Pigment cell distribution in a rapid colour changing amphibian (Litoria wilcoxii)

Mechanical and thermal responsive chiral photonic cellulose hydrogels for dynamic anti-counterfeiting and optical skin

Dynamic responsive structural colored materials have drawn increased consideration in a wide range of applications, such as colorimetric sensors and high-safety tags. However, the sophisticated interactions among the individual responsive parts restrict the advanced design of multimodal responsive photonic materials. Inspired by stimuli-responsive color change in chameleon skin, a simple and effective photo-crosslinking strategy is proposed to construct hydroxypropyl cellulose (HPC) based hydrogels with multiple responsive structured colors. By controlling UV exposure time, the structural color of HPC hydrogels can be effectively controlled in a full-color spectrum. At the same time, HPC hydrogels showcase temperature and mechanical dual-responsive structural colors. In particular, the microstructure of HPC hydrogels undergoes a transition from the chiral nematic phase to the nematic phase under the action of external stretching, leading to a significant reflection of circularly polarized light (CPL) to linearly polarized light (LPL). Given the diverse responsiveness exhibited by HPC hydrogels and their unique structural transition properties under external forces, we have explored their potential applications as dynamic anti-counterfeiting labels and optical skins. This work reveals the great possibility of using structural colored cellulose hydrogels in multi-sensing and optical displays, opening up a new path for the exploration of next-generation flexible photonic devices.

Acclimation and recovery dynamics of behavioral and coloration responses of a common fish (Squalius cephalus) to paracetamol exposure

Freshwater ecosystems are increasingly exposed to pharmaceutical contamination, impacting non-target species. Concentrations can vary over time and location, allowing for potential acclimation or recovery effects. Additionally, parasites might interfere with the absorption and adverse outcomes pathways of pollutants. We examined the combined effects of paracetamol and parasite on the behavior and coloration of the European chub (Squalius cephalus), a ubiquitous fish species, from natural populations. Fish were exposed in mesocosms to acute doses of paracetamol (16 μg g-1 once a day over two days), followed by lower doses during a long-term exposure (1.6 μg g-1 once a week over three weeks), followed by a three-week recovery phase. Acute exposure induced marginal decreases in behavioral activity, and changes in dorsal brightness, hue and UV luminance. Interestingly, the long-term phase alone did not yield notable results on behavior and coloration. However, some effects of the acute exposure persisted during the long-term phase, highlighting that the expression of biological responses may be delayed in relation to past high exposure. Parasitism did not attenuate acute impacts, suggesting parasites may not help mitigate effects of paracetamol on behavior and coloration, but alone increased activity levels slightly. No effects of pollutant exposure, either of the acute or long-term phase, were observed after a recovery phase, indicating ability for recovery dynamics. Overall, our findings emphasize that pollutants effects can be highly transient, with rapid recovery when pollutant exposure ceased. Considering different exposure phases is crucial when assessing the ecological consequences of environmental contaminants.

First Bioprospecting Study of Skin Host-Defense Peptides in Odontophrynus americanus

The adaptation of amphibians to diverse environments is closely related to the characteristics of their skin. The complex glandular system of frog skin plays a pivotal role in enabling these animals to thrive in both aquatic and terrestrial habitats and consists of crucial functions such as respiration and water balance as well as serving as a defensive barrier due to the secretion of bioactive compounds. We herein report the first investigation on the skin secretion of Odontophrynus americanus, as a potential source of bioactive peptides and also as an indicator of its evolutionary adaptations to changing environments. Americanin-1 was isolated and identified as a neutral peptide exhibiting moderate antibacterial activity against E. coli. Its amphipathic sequence including 19 amino acids and showing a propensity for α-helix structure is discussed. Comparisons of the histomorphology of the skin of O. americanus with other previously documented species within the same genus revealed distinctive features in the Patagonian specimen, differing from conspecifics from other Argentine provinces. The presence of the Eberth-Katschenko layer, a prevalence of iridophores, and the existence of glycoconjugates in its serous glands suggest that the integument is adapted to retain skin moisture. This adaptation is consistent with the prevailing aridity of its native habitat.

