Figure 3. Characterization and perception of the iridescent coloration of Morpho butterflies.

(A) and (B): PCAs showing the variation in iridescence for both sexes, (A) in the two sympatric species from French Guiana (M. h. helenor vs. M. a. achilles) and (B) in the two allopatric Ecuadorian subspecies of M. helenor (M. h. theodorus vs. M. h. bristowi). Each point represents the global signal of iridescence of each individual, corresponding to the 21 complete reflectance spectra obtained from the 21 tested angles of illumination. The results of the PERMANOVA are shown on the top left corner of each graph. (C) The chromatic distances (i.e. the visual discrimination rate by a visual model) of the wing reflectance measured with the ‘Specular’ set-up on the proximo-distal plane. Visual modeling was used to calculate the chromatic contrast of blue coloration between allopatric M. helenor subspecies (red) and between the two sympatric sister-species M. helenor and M. achilles (green), as perceived by a Morpho visual system for every angle of illumination measured on the proximo-distal plane. The chromatic contrast likely perceived by UV-sensitive birds is shown in gray. Chromatic contrast of the female wings (top) and male wings (bottom). The threshold of discrimination is shown by the dotted line and set to 1 Just Noticeable Difference (JND). Error bars show the confidence intervals calculated during the bootstrap analysis.

Figure 3—figure supplement 1. Achromatic distances of the wing reflectance measured with the ‘Specular’ set-up on the anteroposterior and proximodistal plane.

Achromatic distances (i.e. the visual discrimination rate of brightness by a visual model) of the wing reflectance measured with the ‘Specular’ set-up on (A) the anteroposterior plane and (B) the proximodistal plane. We used visual modeling to calculate the achromatic contrast found between the blue coloration of the two allopatric populations of M. helenor sampled in Ecuador, as seen by a Morpho visual system (in red) and between the blue coloration of two species of Morphos from French Guiana, as seen by a Morpho visual system (in green). We also added the achromatic contrast of the Morpho wings as seen by the visual system of an avian predator (in gray). We separately measured the achromatic contrast of the female wings (first row of each figure) and male wings (second row of each figure) to account for sexual dimorphism. The dotted line represents the threshold of discrimination by any visual model: visual discrimination is considered possible if the measured chromatic distance is superior to the threshold. The overlap between the confidence intervals and the discrimination threshold shows that neither a bird visual model nor a Morpho visual model could discriminate between the wing brightness of Morphos from allopatric and sympatric populations.

Figure 3—figure supplement 2. Chromatic distances of the wing reflectance measured with the ‘Specular’ set-up on the anteroposterior plane.

We used visual modeling to calculate the chromatic contrast found between the blue coloration of the two allopatric populations of M. helenor sampled in Ecuador, as seen by a Morpho visual system (in red) and between the blue coloration of two species of Morphos from French Guiana, as seen by a Morpho visual system (in green). We also added the chromatic contrast of the Morpho wings as seen by the visual system of an avian predator (in gray). We separately measured the chromatic contrast of the female wings (first row) and male wings (second row) to account for sexual dimorphism. The dotted line represents the threshold of discrimination by any visual model: visual discrimination is considered possible if the measured chromatic distance is superior to the threshold. Overall, the results are similar to the chromatic distances measured on the reflectance spectra extracted from the proximo-distal plane of the Morpho wings (Figure 3C in the main text): the minute hue differences observed between species on the anteroposterior plane of the wings cannot be discriminated in a Morpho visual model, whereas the intraspecific divergent hues measured on the wings of allopatric M. h. bristowi and M. h. theodorus can be discriminated by a Morpho visual model.