Friday, February 22, 2013

Fossil Insect Coloration

The fossil record of insect color illuminated by maturation experiments


1. Maria E. McNamara (a,b)
2. Derek E.G. Briggs (a,c)
3. Patrick J. Orr (b)
4. Neal S. Gupta (d)
5. Emma R. Locatelli (a)
6. Lin Qiu (a)
7. Hong Yang (d)
8. Zhengrong Wang (a)
9. Heeso Noh (e)
10. Hui Cao (e)


a. Department of Geology & Geophysics, Yale University, New Haven, Connecticut 06520, USA

b. UCD School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland

c. Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut 06520, USA

d. Laboratory for Terrestrial Environments, Department of Science and Technology, Bryant University, Smithfield, Rhode Island 02917, USA

e. Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA


Structural coloration underpins communication strategies in many extant insects but its evolution is poorly understood. This stems, in part, from limited data on how color alters during fossilization. We resolve this by using elevated pressures and temperatures to simulate the effects of burial on structurally colored cuticles of modern beetles. Our experiments show that the color generated by multilayer reflectors changes due to alteration of the refractive index and periodicity of the cuticle layers. Three-dimensional photonic crystals are equally resistant to degradation and thus their absence in fossil insects is not a function of limited preservation potential but implies that these color-producing nanostructures evolved recently. Structural colors alter directly to black above a threshold temperature in experiments, identifying burial temperature as the primary control on their preservation in fossils. Color-producing nanostructures can, however, survive in experimentally treated and fossil cuticles that now are black. An extensive cryptic record is thus available in fossil insects to illuminate the evolution of structural color.

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