The genus Oswaldocruzia represents a taxonomically diverse group of nematodes with global distribution. Although Oswaldocruzia species are widespread and exhibit a remarkably wide host range in some species, their genetic diversity and biogeographic patterns remain poorly understood. This study investigated the genetic variability and distribution of Oswaldocruzia spp. in nine anuran species from the genera Bufo, Bufotes, Pelophylax, and Rana across Central Europe and the Balkans. Two species were identified: Oswaldocruzia filiformis and O. ukrainae, each exhibiting a different range of host associations. Phylogenetic analyses based on mitochondrial COI sequences revealed significant haplotype diversity in the generalist O. filiformis, with low geographic and host-associated genetic structuring. In contrast, O. ukrainae, which is closely associated with Bufotes viridis, exhibited only one genetic variant across all samples, highlighting its restricted genetic diversity. The findings emphasize contrasting genetic diversities among nematode parasites exhibiting different levels of host-specificity and expand the known distribution of O. filiformis into new regions of the Balkans. In addition, they highlight the need for additional studies on the ecological and evolutionary factors that influence the genetic diversity of parasites in amphibians.

TITLE: Aperçu de la diversité génétique et de la répartition des espèces des nématodes Oswaldocruzia (Trichostrongylida : Molineidae) en Europe : absence apparente de structuration géographique et populationnelle chez les amphibiens. ABSTRACT: Le genre Oswaldocruzia représente un groupe de nématodes taxonomiquement diversifié, réparti à l’échelle mondiale. Bien que les espèces d’Oswaldocruzia soient répandues et présentent une gamme d’hôtes remarquablement large chez certaines espèces, leur diversité génétique et leurs profils biogéographiques restent mal compris. Cette étude a examiné la variabilité génétique et la répartition des espèces d’Oswaldocruzia chez neuf espèces d’anoures des genres Bufo, Bufotes, Pelophylax et Rana en Europe centrale et dans les Balkans. Deux espèces ont été identifiées : Oswaldocruzia filiformis et O. ukrainae, chacune présentant une gamme différente d’associations d’hôtes. Les analyses phylogénétiques basées sur les séquences COI mitochondriales ont révélé une diversité d’haplotypes significative chez l’espèce généraliste O. filiformis, avec une faible structuration génétique géographique et associée à l’hôte. En revanche, O. ukrainae, étroitement associé à Bufotes viridis, ne présentait qu’une seule variante génétique dans tous les échantillons, soulignant sa diversité génétique limitée. Ces résultats mettent en évidence les diversités génétiques contrastées parmi les nématodes parasites présentant différents niveaux de spécificité d’hôte et étendent la répartition connue d’O. filiformis à de nouvelles régions des Balkans. De plus, ils soulignent la nécessité de mener des études complémentaires sur les facteurs écologiques et évolutifs qui influencent la diversité génétique des parasites des amphibiens.

• Keywords
• Amphibian Nematodes, Genetic Diversity, Host-Parasite Dynamics, Oswaldocruzia filiformis, Phylogeography,
• MeSH
• DNA, Helminth genetics   isolation & purification   MeSH
• Phylogeny MeSH
• Phylogeography MeSH
• Genetic Variation * MeSH
• Haplotypes MeSH
• Host Specificity MeSH
• Electron Transport Complex IV genetics   MeSH
• Bufonidae parasitology   MeSH
• Trichostrongyloidea * genetics   classification   isolation & purification   MeSH
• Trichostrongyloidiasis * veterinary   parasitology   epidemiology   MeSH
• Anura * parasitology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Europe epidemiology   MeSH
• Names of Substances
• DNA, Helminth MeSH
• Electron Transport Complex IV MeSH

Hybrid taxa from the genus Pelophylax can propagate themselves in a modified way of sexual reproduction called hybridogenesis ensuring the formation of clonal gametes containing the genome of only one parental (host) species. Pelophylax grafi from South-Western Europe is a hybrid composed of P. ridibundus and P. perezi genomes and it lives with a host species P. perezi (P-G system). Yet it is unknown, whether non-Mendelian inheritance is fully maintained in such populations. In this study, we characterize P. perezi and P. grafi somatic karyotypes by using comparative genomic hybridization, genomic in situ hybridization, fluorescent in situ hybridization, and actinomycin D-DAPI. Here, we show the homeology of P. perezi and P. grafi somatic karyotypes to other Pelophylax taxa with 2n = 26 and equal contribution of ridibundus and perezi chromosomes in P. grafi which supports F1 hybrid genome constitution as well as a hemiclonal genome inheritance. We show that ridibundus chromosomes have larger regions of interstitial (TTAGGG)n repeats flanking the nucleolus organizing region on chromosome no. 10 and a high quantity of AT pairs in the centromeric regions. In P. perezi, we found species-specific sequences in metaphase chromosomes and marker structures in lampbrush chromosomes. Pericentromeric RrS1 repeat sequence was present in perezi and ridibundus chromosomes, but the blocks were stronger in ridibundus. Various cytogenetic techniques applied to the P-G system provide genome discrimination between ridibundus and perezi chromosomal sets. They could be used in studies of germ-line cells to explain patterns of clonal gametogenesis in P. grafi and broaden the knowledge about reproductive strategies in hybrid animals.

