Compensation-Draft Feedback
The co-evolution of mt and N genes has been proposed to lead to rapid serial fixation of alleles if a positive feedback loop arises as a consequence of changes and counter-changes between coevolving mt and N-mt genes. This idea is called the compensation-draft feedback hypothesis (Oliveira et al. 2008). Compensatory coevolution describes a situation whereby co-functioning sets of mt and N-mt genes are each under strong selection to improve aspects of performance that arise from the products of the other genome (Hill 2020). For instance, it was experimentally demonstrated that in a lab population of nematodes that the mt genome rapidly evolved a novel genotype to compensate for an OXPHOS dysfunction created by a N-mt allele (Christy et al. 2017). This example involves the interaction of protein-coding genes in an experimental lab setting, but for the reasons stated above, in most natural populations, the interacting mt and N gene products may be involved in transcription, translation, and replication of mt genes. The rapid fixation of mt genomes that carried this single adaptive nucleotide change might also have led to fixation of slightly deleterious alleles that happened to be associated with that allele. By this process of compensation-draft feedback, selective sweeps fix one problem while creating future problems that can be fixed through further selective sweeps when solutions happen to evolve. Such a series of selective sweeps would perpetually suppress with-population variation in mt genotypes while rapidly generating unique mt nucleotide sequences among populations thereby giving rise to mt DNA barcode gaps.