Specific color sensitivities of prey and predator explain camouflage in different visual systems

Abstract

In situations of aggressive mimicry, predators adapt their color to that of the substrate on which they sit for hunting, a behavior that is presumed to hide them from prey as well as from their own predators. Females of few crab-spider species encounter such situations when lying on flowers to ambush pollinators. To evaluate the efficiency of spider camouflage on flowers, we measured by spectroradiometry adult female Thomisus onustus and marguerite daisies, Leucanthemum vulgare. We compared chromatic contrast (color used for short-range detection) of each pair of spider and flower to detection thresholds computed in the visual systems of both Hymenopteran prey and passerine bird predator. We also computed achromatic contrast (brightness) used for long-range detection. In both visual systems, each individual spider was efficiently matching the precise color of the flower center on which it was hunting. Being significantly darker than flowers, crab-spiders could in theory be detected at long range by either predator or prey using achromatic contrast. However, long-range detection is unlikely, owing to small spider size. Spiders also generated significant chromatic and achromatic contrasts to both Hymenoptera and bird when moving on flower periphery. Our study is the first to identify which photoreceptors of both prey and predator are involved in camouflage. The analysis suggests more research on bird predation and vision to determine to which extent bird predators effectively constrain spider crypsis. Copyright 2005.bird; camouflage; crab-spider; Hymenoptera; spectrometry