The role of UV in crab spider signals: effects on perception by prey and predators

Abstract

Australian crab spiders Thomisus spectabilis sit on the petals of flowers and ambush prey such as honeybees. White-coloured T. spectabilis reflect in the UV (UV+ spiders) and previous research has shown that their presence, curiously, attracts honeybees to daisies. We applied an UV-absorber (Parsol ® ) to create UV-absorbing (UV-) spiders that did not reflect any light below 395·nm wavelength. These physical changes of visual signals generated by crab spiders caused honeybees to avoid flowers with UV-spiders on their petals. They also affected the perception of UV-spiders by honeybees and a potential avian predator (blue tits). Compared to UV+ spiders, UV-spiders produced less excitation of the UVphotoreceptors in honeybees and blue tits, which translated into a reduced UV-receptor contrast and a reduced overall colour contrast between UV-spiders and daisy petals. Our results reveal that a clean physical elimination of reflection in the UV range affects perception in predators and prey and ultimately changes the behaviour of prey.

Relationship between colouration and body condition in a crab spider that lures pollinators

“…These results, together with those of previous experiments (Bhaskara et al, 2009;Heiling et al, 2005;Heiling et al, 2003;Herberstein et al, 2009), suggest that greater conspicuousness, most likely achieved by a higher E UV contrast, is advantageous for these spiders. This advantage is likely to be the result of the fact that honeybees are attracted to UV-reflective spiders (Heiling et al, 2005;Heiling et al, 2003;Herberstein et al, 2009) and, therefore, the foraging success of highly UV-reflective spiders would be greater than that of UV-dull spiders. Moreover, the fact that colour contrast and condition have a quadratic relationship suggests that the benefit comes after a certain degree of colour contrast has been achieved (Fig.2).…”

The multiple disguises of spiders: web colour and decorations, body colour and movement

“…The second hypothesis states that main raison d'être of ommochromes is signalling, mimicry and crypsis. This is the hypothesis supported by most of the community working on colour changing insects such as stick insects and mantids (Fuzeau-Braesch 1985), including Mantis religiosa, Sphodromantis viridis and Locusta migratoria (Vuillaume 1968), and spiders (Rabaud 1918(Rabaud , 1919Gabritschevsky 1927;Schmalhofer 2000;Chittka 2001;Théry & Casas 2002;Heiling et al 2003Heiling et al , 2005aThéry et al 2005;Théry 2007). In order to test this hypothesis, we need to assess the fitness value of the camouflage and the fitness gain from a change of colour.…”

Background colour matching by a crab spider in the field: a community sensory ecology perspective

“…From these data, it is likely that both chromatic and achromatic contrasts elicited by spiders are noticed by prey. Other crab spider species have been reported to be either chromatically cryptic on a substrate in the perspective of bees, as for Thomisus onustus (Théry and Casas, 2002;Théry et al, 2005), or achromatically cryptic, as for the Australian crab spider Thomisus spectabilis (Heiling et al, 2005). However, there is a lack of knowledge about the role of the chromatic and achromatic crypsis in the prey capture rate and survival rate against birds.…”

“…However, M. vatia can be found hunting on UV-reflecting flowers, such as C. spinosa and Senecio sp. Nothing is known about M. vatia's spectral sensitivities and whether a UV contrast may also act as an attractive stimulus for honeybees, in a similar fashion as the UV-reflecting Australian crab spider T. spectabilis hunting on UV-absorbing flowers (Heiling et al, 2005;Bhaskara et al, 2009). Lunau et al showed that bees innately prefer flowers with strongly contrasting markings (Lunau et al, 1996).…”