Mitochondrial genetic effects on reproductive success: Signatures of positive intra-sexual, but negative inter-sexual pleiotropy

Mitochondria contain their own DNA, and numerous studies have reported that genetic variation in this (mt)DNA sequence modifies the expression of life-history phenotypes. Maternal inheritance of mitochondria adds a layer of complexity to trajectories of mtDNA evolution, because theory predicts the accumulation of mtDNA mutations that are male-biased in effect. While it is clear that mitochondrial genomes routinely harbor genetic variation that affects components of reproductive performance, the extent to which this variation is sex-biased, or even sex-specific in effect, remains elusive. This is because nearly all previous studies have failed to examine mitochondrial genetic effects on both male and female reproductive performance within the one-and-the-same study. Here, we show that variation across naturally-occurring mitochondrial haplotypes affects components of reproductive success in both sexes, in Drosophila melanogaster. However, while we uncovered evidence for positive pleiotropy, across haplotypes, in effects on separate components of reproductive success when measured within the same sex, such patterns were not evident across sexes. Rather, we found a pattern of sexual antagonism across haplotypes on some reproductive parameters. This suggests the pool of polymorphisms that delineate global mtDNA haplotypes is likely to have been partly shaped by maternal transmission of mtDNA and its evolutionary consequences.