diversity. Many freshwater fishes have finely structured and locally adapted populations, but their natural genetic structure can be affected by river engineering schemes across river basins, fish transfers in aquaculture industry and conservation management. The European bitterling (Rhodeus amarus) is a small fish that is a brood parasite of freshwater mussels and is widespread across continental Europe. Its range recently expanded, following sharp declines in the 1970s and 1980s. We investigated its genetic variability and spatial structure at the centre of its distribution at the boundary of three watersheds, testing the role of natural and anthropogenic factors in its genetic structure. RESULTS: Sequences of mitochondrial cytochrome B (CYTB) revealed that bitterling colonised central Europe from two Ponto-Caspian refugia, which partly defines its contemporary genetic structure. Twelve polymorphic microsatellite loci revealed pronounced interpopulation differentiation, with significant small-scale differentiation within the same river basins. At a large scale, populations from the Baltic Sea watershed (middle Oder and Vistula basins) were distinct from those from the Black Sea watershed (Danube basin), while populations from rivers of the North Sea watershed (Rhine, Elbe) originated from the admixture of both original sources. Notable exceptions demonstrated the potential role of human translocations across watersheds, with the upper River Oder (Baltic watershed) inhabited by fish from the Danube basin (Black Sea watershed) and a population in the southern part of the River Elbe (North Sea watershed) basin possessing a signal of admixture from the Danube basin. CONCLUSIONS: Hydrography and physical barriers to dispersal are only partly reflected in the genetic structure of the European bitterling at the intersection of three major watersheds in central Europe. Drainage boundaries have been obscured by human-mediated translocations, likely related to common carp, Cyprinus carpio, cultivation and game-fish management. Despite these translocations, populations of bitterling are significantly structured by genetic drift, possibly reinforced by its low dispersal ability. Overall, the impact of anthropogenic factors on the genetic structure of the bitterling populations in central Europe is limited.

• Klíčová slova
• Cryptic invasions, Freshwater conservation, Game fish stocking, Gene flow, Human-mediated translocation, Phylogeography, Population genetics,
• MeSH
• Bayesova věta MeSH
• druhová specificita MeSH
• frekvence genu genetika   MeSH
• genetická variace MeSH
• kapři genetika   MeSH
• lidé MeSH
• mikrosatelitní repetice genetika   MeSH
• mitochondriální DNA genetika   MeSH
• mitochondrie genetika   MeSH
• populační genetika MeSH
• řeky * MeSH
• sladká voda MeSH
• zeměpis MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Evropa MeSH
• Severní moře MeSH
• Názvy látek
• mitochondriální DNA MeSH

Although sexual reproduction is ubiquitous throughout nature, the molecular machinery behind it has been repeatedly disrupted during evolution, leading to the emergence of asexual lineages in all eukaryotic phyla. Despite intensive research, little is known about what causes the switch from sexual reproduction to asexuality. Interspecific hybridization is one of the candidate explanations, but the reasons for the apparent association between hybridization and asexuality remain unclear. In this study, we combined cross-breeding experiments with population genetic and phylogenomic approaches to reveal the history of speciation and asexuality evolution in European spined loaches (Cobitis). Contemporary species readily hybridize in hybrid zones, but produce infertile males and fertile but clonally reproducing females that cannot mediate introgressions. However, our analysis of exome data indicates that intensive gene flow between species has occurred in the past. Crossings among species with various genetic distances showed that, while distantly related species produced asexual females and sterile males, closely related species produce sexually reproducing hybrids of both sexes. Our results suggest that hybridization leads to sexual hybrids at the initial stages of speciation, but as the species diverge further, the gradual accumulation of reproductive incompatibilities between species could distort their gametogenesis towards asexuality. Interestingly, comparative analysis of published data revealed that hybrid asexuality generally evolves at lower genetic divergences than hybrid sterility or inviability. Given that hybrid asexuality effectively restricts gene flow, it may establish a primary reproductive barrier earlier during diversification than other "classical" forms of postzygotic incompatibilities. Hybrid asexuality may thus indirectly contribute to the speciation process.

