Modulation of host lipid metabolism by virus infection leads to exoskeleton damage in shrimp.

The arthropod exoskeleton provides protection and support and is vital for survival and adaption. The integrity and mechanical properties of the exoskeleton are often impaired after pathogenic infection; however, the detailed mechanism by which infection affects the exoskeleton remains largely unknown. Here, we report that the damage to the shrimp exoskeleton is caused by modulation of host lipid profiles after infection with white spot syndrome virus (WSSV). WSSV infection disrupts the mechanical performance of the exoskeleton by inducing the expression of a chitinase (Chi2) in the sub-cuticle epidermis and decreasing the cuticle chitin content. The induction of Chi2 expression is mediated by a nuclear receptor that can be activated by certain enriched long-chain saturated fatty acids after infection. The damage to the exoskeleton, an aftereffect of the induction of host lipogenesis by WSSV, significantly impairs the motor ability of shrimp. Blocking the WSSV-caused lipogenesis restored the mechanical performance of the cuticle and improved the motor ability of infected shrimp. Therefore, this study reveals a mechanism by which WSSV infection modulates shrimp internal metabolism resulting in phenotypic impairment, and provides new insights into the interactions between the arthropod host and virus.

The small GTPase Cdc42 regulates shell field morphogenesis in a gastropod mollusk.

In most mollusks (conchiferans), the early tissue responsible for shell development, namely, the shell field, shows a common process of invagination during morphogenesis. Moreover, lines of evidence indicated that shell field invagination is not an independent event, but an integrated output reflecting the overall state of shell field morphogenesis. Nevertheless, the underlying mechanisms of this conserved process remain largely unknown. We previously found that actomyosin networks (regularly organized filamentous actin (F-actin) and myosin) may play essential roles in this process by revealing the evident aggregation of F-actin in the invaginated region and demonstrating that nonmuscle myosin II (NM II) is required for invagination in the gastropod Lottia peitaihoensis (= Lottia goshimai). Here, we investigated the roles of the Rho family of small GTPases (RhoA, Rac1, and Cdc42) to explore the upstream regulators of actomyosin networks. Functional assays using small molecule inhibitors suggested that Cdc42 modulates key events of shell field morphogenesis, including invagination and cell rearrangements, while the roles of RhoA and Rac1 may be nonspecific or negligible. Further investigations revealed that the Cdc42 protein was concentrated on the apical side of shell field cells and colocalized with F-actin aggregation. The aggregation of these two molecules could be prevented by treatment with Cdc42 inhibitors. These findings suggest a possible regulatory cascade of shell field morphogenesis in which Cdc42 recruits F-actin (actomyosin networks) on the apical side of shell field cells, which then generates resultant mechanical forces that mediate correct shell field morphogenesis (cell shape changes, invagination and cell rearrangement). Our results emphasize the roles of the cytoskeleton in early shell development and provide new insights into molluscan shell evolution.

Natural photoredox catalysts promote light-driven lytic polysaccharide monooxygenase reactions and enzymatic turnover of biomass.

Lytic polysaccharide monooxygenases (LPMOs) catalyze oxidative cleavage of crystalline polysaccharides such as cellulose and chitin and are important for biomass conversion in the biosphere as well as in biorefineries. The target polysaccharides of LPMOs naturally occur in copolymeric structures such as plant cell walls and insect cuticles that are rich in phenolic compounds, which contribute rigidity and stiffness to these materials. Since these phenolics may be photoactive and since LPMO action depends on reducing equivalents, we hypothesized that LPMOs may enable light-driven biomass conversion. Here, we show that redox compounds naturally present in shed insect exoskeletons enable harvesting of light energy to drive LPMO reactions and thus biomass conversion. The primary underlying mechanism is that irradiation of exoskeletons with visible light leads to the generation of H2O2, which fuels LPMO peroxygenase reactions. Experiments with a cellulose model substrate show that the impact of light depends on both light and exoskeleton dosage and that light-driven LPMO activity is inhibited by a competing H2O2-consuming enzyme. Degradation experiments with the chitin-rich exoskeletons themselves show that solubilization of chitin by a chitin-active LPMO is promoted by light. The fact that LPMO reactions, and likely reactions catalyzed by other biomass-converting redox enzymes, are fueled by light-driven abiotic reactions in nature provides an enzyme-based explanation for the known impact of visible light on biomass conversion.

