Complex interactions with females and rival males limit the evolution of sperm offence and defence

Adam Bjork, William T. Starmer, Dawn M. Higginson, Christopher J. Rhodes, Scott Pitnick

Research output: Contribution to journalArticlepeer-review

64 Scopus citations


Postcopulatory sexual selection favours males which are strong offensive and defensive sperm competitors. As a means of identifying component traits comprising each strategy, we used an experimental evolution approach. Separate populations of Drosophila melanogaster were selected for enhanced sperm offence and defence. Despite using a large outbred population and evidence of substantive genetic variation for each strategy, neither trait responded to selection in the two replicates of this experiment. Recent work with fixed chromosome lines of D. melanogaster suggests that complex genotypic interactions between females and competing males contribute to the maintenance of this variation. To determine whether such interactions could explain our lack of response to selection on sperm offence and defence, we quantified sperm precedence across multiple sperm competition bouts using an outbred D. melanogaster population exhibiting continuous genetic variation. Both offensive and defensive sperm competitive abilities were found to be significantly repeatable only across matings involving ejaculates of the same pair of males competing within the same female. These repeatabilities decreased when the rival male stayed the same but the female changed, and they disappeared when both the rival male and the female changed. Our results are discussed with a focus on the complex nature of sperm precedence and the maintenance of genetic variation in ejaculate characteristics.

Original languageEnglish (US)
Pages (from-to)1779-1788
Number of pages10
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1619
StatePublished - Jul 22 2007


  • Artificial selection
  • Drosophila
  • Genetic interactions
  • Sperm competition
  • Virgin effects

ASJC Scopus subject areas

  • General Immunology and Microbiology
  • General Biochemistry, Genetics and Molecular Biology
  • General Environmental Science
  • General Agricultural and Biological Sciences


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