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Combined cues of male competition influence spermatozoal investment in a moth

Citation

Liu, Junyan et al. (2020), Combined cues of male competition influence spermatozoal investment in a moth, Dryad, Dataset, https://doi.org/10.5061/dryad.zgmsbcc7d

Abstract

  1. 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).
  2. 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.
  3. We demonstrate that males significantly increased their lifetime sperm allocation and production after premating detection of either single (acoustic or chemical) or combined cues (acoustic + chemical, or acoustic + chemical + tactile) from their rivals with combined cues (acoustic + chemical + tactile) somewhat strengthening such response in eupyrene production.
  4. The number of sperm ejaculated by males significantly decreased over successive matings in their lifetime regardless of whether they were exposed to rival cues, but the decline was significantly faster in rival-cue exposed males than in unexposed ones. This suggests that the increase of spermatogenesis cannot fully compensate for that of sperm expenditure in response to rival cues.
  5. We show that 10-h premating rival exposure was sufficient to maximise males’ response in sperm ejaculation and production. The impact of the rival perception on sperm transfer persisted for most of males’ reproductive life, suggesting that the moth males have a long-term memory of sperm competition risk experienced in the early adulthood.

Methods

Through experiments. In Excel.