Avian Feathers Research Articles

Comparative aerodynamics of synthetic badminton shuttlecocks

Badminton synthetic shuttlecocks are known to have significantly different aerodynamic behaviours compared to feathered shuttlecocks due to the difference in designs and use of materials. Given the fragility of avian feathers used for feathered shuttlecocks and the constantly increasing cost of purchase, the interest to assess the current synthetic shuttlecock design as a feasible alternative has re-emerged. The single-piece injection-moulded synthetic shuttlecock has been the mainstream design for the past 50 years; however, little evidence has supported that the design mimics the aerodynamics of feathered shuttlecocks. Recently, a two-part skirt design has emerged proclaiming to have surpassed its synthetic predecessor in regard to matching the aerodynamics of feathered shuttlecocks. In the current study, two different synthetic designs (injection-moulded vs two-part skirt) were benchmarked against a feathered shuttlecock. A wind tunnel test was conducted between 30 and 145 km/h. The drag coefficients of both synthetic shuttlecocks were similar to the feathered shuttlecock up to 105 km/h. Thereafter, the drag coefficient of the injection-moulded design dropped from 0.62 to 0.5 and showing no signs of levelling at speeds over 105 km/h, while the coefficient for two-part skirt design stabilised at approximately 0.55. It was concluded that the two-part skirt design better mimicked the aerodynamics of the feathered shuttlecock.

Developing an ancient epithelial appendage: FGF signalling regulates early tail denticle formation in sharks

BackgroundVertebrate epithelial appendages constitute a diverse group of organs that includes integumentary structures such as reptilian scales, avian feathers and mammalian hair. Recent studies have provided new evidence for the homology of integumentary organ development throughout amniotes, despite their disparate final morphologies. These structures develop from conserved molecular signalling centres, known as epithelial placodes. It is not yet certain whether this homology extends beyond the integumentary organs of amniotes, as there is a lack of knowledge regarding their development in basal vertebrates. As the ancient sister lineage of bony vertebrates, extant chondrichthyans are well suited to testing the phylogenetic depth of this homology. Elasmobranchs (sharks, skates and rays) possess hard, mineralised epithelial appendages called odontodes, which include teeth and dermal denticles (placoid scales). Odontodes constitute some of the oldest known vertebrate integumentary appendages, predating the origin of gnathostomes. Here, we used an emerging model shark (Scyliorhinus canicula) to test the hypothesis that denticles are homologous to other placode-derived amniote integumentary organs. To examine the conservation of putative gene regulatory network (GRN) member function, we undertook small molecule inhibition of fibroblast growth factor (FGF) signalling during caudal denticle formation.ResultsWe show that during early caudal denticle morphogenesis, the shark expresses homologues of conserved developmental gene families, known to comprise a core GRN for early placode morphogenesis in amniotes. This includes conserved expression of FGFs, sonic hedgehog (shh) and bone morphogenetic protein 4 (bmp4). Additionally, we reveal that denticle placodes possess columnar epithelial cells with a reduced rate of proliferation, a conserved characteristic of amniote skin appendage development. Small molecule inhibition of FGF signalling revealed placode development is FGF dependent, and inhibiting FGF activity resulted in downregulation of shh and bmp4 expression, consistent with the expectation from comparison to the amniote integumentary appendage GRN.ConclusionOverall, these findings suggest the core GRN for building vertebrate integumentary epithelial appendages has been highly conserved over 450 million years. This provides evidence for the continuous, historical homology of epithelial appendage placodes throughout jawed vertebrates, from sharks to mammals. Epithelial placodes constitute the shared foundation upon which diverse vertebrate integumentary organs have evolved.

Extreme lightweight structures: avian feathers and bones

Flight is not the exclusive domain of birds; mammals (bats), insects, and some fish have independently developed this ability by the process of convergent evolution. Birds, however, greatly outperform other flying animals in efficiency and duration; for example the common swift (Apus apus) has recently been reported to regularly fly for periods of 10 months during migration. Birds owe this extraordinary capability to feathers and bones, which are extreme lightweight biological materials. They achieve this crucial function through their efficient design spanning multiple length scales. Both feathers and bones have unusual combinations of structural features organized hierarchically from nano- to macroscale and enable a balance between lightweight and bending/torsional stiffness and strength. The complementary features between the avian bone and feather are reviewed here, for the first time, and provide insights into nature's approach at creating structures optimized for flight. We reveal a novel aspect of the feather vane, showing that its barbule spacing is consistently within the range 8–16 μm for birds of hugely different masses such as Anna's Hummingbird (Calypte anna) (4 g) and the Andean Condor (Vultur gryphus) (11,000 g). Features of the feather and bone are examined using the structure-property relationships that define Materials Science. We elucidate the role of aerodynamic loading on observed reinforced macrostructural features and efficiently tailored shapes adapted for specialized applications, as well as composite material utilization. These unique features will inspire synthetic structures with maximized performance/weight for potential use in future transportation systems.