It's not easy being green: Comparing typical skin colouration among amphibians with colour abnormalities associated with chromatophore deficits

Amphibians can obtain their colour from a combination of several different pigment and light reflecting cell types called chromatophores, with defects in one or several of the cells leading to colour abnormalities. There is a need for better recording of colour abnormalities within wild amphibian populations, as this may provide baseline data that can be used to determine changes in environmental conditions and population dynamics, such as inbreeding. In this study, we provide records of several types of chromatophore deficiencies, including those involving iridophores, xanthophores and melanophores, among two Australian tree frog species; the green and golden bell frog, Litoria aurea, and the eastern dwarf tree frog, L. fallax. We explore these colour abnormalities in terms of the chromatophores that have likely been affected and associated with their expression, in combination with typical colour phenotypes, colour variations and colour changes for these species. We intend for our photographs to be used as a visual guide that addresses the need for more accessible information regarding the physical manifestation of different chromatophore defects among amphibians.

Neurotransmitter norepinephrine regulates chromatosomes aggregation and the formation of blotches in coral trout Plectropomus leopardus

Color changes and pattern formations can represent strategies of the utmost importance for the survival of individuals or of species. Previous studies have associated capture with the formation of blotches (areas with light color) of coral trout, but the regulatory mechanisms link the two are lacking. Here, we report that capture induced blotches formation within 4-5 seconds. The blotches disappeared after anesthesia dispersed the pigment cells and reappeared after electrical stimulation. Subsequently, combining immunofluorescence, transmission electron microscopy and chemical sympathectomy, we found blotches formation results from activation of catecholaminergic neurons below the pigment layer. Finally, the in vitro incubation and intraperitoneal injection of norepinephrine (NE) induced aggregation of chromatosomes and lightening of body color, respectively, suggesting that NE, a neurotransmitter released by catecholaminergic nerves, mediates blotches formation. Our results demonstrate that acute stress response-induced neuronal activity can drive rapid changes in body color, which enriches our knowledge of physiological adaptations in coral reef fish.

Immunohistochemical Characterization of Langerhans Cells in the Skin of Three Amphibian Species

The amphibian taxon includes three orders that present different morphological characteristics: Anura, Caudata, and Apoda. Their skin has a crucial role: it acts as an immune organ constituting a physical, chemical, immunological, and microbiological barrier to pathogen insult and conducts essential physiological processes. Amphibians have developed specialized features to protect the vulnerable skin barrier, including a glandular network beneath the skin surface that can produce antimicrobial and toxic substances, thus contributing to the defense against pathogens and predators. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (order: Anura; Shaw, 1802), Amphiuma means (order: Caudata; Garden, 1821), and Typhlonectes natans (order: Apoda; Fischer, 1880) with the following antibodies: Langerin/CD207 (c-type lectin), Major Histocompatibility Complex (MHC)II, and Toll-like receptor (TLR)2 (expressed by different types of DCs). Our results showed Langerhans cells positive for Langerin CD/207 in the epidermis of the three species; moreover, some antigen-presenting cells (APCs) in the connective tissue expressed TLR2 and MHCII. The distribution of the Langerhans cells is very similar in the three amphibians examined, despite their different habitats. A greater knowledge of the amphibian immune system could be useful to better understand the phylogeny of vertebrates and to safeguard amphibians from population declines. Furthermore, the similarities between amphibians' and human skin concerning immunological features may be useful in both biology and translational medicine.

Background matching through fast and reversible melanin-based pigmentation plasticity in tadpoles comes with morphological and antioxidant changes

Facultative colour change is widespread in the animal kingdom, and has been documented in many distantly related amphibians. However, experimental data testing the extent of facultative colour change, and associated physiological and morphological implications are comparatively scarce. Background matching in the face of spatial and temporal environmental variation is thought to be an important proximate function of colour change in aquatic amphibian larvae. This is particularly relevant for species with long larval periods such as the western spadefoot toad, Pelobates cultripes, whose tadpoles spend up to six months developing in temporary waterbodies with temporally variable vegetation. By rearing tadpoles on different coloured backgrounds, we show that P. cultripes larvae can regulate pigmentation to track fine-grained differences in background brightness, but not hue or saturation. We found that colour change is rapid, reversible, and primarily achieved through changes in the quantity of eumelanin in the skin. We show that this increased eumelanin production and/or maintenance is also correlated with changes in morphology and oxidative stress, with more pigmented tadpoles growing larger tail fins and having an improved redox status.

