Meeting Abstract
Mitochondria are a key feature of eukaryotes, and the presence of a mitochondrial (mt) genome in most eukaryotic lineages creates a dynamic of coevolution and conflict with the larger nuclear genome. Several lines of evidence suggest that the nuclear genome must undergo compensatory changes to offset the effects of changes in the mtDNA, which may be under less efficient selection. This creates specific mitonuclear combinations that are “matched” within a population or species, but hybridization between species can lead to mitonuclear “mismatch” and decreased fitness in hybrids. Therefore, mtDNA and mitonuclear interactions have been implicated as primary drivers of speciation in eukaryotes. On the other hand, mtDNA fluidly crosses species boundaries in many hybrid zones, and so-called “mitonuclear discordance” is rampant among animals. To reconcile these seemingly opposite findings, we suggest that they are two evolutionary solutions to the same problem: accumulation of deleterious mutations in mtDNA. Compensatory changes in the nuclear DNA can offset mt-induced harm, leading to mitonuclear match and creating species boundaries. Alternatively, mutation-ridden mtDNA can be replaced by a more fit mt genome from a closely related species. Here, we will present cases of these two scenarios from the available literature, make predictions as to when each would be expected, and suggest future studies to test these hypotheses. We also present relevant results from a case study of Silene, an angiosperm genus with variable rates of mtDNA evolution among closely related species and a history of mitonuclear coevolution.
