Figure 1.

Relative spectral sensitivity of Lake Malawi cichlids obtained under different background conditions. (a-c) Relative spectral sensitivity of three individuals of M. zebra, M. auratus and P. taeniolatus (left to right). The spectral sensitivity of each species was measured under three background conditions: long-wavelength isolation (LW, red), control (green), and intense short-wavelength isolation (SW, blue). In P. taeniolatus, LW was replaced by Dim short-wavelength isolation (Dim-SW, cyan). In M. zebra, the spectral sensitivity curves measured under all conditions show four sensitivity peaks, whereas in M. auratus and P. taeniolatus the complete set of five sensitivity peaks was revealed across all background conditions. Data points were connected with lines to facilitate the identification of sensitivity peaks. (d-i) Visual pigment templates (dashed lines) fitted to spectral sensitivity (circles) measured under two background conditions. (Typically, the examination of two spectral sensitivity curves was sufficient to correlate all sensitivity peaks to cone pigments.) M. zebra: control (D) and SW (G); M. auratus: LW (E) and SW (H); P. taeniolatus: Dim-SW (F) and SW (I). Visual pigment templates: SWS1 (black), SWS2b (violet), SWS2a (blue), RH2b (green), RH2a (orange) and LWS (red). Similar plots were used for all individuals to identify sensitivity peaks and correlate them to cone pigments. See criteria for peak identification in the Methods section. See Additional file 1 for background isolation conditions and quantum catch of cone pigments.