Predation places significant selection pressures on prey species and many have evolved incredible and diverse colour patterns in response. A fascinating example of such adaptive colouration and morphology is masquerade, a camouflage strategy in which organisms resemble innocuous and inedible objects, such as leaves or twigs. Masquerading prey avoid predation by being misclassified as irrelevant parts of the environment, rather than as food.Here we assess a putative case of masquerade in the North Island lichen moth, Declana atronivea (Geometridae), an endemic New Zealand species with intricate black and white forewings that appear to resemble lichen. Lichen masquerade is a type of 'element imitation' in which the object being mimicked forms a common element of the environmental pattern. However, unlike discrete objects, such as leaves and twigs, lichen may be difficult to distinguish as a distinct entity. This raises the question of whether D. atronivea can be said to look like 'a' lichen, or whether its body colouration appears as a component of a larger patch of lichen. In this case, does the lichen resemblance function as a form of masquerade, or is it an example of background matching? Using laboratory experiments with domestic chicks (Gallus gallus) as predators, we investigated whether D. atronivea moths avoid predation by being misclassified as lichen. We exposed naïve and experienced chicks to D. atronivea and compared their responses, predicting that if the moths do benefit from masquerade, chicks with previous experience of lichen would take longer to attack. Our hypothesis was not supported; there was no significant difference in predator interaction regardless of prior experience, suggesting that, in the absence of a matching background, D. atronivea do not benefit from masquerading as lichen. Rather, this may be a case of context-dependent misclassification, or perhaps the forewing colouration promotes concealment through crypsis.
Background matching is perhaps the most ubiquitous form of defensive camouflage in the animal kingdom, an adaptive strategy that relies on the visual resemblance between a prey organism and its background to promote concealment from predators. The importance of background matching has been acknowledged for over a century, yet despite its renown and apparent pervasiveness, few studies exist that have objectively quantified its occurrence and tested the functional significance of background matching in a specific animal study system. The North Island lichen moth Declana atronivea presents a fascinating system to investigate such anti‐predator coloration. This species possesses high contrast black and white forewings that appear to resemble lichen. Here we assessed the contribution of background matching to the antipredator defence of D. atronivea using field predation experiments with realistic models. We found that D. atronivea coloration confers a significant survival advantage against native avian predators when on lichen backgrounds compared to bark backgrounds, with an intermediate level of predation occurring when models were near, but not on lichen. This suggests that D. atronivea wing patterns are an adaptation for background matching. We subsequently used calibrated digital photography, avian vision modelling and image analysis techniques to objectively quantify the degree of background matching exhibited by D. atronivea and assessed the contribution of different visual elements (colour, luminance and pattern) to camouflage in this species. Only the pattern elements of D. atronivea presented a close match to that of the lichen backgrounds, with both chromatic and achromatic cues found to be poor predictors of background matching in this species. This study is one of the first to integrate vision modelling, quantitative image analysis and field predation experiments using realistic models to objectively quantify the level and functional significance of background matching in a real species, and presents an ideal system for further investigating the interrelation between multiple mechanisms of camouflage.
Insects rely on chemical information obtained from their surroundings when locating biologically important resources. Detection of these chemicals is mediated by the antennae, which are endowed with various sensory structures called sensilla. Sensilla type, distribution and density vary among species, between sexes and at different life stages, and may provide important information regarding the ability of individuals to detect and process such external stimuli. The aim of this study was to quantitatively investigate the sensory architecture of larval and adult antennae in the New Zealand magpie moth, Nyctemera annulata (Arctiinae). Using scanning electron microscopy the sensilla were identified and classified into 8 types: trichoid, basiconic, chaetic, auricillic, squamiform, styloconic, coeloconic and Böhm's bristles, with multiple subtypes. Larval antennae were found to possess morphology and sensory structures which are essentially ubiquitous across the Lepidoptera. Sexual dimorphism was apparent in the overall antennal morphology as well as in the distribution, density and morphology of particular types of sensilla in adult N. annulata, which likely represents a divergence in sensory functions based on the different resource cues responded to by males (sex pheromones) and females (host plant odours). This is a rare example of a study which quantifies variation in the numbers and dimensions of all antennal sensilla types for males and females to allow a thorough statistical assessment of sexual dimorphism in antennal sensory architecture.
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