Spider lures exploit insect preferences for floral colour and symmetry

Abstract

Sensory systems can capture only a fraction of available information, which creates opportunities for deceptive signalling. The sensory traps and sensory bias models have proven valuable for explaining how visual systems and environments shape the design of sexual signals, but their application to deceptive signals is largely limited to the context of pollination. Here we use the ‘jewelled’ orb-web spider Gasteracantha fornicata to experimentally test two longstanding hypotheses for the function of deceptive visual lures. Namely, that they: (1) exploit generalised preferences for conspicuous colouration (sensory bias), or (2) co-opt the otherwise-adaptive foraging response of prey toward flowers (sensory traps). In a field-based study we manipulated the conspicuous dorsal signals of female spiders along two axes—colour pattern and symmetry—to generate a gradient of floral resemblance and monitored the per-individual consequences for prey interception. As predicted by the sensory traps model, the most attractive phenotypes were those with flower-like radial symmetry and solid colour patterns, and their attractiveness equaled that of natural spiders. Taken with recent work demonstrating a close resemblance between G. fornicata and sympatric floral ‘models’, and pollinating insects as primary prey items, our results suggest that the deceptive colour-based lures of spiders function as inter-kingdom sensory traps via floral mimicry, and support the broader extension of sensory-based models to deceptive signalling contexts.