Spectral filtering enables trichromatic vision in colorful jumping spiders

Figure 1. Spectral filtering of Habronattus pyrrithrix photoreceptors. (A) Courtship display of male H. pyrrithrix (photo: Colin Hutton). (B) Boomerang-shaped retinas superimposed on principal eye lenses, small red area indicates filter position. (C) Red filter pigment visible in unstained coronal cryosection (14 μm thick) of the principal retina. (D) Tiered retina structure in thin horizontal section of principal retina: a, anterior; p, posterior; l, lateral; m, medial. (E) Red filter pigment visible in unstained horizontal cryosection (14 μm thick) of the principal retina. (F) Diagram of tiered arrangement of green and UV-sensitive photoreceptors in longitudinal view of principal retina center of H. pyrrithrix. Red area indicates long-pass filter pigment, shifting sensitivity of tier 1 photoreceptors from green to red. (G) Normalized visual pigment absorbance difference spectra in proximal (green, n = 11) and distal (violet, n = 2) retinal tiers with best-fit templates. (H) Absorbance (grey) and transmittance (red) of filter at maximal observed thickness (n = 6). (I) Predicted sensitivity of three photoreceptor classes, UV (377 nm), green (530 nm), red (626 nm), after light filtering by optics and filter pigment. All axes in G–I are linear. Spectral filtering enables trichromatic vision in colorful jumping spiders