Diversification of von Willebrand Factor A and Chitin-Binding Domains in Pif/BMSPs Among Mollusks.

Pif is a shell matrix protein (SMP) identified in the nacreous layer of Pinctada fucata (Pfu) comprised two proteins, Pif97 and Pif 80. Pif97 contains a von Willebrand factor A (VWA) and chitin-binding domains, whereas Pif80 can bind calcium carbonate crystals. The VWA domain is conserved in the SMPs of various mollusk species; however, their phylogenetic relationship remains obscure. Furthermore, although the VWA domain participates in protein-protein interactions, its role in shell formation has not been established. Accordingly, in the current study, we investigate the phylogenetic relationship between PfuPif and other VWA domain-containing proteins in major mollusk species. The shell-related proteins containing VWA domains formed a large clade (the Pif/BMSP family) and were classified into eight subfamilies with unique sequential features, expression patterns, and taxa diversity. Furthermore, a pull-down assay using recombinant proteins containing the VWA domain of PfuPif 97 revealed that the VWA domain interacts with five nacreous layer-related SMPs of P. fucata, including Pif 80 and nacrein. Collectively, these results suggest that the VWA domain is important in the formation of organic complexes and participates in shell mineralisation.

Freshwater Mussel (Unio pictorum) Shells Reveal Hydrological and Environmental Change From 1300 BC to the Present Day.

Preserved biological communities can provide baseline data about the historical ecosystems and environmental conditions that preceded recent anthropogenic alteration. Freshwater mussel shells show particularly good preservation, and the shell assemblages commonly found during archaeological excavations can offer insights into past ecosystems. We studied assemblages of Unio pictorum mussel shells from palaeochannel silts associated with the Late Bronze Age site of Must Farm in eastern England (c. 850 BC), on an ancient tributary of the modern-day River Nene. We compared archaeological shells from two sediment horizons (broadly 1300-700 BC) to live individuals collected from two analogous sites on the present-day Nene. Size and growth rate, interannual growth variability and stable isotope (δ18O and δ13C) composition were compared between the populations. Size and the von Bertalanffy growth parameter L∞ differed among all four populations. Mean lengths and L∞ were higher in the two modern populations (mean lengths 77.3 ± SE 0.8 and 73.8 ± SE 1.1 mm, L∞ 91.8 ± 5.4 and 79.0 ± 8.1 mm) than the ancient populations (mean lengths 58.1 ± SE 1.6 mm and 68.4 ± SE 0.9 mm; L∞ 71.5 ± 16.9 and 76.8 ± 6.2 mm). Modern individuals also showed greater variation in age-corrected year-to-year growth. δ13C was lower in modern shells (-11.8‰ for modern shells, -9.03‰ and -9.02‰ for ancient shell populations), potentially reflecting altered hydrological and nutrient regimes. δ18O and δ13C were positively correlated for all but one sampled ancient shell, but not modern shells. These results reflect changes in local environmental conditions, particularly the transition from a shallow, slow-flowing tributary to a deeper, canalised river with faster flow, as well as effects of anthropogenic nutrient enrichment. The findings demonstrate the importance of long-term data in studying anthropogenic ecosystem alteration and avoiding shifting baseline syndrome in conservation planning.

The impact of aragonite saturation variability on shelled pteropods: An attribution study in the California Current System.

