The researchers wanted to see how changing mating conditions affected male fruit flies' reproductive traits. They manipulated the amount of competition between male fruit flies by making some live in monogamous conditions and others in polygamous setups for many generations. They discovered that in situations where males competed directly for females, those from polygamous groups had more success in reproducing compared to monogamous ones. Interestingly, in scenarios where males faced competition after mating, there was no difference in how well they defended their sperm. However, monogamous males performed poorly in competing before mating happened. This suggests that enforced monogamy reduced the pressure on traits needed for winning over females, different from what was expected for traits important after mating.