Experience of mating rivals causes males to modulate sperm transfer in the fly Drosophila pseudoobscura

► We assess the responses to a potential mating rival in a sperm heteromorphic fly. ► Males exposed to rivals subsequently mate for longer and transfer more sperm. ► Males modulate their ejaculate components. ► Males exposed to rivals transfer significantly more eusperm but not parasperm. ► Males exposed to rivals achieve higher fitness through greater offspring production.