Observations from the California Current System (CalCS) indicate that the long-term trend in ocean acidification (OA) and the naturally occurring corrosive conditions for the CaCO3 mineral aragonite (saturation state Ω < 1) have a damaging effect on shelled pteropods, a keystone group of calcifying organisms in the CalCS. Concern is heightened by recent findings suggesting that shell formation and developmental progress are already impacted when Ω falls below 1.5. Here, we quantify the impact of low Ω conditions on pteropods using an individual-based model (IBM) with life-stage-specific mortality, growth, and behavior in a high-resolution regional hindcast simulation of the CalCS between 1984 and 2019. Special attention is paid to attributing this impact to different processes that lead to such low Ω conditions, namely natural variability, long-term trend, and extreme events. We find that much of the observed damage in the CalCS, and specifically >70% of the shell CaCO3 loss, is due to the pteropods' exposure to naturally occurring low Ω conditions as a result of their diel vertical migration (DVM). Over the hindcast period, their exposure to damaging waters (Ω < 1.5) increases from 9% to 49%, doubling their shell CaCO3 loss, and increasing their mortality by ~40%. Most of this increased exposure is due to the shoaling of low Ω waters driven by the long-term trend in OA. Extreme OA events amplify this increase by ~40%. Our approach can quantify the health of pteropod populations under shifting environmental conditions, and attribute changes in fitness or population structure to changes in the stressor landscape across hierarchical time scales.

Continuous variation in the shell colour of the snail Cepaea nemoralis is associated with the colour locus of the supergene.

While the shell of the land snail Cepaea nemoralis is typically classed as yellow, pink, or brown, the reality is that colour variation is continuously distributed. To further understand the origin of the continuous variation, we used crosses of C. nemoralis to compare quantitative measures of the colour with the inferred genotype of the underlying supergene locus. We also used a recently developed linkage map to find quantitative trait loci that may influence colour. The results show that the colour locus of the supergene-at around 31.385 cM on linkage group 11-is involved in determining the quantitative chromatic differences that are perceptible to human vision. We also found some evidence that variation within colour classes may be due to allelic variation at or around the supergene. There are likely other unlinked loci involved in determining colour within classes, but confirmation will require greater statistical power. Although not investigated here, environmental factors, including diet, may also impact upon variation within colour types.

Structural and Functional Analysis of the Amorphous Calcium Carbonate-Binding Protein Paramyosin in the Shell of the Pearl Oyster, Pinctada fucata.

Amorphous calcium carbonate (ACC) is an important precursor phase for the formation of aragonite crystals in the shells of Pinctada fucata. To identify the ACC-binding protein in the inner aragonite layer of the shell, extracts from the shell were used in the ACC-binding experiments. Semiquantitative analyses using liquid chromatography-mass spectrometry revealed that paramyosin was strongly associated with ACC in the shell. We discovered that paramyosin, a major component of the adductor muscle, was included in the myostracum, which is the microstructure of the shell attached to the adductor muscle. Purified paramyosin accumulates calcium carbonate and induces the prism structure of aragonite crystals, which is related to the morphology of prism aragonite crystals in the myostracum. Nuclear magnetic resonance measurements revealed that the Glu-rich region was bound to ACC. Activity of the Glu-rich region was stronger than that of the Asp-rich region. These results suggest that paramyosin in the adductor muscle is involved in the formation of aragonite prisms in the myostracum.

Preserved appendages in a Silurian binodicope: implications for the evolutionary history of ostracod crustaceans.

Ostracod crustaceans originated at least 500 Ma ago. Their tiny bivalved shells represent the most species-abundant fossil arthropods, and ostracods are omnipresent in a wide array of freshwater and marine environments today and in the past. Derima paparme gen. et sp. nov. from the Herefordshire Silurian Lagerstätte (~430 Ma) in the Welsh Borderland, UK, is one of only a handful of exceptionally preserved ostracods (with soft parts as well as the shell) known from the Palaeozoic. A male specimen provides the first evidence of the appendages of Binodicopina, a major group of Palaeozoic ostracods comprising some 135 Ordovician to Permian genera. The appendage morphology of D. paparme, but not its shell, indicates that binodicopes belong to Podocopa. The discovery that the soft-part morphology of binodicopes allies them with podocopes affirms that using the shell alone is an unreliable basis for classifying certain fossil ostracods, and knowledge of soft-part morphology is critical for the task. Current assignment of many fossil ostracods to higher taxa, and therefore the evolutionary history of the group, may require reconsideration.

