Routine mitochondrial recombination drives rapid concerted evolution of duplicated control regions in a wild fish.

Duplications and concerted evolution of control regions (CRs) in animal mitogenomes have been reported across diverse taxa, yet the tempo and mechanism of gene conversion remain poorly understood. Here, we assembled the complete mitochondrial genome of the western Indian ricefish Oryzias setnai and found that the CR is duplicated. Comparative analysis of CR1 and CR2 sequences across individuals sampled throughout the species' range revealed that they are identical in most individuals, and differ by only one or two mutations in the rest-indicating recent and ongoing concerted evolution. We estimated that gene conversion events occur at a rapid pace, on the order of once every 1000 years or less. Using both short- and long-read amplicon sequencing, we directly detected a substantial number of recombinant mitogenome molecules resulting from homologous recombination between CR paralogues. This provides the first clear evidence that homologous recombination is the mechanism driving mitochondrial gene conversion. Our findings challenge the prevailing view that recombination in animal mitochondria is exceedingly rare, and demonstrate that mitogenome recombination can occur routinely in natural populations.