Aggregated oviposition in Rhodnius prolixus, sensory cues and physiological consequences

Females of the haematophagous bug Rhodnius prolixus attach their eggs in clusters on substrates related to their hosts, such as nests or avian feathers. Because the hosts are an enormous food resource as well as potential predators, the choice of the site and pattern of oviposition could have an important adaptive value. Here we investigated proximate and a potential ultimate cause of this aggregated pattern of laid eggs. First, we studied proximal causes by analyzing the use of chemical or physical cues associated with aggregated oviposition in R. prolixus. For all terrestrial organisms there is a trade-off between exchange of respiratory gases and water loss. Particularly, insect eggs are highly susceptible to this trade-off because they do not obtain water from the environment, hence our second objective is to study the possible mechanisms involved in dehydration resistance in this species. Therefore we examined the dynamics of change in CO2 release rate (ṀCO2), and water loss rate (ṀH2O) in relation to embryo development as energetic demands increase, and tested the energetic or hygric efficiency hypothesis as a potential ultimate cause of aggregated oviposition. This hypothesis states that grouped eggs consume less energy or lose less water than equal numbers of isolated eggs, the latter being more susceptible to dehydration. Results indicated the use of physical external cues such as dummy eggs or edges of the oviposition substrates, but we did not find any chemical cues associated with the aggregated pattern of oviposition. There are no energetic or hygric benefits associated with egg’s aggregated pattern. However, when we analyzed the ṀCO2 and ṀH2O change in relation to embryo development, we found a fairly constant and low ṀH2O albeit a clear increase in ṀCO2, suggesting a tightly control of egg’s desiccation tolerance. This high resistance to desiccation coupled with a temporal strategy of hatching allows R. prolixus embryos to successfully develop and hatch under harsh environmental conditions.

Microscopic and immunohistochemical analyses of the claw of the nesting dinosaur, Citipati osmolskae.

One of the most well-recognized Cretaceous fossils is Citipati osmolskae (MPC-D 100/979), an oviraptorid dinosaur discovered in brooding position on a nest of unhatched eggs. The original description refers to a thin lens of white material extending from a manus ungual, which was proposed to represent original keratinous claw sheath that, in life, would have covered it. Here, we test the hypothesis that this exceptional morphological preservation extends to the molecular level. The fossil sheath was compared with that of extant birds, revealing similar morphology and microstructural organization. In living birds, the claw sheath consists primarily of two structural proteins; alpha-keratin, expressed in all vertebrates, and beta-keratin, found only in reptiles and birds (sauropsids). We employed antibodies raised against avian feathers, which comprise almost entirely of beta-keratin, to demonstrate that fossil tissues respond with the same specificity, though less intensity, as those from living birds. Furthermore, we show that calcium chelation greatly increased antibody reactivity, suggesting a role for calcium in the preservation of this fossil material.

Biomimetic Construction of Non‐Iridescent Structural Color Films with High Hydrophobicity and Good Mechanical Stability Induced by Chaotic Convective Coassembly Method

This article presents an originative strategy to biomimetically construct non‐iridescent structural color films with high hydrophobicity and good mechanical stability. In this strategy, the amorphous array of polystyrene (PS) particles is easily fabricated via a simple chaotic convective flow coassembly method to imitate the amorphous nanostructures of avian feathers. An amorphous array is locked by introducing fluorinated polyacrylate (FPA) latex to the voids between the PS particles as binder, which is similar to the locking effect of an organism of a bird's wing. Meanwhile, the high hydrophobicity (140° contact angle) and good mechanical stability of the films are obtained owing to hydrophobicity of FPA and high roughness of the amorphous array. The as‐prepared films retain their brilliant colors under natural light, and this property is essential for their applications in full‐color displays and responsive materials.