A novel exoskeletal-derived C-type lectin facilitates phagocytosis of hemocytes in the oriental river prawn Macrobrachium nipponense.

C-type lectins (CTLs) execute critical functions in multiple immune responses of crustaceans as a member of pattern recognition receptors (PRRs) family. In this study, a novel CTL was identified from the exoskeleton of the oriental river prawn Macrobrachium nipponense (MnLec3). The full-length cDNA of MnLec3 was 1150 bp with an open reading frame of 723 bp, encoding 240 amino acids. MnLec3 protein contained a signal peptide and one single carbohydrate-recognition domain (CRD). MnLec3 transcripts were widely distributed at the exoskeleton all over the body. Significant up-regulation of MnLec3 in exoskeleton after Aeromonas hydrophila challenged suggested the involvement of MnLec3 as well as the possible function of the exoskeleton in immune response. In vitro tests with recombinant MnLec3 protein (rMnLec3) manifested that it had polysaccharide binding activity, a wide spectrum of bacterial binding activity and agglutination activity only for tested Gram-negative bacteria (Escherichia coli, Vibrio anguillarum and A. hydrophila). Moreover, rMnLec3 significantly promoted phagocytic ability of hemocytes against A. hydrophila in vivo. What's more, MnLec3 interference remarkably impaired the survivability of the prawns when infected with A. hydrophila. Collectively, these results ascertained that MnLec3 derived from exoskeleton took an essential part in immune defense of the prawns against invading bacteria as a PRR.

Controls on the Barium and Strontium Isotopic Records of Water Chemistry Preserved in Freshwater Bivalve Shells.

Biogenic carbonates, including bivalve shells, record past environmental conditions, but their interpretation requires understanding environmental and biological factors that affect trace metal uptake. We examined stable barium (δ138Ba) and radiogenic strontium (87Sr/86Sr) isotope ratios in the aragonite shells of four native freshwater mussel species and two invasive species in five streams and assessed the effects of species identity, growth rate, and river water chemistry on shell isotopic composition. Shells were robust proxies for Sr, accurately reflecting 87Sr/86Sr ratios of river water, regardless of species or growth rate. In contrast, shell δ138Ba values, apart from invasive Corbicula fluminea, departed widely from those of river water and varied according to species and growth rate. Apparent fractionation between river water and the shell (Δ138Bashell-water) reached -0.86‰, the greatest offset observed for carbonate minerals. The shell deposited during slow growth periods was more enriched in lighter Ba isotopes than the rapidly deposited shell; thus, this phenomenon cannot be explained by aragonite precipitation kinetics. Instead, biological ion transport processes linked to growth rate may be largely responsible for Ba isotope variation. Our results provide information necessary to interpret water chemistry records preserved in shells and provide insights into biomineralization processes and bivalve biochemistry.

Hierarchical diversity partitioning of microscopic epibiont community on intertidal molluscan shells and inert surfaces over three geographic regions in Japan.

