posted on 2018-05-09, 10:11authored byAndrew J. Parnell, James E. Bradford, Emma V. Curran, Adam L. Washington, Gracie Adams, Melanie N. Brien, Stephanie L. Burg, Carlos Morochz, Patrick A. Fairclough, Pete Vukusic, Simon MartinSimon Martin, Scott Doak, Nicola J. Nadeau
Iridescence is an optical phenomenon whereby colour changes with the illumination and viewing angle. It can be produced by thin film interference or diffraction. Iridescent optical structures are fairly common in nature, but relatively little is known about their production or evolution. Here we describe
the structures responsible for producing blue-green iridescent colour in Heliconius butterflies. Overall the wing scale structures of iridescent and
non-iridescent Heliconius species are very similar, both having longitudinal ridges joined by cross-ribs. However, iridescent scales have ridges composed
of layered lamellae, which act as multilayer reflectors. Differences in brightness between species can be explained by the extent of overlap of the lamellae and their curvature as well as the density of ridges on the scale. Heliconius are well known for their Mullerian mimicry. We find that iridescent structural colour is not closely matched between co-mimetic species. Differences appear less pronounced in models of Heliconius vision than models of avian vision, suggesting that they are not driven by selection to avoid heterospecific courtship by co-mimics. Ridge profiles appear to evolve relatively slowly, being similar between closely related taxa, while ridge density evolves faster and is similar between distantly related co-mimics.
Funding
This work was funded by a Natural Environment Research Council (NERC) fellowship (NE/K008498/1) to N.J.N. J.E.B. was funded under the NERC Research Experience Placements (REP) scheme. E.C. and M.B. are funded by the NERC doctoral training
partnership, ACCE. A.L.W. was funded via InnovateUK.
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
Department
Materials
Published in
Journal of the Royal Society Interface
Volume
15
Issue
141
Citation
PARNELL, A.J. ... et al, 2018. Wing scale ultrastructure underlying convergent and divergent iridescent colours in mimetic Heliconius butterflies. Journal of the Royal Society Interface, 15 (141), 20170948.
This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: http://creativecommons.org/licenses/ by/4.0/
Acceptance date
2018-03-26
Publication date
2018
Notes
This is an Open Access Article. It is published by Royal Society, The under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/