Structure and homology ofPsittacosaurustail bristles

AbstractWe examined bristle‐like appendages on the tail of the Early Cretaceous basal ceratopsian dinosaurPsittacosauruswith laser‐stimulated fluorescence imaging. Our study reveals previously unknown details of these structures and confirms their identification as integumentary appendages. For the first time, we show that most bristles appear to be arranged in bundles and that they exhibit a pulp that widens towards the bristle base. We consider it likely that the psittacosaur bristles are structurally and developmentally homologous to similar filamentous appendages of other dinosaurs, namely the basal heterodontosauridTianyulongand the basal therizinosauroid theropodBeipiaosaurus, and attribute the greater robustness of the bristles ofPsittacosaurusto a higher degree of cornification and calcification of its integument (both skin and bristles). Although the psittacosaur bristles are probably homologous with avian feathers in their origin from discrete cell populations, it is uncertain whether they developed from a follicle, one of the developmental hallmarks of true feathers. In particular, we note a striking resemblance between the psittacosaur bristles and the cornified spine on the head of the horned screamer,Anhima cornuta, an extant anseriform bird. Similar, albeit thinner keratinous filaments of extant birds are the ‘beard’ of the turkey,Meleagris gallopavo, and the crown of the Congo peafowl,Afropavo congensis. All of these structures of extant birds are distinct from true feathers, and because at least the turkey beard does not develop from follicles, detailed future studies of their development would be invaluable towards deepening our understanding of dinosaur filamentous integumentary structures.

A Lambayeque sacrificial temple

Seven females and one male were sacrificed and buried beneath the floor of a Lambayeque temple at the site of Dos Cabezas, on the north coast of Peru. These burials provide a wealth of information about the Lambayeque people whose civilization flourished between c. 900 and 1470 C.E. Each of the individuals had been put to death by strangulation and buried with a remarkable array of associated objects. The preponderance of avian iconography and feathers that were associated with the burials may allude to the nature of this temple and the individuals who were sacrificed and buried beneath its floors.

Bio-Inspired Structural Colors Produced via Self-Assembly of Synthetic Melanin Nanoparticles.

Structural colors arising from interactions of light with submicron scale periodic structures have been found in many species across all taxa, serving multiple biological functions including sexual signaling, camouflage, and aposematism. Directly inspired by the extensive use of self-assembled melanosomes to produce colors in avian feathers, we set out to synthesize and assemble polydopamine-based synthetic melanin nanoparticles in an effort to fabricate colored films. We have quantitatively demonstrated that synthetic melanin nanoparticles have a high refractive index and broad absorption spanning across the UV-visible range, similar to natural melanins. Utilizing a thin-film interference model, we demonstrated the coloration mechanism of deposited films and showed that the unique optical properties of synthetic melanin nanoparticles provide advantages for structural colors over other polymeric nanoparticles (i.e., polystyrene colloidal particles).

Mercury levels in avian feathers from different trophic levels of eight families collected from the northern region of Iran.

Mercury levels were determined in feathers from 83 birds belonging to 18 species (eight families), all collected from the northern region of Iran. Mercury levels were evaluated in relation to taxonomic affiliation and feeding strategies. Mercury levels in the feathers were between 0.05 ± 0.01 and 1.10 ± 0.15μg g(-1) dry weight, and there was a significant effect of taxonomic groups (p < 0.05). The highest mercury levels were found in Accipitridae, and mercury was not detected in the family Upupidae. The pattern for mercury levels was Accipitridae > Pelecanidae > Sternidae > Ardeidae > Anatidae > Rallidae > Phasianidae (p < 0.05). Significant differences (p < 0.05) in the mean mercury levels were found among species as a function of feeding method and trophic level. Mercury levels were highest in the carnivorous species and lowest in the herbivorous species. Mercury levels in feathers of birds in this study were generally below the thresholds reported to affect reproduction.

Elucidation of the chemical composition of avian melanin

Our understanding of the chemical composition of melanin remains limited, due to a paucity of direct measurements. Avian feathers have an unparalleled diversity of melanin-based color mirroring their complex chemistry. Synchrotron-based photoionization mass spectrometry is used to determine the chemical composition of melanin from samples of black, brown, grey and iridescent feathers.

Avian feathers as a non-destructive bio-monitoring tool of trace metals signatures: A case study from severely contaminated areas

The concentrations of trace metals were assessed using feathers of cattle egrets (Bubulcus ibis), collected within two industrial areas of Pakistan, Lahore and Sialkot. We found, in order of descending concentration: Zinc (Zn), Iron (Fe), Nickel (Ni), Copper (Cu), Cadmium (Cd), and Manganese (Mn), Chromium (Cr), Arsenic (As), and Lithium (Li), without any significant difference (except Fe, Zn, and Ni) between the two areas. The concentrations of trace metals, we recorded were among the highest ever reported in the feathers of avian species worldwide. The concentrations of Cr, Pb, Cd were above the threshold that affects bird reproductive success. The high contamination by heavy metals in the two areas is due to anthropogenic activities as well to natural ones (for As and Fe). The bioaccumulation ratios in eggs and feathers of the cattle egret, their prey, and the sediments from their foraging habitats, confirmed that avian feathers are a convenient and non-destructive sampling tool for the metal contamination. The results of this study will contribute to the environmental management of the Lahore and Sialkot industrial areas.

