Blue reflectance in tarantulas is evolutionarily conserved despite nanostructural diversity.

Area of Science:

• Evolutionary biology
• Biophysics
• Animal coloration

Background:

• Biological photonic nanostructures influence color diversity.
• Sexual selection often drives color evolution in species with structural colors.
• Tarantulas (Araneae: Theraphosidae) present a unique case for studying color evolution.

Purpose of the Study:

• Investigate the evolutionary patterns of nanostructural diversification and blue coloration in tarantulas.
• Determine the mechanisms driving the conservation of blue color in this clade.
• Contrast the role of natural versus sexual selection in tarantula coloration.

Main Methods:

• Phylogenetic reconstruction
• Scanning electron microscopy (SEM)
• Spectrophotometry
• Optical modeling

Main Results:

• Tarantulas show remarkable conservation of blue color, peaking around 450 nm, despite nanostructural diversification.
• Both quasi-ordered and multilayer nanostructures generate this conserved blue color across phylogenetically distant species.
• Tarantula color perception and courtship displays suggest blue coloration is not sexually selected.

Conclusions:

• Natural selection, rather than sexual selection, has driven the convergence on similar blue coloration in tarantulas.
• Divergent nanostructural mechanisms evolved to produce similar blue structural colors, contrasting typical patterns of sexual selection.
• This study highlights natural selection's role in shaping structural color through convergent evolution in tarantulas.