Protective value of spots and stripes in aposematic patterns

Abstract

Aposematic animals commonly use conspicuous visual signals such as colour and pattern to warn predators of unprofitability. While the function of colour in aposematic signals is wellunderstood, patterns have received little attention. Patterns are incredibly diverse among aposematic species and commonly vary in shape, size, and number of pattern elements. They may stimulate predator memory, or facilitate avoidance learning to increase signal efficacy. While common in aposematic signals, few studies have investigated the comparative protective value of different pattern types (e.g. spots, stripes) in isolation from other visual signals, such as colour. This study aimed to determine the protective value of spotted and striped patterns independent of other visual signals. I looked at the patterning of 155 Australian lady beetle species (Coleoptera: Coccinellidae) and applied the most common pattern types to paper targets. Patterned targets were presented to Australian magpies / Djarrarawunang (Gymnorhina tibicen) to determine the relative protective values of each pattern. I found no significant difference in protective value among the spotted and striped targets and no significant difference in protective value between the patterned targets and a uniformly coloured unpatterned target. Similarly, I found no significant difference between the times taken for magpies to complete training or experimental trials. However, I found that targets placed on the left-side of the experimental apparatus were selected significantly faster than targets placed on the right. These results may suggest that pattern in the absence of colour is not effective as an aposematic signal against avian predators, or that the patterns used have a function outside of aposematic signalling. These results aid in explaining the diversity of patterns in nature, provide insights into the function of patterns in predator-prey systems and add to our knowledge of side-biases in magpies.

Date of Award	2023
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Kate Umbers (Supervisor)