Transcriptomic and proteomic analyses reveal the common and unique pathway(s) underlying different skin colors of leopard coral grouper (Plectropomus leopardus)

To gain a comprehensive and unbiased molecular understanding of the different skin colors of P. leopardus, we used Illumina HiSeq 2500 and TMT (Tandem Mass Tag) to compare transcription and protein levels between red and black skin of P. leopardus. We identified 797 upregulated and 314 downregulated genes (differentially expressed genes; DEGs) in red (RG) compared with black (BG) skin of P. leopardus. We also identified 377 differentially abundant proteins (DAPs), including 314 upregulated and 63 downregulated proteins. These DEGs and DAPs were significantly enriched in melanin synthesis (e.g., pyrimidine metabolism, Phenylalanine, tyrosine, and tryptophan biosynthesis, melanogenesis, phenylalanine metabolism, and tyrosine metabolism), oxidative phosphorylation (e.g., phosphonate and phosphinate metabolism, and oxidative phosphorylation), energy metabolism (e.g., HIF-1, glycolysis/gluconeogenesis, fatty acid biosynthesis, and fatty acid degradation), and signal transduction (e.g., Wnt, calcium, MAPK, and cGMP-PKG signaling pathways), etc. Further analysis of MAPKs showed that the activation levels of its main members JNK1 and ERK1/2 differed significantly between red and black skin colors. After RNAi was used to interfere with ERK1/2, it was found that the local skin of the tail of P. leopardus would turn black. Combined transcriptome and proteome analysis showed that most DEGs-DAPs in red skin were higher than in black skin (58 were upregulated, 1 was downregulated, and 4 were opposite). These DEGs-DAPs showed that the differences between red and black skin tissues of P. leopardus were related primarily to energy metabolism, signal transduction and cytoskeleton. These findings are not only conducive to understand the skin color regulation mechanism of P. leopardus and other coral reef fish, but also provide an important descriptive to the breeding of color strains. SIGNIFICANCE OF THE STUDY: The skin color of P. leopardus gradually darkens or blackens due to environmental factors such as changes in light intensity and human activities, and this directly affects its ornamental and economic value. In this study, RNAseq and TMT were used to conduct comparative quantitative transcriptomics and proteomics and analyze differences between red and black P. leopardus skin. The results showed that energy metabolism, signal transduction and cytoskeleton were the main metabolic pathways causing their skin color differences. These findings contribute to existing data describing fish skin color, and provide information about protein levels, which are of great significance to a deeper understanding of the skin color regulation mechanism in P. leopardus and other coral reef fishes.

Bioinspired Color Elastomers Combining Structural, Dye, and Background Colors

Organisms that alter body color undergo color change in response to environmental variations and stimuli by combining chromatophores that develop colors by various mechanisms. Inspired by their body color changes, we can develop sensors and optical materials that change colors in response to multiple stimuli, such as mechanical and light stimuli. In this study, we report on bioinspired composite elastomers that exhibit various color changes as the pigment color, structural color, and background color change. These composite elastomers exhibit structural colors due to their fine structures in which fine silica particles form colloidal crystals, and the structural colors reversibly change as the elastomers elongate. Furthermore, photochromic dyes can reversibly change color depending on the wavelength of irradiated light when they are introduced to the composite elastomers. Since the structural color is one of the three primary colors of light and the pigment color is the color that corresponds to the three primary colors of a pigment, each color becomes vivid when the background color is black or white. Thus, we clarify that the composite elastomers exhibit various color changes due to the combination of structural color change in response to the mechanical stimulus, pigment color change in response to light irradiation, and background color change.

Does dietary β-carotene influence ontogenetic colour change in the southern corroboree frog?

Ontogenetic colour change occurs in a diversity of vertebrate taxa and may be closely linked to dietary changes throughout development. In various species, red, orange and yellow colouration can be enhanced by the consumption of carotenoids. However, a paucity of long-term dietary manipulation studies means that little is known of the role of individual carotenoid compounds in ontogenetic colour change. We know even less about the influence of individual compounds at different doses (dose effects). The present study aimed to use a large dietary manipulation experiment to investigate the effect of dietary β-carotene supplementation on colouration in southern corroboree frogs (Pseudophryne corroboree) during early post-metamorphic development. Frogs were reared on four dietary treatments with four β-carotene concentrations (0, 1, 2 and 3 mg g-1), with frog colour measured every 8 weeks for 32 weeks. β-Carotene was not found to influence colouration at any dose. However, colouration was found to become more conspicuous over time, including in the control treatment. Moreover, all frogs expressed colour maximally at a similar point in development. These results imply that, for our study species, (1) β-carotene may contribute little or nothing to colouration, (2) frogs can manufacture their own colour, (3) colour development is a continual process and (4) there may have been selection for synchronised development of colour expression. We discuss the potential adaptive benefit of ontogenetic colour change in P. corroboree. More broadly, we draw attention to the potential for adaptive developmental synchrony in the expression of colouration in aposematic species.