Dkk2/Frzb in the dermal papillae regulates feather regeneration

Avian feathers have robust growth and regeneration capability. To evaluate the contribution of signaling molecules and pathways in these processes, we profiled gene expression in the feather follicle using an absolute quantification approach. We identified hundreds of genes that mark specific components of the feather follicle: the dermal papillae (DP) which controls feather regeneration and axis formation, the pulp mesenchyme (Pp) which is derived from DP cells and nourishes the feather follicle, and the ramogenic zone epithelium (Erz) where a feather starts to branch. The feather DP is enriched in BMP/TGF-β signaling molecules and inhibitors for Wnt signaling including Dkk2/Frzb. Wnt ligands are mainly expressed in the feather epithelium and pulp. We find that while Wnt signaling is required for the maintenance of DP marker gene expression and feather regeneration, excessive Wnt signaling delays regeneration and reduces pulp formation. Manipulating Dkk2/Frzb expression by lentiviral-mediated overexpression, shRNA-knockdown, or by antibody neutralization resulted in dual feather axes formation. Our results suggest that the Wnt signaling in the proximal feather follicle is fine-tuned to accommodate feather regeneration and axis formation.

Eocene fossil feather from King George Island, South Shetland Islands, Antarctica

AbstractThe first fossil avian feather from Antarctica is reported here, from the early to middle Eocene Fossil Hill Formation at Fildes Peninsula, King George Island, Antarctica. Characteristics such as its form, asymmetry of vanes, closed-pennaceous vanes with barbules and a deep ventral groove indicate that the feather was used for flight. The site from which the feather was collected is known to yield a variety of well-preserved trace fossils, palaeobotanical and palaeoenvironmental remains, suggesting a shorebird ecotype for the owner of this feather, certainly belonging to a Neornithes. The continental position, preservation as an external mould and type of feather makes this specimen a novel and an exceedingly rare record.

The fate of archaeological keratin fibres in a temperate burial context: microtaphonomy study of hairs from Marie de Bretagne (15th c., Orléans, France)

When exceptionally preserved, hairs, wools, the skin stratum corneum and avian feathers can provide a wealth of archaeological and paleontological information. Long-term preservation of their information potential lies in the taphonomy (long-term behaviour laws) of keratin-based fibres and films. Here, we study the microscopic properties of archaeological hairs from the mediaeval burial of Marie de Bretagne (15th c., Orléans, France) preserved in a temperate environment, using complementary laboratory and synchrotron-based analytical instruments. We show that (a) the fibrillar keratin content of hair is exceptionally well preserved yet with limited degradation of the hair outer cortex in some hair strands, (b) exceptional preservation is attributed to the diffusion of copper and lead in the hair, (c) a posteriori examination led to the discovery of fragments of copper-based artefacts. We propose a possible scenario that led to the preservation of these tissues and discuss the archaeological interpretation of the microtaphonomy of these bioarchaeological remains.

Structure and Mechanical Property of Asio Otus Feather Barbs

Avian feather is the outstanding protein fiber structure that still lacks an interpretation generally acceptable in any detail. In this paper, asio otus feathers were morphological represented and their barbs were mechanical characterized by a developed micro-tensile tester with a load resolution of 0.25 mN and a displacement resolution of 10 nm. With a tensile loading speed at 0.02 μm/s, Young’s modulus of the flight feather barbs with length of 1450-1900 μm was calculated to be 3.13-3.66 GPa, higher than 1.47-2.04 GPa for the down feather barbs with length of 520-710 μm. It is concluded that the asio otus’s flight feathers on its wing and tail are more rigid than the down feathers on its body.

Shaping organs by a wingless-int/Notch/nonmuscle myosin module which orients feather bud elongation.

