Abstract
Many animals have bright colours to warn predators that they have defences and are not worth attacking. However, it remains unclear whether the strength of warning colours reliably indicate levels of defence. Few studies have unambiguously established if warning signals are honest, and have rarely considered predator vision or conspicuousness against the background. Importantly, little data exists either on how differences in signal strength translate into survival advantages. Ladybirds exhibit impressive variation in coloration both among and within species. Here we demonstrate that different levels of toxicity exist among and within ladybird species, and that signal contrast against the background is a good predictor of toxicity, showing that the colours are honest signals. Furthermore, field experiments with ladybird models created with regards to predator vision show that models with lower conspicuousness were attacked more frequently. This provides one of the most comprehensive studies on signal honesty in warning coloration to date.
Highlights
To a constant arms race between toxicity, coloration and predator perception or toxic resistance[18]
These analyses showed no evidence for a phylogenetic signal, are somewhat inconclusive when dealing with small sample sizes[28]
Our results show that a closely related group of highly variable species differ in their level of toxicity, and with the exception of one species, this correlates with their level of conspicuousness against their natural backgrounds
Summary
To a constant arms race between toxicity, coloration and predator perception or toxic resistance[18]. Cortesi & Cheney[6] provided evidence for honesty in the aposematic signals of marine opistobranchs by measuring coloration according to predator visual systems (two species of fish), taking into account the contrast of the signals against the background, and assessing toxicity through bioassays using brine shrimp. While this is an important contribution to the study of honesty in aposematic organisms, the perception of signals in water and terrestrial environments differs considerably[20], and how accurately this finding can be extrapolated to terrestrial systems is unclear. We aimed to establish if bird predators rely on specific colour cues to avoid certain species of ladybirds, or if they effectively generalise their predatory decisions based on a broad rejection rule to avoid prey with more conspicuous coloration[7]
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