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

The selective factors that shape phenotypic diversity in prey communities with aposematic animals are diverse and coincide with similar diversity in the strength of underlying secondary defences. However, quantitative assessments of colour pattern variation and the strength of chemical defences in assemblages of aposematic species are lacking. We quantified colour pattern diversity using Quantitative Colour Pattern Analysis (QCPA) in 13 Dorid nudibranch species (Infraorder: Doridoidei) that varied in the strength of their chemical defences. We accounted for the physiological properties of a potential predator’s visual system (a triggerfish, Rhinecanthus aculeatus ) and modelled the appearance of nudibranchs from multiple viewing distances (2cm and 10cm). We identified distinct colour pattern properties associated with the presence and strength of chemical defences. Colour patterns were also less variable among species with chemical defences when compared to undefended species. This confirms correlations between secondary defences and diverse, bold colouration while showing that chemical defences coincide with decreased colour pattern variability among species. Our study suggests that complex spatiochromatic properties of colour patterns perceived by potential predators can be used to make inferences on the presence and strength of chemical defences. ### Competing Interest Statement The authors have declared no competing interest.