The wavelength sensitivities of animal photoreceptors strongly influence the visual contrast of objects in the environment, thereby constraining visually-guided behaviors. Outside of the human visual wavelength range, ultraviolet sensitivity in many species provides important and behaviorally relevant visual contrast. However, at the opposite end of the spectrum, the potential benefit of far-red sensitivity remains unclear. We investigated the potential benefit of long wavelength sensitivity by modelling the visual contrast of a wide range of jewel beetle colours against the flowers and leaves of their host plants to hypothetical insect visual systems. We find that the presence of a long wavelength sensitive (LWS) photoreceptor enhances the contrasts of pairwise comparisons between leaves, flowers and beetles. When we varied the wavelength of maximum sensitivity (λmax) for the LWS receptor in a tetrachromatic system, contrasts between beetles, flowers and leaves were all enhanced with increasing λmax from 580 nm to at least 640 nm. These results show the visual advantage of longer LWS receptors in discrimination against vegetation and highlight the potential adaptive value of long wavelength and far-red sensitivity in insects.
|Date made available||31 Aug 2020|