Cell organization of barb ridges in regenerating feathers of the quail: implications of the elongation of barb ridges for the evolution and diversification of feathers

This ultrastructural study on the regenerating feathers of quail describes the cellular organization of the barb ridges responsible for the ramification of adult feathers. Bilateral symmetry of the barb ridges determines the organization of feather cells into feather branching. The length of the barb ridges, derived from the number of cells associated to form the barbule plates, determines the length of the barbule branching. Long chains of barb cells form long barbs that branch from the rachis with an increase of feather size. Supportive cells function as spacers between the barbule cells. New cells derive from stem cells localized in the collar region of the feather follicle, as indicated from the re‐organization of collar cells into barb ridges (a morphogenetic process inherited from that of embryonic feathers), production of an embryonic type of keratin (feather keratin), permanence of periderm granules (typical embryonic organelles) in barb vane ridge cells. Variations in the process of barb ridge morphogenesis allow the fusion of ridges into a rachis. The differentiation of hooklets contributes to the origin of planar feathers. Separation between rachis and merging barb ridges is by supportive cells, derived from the marginal plates of the barb ridges. Speculations on the evolution and diversification of feathers are presented.     

Mechanical and structural adaptations to migration in the flight feathers of a Palaearctic passerine

Current avian migration patterns in temperate regions have been developed during the glacial retreat and subsequent colonization of the ice‐free areas during the Holocene. This process resulted in a geographic gradient of greater seasonality as latitude increased that favoured migration‐related morphological and physiological (co)adaptations. Most evidence of avian morphological adaptations to migration comes from the analysis of variation in the length and shape of the wings, but the existence of intra‐feather structural adjustments has been greatly overlooked despite their potential to be under natural selection. To shed some light on this question, we used data from European robins Erithacus rubecula overwintering in Campo de Gibraltar (Southern Iberia), where sedentary robins coexist during winter with conspecifics showing a broad range of breeding origins and, hence, migration distances. We explicitly explored how wing length and shape, as well as several functional (bending stiffness), developmental (feather growth rate) and structural (size and complexity of feather components) characteristics of flight feathers, varied in relation to migration distance, which was estimated from the hydrogen stable isotope ratios of the summer‐produced tail feathers. Our results revealed that migration distance not only favoured longer and more concave wings, but also promoted primaries with a thicker dorsoventral rachis and shorter barb lengths, which, in turn, conferred more bending stiffness to these feathers. We suggest that these intra‐feather structural adjustments could be an additional, largely unnoticed, adaptation within the avian migratory syndrome that might have the potential to evolve relatively quickly to facilitate the occupation of seasonal environments.     

Theory of the development of curved barbs and their effects on feather morphology

Feathers exhibit an extraordinary diversity of shapes, which are used by birds to accomplish a diverse set of functions. Pennaceous feathers have a double branched morphology that develops from a tube of epidermis, and variation in branch geometry determines feather shape. Feather development is both complex (i.e., a simple developmental modification can have multiple effects on mature feather shape), and redundant (i.e., different developmental modifications can create the same shape). Due to this, it is not readily apparent how different feather shapes develop. In many feathers, barbs are not straight, but instead curve in toward, or away, from the feather tip. Barb curvature can affect the shape of mature feathers but the development of curved barbs is unknown. Previous research has hypothesized that barb curvature could develop either during the helical growth of barb ridges in the tubular feather germ, or during barb angle expansion as the feather unfurls from the sheath. To better understand the development of curved barbs and their effects on mature feathers we present a theoretical model of curved barb development and test the model with empirical investigations of feathers. We find that curved barbs affect many aspects of feather morphology including vane width, barb length, and barb spacing. In real feathers, curved barbs can develop both during helical barb ridge growth and during barb angle expansion, with most of the observed curvature due to barb angle expansion. Our results demonstrate that barb angle expansion as a feather unfurls from the sheath is a complex and dynamic process that plays an important role in determining the shape and structure of mature feathers. Curved barbs create heterogeneity in barb geometry within the feather vane, which could have important implications for aerodynamic function and the development of within feather pigmentation patterns. J. Morphol. 277:995–1013, 2016. © 2016 Wiley Periodicals, Inc.     

