Nanostructural Influence on Optical and Thermal Properties of Butterfly Wing Scales Across Forest Vertical Strata

Abstract

Butterfly wing scales feature complex nanostructures that influence wing coloration and various mechanical and optical properties. This configuration plays a key role in ecological interactions, flight conditions, and thermoregulation, facilitated by interactions with environmental electromagnetic energy. In tropical forests, butterflies occupy distinct vertical habitats, experiencing significant light and temperature variations. While wing nanostructures have been widely studied, their variation across different vertical flight preferences remains underexplored. This study investigates the wing nanostructures of 12 tropical butterfly species from the Nymphalidae family, focusing on their optical, morphological, and thermal properties across different forest strata. We analyzed the optical response through diffuse reflectance in the UV, Vis, and NIR ranges, correlating these findings with nanostructural configuration and thermal stability using thermogravimetric analysis (TGA). Our results reveal a significant correlation between flight stratification and wing optical responses, alongside distinct nanostructural features within each stratum. This study demonstrates the variability in butterfly wing nanostructures along the vertical stratification of the forest to cope with environmental conditions, raising new questions for future research on eco-evolutionary flight and thermal adaptations. Additionally, this underscores the importance of understanding how these structural adaptations influence butterfly interactions with their environment and their evolutionary success across different forest strata.

Keywords: diffuse reflectance; flight preference; spectroscopy; thermogravimetry; tropical forest; vertical stratification.

Figure 1

Areas of the wings analyzed spectrally and microscopically represented in red squares.

Figure 2

Macrophotographs and optical microscopy stacked images using 10× and 40× objectives: (a) Heliconius hecalesia (representative of canopy), (b) Archaeoprepona demophon (representative of mid-stratum), and (c) Caligo atreus (representative of understory). Additional species analyzed from each stratum are shown in Supplementary Material Figure S1.

Figure 3

Morphological classification of nanostructures.

Figure 4

SEM micrographs of the discal area of the forewing at different magnifications of (a) Heliconius hecalesia (representative of canopy), (b) Archaeoprepona demophon (representative of mid-stratum), and (c) Caligo atreus (representative of understory).

Figure 5

Diffuse reflectance response (I, u.a.) in the NIR, visible, and UV ranges (λ, nm) for (a) Heliconius hecalesia (representative of canopy), (b) Archaeoprepona demophon (representative of mid-stratum), and (c) Caligo atreus (representative of understory).

Figure 6

Linear correlations between (a) stratification index of the 12 species and the reflectance indices in the visible (R² = 0.6), NIR (R² = 0.41), and UV (R² = 0.36) ranges; (b) NIR and Vis indices of forewings and hindwings (R² = 0.9); (c) UV and Vis indices of forewings and hindwings (R² = 0.26); and (d) NIR and UV indices of forewings and hindwings (R² = 0.04).

Figure 7

(a) Box-and-whisker plots for reflectance data in the NIR, Vis, and UV light ranges according to the forest stratum of the species; (b) hierarchical dendrogram of the species based on the combined UV, Vis, and NIR reflectance indices.

Figure 8

(a) Thermogram obtained from fore- and hindwing of each species (complete thermograms, see Figure S3); (b) mass loss (%) for each species by temperature range.