Mitochondria are maternally inherited; males never pass on their mitochondria to their children. This has evolutionary implications because it renders natural selection ineffective at removing mutations in the mitochondrial DNA (mtDNA) when these mutations only effect males. In other words, whether an mtDNA mutation establishes in a population, or goes extinct, depends exclusively on how that mutation affects the chances of females successfully reproducing. If an mtDNA mutation appears that decreases the chances of females reproducing, then the mutation is likely to be removed by selection (i.e., females that carry the mutation are less likely to reproduce than females that do not carry the mutation). Conversely, if an mtDNA mutation arises that increases the chances of females reproducing, selection should favour it, and the mutation should increase in frequency (i.e., females that carry the mutation are more likely to reproduce than females that don’t carry it). But, what about the case of a “sex-specific” mtDNA mutation – specifically, a mutation that either has no effects on the reproductive outcomes of females, or even beneficial effects on females, but which severely decreases the chances of males reproducing? Somewhat ironically, selection will classify this mutation as benign or beneficial, since it does not decrease the chances of females reproducing, and that mutation can persist (females will pass on the mutation).
This is, in essence, the evolutionary logic underlying a hypothesis that has come to be known as “Mother’s Curse”, and it predicts that mtDNA sequences will be enriched for mutations that impair male fertility, but which have no negative effects on females.
In this talk, I will first outline this theory, and its key predictions. I will then detail experimental evidence that supports the prediction that these male-sterilising mtDNA mutations may be pervasive in animals. Our experiments come from studies in the fruit fly, Drosophila melanogaster, but recent evidence for the Mother’s Curse effect extends to mice, hares and humans. Finally, I will discuss the potential for these foundational evolutionary findings to contribute to real-world applications, focusing on novel approaches to pest control and male contraception.