D and V indicate the dorsal and ventral abdominal regions, respectively. In the transcriptomic data of O. A maximum likelihood phylogeny is shown, but neighbor-joining and Bayesian phylogenies exhibit substantially the same topologies.
Blue and gray shading indicates O. Accession numbers or annotation identities are shown in parentheses. The conserved histidine motif is boxed.
In this study, we found that mature males of O. Adult insects of O. The reflected spectral radiances were converted to relative reflectance by normalization with a white reflectance standard Spectralon USRS—, Labsphere. To elucidate the biochemical properties of dragonfly wax, surface wettability and solubility were examined.
Surface wettability was evaluated on the basis of the contact angle of water micro-droplet on the samples. Each sample was fixed on a glass substrate, and a micro-droplet of distilled water about 1. Wax solubility was analyzed by treating the dissected abdominal segment 5 with hexane or chloroform for 30 min. To identify the molecular composition of dragonfly wax, wax samples were extracted from living specimens with chloroform or hexane. The mass spectrometer was operated in the scan mode with 70 eV ionazation voltage as electron ionization. Histological examinations, wettability tests, and GC-MS analyses were conducted using different samples.
To confirm whether the very long-chain methyl ketones form the scale-like fine structures, 2-pentacosanone, the major component of dragonfly wax was chemically synthesized from 1-tetracosanol via 1-tetracosanal and 2-pentacosanol. Pyridinium chlorochromate PCC, 1. The mixture was filtered through Celite and washed with diethyl ether. The combined filtrate and washings were filtered through florisil 15 g , washed with diethyl ether mL and concentrated in vacuo.
The residue was chromatographed on silica gel 15 g and concentrated in vacuo to give a white solid of 1-tetracosanal mg, 0. A solution of 1-tetracosanal mg, 0. The organic layer was dried with anhydrous magnesium sulfate and concentrated in vacuo. PCC mg, 1. The residue was recrystallized from hexane to give a white solid of 2-pentacosanone mg, 0.
Each sample was dissolved in CDCl 3 and 1 H spectrum was acquired. Biomimetic wax surfaces were composed of micro crystals of 2-pentacosanone. Heated 2-pentacosanone was recrystallized on gold-coated glass plates by different cooling processes: 1 continuous dropping of micro fused material of 1. To investigate the genes involved in wax production, total RNA samples were extracted from the freshly dissected abdomens of O.
RNA sequencing was performed as described previously Futahashi et al. The raw reads were subjected to de novo assembly using the Trinity program Grabherr et al. Bootstrap values for neighbor-joining and maximum likelihood phylogenies were obtained by resampling. In the interests of transparency, eLife includes the editorial decision letter and accompanying author responses. A lightly edited version of the letter sent to the authors after peer review is shown, indicating the most substantive concerns; minor comments are not usually included.
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Thank you for submitting your article "Molecular basis of UV-reflective surface wax in dragonflies" for consideration by eLife. Your article has been reviewed by two peer reviewers, and the evaluation has been overseen by a Reviewing Editor and Patricia Wittkopp as the Senior Editor.
Molecular basis of wax-based color change and UV reflection in dragonflies | eLife
The following individual involved in review of your submission has agreed to reveal his identity: Beatriz Willink Reviewer 2. The reviewers have discussed the reviews with one another and the Reviewing Editor has drafted this decision to help you prepare a revised submission.
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This is an integrative and complete study examining the structure, biochemical composition and proximate molecular mechanisms for the production of UV-reflective wax in dragonflies. In this well-written manuscript, the authors inquire into substantial gaps in our understanding of the structural coloration of insects and provide insights of relevance across fields, from animal physiology, evolution and ecology to material science.
The study focuses on a common dragonfly species which produces sexually-dimorphic wax recovering different parts of the abdominal cuticle. The authors examine the reflective properties of this substance, its microscopic structure, chemical composition and other properties, to then identify key genes associated with its production. These results are discussed with reference to the ecological conditions that might have favored the evolution of such wax production, and its diversity across a few related species is also briefly touched upon. As such the manuscript should be of interest to entomologist, ecologist as well as physicist and material scientists working on biomimetic and bio-inspired soft matter properties.
Whereas we appreciate that UV reflectance is the focus of your manuscript the wax may increase the general visibility, so beyond the UV spectrum too. An alternative interpretation of the photographs and the reflectance spectra is that the function of the wax is to increase the visibility more generally, by enhanced scattering, in a wide wavelength range, from the far-UV up to the infrared, i. It would be great if this perspective can be considered and discussed in the Introduction and Discussion.
Whereas we agree that a focus on UV light makes sense from the perspective that not all animals use the UV spectrum, and it is thus of interest when the UV spectrum is used, the discussion becomes stronger when the vision of dragonflies is considered beyond the UV spectrum initially.
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This also provides context to clarify any limitations in the interpretation of the data. So, framing the differences carefully with help the reader interprets the findings more accurately. Further, the value of the paper remains unequivocal when the message is broadened to include that males crucially increase their general visibility, in the UV as well as in the blue and green wavelength ranges, by secreting a strongly scattering wax layer. To better reflect this general relevance, we also recommend making the title more inclusive in case you agree.
Otherwise, we would like you to carefully consider these revisions in the Discussion and conclusion as well as in the Abstract as a baseline. Here, potential roles of UV reflectance for physical protection and communication are hinted, but for most readers it might not be immediately clear what can we gain from understanding how UV-reflectance is attained in this particular group of insects.
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Perhaps the authors could elaborate on what they refer to as "other ecological aspects" for which UV reflectance might important, whether in dragonflies or other animals. They could also address how understanding the chemical composition and structure of this wax can be useful to understand and replicate its functions, or more generally, to understand the diversity of mechanisms by which similar ecological functions can be attained in different organisms. For example, the objective of the phylogenetic analyses described in the Materials and methods was not clear to me until I had a look at the supplementary figures.
We also could not find the legends for the supplementary figures, so several of their details were not entirely clear. Similarly, it should be clarified what is the aim of the wettability assay and how results in Figure 4A-D are interpreted.
Abstract: "Many animals change their body color for visual signaling and environmental adaptation. Some dragonflies show wax-based color change and ultraviolet UV reflection, but biochemical properties underlying the phenomena are totally unknown. Here we investigated the UV-reflective abdominal wax of dragonflies…". Introduction: "Many organisms exhibit a variety of body color patterns for visual communication and environmental adaptation.
UV reflection has been reported from numerous organisms, which may be important not only for protection against UV-induced damage but also for visual signaling…". Results and Discussion: "We compared wax-based body color change and UV reflection patterns of adult insects of O. Conclusion and Perspective: "In this study, we found that mature males of O. Because peak wavelengths of the shortest and longest wavelength receptors remain unknown in O. Several studies have reported that a pruinose wax layer on the body surface accounts for UV reflection patterns in dragonflies Silberglied, ; Robertson, ; Hilton, ; Gorb, ; Harris et al.
We added the initial sentence explaining the aim of the described analyses in the Materials and methods as follows:. We are sorry for forgetting the legends of the supplementary figures at the previous submission. We have now included these legends. The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication. This article is distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use and redistribution provided that the original author and source are credited.
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