title: Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi.
abstract: The wing scales of the Green Hairstreak butterfly Callophrys rubi consist of crystalline domains with sizes of a few micrometers, which exhibit a congenitally handed porous chitin microstructure identified as the chiral triply periodic single-gyroid structure. Here, the chirality and crystallographic texture of these domains are investigated by means of electron tomography. The tomograms unambiguously reveal the coexistence of the two enantiomeric forms of opposite handedness: the left- and right-handed gyroids. These two enantiomers appear with nonequal probabilities, implying that molecularly chiral constituents of the biological formation process presumably invoke a chiral symmetry break, resulting in a preferred enantiomeric form of the gyroid structure. Assuming validity of the formation model proposed by Ghiradella H (1989) J Morphol 202(1):69-88 and Saranathan V, et al. (2010) Proc Natl Acad Sci USA 107(26):11676-11681, where the two enantiomeric labyrinthine domains of the gyroid are connected to the extracellular and intra-SER spaces, our findings imply that the structural chirality of the single gyroid is, however, not caused by the molecular chirality of chitin. Furthermore, the wing scales are found to be highly textured, with a substantial fraction of domains exhibiting the <001> directions of the gyroid crystal aligned parallel to the scale surface normal. Both findings are needed to completely understand the photonic purpose of the single gyroid in gyroid-forming butterflies. More importantly, they show the level of control that morphogenesis exerts over secondary features of biological nanostructures, such as chirality or crystallographic texture, providing inspiration for biomimetic replication strategies for synthetic self-assembly mechanisms.
authors.affiliation: Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany;
authors.forename: Benjamin
authors.initials: B
authors.lastname: Winter
authors.affiliation: Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany;
authors.forename: Benjamin
authors.initials: B
authors.lastname: Butz
authors.affiliation: Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany;
authors.forename: Christel
authors.initials: C
authors.lastname: Dieker
authors.affiliation: School of Engineering and Information Technology, Mathematics & Statistics, Murdoch University, Murdoch, 6150 WA, Australia;
authors.forename: Gerd E
authors.initials: GE
authors.lastname: Schröder-Turk
authors.affiliation: Theoretische Physik, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Mecke
authors.affiliation: Institute of Micro- and Nanostructure Research and Center for Nanoanalysis and Electron Microscopy, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany; erdmann.spiecker@fau.de.
authors.forename: Erdmann
authors.initials: E
authors.lastname: Spiecker
mesh_terms: D000818:Animals; D002080:Butterflies / Q000033:anatomy & histology*; D017348:Microscopy, Electron, Scanning Transmission; D014921:Wings, Animal / Q000033:anatomy & histology* / Q000648:ultrastructure
keywords: butterfly wing scales; chirality; crystallographic texture; electron tomography; photonic crystal