Combined cues of male competition influence spermatozoal investment in a moth

Male animals usually raise their sperm allocation after detecting sperm competition risk. To date, only a few studies have investigated the cues used by males to sense and respond to rivals. Yet, it is still largely unknown whether males respond to single or combined cues and whether they can increase their lifetime spermatozoal investment after a perception of rival cue(s). Here we postulate that males increase ejaculation and production of sperm after detecting combined cues from rivals, but such response quickly diminishes after the cues are removed. We exposed newly emerged and virgin focal males of the moth Ephestia kuehniella to various rival cues and then permanently removed the cues. We introduced a virgin female to an exposed focal male and an unexposed focal male, respectively, per day and counted the number of sperm transferred by the focal males in each mating and recovered in their body after death. We demonstrate that males significantly increased their lifetime s...