Karyological Study of Acanthocephalus lucii (Echinorhynchida): The Occurrence of B Chromosomes in Populations from PCB-Polluted Waters

Abstract

In this study, we performed a cytogenetic analysis of Acanthocephalus lucii specimens from three sites with different levels of environmental pollution. Standard and fluorochrome staining (CMA3/DAPI), fluorescence in situ hybridization (FISH) with 18S rDNA and histone H3 probes, and silver impregnation were performed. Chromosome complements of 2n = 7/8 (male/female), n = 1m + 2sm + 1a (X), and CMA3-positive bands in all chromosomes were found in all three populations. FISH revealed one 18S rDNA locus on the X chromosome and one locus of H3 histone genes on the first chromosome pair. At the intraspecific level, the populations differed in the presence of supernumerary B chromosomes, which were found in all specimens from Zemplínska Šírava and in 89.4% of specimens from the Laborec River, but not at the reference site. The first two sites are considered to be water bodies with high toxin contamination. Based on this fact, we assume an increased frequency of chromosome breaks leading to the formation of DNA fragments that have the potential to form B chromosomes. The present results add to the very limited data on the organization of multigene families in the genome of Acanthocephala and suggest a possible causal link between water pollution and the occurrence of B chromosomes in fish parasites.

Chromosomal mapping of 5S rDNA in two species of the genus Acanthocephalus(Echinorhynchida)

“…Chromosomal inversions, more often pericentric than paracentric, are widespread in the plant and animal kingdoms, as cytogenetic techniques have shown (Locke et As this study is the rst description of the chromosomal location of 5S rDNA clusters in Acanthocephala, it is not possible to consider the existence of a single cluster as ancestral. Nevertheless, the location of 5S rDNA seems to follow a pattern that contrasts with the number and location of 18S rDNA on chromosomes in the karyotypes of Acanthocephala species, where higher variability has been observed (Bombarová et al 2007;Orosová et al 2023;Marková et al 2024).…”

“…The results of our present work are part of a larger project in which we are devoting ourselves to a detailed karyological analysis of representatives of the parasite group Acanthocephala. The karyotypes of the studied species A. lucii and A. anguillae were determined in our recently published work (Orosová et al 2023;Marková et al 2024); 2n = 7/8 (male/female); n = 1m + 1m-sm + 1a + 1a (X) in the former and 2n = 7/8 n = 1m + 2sm + 1a (X) in the latter.…”

“…Recent cytogenetic studies using FISH with repetitive DNA probes (rDNA and histone genes) showed that the 18S rDNA sequence is present on one chromosome pair (chromosome X) in A. lucii and on two autosomal pairs in A. anguillae. At the same time, a clustered arrangement of histone H3 genes was found on one autosomal pair in A. lucii, while these sequences are scattered on all chromosomes in A. anguillae (Orosová et al 2023;Marková et al 2024). In two morphologically very similar species, Pomphorhynchus laevis and P. tereticollis, different chromosomal positions of the rRNA genes were found (Bombarová et al 2007).…”

“…4). The main and only noticeable difference is the morphology of the third pair of chromosomes, which is submetacentric in the karyotype of A. lucii, but acrocentric in A. anguillae (Špakulová et al 2002;Orosová et al 2023;Marková et al 2024). This pair No.…”

“…Biological material Specimens of both species were collected from sh from the Zemplínska Šírava reservoir (48°47′09.0″N 21°57′20.5″E), eastern Slovakia (detailed information on the collected sh, the process of their processing and parasite collection can be found in Orosová et al 2023;Marková et al 2024). Spread chromosome preparations were obtained from both sexes following the "hot plate" technique described in details in Orosová and Špakulová (2018).…”