Weak population‐genetic structure of a widely distributed nematode parasite of frogs in the western Palearctic

Abstract

The genetic structure of parasite populations is affected by various factors such as host–parasite interactions, life‐history strategies, and the evolutionary histories of both interacting organisms. In this study, we investigated the distribution, prevalence, and population‐genetic structure of Icosiella neglecta (Spirurida, Onchocercidae), a nematode parasite found in Ranidae frogs. We reported this parasite from eight species of water frogs (genus Pelophylax) in Europe, the Middle East, and Central Asia. Its prevalence across investigated localities varied from 3.03% to 95.83%. Based on nucleotide variation in a 28S ribosomal RNA gene, all investigated I. neglecta sequences formed a well‐supported phylogenetic clade and were placed in the sister position to the genus Ochoterenella. Despite the substantial genetic variability in a mitochondrial cytochrome c oxidase subunit I (COI) fragment (33 unique haplotypes recognized among 91 sequences), we found only weak population‐genetic structure across the study area. There was no obvious association of COI haplotypes with geography, except haplotypes from eastern Turkey, Lebanon, and Iraq which formed a homogeneous, albeit only weakly differentiated group. The historical demographic analyses suggest that the species underwent a sudden and relatively recent population expansion. According to our results, we assume that the population‐genetic structure of I. neglecta might be linked to the evolutionary history and dispersal of its dipteran vectors than water frog hosts.

Icosiella neglecta (Nematoda, Onchocercidae) in Ukraine: Occurrence, Hosts, Morphological and Molecular Characterisation

“…The new sequence appeared to be identical to three of four other sequences from the country and 42 sequences from other parts of the western Palaearctic, particularly, from Eastern Europe, Transcaucasia, and several Balkan countries. We assume that the population-genetic structure of I. neglecta in Ukraine is weak and not associated with the geography of the species populations within the country, similar to that discovered by Mikulíček et al (2021) in the I. neglecta distribution area.…”

“…On the other hand, the nematode may be absent in some regions and frog populations due to the absence of its intermediate hosts and vectors, mainly Forcipomyia velox (Winnertz) (Ceratopogonidae) (Desportes, 1942). Mikulíček et al (2021) suggested that the vectors of I. neglecta might have contributed to the relatively recent spread of the parasite. The recent spread of I. neglecta in northern Ukraine is apparent from the comparison of the information from previous surveys in this region with the results of the present study.…”

“…Both obtained sequences appeared to be identical to the corresponding ones from I. neglecta specimens from Ukraine available in Gen-Bank (accession numbers KP760138 and KP760189). Additionally, 87 COI sequences were retrieved from the supplementary fi le to Mikulíček et al (2021) for comparison (fi g. 7). Th e whole set included three sequences from western Ukraine (Zakarpatska Oblast): Ukraine 4136, 4138, and 4152 and one from the outskirts of Kyiv (KP760189).…”

“…Nine known species of the genus were reported from various parts of Eurasia and northern Africa (Bursey et al, 2003). Icosiella neglecta is the only species widely distributed in the western Palaearctic (Bain & Purnomo, 1984;Mikulíček et al, 2021). Th e species was initially named and briefl y described as Filaria neglecta Diesing, 1851 from the frog, Pelophylax esculentus (Linnaeus), by Diesing (1851).…”

“…Presently, I. neglecta is known as a parasite of Ranidae, mostly Pelophylax spp., rarely occurring in Rana spp., Discoglissidae, Hylidae, and Bufonidae (Baker, 1987). Mikulíček et al (2021) investigated the population-genetic structure of I. neglecta in its distribution area, from the Iberian Peninsula to Central Asia, and reported low inter-population diff erentiation. Th e sample of nematodes studied by these authors included several specimens from Zakarpatska Oblast (administrative region) in western Ukraine.…”