Aposematism: Unpacking the Defences. (July 2019)

• Record Type: Journal Article
• Authors: Caro, Tim; Ruxton, Graeme
• Is Part Of: Trends in ecology & evolution. Volume 34:Number 7(2019)
• Page Start: 595
• Page End: 604
• Publication Date: 2019-07
• Subjects: Ecology -- Periodicals; Evolution (Biology) -- Periodicals; 576.8
• DOI: 10.1016/j.tree.2019.02.015
• Languages: English
• ISSNs: 0169-5347

Abstract

Abstract : Aposematic coloration is commonly considered to signal unpalatability, yet animals advertise malodour, spines, and weaponry as well as toxins, some of which can be seen at a distance whereas others are hidden from predators. Separating defences into overt and covert categories in this way and whether they act before, during contact, or following ingestion generates new insights into the evolution of aposematism. Signals drawing attention to overt defences are difficult to fake whereas signals advertising covert defences can deceive would-be predators, and those acting later in the predatory sequence are more likely to be dishonest. These two orthogonal defence categorizations help to frame where dishonest signalling occurs in nature, set limits on deception by dishonest Batesian mimics, and prompt new questions. Highlights: Aposematic signals advertise that animals are unpalatable or dangerous. Usually they comprise a conspicuous visual signal paired with an antipredator defence. Ordinarily it is assumed that such signals denote unpalatability, yet we know that animals advertise many other types of defences, including stings, spines, and weaponry, as well as toxins. Some defences are therefore overt and can be seen at a distance; others, the physiological defences, are hidden from a potential predator. Dividing defences into these categories gives surprising new insights into the evolution of aposematism. We collate examples of defences from both invertebrates and vertebrates that are morphological, and hence obvious, or physiological and behavioural and that are hidden, and show how they are situated at different stages of the predator–prey interaction. This new formulation of aposematic defence signalling has implications for our understanding of the evolution of signal honesty. Signals that are intimately linked to the defence are more likely to be qualitatively honest, whereas those that are hidden are open to cheating. This has implications for the evolution of Batesian and Müllerian mimicry.