Abstract: The presence of conspicuous colouration in predators is puzzling because
natural selection is expected to favour cryptic or disruptive colouration, making
predators less detectable by prey. However, the prey attraction hypothesis proposes
that conspicuous colour patterns in spiders increase their foraging success by luring
prey. Using manipulative experiments we tested the prey attraction hypothesis for 10 the three most common colour morphs of the orb-weaver Gasteracantha cancriformis
(yellow, white, and black and white), as well as individuals painted black and indi-
viduals painted yellow. Contrary to our predictions, the black painted spiders had the
highest number of damaged areas in webs (an indirect measure of foraging success).
Black painted spiders were also observed more often consuming prey and with prey 15 remains in the web, although the trend was not significant. Furthermore, there was no
difference in the number of prey intercepted by webs of each spider colour and, in the
laboratory, Drosophila melanogaster did not choose any of the spider colours prefer-
entially. Our results suggest that colouration in G. cancriformis is costly or neutral in
terms of foraging success. Alternatively, we propose that colouration in Gasteracantha 20 could be an aposematic signal.
Abstract: 1. Australian crab spiders exploit the plant�pollinator mutualism by reflecting UV light that attracts pollinators to the flowers where they sit. However, spider UV reflection seems to vary broadly within and between individuals and species, and we are still lacking any comparative studies of prey and/or predator behaviour towards spider colour variation. 2. Here we looked at the natural variation in the coloration of two species of Australian crab spiders, Thomisus spectabilis and Diaea evanida, collected from the field. Furthermore, we examined how two species of native bees responded to variation in colour contrast generated by spiders sitting in flowers compared with vacant flowers. We used data from a bee choice experiment with D. evanida spiders and Trigona carbonaria bees and also published data on T. spectabilis spiders and Austroplebeia australis bees. 3. In the field both spider species were always achromatically (from a distance) undetectable but chromatically (at closer range) detectable for bees. Experimentally, we showed species-specific differences in bee behaviour towards particular spider colour variation: T. carbonaria bees did not show any preference for any colour contrasts generated by D. evanida spiders but A. australis bees were more likely to reject flowers with more contrasting T. spectabilis spiders. 4. Our study suggests that some of the spider colour variation that we encounter in the field may be partly explained by the spider's ability to adjust the reflectance properties of its colour relative to the behaviour of the species of prey available.
Abstract: Sit-and-wait predators have evolved several traits that increase the probability of encountering prey, including lures that attract prey. Although most crab spiders (Thomisidae) are known by their ability to change colour in order to match the background, a few crab spiders use a different strategy. They are UV-reflective, creating a contrast against UV-absorbing flowers that is attractive for pollinators. The nature of the relationship between colour and foraging success is unknown, as well as how spiders trade-off potential costs and benefits of UV-reflectance. Therefore, this study aimed to investigate the relationship between spider colouration, foraging success and background colouration in a crab spider species known to lure pollinators via UV- reflectance (Thomisus spectabilis). Field data revealed that spider body condition - proxy of past foraging success - has a quadratic relationship with UV-reflectance and overall colour contrast: highest UV and colour contrast yielded the highest condition values, but there was no substantial difference between the condition of spiders with medium and low UV values. We experimentally tested the effect of satiation and background colour on spider colour change. Throughout the experiment, spiders increased their UV-reflectance regardless of their food intake, suggesting that UV- reflectance is not caused by spider condition. While spiders responded to different backgrounds by subtly changing their body colour, this did not result in colour matching. We believe that the observed variation in UV-reflectance and hence conspicuousness in the field coupled with the spiders� reaction to our manipulation could be the result of plasticity in response to prey.
Abstract: Several orb-web spiders build conspicuous decorations in their webs. The prey attraction hypothesis proposes that decorations increase spider foraging success by attracting prey, and that attraction is linked to UV reflectance. Alternatively, the web advertisement hypothesis proposes that decorations are a signal that advertises the presence of the web to large animals. We tested both hypotheses for the web silk tufts of <I>Gasteracantha cancriformis</I>. Even though tufts are UV reflective, we did not find support for the prey attraction hypothesis. In the field, when webs with tufts painted black and control webs were compared, there were no differences in the number of prey captured, number of damaged areas in webs and type of prey captured. In the laboratory, <I>Drosophila melanogaster</I> did not demonstrate preference for tufted silk lines versus non-tufted silk lines. Our data also did not give support for the web advertisement hypothesis. The proportion of web destruction was similar between web with tufts painted black and control webs during four days of experimentation. Therefore, two of the most favoured hypotheses that attempt to explain decorations do not apply for web silk tufts in our study system. Instead we propose that silk tufts might be an aposematic signal.