• Keywords
• Pelophylax grafi, Pelophylax perezi, comparative genomic hybridization, fluorescent in situ hybridization, hybridogenesis, karyotype,
• MeSH
• Centromere * genetics   MeSH
• In Situ Hybridization, Fluorescence MeSH
• Karyotyping MeSH
• Ranidae * genetics   MeSH
• Comparative Genomic Hybridization MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

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.

• Keywords
• apparent competition, hybridization, meiosis, population dynamics, speciation,
• Publication type
• Journal Article MeSH
• Review MeSH

Parasites might represent a helpful tool in understanding the historical dispersion and phylogeography of their hosts. In order to reveal whether the migration routes and diversification of hosts can be traceable in the genetic structures of their parasites, we investigated the diversity of paramphistomoid trematodes of Pelophylax frogs in 2 geographically distant European regions. Water frogs belonging to the genus Pelophylax represent a striking example of a species with a high variety of ecological adaptations and a rich evolutionary history. The parasites were collected from 2 Balkan endemic species, P. epeiroticus and P. kurtmuelleri, and 2 species in Slovakia, P. esculentus and P. ridibundus. While in Slovakia, Pelophylax frogs harboured 2 species, the diplodiscid Diplodiscus subclavatus and the cladorchiid Opisthodiscus diplodiscoides, only the former was recorded in the south-western Balkans. Remarkably high genetic diversity (16 unique mitochondrial cox1 haplotypes, recognized among 60 novel sequences) was observed in D. subclavatus, and subsequent phylogenetic analyses revealed a strong population-genetic structure associated with geographical distribution. We also evidenced the existence of 2 divergent D. subclavatus cox1 haplogroups in the south-western Balkans, which might be associated with the historical diversification of endemic water frogs in the regional glacial microrefugia.

• Keywords
• Balkan Peninsula, Diplodiscus subclavatus, Opisthodiscus diplodiscoides, Pelophylax, haplotype diversity, population genetics,
• MeSH
• Phylogeny MeSH
• Phylogeography MeSH
• Genetic Variation MeSH
• Parasites * MeSH
• Ranidae MeSH
• Trematoda * genetics   MeSH
• Water MeSH
• Anura MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Water MeSH

Interspecific hybridization can disrupt canonical gametogenic pathways, leading to the emergence of clonal and hemiclonal organisms. Such gametogenic alterations usually include genome endoreplication and/or premeiotic elimination of one of the parental genomes. The hybrid frog Pelophylax esculentus exploits genome endoreplication and genome elimination to produce haploid gametes with chromosomes of only one parental species. To reproduce, hybrids coexist with one of the parental species and form specific population systems. Here, we investigated the mechanism of spermatogenesis in diploid P. esculentus from sympatric populations of P. ridibundus using fluorescent in situ hybridization. We found that the genome composition and ploidy of germ cells, meiotic cells, and spermatids vary among P. esculentus individuals. The spermatogenic patterns observed in various hybrid males suggest the occurrence of at least six diverse germ cell populations, each with a specific premeiotic genome elimination and endoreplication pathway. Besides co-occurring aberrant cells detected during meiosis and gamete aneuploidy, alterations in genome duplication and endoreplication have led to either haploid or diploid sperm production. Diploid P. esculentus males from mixed populations of P. ridibundus rarely follow classical hybridogenesis. Instead, hybrid males simultaneously produce gametes with different genome compositions and ploidy levels. The persistence of the studied mixed populations highly relies on gametes containing a genome of the other parental species, P. lessonae.

• Keywords
• Amphispermy, Bivalents, FISH, Gametogenesis, Hybridogenesis, Meiosis, Pelophylax, Spermatid,
• MeSH
• Gametogenesis * MeSH
• In Situ Hybridization, Fluorescence MeSH
• Humans MeSH
• Semen MeSH
• Anura * MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Ukraine MeSH

Triggers and biological processes controlling male or female gonadal differentiation vary in vertebrates, with sex determination (SD) governed by environmental factors or simple to complex genetic mechanisms that evolved repeatedly and independently in various groups. Here, we review sex evolution across major clades of vertebrates with information on SD, sexual development and reproductive modes. We offer an up-to-date review of divergence times, species diversity, genomic resources, genome size, occurrence and nature of polyploids, SD systems, sex chromosomes, SD genes, dosage compensation and sex-biased gene expression. Advances in sequencing technologies now enable us to study the evolution of SD at broader evolutionary scales, and we now hope to pursue a sexomics integrative research initiative across vertebrates. The vertebrate sexome comprises interdisciplinary and integrated information on sexual differentiation, development and reproduction at all biological levels, from genomes, transcriptomes and proteomes, to the organs involved in sexual and sex-specific processes, including gonads, secondary sex organs and those with transcriptional sex-bias. The sexome also includes ontogenetic and behavioural aspects of sexual differentiation, including malfunction and impairment of SD, sexual differentiation and fertility. Starting from data generated by high-throughput approaches, we encourage others to contribute expertise to building understanding of the sexomes of many key vertebrate species. 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 I)'.

• Keywords
• evolution, genomics, reproduction, sex chromosomes, sex determination, vertebrates,
• MeSH
• Biological Evolution * MeSH
• Genome Size * MeSH
• Evolution, Molecular MeSH
• Vertebrates genetics   MeSH
• Ovary growth & development   MeSH
• Sex Chromosomes genetics   MeSH
• Sex Determination Processes * MeSH
• Sex Differentiation genetics   MeSH
• Testis growth & development   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH