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Multimodal warning signals for a multiple predator world


Aposematism is an anti-predator defence, dependent on a predator’s ability to associate unprofitable prey with a prey-borne signal1. Multimodal signals should vary in efficacy according to the sensory systems of different predators; however, until now, the impact of multiple predator classes on the evolution of these signals had not been investigated2,3. Here, using a community-level molecular phylogeny to generate phylogenetically independent contrasts, we show that warning signals of tiger moths vary according to the seasonal and daily activity patterns of birds and bats—predators with divergent sensory capacities. Many tiger moths advertise chemical defence4,5 using conspicuous colouration and/or ultrasonic clicks3,6. During spring, when birds are active and bats less so, we found that tiger moths did not produce ultrasonic clicks. Throughout both spring and summer, tiger moths most active during the day were visually conspicuous. Those species emerging later in the season produced ultrasonic clicks; those that were most nocturnal were visually cryptic. Our results indicate that selective pressures from multiple predator classes have distinct roles in the evolution of multimodal warning displays now effective against a single predator class. We also suggest that the evolution of acoustic warning signals may lack the theoretical difficulties associated with the origination of conspicuous colouration.

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Figure 1: Representatives of each visual class.
Figure 2: Representative sonograms.
Figure 3: 50% majority consensus phylogram of the bayesian trees.
Figure 4: Phylogenetically independent contrasts (mean ± s.e.).

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All sequences were submitted to GenBank under accession numbers EU333575EU333652.


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We thank R. Hoebeke for access to the Cornell University Insect Collection, T. Eisner for the loan of ultraviolet photography equipment, and the 15 people who scored the photographs. J.M.R. thanks M. Fitzpatrick for discussion. J. Barber, C. Beatty, I. Cuthill, T. Eisner and J. Fullard provided detailed comments that improved the manuscript. This study was funded by research grants to J. Fullard (NSERC), R. Hoy (NIDCD) and J.M.R. (NSERC and DNSRC). Molecular work was conducted at Cornell in the laboratory of R. Harrison and the Evolutionary Genetics Core Facility.

Author Contributions M.L.N. was responsible for genetic analyses. J.M.R. was responsible for behavioural, comparative and signal analyses. J.M.R. wrote the manuscript.

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Correspondence to John M. Ratcliffe or Marie L. Nydam.

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Ratcliffe, J., Nydam, M. Multimodal warning signals for a multiple predator world. Nature 455, 96–99 (2008).

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