• Klíčová slova
• balance hypothesis, coalescence, evolution of asexuality, hybridization, phylogeography, speciation,
• MeSH
• druhová specificita MeSH
• genetická variace MeSH
• haplotypy genetika   MeSH
• hybridizace genetická * MeSH
• křížení genetické MeSH
• máloostní genetika   MeSH
• nepohlavní rozmnožování genetika   MeSH
• populační genetika MeSH
• reprodukční izolace MeSH
• vznik druhů (genetika) * MeSH
• zeměpis MeSH
• zvířata MeSH
• zygota fyziologie   MeSH
• Check Tag
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Interspecific hybridization, polyploidization and transitions from sexuality to asexuality considerably affect organismal genomes. Especially the last mentioned process has been assumed to play a significant role in the initiation of chromosomal rearrangements, causing increased rates of karyotype evolution. We used cytogenetic analysis and molecular dating of cladogenetic events to compare the rate of changes of chromosome morphology and karyotype in asexually and sexually reproducing counterparts in European spined loach fish (Cobitis). We studied metaphases of three sexually reproducing species and their diploid and polyploid hybrid clones of different age of origin. The material includes artificial F1 hybrid strains, representatives of lineage originated in Holocene epoch, and also individuals of an oldest known age to date (roughly 0.37 MYA). Thereafter we applied GISH technique as a marker to differentiate parental chromosomal sets in hybrids. Although the sexual species accumulated remarkable chromosomal rearrangements after their speciation, we observed no differences in chromosome numbers and/or morphology among karyotypes of asexual hybrids. These hybrids possess chromosome sets originating from respective parental species with no cytogenetically detectable recombinations, suggesting their integrity even in a long term. The switch to asexual reproduction thus did not provoke any significant acceleration of the rate of chromosomal evolution in Cobitis. Asexual animals described in other case studies reproduce ameiotically, while Cobitis hybrids described here produce eggs likely through modified meiosis. Therefore, our findings indicate that the effect of asexuality on the rate of chromosomal change may be context-dependent rather than universal and related to particular type of asexual reproduction.

• MeSH
• biologická evoluce * MeSH
• diploidie * MeSH
• karyotyp * MeSH
• máloostní genetika   MeSH
• nepohlavní rozmnožování genetika   MeSH
• triploidie * MeSH
• zvířata MeSH
• Check Tag
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Distinguishing between hybrid introgression and incomplete lineage sorting causing incongruence among gene trees in that they exhibit topological differences requires application of statistical approaches that are based on biologically relevant models. Such study is especially challenging in hybrid systems, where usual vectors mediating interspecific gene transfers--hybrids with Mendelian heredity--are absent or unknown. Here we study a complex of hybridizing species, which are known to produce clonal hybrids, to discover how one of the species, Cobitis tanaitica, has achieved a pattern of mito-nuclear mosaic genome over the whole geographic range. We appplied three distinct methods, including the method using solely the information on gene tree topologies, and found that the contrasting mito-nuclear signal might not have resulted from the retention of ancestral polymorphism. Instead, we found two signs of hybridization events related to C. tanaitica; one concerning nuclear gene flow and the other suggested mitochondrial capture. Interestingly, clonal inheritance (gynogenesis) of contemporary hybrids prevents genomic introgressions and non-clonal hybrids are either absent or too rare to be detected among European Cobitis. Our analyses therefore suggest that introgressive hybridizations are rather old episodes, mediated by previously existing hybrids whose inheritance was not entirely clonal. Cobitis complex thus supports the view that the type of resulting hybrids depends on a level of genomic divergence between sexual species.

• MeSH
• genom * MeSH
• hybridizace genetická * MeSH
• máloostní genetika   MeSH
• mitochondriální DNA genetika   MeSH
• molekulární evoluce MeSH
• rozmnožování MeSH
• vznik druhů (genetika) MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• mitochondriální DNA MeSH

Given the hybrid genomic constitutions and increased ploidy of many asexual animals, the identification of processes governing the origin and maintenance of clonal diversity provides useful information about the evolutionary consequences of interspecific hybridization, asexuality and polyploidy. In order to understand the processes driving observed diversity of biotypes and clones in the Cobitis taenia hybrid complex, we performed fine-scale genetic analysis of Central European hybrid zone between two sexual species using microsatellite genotyping and mtDNA sequencing. We found that the hybrid zone is populated by an assemblage of clonally (gynogenetically) reproducing di-, tri- and tetraploid hybrid lineages and that successful clones, which are able of spatial expansion, recruit from two ploidy levels, i.e. diploid and triploid. We further compared the distribution of observed estimates of clonal ages to theoretical distributions simulated under various assumptions and showed that new clones are most likely continuously recruited from ancestral populations. This suggests that the clonal diversity is maintained by dynamic equilibrium between origination and extinction of clonal lineages. On the other hand, an interclonal selection is implied by nonrandom spatial distribution of individual clones with respect to the coexisting sexual species. Importantly, there was no evidence for sexually reproducing hybrids or clonally reproducing non-hybrid forms. Together with previous successful laboratory synthesis of clonal Cobitis hybrids, our data thus provide the most compelling evidence that 1) the origin of asexuality is causally linked to interspecific hybridization; 2) successful establishment of clones is not restricted to one specific ploidy level and 3) the initiation of clonality and polyploidy may be dynamic and continuous in asexual complexes.

• MeSH
• diploidie * MeSH
• genotyp MeSH
• máloostní genetika   MeSH
• mikrosatelitní repetice genetika   MeSH
• mitochondriální DNA genetika   MeSH
• polyploidie * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• mitochondriální DNA MeSH