How organs are shaped to specific forms is a fundamental issue in developmental biology. To address this question, we used the repetitive, periodic pattern of feather morphogenesis on chicken skin as a model. Avian feathers within a single tract extend from dome-shaped primordia to thin conical structures with a common axis of orientation. From a systems biology perspective, the process is precise and robust. Using tissue transplantation assays, we demonstrate that a "zone of polarizing activity," localized in the posterior feather bud, is necessary and sufficient to mediate the directional elongation. This region contains a spatially well-defined nuclear β-catenin zone, which is induced by wingless-int (Wnt)7a protein diffusing in from posterior bud epithelium. Misexpressing nuclear β-catenin randomizes feather polarity. This dermal nuclear β-catenin zone, surrounded by Notch1 positive dermal cells, induces Jagged1. Inhibition of Notch signaling disrupts the spatial configuration of the nuclear β-catenin zone and leads to randomized feather polarity. Mathematical modeling predicts that lateral inhibition, mediated by Notch signaling, functions to reduce Wnt7a gradient variations and fluctuations to form the sharp boundary observed for the dermal β-catenin zone. This zone is also enriched for nonmuscle myosin IIB. Suppressing nonmuscle myosin IIB disrupts directional cell rearrangements and abolishes feather bud elongation. These data suggest that a unique molecular module involving chemical-mechanical coupling converts a pliable chemical gradient to a precise domain, ready for subsequent mechanical action, thus defining the position, boundary, and duration of localized morphogenetic activity that molds the shape of growing organs.

Crocodile Head Scales Are Not Developmental Units But Emerge from Physical Cracking

Various lineages of amniotes display keratinized skin appendages (feathers, hairs, and scales) that differentiate in the embryo from genetically controlled developmental units whose spatial organization is patterned by reaction-diffusion mechanisms (RDMs). We show that, contrary to skin appendages in other amniotes (as well as body scales in crocodiles), face and jaws scales of crocodiles are random polygonal domains of highly keratinized skin, rather than genetically controlled elements, and emerge from a physical self-organizing stochastic process distinct from RDMs: cracking of the developing skin in a stress field. We suggest that the rapid growth of the crocodile embryonic facial and jaw skeleton, combined with the development of a very keratinized skin, generates the mechanical stress that causes cracking.

Alterations in the infrared spectral signature of avian feathers reflect potential chemical exposure: A pilot study comparing two sites in Pakistan

Chemical contamination of ecosystems is a global issue with evidence that pollutants impact on living organisms in a harmful fashion. Developing sensor approaches that would allow the derivation of biomarkers or signatures of effect in target sentinel organisms and monitor environmental chemical contamination in a high throughput manner is of utmost importance. As biomolecules absorb infrared (IR), signature vibrational spectra related to structure and function can be derived. In light of this, we tested the notion that IR spectra of bird feathers might reflect environmental chemical contaminant exposure patterns. Feathers were collected from monospecific heronries of cattle egret based in two independent locations (Trimu vs. Mailsi) in the Punjab province of Pakistan; these sites were found to differ in their chemical contamination patterns. Feather samples were chemically analyzed for polychlorinated biphenyls, polybrominated diphenyl ethers, organochlorines and heavy metals. Attenuated total reflection Fourier-transform IR (ATR-FTIR) spectroscopy was employed to derive a spectral signature of individual feathers. Resultant IR spectra were then subjected to canonical correspondence analysis (CAA) to determine whether feather spectral signatures correlate to chemical exposure. Additionally, we explored if principal component analysis (PCA) and linear discriminant analysis (LDA) could be applied to distinguish site-specific differences; linear discriminant function (LDF) was also applied to classify sites. The sampled feathers varied in their chemical exposure patterns depending on whether they were sourced from one site associated with heavy metal exposure or the other which suggested high organic pollutant exposures. CCA of chemical and spectral data showed a correlation between spectral signatures and chemical exposure. PCA-LDA readily distinguished feathers from the two different sites. Discriminating alterations were identified and these were associated with protein and lipid regions in IR spectra. Additionally, LDF showed that the classification rate of spectral categories correlated well with the two chemical exposure patterns (93.6% for Trimu feathers and 91.77% for Mailsi feathers). This pilot study suggests that IR spectra derived from feathers reflect background chemical exposure and points to a novel monitoring tool for contamination.

The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type

Elongated skin projections of the reptile Longisquama insignis from the Triassic of Kyrgyzstan are preserved as imprints on the only skeletal specimen and on seven additional pairs of fossil slabs and counter-slabs from the same locality and horizon. The integumentary structures became a matter of debate when they were assessed as “non-avian feathers” homologous to avian feathers. Conflicting interpretations of their morphology and relationship to other appendage types arose from the ambiguity of the fossil skin impressions. On the basis of comparative description of the individual morphology of all yet known Longisquama specimens we address aspects of taphonomy, development, and function and define to what extent Longisquama’s appendages share characteristics of avian vaned feathers. We explain the existing feather similarity by their development from a filamentous primordium and a complex sequence of individual processes, some of which are reminiscent of processes observed in feather development. Such an interpretation is in agreement with a set of homologous mechanisms of appendage morphogenesis in an archosauromorph clade including Longisquama and feather-bearing archosaurs but does not necessarily require that the appendages of Longisquama themselves are feathers or high-level feather homologues.