Pattern contrast influences wariness in na\xefve predators towards aposematic patterns

C G Halpin,J Skelhorn,J M Harris,I C Cuthill,O Penacchio,P G Lovell,C Rowe

doi:10.1038/s41598-020-65754-y

C G Halpin, J Skelhorn + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-65754-y

Copy DOI

Abstract

An apparent and common feature of aposematic patterns is that they contain a high level of achromatic (luminance) contrast, for example, many warning signals combine black spots and stripes with a lighter colour such as yellow. However, the potential importance of achromatic contrast, as distinct from colour contrast, in reducing predation has been largely overlooked. Here, using domestic chicks as a model predator, we manipulated the degree of achromatic contrast in warning patterns to test if high luminance contrast in aposematic signals is important for deterring naïve predators. We found that the chicks were less likely to approach and eat prey with high contrast compared to low contrast patterns. These findings suggest that aposematic prey patterns with a high luminance contrast can benefit from increased survival through eliciting unlearned biases in naïve avian predators. Our work also highlights the importance of considering luminance contrast in future work investigating why aposematic patterns take the particular forms that they do.

Highlights

An apparent and common feature of aposematic patterns is that they contain a high level of achromatic contrast, for example, many warning signals combine black spots and stripes with a lighter colour such as yellow
Our study clearly shows that increasing the luminance contrast in a prey’s warning pattern deters naïve predators: chicks were less likely to approach and eat prey with high contrast compared to low contrast patterns
This suggests that the high luminance contrast found in patterns of many aposematic prey, which often involve spots and stripes, could elicit unlearned biases and enhance survival even against predators with excellent colour vision, as well as those that have to rely on achromatic vision alone[28]

Summary

Introduction

An apparent and common feature of aposematic patterns is that they contain a high level of achromatic (luminance) contrast, for example, many warning signals combine black spots and stripes with a lighter colour such as yellow. Using domestic chicks as a model predator, we manipulated the degree of achromatic contrast in warning patterns to test if high luminance contrast in aposematic signals is important for deterring naïve predators. Avian predators may find patterns with high levels of luminance contrast intrinsically more visually stimulating than uniform coloration[19]: luminance contrast is used in both edge detection and texture discrimination[20,21], which is important for object recognition[22,23] This may make patterns with high luminance contrast easier for birds, and other predators, to recognise and remember[24] and could help to facilitate colour avoidance learning[25]. We predicted that if high luminance contrast was important, naïve predators should be less likely to approach and attack prey with high- compared to low-contrast patterning

Methods

Results

Conclusion