Fig. 4.

Percentage of pairs of Heliconius yellows (n = 351 pairs) (yellow) and non-Heliconius yellows (n = 253) (white) that differ as modeled through the eyes of H. erato and D. iulia under dim illumination. (A) Forest shade and (B) open habitat irradiance spectra measurements used in the calculations were obtained at field sites in Oaxaca, Mexico. Results for the Heliconius UVRh1, UVRh2, and LWRh receptor combination are compared to the Dryas UVRh, BRh, and LWRh receptor combination. Other possible receptor combinations are shown in Table S3. Threshold (ΔS) units of just noticeable differences (JNDs) of one, two, and three were chosen to account for the difficulty in estimating true noise values in the butterfly (44). For both visual systems, more Heliconius yellows differ by one, two, or three JNDs making it very likely that more of these colors can be discriminated. Bars indicate 95% confidence intervals.