As a consequence of investigating the short-term fitness consequences of mate choice, researchers had largely come to believe that sexual selection is beneficial. However, conflicts between the sexes are ubiquitous and could erode fitness. Although sexual conflict is widespread, its evolutionary consequences remain largely unknown.
In the new study, which broadens our understanding of sexual selection and sexual conflict, Oliver Martin and David Hosken from the University of Zrich subjected flies to experimental evolution for 44 generations and looked at the fitness consequences of evolving under high, low, or relaxed sexual conflict. Their results indicate that foreign males from the conflict populations are more costly to females than familiar males and that sexual selection can be costly to fitness. However, they also found that at intermediate levels of sexual conflict, benefits of sexual selection may outweigh these costs.
These findings support previous work indicating that sexual conflict can cause rapid population divergence, although the proximate mechanism(s) involved remains unknown. Additionally, this work highlights the fact that sexual selection can be costly and generate a fitness load.