The dynamics of mitochondrial mutations causing male infertility in spatially structured populations

Mitochondrial genomes are usually inherited maternally and therefore there is no direct selection against mutations that have deleterious effects in males only (mother's curse). This is true in particular for mitochondrial mutations that reduce the fertility of their male carriers, as has been reported in a number of species. Using both analytical methods and computer simulations, we demonstrate that spatial population structure can induce strong selection against such male infertility mutations. This is because (1) infertile males may reduce the fecundity of the females they mate with and (2) population structure induces increased levels of inbreeding, so that the fitness of females carrying the mutation is more strongly reduced than the fitness of wild-type females. Selection against mitochondrial male infertility mutations increases with decreasing deme size and migration rates, and in particular with female migration rates. On the other hand, the migration model (e.g., island or stepping stone model) has generally only minor effects on the fate of the mitochondrial mutations.