Figure 2. Differences in hue and brightness on the proximo-distal plane of Morpho wings.

(A) Illustration of the two protocols used to assess the differences in Morpho wing reflectance. The ‘Specular’ set-up allows for the quantification of the wing color variations, while the ‘tilt’ set-up can be used to quantify brightness variation for each Morpho wing (see Appendix 1 for extended methods). Variations of hue (B and C) and brightness (D and E) calculated from the wing reflectance measured with the ‘Specular’ set-up, and variations of brightness calculated from the wing reflectance measured from the ‘tilt’ set-up (F and G). Those hue and brightness parameters were calculated for the allopatric M. h. theodorus and M. h. bristowi (first column in orange and purple) and for the sympatric M. h. helenor and M. a. achilles (second column in green and blue) on the proximal-plane plane of their wings (I=illumination on the internal side of the wings, E=illumination on the external side of the wings). See Appendix 2—table 1 for the PERMANOVA analyses describing those graphs.

Figure 2—figure supplement 1. Differences in chroma on the proximo-distal and anteroposterior plane of Morpho wings.

Variation of the chroma parameter measured on the proximo-distal plane (A and B) and anteroposterior plane (C and D) calculated from the wing reflectance measured with “Specular” set-up. The chroma parameter was calculated for the sympatric M. h. helenor and M. a. achilles (first column in green and blue) and for the allopatric M. h. theodorus and M. h. bristowi (second column in orange and purple). The results of the permutation-based ANOVAs performed in order to test whether the sex, the taxa, or the angle of illumination has an effect on the estimated chroma are shown in (E). The chroma parameter is a proxy describing the intensity of the color reflected by the dorsal side of Morpho wings. As for every optical parameter measured, chroma is significantly different at every angle of illumination, suggesting that variations of chroma can be observed on the wings of Morpho butterflies (iridescence). Overall, we can see on every graph that the colors measured at a wide specular angle (30° to 45° in every tested direction) have the highest chroma, suggesting the existence of a more intense color signal at extreme angles of illumination. On the proximo-distal plane (A and B), chroma is significantly different between males and females. The graphs show that males tend to be more saturated than females, especially at extreme angles. On the anteroposterior plane, especially among the sympatric Morpho species analysis (C), the chroma of males is overall higher than the female’s, except at 45° angles of illumination where it drops for males but increases for females. The chroma parameter is always significantly different between M. h. bristowi and M. h. theodorus subspecies on both planes of illumination (B and D), and is also similar between sympatric M. h. helenor and M. a. achilles (A and C), consistent with convergence of the intensity of color saturation between sympatric species.

Figure 2—figure supplement 2. Differences in hue and brightness on the anteroposterior plane of Morpho wings.

Variations in hue (A and B) and brightness (C and D) calculated from the wing reflectance measured with the “specular” set-up on the anteroposterior plane, and variations of brightness calculated from the wing reflectance measured from the “tilt” set-up (E and F) on the anteroposterior plane. Differences in hue and brightness of the anteroposterior plane of the wings are shown for both the interspecific (first column in green and blue) and intraspecific comparisons (second column in orange and purple). The results of the permutation-based ANOVAs performed in order to test whether the sex, the taxa, or the angle of illumination has an effect on the estimated hue and brightness are shown in (G). In addition to the proximo-distal data presented in the main text (Figure 2), the analysis of the reflectance of Morpho wings on their anteroposterior plane shows that this plane is also iridescent as significant variations of hue and brightness are measured at different angles. The effect of sex on the variation of brightness is always significant no matter the pair tested or the method of measurement: the brightness of Morpho wings on this plane is thus sexually dimorphic (C, D, E, and F) as was found on the proximo-distal plane. However, the ‘tilt’ wing reflectance measurements of the brightness (E and F) are not as straightforward as the measurements taken on the proximo-distal plane showing that males were brighter than females (Figure 2F and G). Here, we observe that allopatric males are indeed brighter than females (F), but the Amazonian males from French Guiana are not as clearly different from their respective females (E). The difference in brightness between males and females in those two localities is also less important than the differences in brightness found between males and females measured on the proximo-distal plane (Figure 2F and G). This difference of brightness could be explained by the physical structures of the scales that could potentially better reflect light intensity on the proximo-distal plane than on the anteroposterior plane, generating more important shifts in brightness during a flapping flight motion. Finally, a significant effect of hue was found between the two allopatric populations of M. helenor (B) and between the two sympatric Morpho species (A). Conversely, no hue variation was found between the sympatric Morpho species on the proximo-distal plane (Figure 2B). Nevertheless, divergence in hue was found to be more important between the allopatric M. helenor subspecies than between the sympatric M. h. helenor and M. a. achilles, consistent with stronger convergence in coloration between sympatric species.