What maintains signal honesty in animal colour displays used in mate choice?

Ryan Weaver, Rebecca Elizabeth Koch, Geoffrey Hill

Research output: Contribution to journalReview ArticleResearchpeer-review

69 Citations (Scopus)


Many of the colour displays of animals are proposed to have evolved in response to female mate choice for honest signals of quality, but such honest signalling requires mechanisms to prevent cheating. The most widely accepted and cited mechanisms for ensuring signal honesty are based on the costly signalling hypothesis, which posits that costs associated with ornamentation prevent low-quality males from being highly ornamented. Alternatively, by the index hypothesis, honesty can be achieved via cost-free mechanisms if ornament production is causally linked to core physiological pathways. In this essay, we review how a costly signalling framework has shaped empirical research in mate choice for colourful male ornaments and emphasize that alternative interpretations are plausible under an index signalling framework. We discuss the challenges in both empirically testing and distinguishing between the two hypotheses, noting that they need not be mutually exclusive. Finally, we advocate for a comprehensive approach to studies of colour signals that includes the explicit consideration of cost-free mechanisms for honesty. This article is part of the themed issue ‘Animal coloration: production, perception, function and application’.

Original languageEnglish
Article number20160343
Number of pages8
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Issue number1724
Publication statusPublished - 22 May 2017
Externally publishedYes


  • Cost-free signal
  • Costly signal
  • Handicap
  • Honest signal
  • Index signal
  • Resource trade-off

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