Sexual conflict
A well-documented example is the seminal fluid of Drosophila melanogaster, which up-regulates females' egg-laying rate and reduces her desire to re-mate with another male (serving the male's interests), but also shortens the female's lifespan, so reducing her fitness."A hormone called 'sex peptide'... causes the female to become uninterested in mating... also males have components in their sperm which kill old sperm from previous males".92