A behavioural analysis of colour vision in the antCataglyphis bicolor (Formicidae, Hymenoptera)

SummaryThe colour vision of worker antsCataglyphis bicolor was investigated by means of a colour mixture apparatus (Fig. 1). In freely walking ants the spontaneous phototactic choice behaviour as well as the choice behaviour after previous training to monochromatic or white light stimuli were tested in the spectral range 320≦λ≦ 627 nm. For all wavelengths standard intensities (I0.5) were used that caused equal attractiveness and thus exhibited equal subjective brightness for the ants.1.The spectral sensitivity function of the spontaneous phototactic choice behaviour is characterised by four peaks (λmax=342, 425, 505, and 570 nm). The relative heights of the peaks are about 5.5∶1.0∶1.0∶0.5, respectively (Fig. 5).2.The visual system of the ant can selectively be adapted to all four ranges which the ant is maximally sensitive to (Fig. 6). The difference spectrum in Fig. 7 shows the spectral sensitivity curve of the postulated long-wavelength receptor type (λmax=570 nm).3.A wavelength discrimination function was obtained by means of training experiments. It is characterised by three maxima (λmax=382, 449, and 550 nm). The accuracy of discrimination varies as follows: 382>449>550 nm (Fig. 8).4.Spectral lights ofλmax=342, 434, and 506 nm appear to the ants as maximally saturated hues. The yellow range seems to be moderately saturated (Fig. 9).5.Colour mixture experiments show that the hue continuously varies along the wavelength scale and that the spectral range which the ant is sensitive to is closed via the ant-purple range (Fig. 10).6.All 16 tested monochromatic lights and antpurple are distinctly discriminated from a white light stimulus, i.e. a “white instance” also exists in the ant's colour vision system.7.Four pairs of complementary colours were tested, including ant-purple. Complementary colours are the wavelengths 342 and 504, 434 and 574, 382 and 550, 351/574 and 449 nm when presented by the relative intensities 0.37 to 0.63, 0.32 to 0.68, 0.25 to 0.75, and 0.25/0.25 to 0.50, respectively (Fig. 13).8.The hypothesis of a tetrachromatic colour vision system in the antCataglyphis bicolor is tentatively discussed. Four spectral types of receptors are postulated (R345, R430, r505 and r570) and different possibilities of how to build a yellow receptor (R570) are considered. A hypothetical chromaticity diagram is proposed (Fig. 17).