Sub‐micrometer insights into the cytoskeletal dynamics and ultrastructural diversity of butterfly wing scales

Abstract

Background The color patterns that adorn lepidopteran wings are ideal for studying cell type diversity using a phenomics approach. Color patterns are made of chitinous scales that are each the product of a single precursor cell, offering a 2D system where phenotypic diversity can be studied cell by cell, both within and between species. Those scales reveal complex ultrastructures in the sub‐micrometer range that are often connected to a photonic function, including iridescent blues and greens, highly reflective whites, or light‐trapping blacks. Results We found that during scale development, Fascin immunostainings reveal punctate distributions consistent with a role in the control of actin patterning. We quantified the cytoskeleton regularity as well as its relationship to chitin deposition sites, and confirmed a role in the patterning of the ultrastructures of the adults scales. Then, in an attempt to characterize the range and variation in lepidopteran scale ultrastructures, we devised a high‐throughput method to quickly derive multiple morphological measurements from fluorescence images and scanning electron micrographs. We imaged a multicolor eyespot element from the butterfly Vanessa cardui (V. cardui), taking approximately 200 000 individual measurements from 1161 scales. Principal component analyses revealed that scale structural features cluster by color type, and detected the divergence of non‐reflective scales characterized by tighter cross‐rib distances and increased orderedness. Conclusion We developed descriptive methods that advance the potential of butterfly wing scales as a model system for studying how a single cell type can differentiate into a multifaceted spectrum of complex morphologies. Our data suggest that specific color scales undergo a tight regulation of their ultrastructures, and that this involves cytoskeletal dynamics during scale growth.

Developmental, cellular, and biochemical basis of transparency in the glasswing butterflyGreta oto

“…Recently, (32) showed that actin bundles play different roles in shaping scales and bristles in the mosquito Aedes aegypti, in which developing bristles contained symmetrically organized actin bundles, while actin bundle distribution in scales became more asymmetrically organized. Given that actin dynamics play a variety of roles in regulating the development of bristles and scales (6,7,32,33), we hypothesize that modifications in F-actin organization of scales in the transparent wing of G. oto are responsible in part for their narrow bristle-like and forked morphologies. In D.…”

“…Each scale can generate color through pigmentation via molecules that selectively absorb certain wavelengths of light, structural coloration, which results from light interacting with the physical nanoarchitecture of the scale, or a combination of both pigmentary and structural coloration (4,5). Cytoskeletal dynamics, including highly organized F-actin filaments during scale cell development, play essential roles in wing scale elongation and prefigure aspects of scale ultrastructure (6,7).…”

Actin bundles play a different role in shaping scales compared to bristles in the mosquito Aedes aegypti

“…Thus, bristle and hair generate actin filament bundles, but employ different strategies to assemble these into vastly different shapes 10 . There is little information on the role of actin bundles in shaping insect scales 11 , 12 . The first paper that described the cytoskeleton organization of scales was on the mill moth ( Ephestia kuenilla ), which revealed two main cytoplasmic elements: actin bundles (referred to in the text as 60 Å fibrils) and microtubules (MTs) 13 .…”

Non‐model organisms and unique approaches are needed for the future of evo‐devo

“…High resolution micro CT is applied to generate a 3‐D morphometric dataset documenting the developmental progression of the spiral in the little skate's intestine . The latest scanning electron microscopy technologies, which allow high resolution imaging of large areas, is combined with digital imaging and automated image analyses to study the ultrastructural diversity of butterfly wing scales . Confocal imaging is used to generate extremely detailed images of veiled chameleon embryos, proving the clearest view to date of early developmental stages in this species, in addition to documenting the progression of neural crest development .…”

“…5 The latest scanning electron microscopy technologies, which allow high resolution imaging of large areas, is combined with digital imaging and automated image analyses to study the ultrastructural diversity of butterfly wing scales. 12 Confocal imaging is used to generate extremely detailed images of veiled chameleon embryos, proving the clearest view to date of early developmental stages in this species, in addition to documenting the progression of neural crest development. 1 A full embryological staging series is presented for Xenopus tropicalis, which is an exciting new tool that will facilitate detailed comparative studies with Xenopus laevis.…”