Multifaceted Camouflage and Rare Wing Pattern Asymmetry in the North Island Lichen Moth, Declana atronivea

Abstract

Predation is one of the strongest and most important selection pressures to be faced in the animal kingdom. Indeed, it is from this central biological problem of defence and self-preservation that natural selection has crafted such an incredible diversity of adaptations and specialisations. In the constant battle for survival, many prey species have evolved various behavioural, chemical, and/or morphological defensive mechanisms to avoid being eaten. Of these, the expression of protective colouration is perhaps the most fascinating, encompassing all the extraordinary visual properties of animals that can deter predators through bright and conspicuous warning signals or that can conceal prey through resemblances to the environment. The latter refers to a form of antipredator colouration called camouflage, which functions to reduce the probability of a prey animal being detected or recognised by predators. This is achieved through a range of strategies, including background matching (in which the appearance of an animal matches the visual components of the background so that it may blend in and remain undetected), disruptive colouration (in which high contrast markings break up surface continuity and create false edges, effectively obscuring the animal’s outline and hindering detection or recognition of true shape), and masquerade (whereby an animal resembles an uninteresting and inedible object of the environment, such as a leaf or a twig, causing predators to misclassify it as something of no value, thus hindering correct recognition). These camouflage strategies function through different mechanisms that exploit the perceptual and cognitive processes of predator visual systems but are not necessarily mutually exclusive and may operate in tandem to enhance the protective value of camouflage. This thesis examined the idea of multifaceted camouflage by investigating the role of different camouflage mechanisms in an endemic Aotearoa | New Zealand moth. The North Island lichen moth, Declana atronivea (Geometridae), presents a fascinating system with which to explore the intricacies of camouflage. This charismatic moth possesses high contrast black and white forewings with discreetly textured wing scales that appear to resemble lichen. The wing patterns are particularly interesting in that they also exhibit marginal markings (that overlap the wing edge) and asymmetric elements (both among and within individuals), the latter of which is exceptionally rare in nature. Here, I investigated the functional significance of the forewing colour patterns of D. atronivea as an antipredator adaptation. Using a range of experimental methods and analytical tools, including lab and field predation experiments, predator vision modelling, colour pattern analysis, and geometric-morphometric techniques, I was able to objectively quantify whether D. atronivea’s colouration may contribute to camouflage through the different mechanisms of masquerade, background matching, and disruptive colouration. I further explored the inherent variation in the pattern elements of D. atronivea to highlight this species as one of the first documented examples of wing pattern asymmetry in an insect, and to assess the role of such asymmetry for camouflage. I first explored whether the colouration of D. atronivea may have been adapted for lichen masquerade, that is, whether their colour patterns cause predators to misclassify them as lichen. Using laboratory predation experiments with naïve and experienced chick (Gallus gallus) predators, I demonstrated that the moths do not benefit from such element imitation in the absence of a matching lichen background. I subsequently expanded on this to examine the adaptive significance of background matching on lichen and the putative function of element imitation masquerade in the context of a matching background using field predation experiments with paper moth models and wild avian predators. I also objectively quantified the degree of background matching through avian vision modelling and colour analysis techniques. This study demonstrated that the colour patterns of D. atronivea confer a significant survival advantage through background matching on lichen, with an intermediate level of protection gained when near lichen. This suggests that D. atronivea colouration is likely adapted for background matching, but may provide a lower degree of benefit via element imitation masquerade when near to lichen patches. The colour patterns of D. atronivea were found to be a close match to the pattern elements of lichen but were dissimilar to the chromatic and achromatic properties of these substrates, indicating that it is likely the pattern elements of the forewings that are important for conferring protection through background matching. Following on from this, I then investigated whether the colour patterns of D. atronivea may also be adapted for disruptive colouration; that the high contrast marginal markings on the forewings promote concealment from predators through edge disruption. Using vision modelling, colour analysis, and field predation experiments, I presented evidence to support the occurrence and functional significance of edge disruptive colouration in D. atronivea. Lastly, I examined the inherent colour pattern variation present in D. atronivea. Using geometric- morphometrics, I determined that this species exhibits pronounced wing pattern asymmetry among and within individuals. I further explored the functional role of such asymmetry for antipredator defence using field predation experiments and demonstrated that these asymmetrical pattern elements enhance the protective value of their camouflage. This study represents the first documented example of adaptive colour pattern asymmetry in a cryptic species. Overall, each investigation into masquerade, background matching and disruptive colouration suggests that the colour patterns of D. atronivea may be adapted for a multifaceted suite of camouflage mechanisms. However, the relative contribution of these various camouflage strategies for antipredator defence in this species is uncertain and future work is required to disentangle the different mechanisms and how they function to promote protection from predators. This research is, to my knowledge, the first study to objectively quantify and demonstrate the functional significance of masquerade, background matching, disruptive colouration, and colour pattern asymmetry in a single species, and presents a foundation for further investigation into the multifaceted nature of camouflage.