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.

Department of Animal Physiology Faculty of Science Pavol Jozef Šafárik University in Košice Šrobárova 2 040 01 Košice Slovakia

Department of Zoology Faculty of Natural Sciences Comenius University in Bratislava Ilkovičova 6 842 15 Bratislava Slovakia

Department of Zoology Faculty of Natural Sciences Comenius University in Bratislava Ilkovičova 6 842 15 Bratislava Slovakia Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 2 611 37 Brno Czechia Unit for Environmental Sciences and Management North West University Potchefstroom 2520 South Africa

Department of Zoology Faculty of Science Pavol Jozef Šafárik University in Košice Šrobárova 2 040 01 Košice Slovakia

Institute of Parasitology Slovak Academy of Sciences 04001 Košice Slovakia

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