Structurally assisted super black in colourful peacock spiders

Dakota E. McCoy*, Victoria E. McCoy, Nikolaj Kofoed Mandsberg, Anna V. Shneidman, Joanna Aizenberg, Richard O. Prum, David Haig

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

Male peacock spiders ( Maratus, Salticidae) compete to attract female mates using elaborate, sexually selected displays. They evolved both brilliant colour and velvety black. Here, we use scanning electron microscopy, hyperspectral imaging and finite-difference time-domain optical modelling to investigate the deep black surfaces of peacock spiders. We found that super black regions reflect less than 0.5% of light (for a 30° collection angle) in Maratus speciosus (0.44%) and Maratus karrie (0.35%) owing to microscale structures. Both species evolved unusually high, tightly packed cuticular bumps (microlens arrays), and M. karrie has an additional dense covering of black brush-like scales atop the cuticle. Our optical models show that the radius and height of spider microlenses achieve a balance between (i) decreased surface reflectance and (ii) enhanced melanin absorption (through multiple scattering, diffraction out of the acceptance cone of female eyes and increased path length of light through absorbing melanin pigments). The birds of paradise (Paradiseidae), ecological analogues of peacock spiders, also evolved super black near bright colour patches. Super black locally eliminates white specular highlights, reference points used to calibrate colour perception, making nearby colours appear brighter, even luminous, to vertebrates. We propose that this pre-existing, qualitative sensory experience-'sensory bias'-is also found in spiders, leading to the convergent evolution of super black for mating displays in jumping spiders.
Original languageEnglish
Article number20190589
JournalProceedings of the Royal Society B: Biological Sciences
Volume286
Issue number1902
Number of pages9
ISSN0962-8452
DOIs
Publication statusPublished - 2019

Keywords

  • Microlens arrays
  • Peacock spiders
  • Sexual selection
  • Structural colour

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