Mapping the variation in spider body colouration from an insect perspective

Abstract

Colour variation is frequently observed in spiders. Such variation can impact fitness by affecting the way spiders are perceived by relevant observers such as prey (i.e. by resembling flower signals as visual lures) and predators (i.e. by disrupting search image formation). Verrucosa arenata is an orb-weaving spider that presents colour variation in a conspicuous triangular pattern on the dorsal part of the abdomen. This pattern has predominantly white or yellow colouration, but also reflects light in the UV part of the spectrum. We quantified colour variation in V. arenata from images obtained using a full spectrum digital camera. We obtained cone catch quanta and calculated chromatic and achromatic contrasts for the visual systems of Drosophila melanogaster and Apis mellifera. Cluster analyses of the colours of the triangular patch resulted in the formation of six clusters and three clusters in the colour space of D. melanogaster and A. mellifera, respectively. Significant differences were found between morphs for both visual systems in contrasts between the colour pattern and two backgrounds against which it would be viewed. Yellow spiders showed higher chromatic contrast than white spiders, while white spiders showed higher achromatic contrast. Therefore, there are perceptual differences between V. arenata colour morphs in the visual systems of potential relevant observers which could pose an important selective pressure on this trait. A variation in the contribution of colour channels to the colour pattern observed in colour maps constructed from reflectance values of individual pixels could influence the way the pattern is perceived, and its resemblance to attractive flower signals.