title: Wavelength discrimination in the hummingbird hawkmoth Macroglossum stellatarum.
abstract: Despite the strong relationship between insect vision and the spectral properties of flowers, the visual system has been studied in detail in only a few insect pollinator species. For instance, wavelength discrimination thresholds have been determined in two species only: the honeybee (Apis mellifera) and the butterfly Papilio xuthus. Here, we present the wavelength discrimination thresholds (Δλ) for the hawkmoth Macroglossum stellatarum. We compared the data with those found for the honeybee, the butterfly P. xuthus and the predictions of a colour discrimination model. After training moths to feed from a rewarded disc illuminated with a monochromatic light, we tested them in a dual-choice situation, in which they had to choose between light of the training wavelength and a novel unrewarded wavelength. To characterise the Δλ function, we decreased the difference between wavelengths in subsequent tests. We also varied the light intensity to test its effect on the discrimination capacity. In agreement with the predictions of the model, we found two expected minima of discrimination where photoreceptor sensitivities overlap, as well as a third, minor, unpredicted minimum around the peak of the blue photoreceptor. Macroglossum stellatarum is capable of discriminating between lights with a wavelength difference of 1-2 nm. These discrimination minima are similar to those found for the tetrachromatic P. xuthus, and are better than those of the honeybee. The moth is also capable of using achromatic information to discriminate between lights of long wavelengths.
authors.affiliation: Department of Functional and Evolutionary Ecology, Estación Experimental de Zonas Áridas (EEZA-CSIC), Carretera de Sacramento, s/n, La Cañada de San Urbano, Almería 04120, Spain meirecuesta@gmail.com.
authors.forename: Francismeire J
authors.initials: FJ
authors.lastname: Telles
authors.affiliation: Lund Vision Group, Department of Biology, Lund University, Sölvegatan 35, Lund 22362, Sweden.
authors.forename: Almut
authors.initials: A
authors.lastname: Kelber
authors.affiliation: Department of Functional and Evolutionary Ecology, Estación Experimental de Zonas Áridas (EEZA-CSIC), Carretera de Sacramento, s/n, La Cañada de San Urbano, Almería 04120, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Rodríguez-Gironés
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D003118:Color Perception; D003463:Cues; D004193:Discrimination Learning; D008027:Light; D009036:Moths / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology; D014785:Vision, Ocular
keywords: Achromatic information; Chromatic information; Insect vision; Macroglossum stellatarum; Visual system; Wavelength discrimination