Chemical defences indicate distinct colour patterns with reduced variability in aposematic nudibranchs

Abstract

Predators learn and memorise the association between conspicuous colour patterns of aposematic prey and their underlying chemical or secondary defences. Consequently, variation in signal design within a species should be selected against, because it can decrease the rate of predator learning and enhance the rates of predator errors. However, quantitative assessments have not been made on whether the strength of chemical defences influences colour pattern variation. We examined this by quantifying colour pattern variation using Quantitative Colour Pattern Analysis (QCPA) in 12 Dorid nudibranch species (Infraorder: Doridoidei) that varied in their unpalatability. We accounted for the physiological limitations of a potential predator visual system (a triggerfish,Rhinecanthus aculeatus), modelling animal appearance along an escalating predation sequence. We found that various colour pattern statistics were less variable in highly unpalatable species, with pattern statistics being up to 72% less variable than those of more palatable species. No correlations indicating the opposite were found across 157 colour pattern statistics. However, the strength and number of correlations depended on viewing distance. Our results suggest that low colour pattern variability could be favourable for aposematic signalling in Dorid nudibranchs. We provide evidence for distance-dependent signalling facilitating context-specific feature selection in multicomponent visual signals.

Chemical defences indicate bold colour patterns with reduced variability in aposematic nudibranchs

“…Data accessibility. The raw colour pattern data can be accessed on UQ's e-space [119]. Supplementary material is available online [120].…”