Chromosomal rDNA Distribution Patterns in Clonal Triploid Hybrids (Teleostei, Cobitidae): Insights into Parental Genomic Contributions.

Interspecific hybridization between relative species (with a diploid genome designated as TT), (EE) and (NN) and the successive polyploidization with transitions from sexuality to asexuality experienced by triploid hybrids likely influence their chromosomal rearrangements, including rearrangements of ribosomal DNA (rDNA) distribution patterns. Previously, we documented distinct karyotypic differences: exhibited bi-armed chromosomes while showed uni-armed chromosomes with rDNA-positive hybridization signals, respectively. In this study, fluorescence in situ hybridization (FISH) with rDNA and rDNA probes was used to analyze and compare chromosomal distribution patterns of rDNAs in clonally reproduced triploid hybrids of different genomic constitutions ETT, ETN, EEN and EET (referred to using acronyms denoting the haploid genomes of their parent species), and their parental species. triploid hybrids exhibited intermediate karyotypes with ribosome synthesis sites on chromosomes inherited from both parents, showing no evidence of nucleolar dominance. The rDNA pattern derived from the genome was more stable in the hybrids' karyotypes. Two and one submetacentric chromosomes with co-localized rDNAs were effective markers to ascertain diploid (EE) and haploid (E) genomes within the genome of triploid hybrids, respectively. Fewer rDNA loci were observed in diploid (TT) and haploid (T) chromosome sets from in ETT and EET females. and exhibited similar rDNA distribution patterns. The karyotypes of triploid hybrids reflect the genomic contributions of their parental species. Variability in rDNA distribution patterns suggests complex genomic interactions in hybrids resulting from polyploidization and hybridization, potentially influencing their reproductive potential.