THE CONSPICUOUSNESS OF MALE DAMSELFLY COLORS AS VISUAL SIGNALS IN RELATION TO AMBIENT LIGHT AND VISUAL BACKGROUNDS.

T.D. Schultz, A.M. Bucy, and C.N. Anderson. Department of Biology, Denison University, Granville, OH 43023

Male damselfly colors are visual signals of sexual identity that may reduce harrassment of males in species that exhibit scramble competition for mates. Such aposematic signals should be maximally conspicuous under the specific light environments where males interact. This prediction was tested by comparing the reflectance spectra of males from seven sympatric species of Enallagma damselflies with the radiance spectra of the ambient light and visual backgrounds of their respective microhabitats. The flight times and locations of the males from each species were identified by field observation. The spectra of ambient radiation, visual backgrounds, and male reflectance were measured with a portable spectroradiometer and the conspicuousness of each species was determined statistically. Male coloration differed among species but each species was highly conspicuous within its respective light environment. Males flying during midday over open water all exhibited blue colors that were the most bright under ambient daylight and exhibited the greatest contrast with the pond surface. Males that flew late in the afternoon or at dusk reflected longer wavelengths than species active at midday. Males that consistently perched on vegetation exhibited colors that contrasted with the background vegetation.