An aposematic colour‐polymorphic moth seen through the eyes of conspecifics and predators – Sensitivity and colour discrimination in a tiger moth

Abstract

Although predation is commonly thought to exert the strongest selective pressure on coloration in aposematic species, sexual selection may also influence coloration. Specifically, polymorphism in aposematic species cannot be explained by natural selection alone. Males of the aposematic wood tiger moth (Arctia plantaginis) are polymorphic for hindwing coloration throughout most of their range. In Scandinavia, they display either white or yellow hindwings. Female hindwing coloration varies continuously from bright orange to red. Redder females and yellow males suffer least from bird predation. White males often have higher mating success than yellow males. Therefore, we ask whether females can discriminate the two male morphs by colour. Males approach females by following pheromone plumes from a distance, but search visually at short range. This raises the questions whether males discriminate female coloration and, in turn, whether female coloration is also sexually selected. Using electroretinograms, we found significantly larger retinal responses in male than female A. plantaginis, but similar spectral sensitivities in both sexes, with peaks in the UV (349 nm), blue (457 nm) and green (521 nm) wavelength range. According to colour vision models, conspecifics can discriminate white and yellow males as separate morphs, but not orange and red females. For moths and birds (Cyanistes caeruleus), white males are more conspicuous against green and brown backgrounds, mostly due to UV reflectivity, and red females are slightly more conspicuous than orange females. The costly red coloration among females is likely selected by predator pressure, not by conspecifics, whereas male colour polymorphism is probably maintained, at least partly, by the opposing forces of predation pressure favouring yellow males, and female preference for white males. Whether or not the preference for white males is based on visual cues requires further testing. The evolution of polymorphic aposematic animals can be better understood when the visual system of the species and their predators is taken into consideration. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13100/suppinfo is available for this article.

Multiple modalities in insect warning displays have additive effects against wild avian predators

“…1a), and vision models have indicated that all these colours are conspicuous on a green background in the eyes of blue tits (Lindstedt et al 2011;Nokelainen et al 2012;Henze et al 2018). Forewings are clearly visible for blue tits too, but their colouration does not differ between the two male morphs (Henze et al 2018).…”

“…An assay started by presenting the bird with the assigned model treatment placed on a green background ( Fig. 2), as this is the most common background in which these moths are found in the wild (Nokelainen 2013) and because, in the eyes of a blue tit, both white and yellow males of A. plantaginis have a similar contrast against a green background (Henze et al 2018). During the assay, two of the authors (BR and EBS) recorded the bird latency to approach the petri dish where the fake moth was offered ( Fig.…”

“…In the eyes of a blue tit, white and yellow males of A. plantaginis have a similar contrast against a green background (Henze et al 2018). However, yellow males have been argued to have better warning signals in previous studies using either true moths (Nokelainen et al 2012) or models similar to the ones used here which were deployed across different populations (Nokelainen et al 2014).…”

The appearance of mimetic Heliconius butterflies to predators and conspecifics

“…A further study on Batesian mimics found differences between the sexes and wing surfaces, with females being better mimics and the dorsal side having better resemblance to mimic models (Su et al 2015). Other study systems have also investigated warning signal evolution and utilized vision modelling such as in Anolis lizards (Fleishman et al 2016), ladybirds (Arenas and Stevens 2017), and tiger moths (Henze et al 2018).…”

Multimodal Aposematic Signals and Their Emerging Role in Mate Attraction

“…In addition, their chemical defenses are affected by resource availability during early life (Brain, 2016;Furlanetto, 2017; Figure 9). As the moths are most active during daylight hours (Rojas et al, 2015a) they are vulnerable to predation by birds, particularly while resting on the vegetation, where they are clearly conspicuous Henze et al, 2018). Likewise, they can be vulnerable to attacks by invertebrate predators, especially when the temperature is not high enough for the moth to initiate flight, or when it is eclosing from the pupa and its wings are not yet fully extended.…”