title: The evolution of index signals to avoid the cost of dishonesty.
abstract: Animals often convey useful information, despite a conflict of interest between the signaller and receiver. There are two major explanations for such 'honest' signalling, particularly when the size or intensity of signals reliably indicates the underlying quality of the signaller. Costly signalling theory (including the handicap principle) predicts that dishonest signals are too costly to fake, whereas the index hypothesis predicts that dishonest signals cannot be faked. Recent evidence of a highly conserved causal link between individual quality and signal growth appears to bolster the index hypothesis. However, it is not clear that this also diminishes costly signalling theory, as is often suggested. Here, by incorporating a mechanism of signal growth into costly signalling theory, we show that index signals can actually be favoured owing to the cost of dishonesty. We conclude that costly signalling theory provides the ultimate, adaptive rationale for honest signalling, whereas the index hypothesis describes one proximate (and potentially very general) mechanism for achieving honesty.
authors: Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK jay.biernaskie@zoo.ox.ac.uk.
authors: Jay M
authors: JM
authors: Biernaskie
authors: Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK St John's College, University of Oxford, Oxford OX1 3JP, UK.
authors: Alan
authors: A
authors: Grafen
authors: Jesus College, University of Oxford, Oxford OX1 3DW, UK Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
authors: Jennifer C
authors: JC
authors: Perry
mesh_terms: D000819:Animal Communication; D000818:Animals; D005075:Biological Evolution; D008192:Deception; D005716:Game Theory; D008962:Models, Theoretical; D010641:Phenotype; D012726:Sexual Behavior, Animal
keywords: condition dependence; costly signalling; handicap principle; honest signalling; indices; sexual selection