Diversity in warning coloration is easily recognized by avian predators

Abstract

Warning coloration is a widespread strategy to alert predators about prey unprofitability. The success of this strategy partly depends on predators being able to learn and recognize certain signals as indicators of toxicity, and theory predicts that this is easier if signals converge on similar colours. However, the diversity in warning signal form is astonishing, contradicting predictions. Here, we quantified ladybird signal diversity with respect to avian vision, measuring how unique and discernible each signal is from one another. In addition, we measured signal conspicuousness against a series of backgrounds, namely an average green, average brown, and where we collected each species, to determine whether signals are more contrasting against the ladybirds' local substrates than compared to average ones. This allowed us to establish whether there are local adaptations in conspicuousness that promote signal diversity. We found that while ladybird signals are unique and recognizable, specialist species are more contrasting against the background they are most commonly found on. However, overall our study suggests that warning signals have evolved to be effective against a wide range of natural backgrounds, partly explaining the success of this strategy in nature.

Keywords: aposematism; contrast; diversity; ladybird; vision.

Figure 1

Phylogenetic reconstruction of the ladybird species included in this study using the RaxML algorithm. The phylogenetic signal analyses showed that the relatedness between species is not correlated with attributes of coloration.

Figure 2

Discriminant plot for nine colour attributes of ladybird coloration. The ellipse around each species represents the 50% of the distribution measuring the Euclidean distance between the centre and every point of each species.

Figure 3

Species conspicuousness (colour contrast) against their own background (where they were collected – white), an average green background (green) and an average brown background (brown). There are significant differences in conspicuousness related to the species and the type of background analysed.

Figure 4

Conspicuousness (colour contrast) is affected by habitat use (generalists vs. specialists). The notch on the boxplots represents the 95% confidence interval of each set of data.