Evidence for Paternal Mitochondrial DNA Leakage in Diploid Hybrid Fish Lineages

Distant hybridization induces genomic instability in offspring, driving the occurrence of gene recombination and mutation. Analysis of the genomic genetic composition can be used to infer the genetic evolutionary relationships between species. Based on the improved diploid carp (IDC) and the improved diploid scattered mirror carp (IDMC) lineages derived from distant hybridization between female common carp and male blunt snout bream, this study analyzed the genetic variation in their mitochondrial genomes to investigate the impact of distant hybridization on mitochondrial DNA (mtDNA) structural variation. Analysis of complete mitochondrial genome sequence structure and composition revealed subtle structural divergence across generations in both the IDC and IDMC lineages. Analysis of the protein-coding gene sequence structure demonstrated mitochondrial genome structure instability in nascent hybrid diploid lineages. Yet, subsequent self-crossing significantly narrowed the range of structural variation within each lineage. Furthermore, analysis of the genetic variation in the mitochondrial genome sequence structure revealed that paternal base insertions occurred in both F₁ lineages, accompanied by mutations predominantly consistent with those in crucian carp. The results of this study also indicated that the strictness of the paternal mtDNA elimination mechanism varied significantly among polymorphic individuals across different generations of the hybrid lineages, reflecting the randomness of paternal leakage.