Microscopic epibionts on molluscan shells are a component of the biodiversity of intertidal coastal areas. Because molluscan shells are discrete habitats for the epibiont community, and the molluscan basibionts belong to the local community, epibiont diversity can be evaluated hierarchically by basibiont categories including species. To evaluate the structure of epibiont diversity and effects of taxonomic resolution on the evaluation, epibionts on molluscan shells and inert surfaces were investigated at three geographically distant sites in Japan. In total, 94 species-level taxonomic units of epibionts were obtained from 31 basibiont molluscan species and inert surfaces (plastics and rock chips). The density and the species richness at the site of the lowest latitude were significantly lower than those at the other sites. The epibiont community differed between the three sites, although the major portion of the epibionts were diatoms. Between-site diversity contributed most of the total diversity of the species richness and Simpson diversity in the five levels of the hierarchical partitioning: sample (individual basibiont), basibiont species (molluscan species), surface group (bivalves, chitons + limpets, and globose gastropods), site, and the total. The taxonomic resolution did not markedly affect the variability of communities between the three sites, although the taxon richness was reduced to 51 in the genus-level analysis. The lower taxonomic resolution (genus level); however, increased the contribution of the within-sample and decreased the contribution of ß diversities at the higher hierarchies, leading to a possible overestimation of biotic homogenization between the communities.

The fungus Aphanoascella galapagosensis affects bacterial diversity of Galapagos giant tortoise carapaces.

AIMS: This study aimed to describe the bacterial microbiome associated with the carapace of three species of Galapagos giant tortoises (Chelonoidis porteri, Chelonoidis donfaustoi, and Chelonoidis vandenburghi) and determine the potential effect of the whitish lesions caused by the fungus Aphanoascella galapagosensis. METHODS AND RESULTS: We used Oxford Nanopore's MinION to evaluate the external bacterial microbiome associated with the carapaces from the aforementioned species. Taxonomic assignment was carried out by Bugseq and the bacterial communities were compared between carapaces with and without lesions using a NMDS with Bray-Curtis as the dissimilarity index. We found four genera of bacteria that were ubiquitous throughout all individuals, suggesting the presence of shared taxa. The results also displayed a significant difference in the microbiome between carapaces with and without lesions, and for species-carapace interaction, but not among species. CONCLUSIONS: This study establishes a baseline of the bacterial diversity of the carapace within three Galapagos giant tortoise species, showcasing the presence of a distinctive microbial community. Furthermore, our findings suggest a significant influence of the fungus Aphanoascella galapagosensis on the bacterial populations inhabiting the carapace of these reptiles.

Chitin extraction from crab shells and synthesis of chitin @metakaolin composite for efficient amputation of Cr (VI) ions.

The present research study combines chitin from shrimp waste with the oxide-rich metakaolin. Metakaolin is a blend of mixed oxides rich in silica and alumina with good adsorbent properties. The chitin@metakaolin (CHt@M.K.) composite was synthesized and characterized using FTIR, SEM, TGA, XRD and XPS techniques. Cr(VI) removal studies were compared for chitin and CHt@M.K. through adsorption. It was found that the adsorption capacity of CHt@M.K. is 278.88 mg/g, almost double that of chitin, at pH 5.0 in just 120 min of adsorption. Isotherm models like Langmuir, Freundlich, Temkin and Dubinin-Radushkevich were investigated to comprehend the adsorption process. It was revealed that Langmuir adsorption isotherm is most suitable to elucidate Cr(VI) adsorption on CHt@M.K. The adsorption kinetics indicate that pseudo first order was followed, indicating that the physisorption was the process that limited the sorption process rate. The positive enthalpy change (20.23 kJ/mol) and positive entropy change (0.083 kJ/mol K) showed that the adsorption process was endothermic and more random at the solid-liquid interface. The negative free energy change over entire temperature range was an indicator of spontaneity of the process. Apart from all these, the non-covalent interactions between Cr(VI) and composite were explained by quantum calculations based models.

Resourceful application and mechanism of oyster shell-microalgae synergistic system：Sustainable treatment of harsh low carbon nitrogen ratio actual wastewater.

