Structurally assisted super black in colourful peacock spiders.

Area of Science:

• Zoology
• Biophysics
• Materials Science

Background:

• Male peacock spiders (Maratus) use elaborate visual displays for mate attraction, incorporating both bright colors and deep black.
• Super black coloration, observed in both peacock spiders and birds of paradise, is hypothesized to enhance the perception of adjacent colors.

Purpose of the Study:

• To investigate the structural and optical properties of the super black surfaces in two species of peacock spiders (Maratus speciosus and Maratus karrie).
• To understand the functional role of these super black regions in the context of sexual selection and mate attraction.

Main Methods:

• Scanning electron microscopy (SEM) to visualize microscale surface structures.
• Hyperspectral imaging to analyze light reflectance properties.
• Finite-difference time-domain (FDTD) optical modeling to simulate light-matter interactions.

Main Results:

• Super black regions in Maratus speciosus and Maratus karrie reflect less than 0.5% of incident light.
• Microscale structures, including high, tightly packed cuticular bumps (microlens arrays) and dense black brush-like scales, were identified as key to achieving super black.
• Optical models indicate these structures balance reduced reflectance with enhanced melanin absorption via multiple scattering and increased light path length.

Conclusions:

• The evolved microstructures in peacock spiders create super black surfaces that minimize specular highlights, thereby increasing the perceived brightness and luminosity of nearby colorful display elements.
• This phenomenon suggests a convergent evolution of super black for mating displays, potentially driven by a 'sensory bias' where the visual system of the receiver (female spider) is primed to perceive enhanced contrast.
• The findings highlight the intricate relationship between structural coloration, material properties, and behavioral ecology in sexual selection.