Chromosomal inheritance of parental rDNAs distribution pattern detected by FISH in diploid F₁ hybrid progeny of Cobitis (Teleostei, Cobitidae) species has non‐Mendelian character

Abstract

This study was conducted to describe the major and the minor rDNA chromosome distribution in the spined loach Cobitis taenia (2n = 48) and the Danubian loach Cobitis elongatoides (2n = 50), and their laboratory‐produced diploid reciprocal F1 hybrid progeny. It was tested by fluorescence in situ hybridisation (FISH) whether the number of 28s and 5s rDNA sites in the karyotypes of diploid hybrids corresponds to the expectations resulting from Mendelian ratio and if nucleolar organiser regions (NOR)were inherited from both parents or nucleolar dominance can be observed in the induced F1 hybrid progeny. Ten (females) or twelve (males) 28s rDNA loci were located in nine uniarm chromosomes of C. taenia. Two of such loci terminally bounded on one acrocentric chromosome were unique and indicated as specific for this species. Large 5s rDNA clusters were located on two acrocentric chromosomes. In C. elongatoides of both sexes, six NOR sites in terminal regions on six meta‐submetacentric chromosomes and two 5s rDNA sites on large submetacentrics were detected. The F1 hybrid progeny (2n = 49) was characterised by the intermediate karyotype with the sites of ribosome synthesis on chromosomes inherited from both parents without showing nucleolar dominance. 5s rDNA sites were detected on large submetacentric and two acrocentric chromosomes. The observed number of both 28s and 5s rDNAs signals in F1 diploid Cobitis hybrids was disproportionally inherited from the two parental species, showing inconsistency with the Mendelian ratios. The presented rDNA patterns indicate some marker chromosomes that allow the species of the parental male and female to be recognised in hybrid progeny. The 5s rDNA was found to be a particularly effective diagnostic marker of C. elongatoides to partially discern genomic composition of diploid Cobitis hybrids and presumably allopolyploids resulting from their backcrossing with one of the parental species. Thus, the current study provides insight into the extent of rDNA heredity in Cobitis chromosomes and their cytotaxonomic character.

First cytogenetic characterization of the Amazon Catfish Leiarius marmoratus (Gill, 1870) and its hybrid with Pseudoplatystoma reticulatum (Eigenmann & Eigenmann, 1889)

“…Otherwise, Ag-NORs were very specific for the hybrid, located in two non-homologous chromosomes different in size, allowing an accurate diagnosis of the hybrid. The presence of NORs in chromosomes with distinct morphology have been previously detected for hybrids of Pimelodus (Hashimoto et al 2009) and a similar situation was observed for species of Cobitiis and their hybrids (Grabowska et al 2019). A considerable number of metaphases or nucleolus with only one active NOR indicated dominant rDNA expression of one parental species in the hybrid, fact already described for other hybrid of fishes (Hashimoto et al, 2012;Prado et al, 2012).…”

Cytogenetic Characterization of Seven Novel satDNA Markers in Two Species of Spined Loaches (Cobitis) and Their Clonal Hybrids

“…We successfully applied our markers on chromosomes of hybrid individuals and found them suitable to unambiguously identify their genomic composition. Earlier, cytological identification of species from this complex comprised only of the description of chromosomal morphology and rDNA markers (5S rDNA, 28S rDNA) [ 19 ]. However, rDNA markers in C. taenia , are highly polymorphic even within different individuals from the same population [ 22 , 81 ], making them an insufficient tool to observe evolutionary traits or unambiguously infer the genomic composition of hybrids.…”

“…Typically, precise genome and/or ploidy identification relied on a combination of multiple diagnostic approaches: sequencing of multiple mitochondrial and nuclear loci, allozyme, and cytogenetic analyses (e.g., karyotyping and C-banding, rDNA FISH) [ 9 , 18 , 19 ]. However, many important scientific questions regarding the consequences of hybridization, polyploidy, and asexuality on chromosomal and genome evolution require more fine-scale markers allowing the identification of sub-genomes within the nuclei of hybrids.…”