Microalgal technology holds great promise for both low C/N wastewater treatment and resource recovery simultaneously. Nevertheless, the advancement of microalgal technology is hindered by its reduced nitrogen removal efficiency in low C/N ratio wastewater. In this work, microalgae and waste oyster shells were combined to achieve a total inorganic nitrogen removal efficiency of 93.85% at a rate of 2.05 mg L-1 h-1 in low C/N wastewater. Notably, over four cycles of oyster shell reuse, the reactor achieved an average 85% ammonia nitrogen removal extent, with a wastewater treatment cost of only $0.092/ton. Moreover, microbial community analysis during the reuse of oyster shells revealed the critical importance of timely replacement in inhibiting the growth of non-functional bacteria (Poterioochromonas_malhamensi). The work demonstrated that the oyster shell - microalgae system provides a time- and cost-saving, environmental approach for the resourceful treatment of harsh low C/N wastewater.

Azithromycin removal using pine bark, oak ash and mussel shell.

Adsorption is considered an interesting option for removing antibiotics from the environment because of its simple design, low cost, and potential efficiency. In this work we evaluated three by-products (pine bark, oak ash, and mussel shell) as bio-adsorbents for the antibiotic azithromycin (AZM). Furthermore, they were added at doses of 48 t ha-1 to four different soils, then comparing AZM removal for soils with and without bio-adsorbents. Batch-type experiments were used, adding AZM concentrations between 2.5 and 600 µmol L-1 to the different bio-adsorbents and soil + bio-adsorbent mixtures. Regarding the bio-adsorbents, oak ash showed the best adsorption scores (9600 µmol kg-1, meaning >80% retention), followed by pine bark (8280 µmol kg-1, 69%) and mussel shell (between 3000 and 6000 µmol kg-1, 25-50% retention). Adsorption data were adjusted to different models (Linear, Freundlich and Langmuir), showing that just mussel shell presented an acceptable fitting to the Freundlich equation, while pine bark and oak ash did not present a good adjustment to any of the three models. Regarding desorption, the values were always below the detection limit, indicating a rather irreversible adsorption of AZM onto these three by-products. Furthermore, the results showed that when the lowest concentrations of AZM were added to the not amended soils they adsorbed 100% of the antibiotic, whereas when the highest concentrations of AZM were spread, the adsorption decreased to 55%. However, when any of the three bio-adsorbents was added to the soils, AZM adsorption reached 100% for all the antibiotic concentrations used. Desorption was null in all cases for both soils with and without bio-adsorbents. These results, corresponding to an investigation carried out for the first time for the antibiotic AZM, can be seen as relevant in the search of low-cost alternative treatments to face environmental pollution caused by this emerging contaminant.

Optimization of Enzymatic Deproteination of Northern Shrimp (Pandalus borealis) Shell Chitin Using Commercial Proteases.

Shrimp shells are a key source of chitin, commonly extracted through chemical methods, which may cause minor molecular damage. Nowadays, there is great interest in achieving close to zero protein content in crude chitin in order to use it for high-end markets. Therefore, this study optimized the enzymatic deproteination using two commercial proteases (SEB Pro FL100 and Sea-B Zyme L200) for effective and fast removal of residual protein from Northern shrimp (Pandalus borealis) shell chitin for the first time. The protein content was determined using both the Kjeldahl method and amino acid analysis using gas chromatography-mass spectrometry (GC-MS). The performance of papain (Sea B Zyme L200) was superior to fungal protease (SEB Pro FL100) for this application, and it achieved residual protein content of 2.01%, while the calculated optimum for the latter enzyme was 6.18%. A model was developed using 24 factorial design, and it was predicted that the lowest residual protein content using fungal protease and papain could be achieved at the following conditions: a pH of 4.2 and 7, and an enzyme concentration of 4 and 1.5%, respectively. Thus, the low-protein content obtained using enzymatic deproteination could be an alternative approach to the traditional methods, indicating their potential to produce premium-quality chitin.

High Degree of Polymerization of Chitin Oligosaccharides Produced from Shrimp Shell Waste by Enrichment Microbiota Using Two-Stage Temperature-Controlled Technique of Inducing Enzyme Production and Metagenomic Analysis of Microbiota Succession.

