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Signal detectability and boldness are not the same: the function of defensive coloration in nudibranchs is distance-dependent

journal contribution
posted on 2023-08-08, 06:52 authored by CP van den Berg, John EndlerJohn Endler, KL Cheney
Aposematic signals visually advertise underlying anti-predatory defences in many species. They should be detectable (e.g. contrasting against the background) and bold (e.g. using internal pattern contrast) to enhance predator recognition, learning and memorization. However, the signalling function of aposematic colour patterns may be distance-dependent: signals may be undetectable from a distance to reduce increased attacks from naïve predators but bold when viewed up close. Using quantitative colour pattern analysis, we quantified the chromatic and achromatic detectability and boldness of colour patterns in 13 nudibranch species with variable strength of chemical defences in terms of unpalatability and toxicity, approximating the visual perception of a triggerfish ( Rhinecanthus aculeatus ) across a predation sequence (detection to subjugation). When viewed from an ecologically relevant distance of 30 cm, there were no differences in detectability and boldness between well-defended and undefended species. However, when viewed at closer distances (less than 30 cm), well-defended species were more detectable and bolder than undefended species. As distance increased, detectability decreased more significantly than boldness for defended species. For undefended species, boldness and detectability remained comparatively consistent, regardless of viewing distance. We provide evidence for distance-dependent signalling in aposematic nudibranchs and highlight the importance of distinguishing signal detectability from boldness in studies of aposematism.

History

Journal

Proceedings of the Royal Society B: Biological Sciences

Volume

290

Pagination

1-9

Location

London, Eng.

ISSN

0962-8452

eISSN

1471-2954

Language

English

Publication classification

C1 Refereed article in a scholarly journal

Issue

2003

Publisher

The Royal Society Publishing

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