Comparative metabolomics analysis of pigmentary and structural coloration in discus fish (Symphysodon haraldi)

Discus fish have a variety of body colors including pigmentary and structural colors, studies on specific substances and related metabolic pathways associated with body coloration, however, are scarce to the present. Here, we used single-color (blue, yellow and white) of discus for comparative metabolomics analysis of pigmentary and structural coloration. Statistical model showed significant separations between three colors of discus, suggesting the distinct metabolite profiles of discus pigmentary and structural colors. More astaxanthin was found in yellow discus, which might be the cause of yellow pigmentary color. Moreover, docosahexaenoic acid, arachidonic acid, linoleic acid, eicosapentaenoic acid, 1-stearoyl-2-oleoyl-sn-glycerol 3-phosphocholine, dodecanoic acid and myristic acid related to lipid metabolism and pathways of ABC transporters and biosynthesis of unsaturated fatty acids were more enriched in yellow discus. More adenine, xanthine and hypoxanthine were enriched in blue discus, which might account for the blue structural color. Moreover, amino acids associated with purine biosynthesis, e.g., L-alanine and L-isoleucine, were reduced but pathways of protein digestion and absorption, aminoacyl-tRNA biosynthesis, purine metabolism and glycine, serine and threonine metabolism were enriched in blue discus. Overall, these results reveal specific chromophores and related metabolic pathways involved in pigmentary and structural coloration of discus fish. SIGNIFICANCE: We detected specific chromophores present in skin of pigmentary and structural colors of discus and revealed potential metabolic pathways associated with body coloration. These results contribute to our understanding of the mechanism of body color formation in discus fish.

Social and physiological drivers of rapid colour change in a tropical toad

Dynamic sexual dichromatism occurs when males and females differ in colouration for a limited time. Although this trait has been primarily studied in cephalopods, chameleons, and fishes, recent analyses suggest that dynamic dichromatism is prevalent among anurans and may be mediated through sexual selection and sex recognition. Yellow toads, Incilius luetkenii, exhibit dynamic dichromatism during explosive breeding events at the onset of the rainy season: males change from a cryptic brown to a bright yellow and back again during the brief mating event. We tested the hypothesis that dynamic dichromatism in yellow toads is influenced by conspecific interactions and mediated through sex hormones and stress hormones. We placed male toads into one of four social treatments (with three other males, one male, one female, or no other toads). Immediately before and after each one-hour treatment, we quantified male colour with a reflectance spectrometer and we collected a blood sample to assess plasma concentrations of both testosterone and corticosterone. We found that males held with conspecific animals showed the brightest yellow colour and showed little or no change in their corticosterone levels. Across treatments, toads with duller yellow colour had higher levels of corticosterone. Male colour showed no association with testosterone. Interestingly, males showed substantial temporal variation in colour and corticosterone: toads were duller yellow and exhibited greater levels of corticosterone post-treatment across subsequent days at the onset of the rainy season. Our findings reveal that both conspecific interactions and corticosterone are involved in the dynamic colour change of yellow toads.

The Cavefish Oreonectes jiarongensis can be Induced to Differentiate and Recover under the Light Condition

This research indicated that one cave fish species of Oreonectes jiarongensis can recover the transparent to black under the light condition, this species belongs to the Oreonectes, Nemacheilinae, and distributes in Libo County, Guizhou Province, China. The changing process time was 14 days. This is the first time that suggests the cave vertebrates which lived in the dark environment not longer time could change the body color in the light environment, and has a new adaptive strategy for the darkness condition. The result may indicate that this species entrance the underground river not so long time, and the genes not mutation, which control the melanin express, it still has the physiological regulation mechanism under the light condition.