The direct enzymatic conversion of untreated waste shrimp and crab shells has been a key problem that plagues the large-scale utilization of chitin biological resources. The microorganisms in soil samples were enriched in two stages with powdered chitin (CP) and shrimp shell powder (SSP) as substrates. The enrichment microbiota XHQ10 with SSP degradation ability was obtained. The activities of chitinase and lytic polysaccharide monooxygenase of XHQ10 were 1.46 and 54.62 U/mL. Metagenomic analysis showed that Chitinolyticbacter meiyuanensis, Chitiniphilus shinanonensis, and Chitinimonas koreensis, with excellent chitin degradation performance, were highly enriched in XHQ10. Chitin oligosaccharides (CHOSs) are produced by XHQ10 through enzyme induction and two-stage temperature control technology, which contains CHOSs with a degree of polymerization (DP) more significant than ten and has excellent antioxidant activity. This work is the first study on the direct enzymatic preparation of CHOSs from SSP using enrichment microbiota, which provides a new path for the large-scale utilization of chitin bioresources.

Microstructural design for mechanical-optical multifunctionality in the exoskeleton of the flower beetle Torynorrhina flammea.

Biological systems have a remarkable capability of synthesizing multifunctional materials that are adapted for specific physiological and ecological needs. When exploring structure-function relationships related to multifunctionality in nature, it can be a challenging task to address performance synergies, trade-offs, and the relative importance of different functions in biological materials, which, in turn, can hinder our ability to successfully develop their synthetic bioinspired counterparts. Here, we investigate such relationships between the mechanical and optical properties in a multifunctional biological material found in the highly protective yet conspicuously colored exoskeleton of the flower beetle, Torynorrhina flammea Combining experimental, computational, and theoretical approaches, we demonstrate that a micropillar-reinforced photonic multilayer in the beetle's exoskeleton simultaneously enhances mechanical robustness and optical appearance, giving rise to optical damage tolerance. Compared with plain multilayer structures, stiffer vertical micropillars increase stiffness and elastic recovery, restrain the formation of shear bands, and enhance delamination resistance. The micropillars also scatter the reflected light at larger polar angles, enhancing the first optical diffraction order, which makes the reflected color visible from a wider range of viewing angles. The synergistic effect of the improved angular reflectivity and damage localization capability contributes to the optical damage tolerance. Our systematic structural analysis of T. flammea's different color polymorphs and parametric optical and mechanical modeling further suggest that the beetle's microarchitecture is optimized toward maximizing the first-order optical diffraction rather than its mechanical stiffness. These findings shed light on material-level design strategies utilized in biological systems for achieving multifunctionality and could thus inform bioinspired material innovations.

A modern scleractinian coral with a two-component calcite-aragonite skeleton.

One of the most conserved traits in the evolution of biomineralizing organisms is the taxon-specific selection of skeletal minerals. All modern scleractinian corals are thought to produce skeletons exclusively of the calcium-carbonate polymorph aragonite. Despite strong fluctuations in ocean chemistry (notably the Mg/Ca ratio), this feature is believed to be conserved throughout the coral fossil record, spanning more than 240 million years. Only one example, the Cretaceous scleractinian coral Coelosmilia (ca. 70 to 65 Ma), is thought to have produced a calcitic skeleton. Here, we report that the modern asymbiotic scleractinian coral Paraconotrochus antarcticus living in the Southern Ocean forms a two-component carbonate skeleton, with an inner structure made of high-Mg calcite and an outer structure composed of aragonite. P. antarcticus and Cretaceous Coelosmilia skeletons share a unique microstructure indicating a close phylogenetic relationship, consistent with the early divergence of P. antarcticus within the Vacatina (i.e., Robusta) clade, estimated to have occurred in the Mesozoic (ca. 116 Mya). Scleractinian corals thus join the group of marine organisms capable of forming bimineralic structures, which requires a highly controlled biomineralization mechanism; this capability dates back at least 100 My. Due to its relatively prolonged isolation, the Southern Ocean stands out as a repository for extant marine organisms with ancient traits.