Fault bars in bird feathers: mechanisms,and ecological and evolutionary causes and consequences

Fault bars are narrow malformations in feathers oriented almost perpendicular to the rachis where the feather vein and even the rachis may break. Breaks in the barbs and barbules result in small pieces of the feather vein being lost, while breaks in the rachis result in loss of the distal portion of the feather. Here, we provide a comprehensive review of 74 papers on fault bar formation in hopes of providing a clearer approach to their study. First, we review the evidence that the propensity to develop fault bars is modified by natural selection. Given that fault bars persist in the face of survival costs, we conclude that they must be an unfortunate consequence of some alternative adaptation that outweighs the fitness costs of fault bars. Second, we summarize evidence that the development of fault bars is triggered by psychological stress such as that of handling or predation attempts, and that they persist because the sudden contractions of the muscles in the feather follicle that control fright moults also causes the development of fault bars in growing feathers. Third, we review external and physiological (e.g. corticosterone) agents that may affect the likelihood that an acute stress will result in a growing feather exhibiting a fault bar. These modifying factors have often been treated as fundamental causes in the earlier literature on fault bars. Fourth, we then use this classification to propose a tentative model where fault bars of different severity (from light to severe) are the outcome of the interaction between the propensity to produce fault bars (which differs between species, individuals and feather follicles within individuals) and the intensity of the perturbation. This model helps to explain contradictory results in the literature, to identify gaps in our knowledge, and to suggest further studies. Lastly, we discuss ways in which better understanding of fault bars can inform us about other aspects of avian evolutionary ecology, such as the physiology of moult, the integration of moult into avian life cycles, and the strategies used to minimize stress during moult. Moreover, the study of fault bars may be relevant to understanding the aerodynamics of flight and the early evolution of flight.     

Solution structure of the calmodulin‐like C‐terminal domain of Entamoeba α‐actinin2

Cell motility is dependent on a dynamic meshwork of actin filaments that is remodelled continuously. A large number of associated proteins that are severs, cross‐links, or caps the filament ends have been identified and the actin cross‐linker α‐actinin has been implied in several important cellular processes. In Entamoeba histolytica, the etiological agent of human amoebiasis, α‐actinin is believed to be required for infection. To better understand the role of α‐actinin in the infectious process we have determined the solution structure of the C‐terminal calmodulin‐like domain using NMR. The final structure ensemble of the apo form shows two lobes, that both resemble other pairs of calcium‐binding EF‐hand motifs, connected with a mobile linker. Proteins 2016; 84:461–466. © 2016 Wiley Periodicals, Inc.     

Characterization of a new keratinolytic Trichoderma atroviride strain F6 that completely degrades native chicken feather

Aims:  To isolate novel nonpathogenic fungus that completely degrades native chicken feather and characterize its keratinases. Methods and Results:  Feather‐degrading fungi were isolated from decaying feathers using a novel method based on simulating decaying process in the environment. The isolate F6 with high keratinolytic activity was identified as Trichoderma atroviride based on morphological traits and ITS1‐5·8S‐ITS2 sequence analysis. The purified dominant component of keratinase had a molecular mass of 21 kDa. The purified keratinase belonged to serine protease. Its isoelectric point, molecular weight, optimum pH, optimum temperature, and substrate specificity are different from those of other serine proteases of Trichoderma species. The optimum pH and temperature values of purified keratinase were consistent with those of crude keratinase. However, the differences between crude and purified enzymes such as thermostability, resistance to Ba²⁺, Mn²⁺, Hg²⁺, Zn²⁺, Cu²⁺, 1,10‐phenanthroline, 2,2′‐bipyridyl, and PMSF (phenylmethylsulfonyl fluoride) were observed. Conclusions:  The results suggested the purified keratinase is predominantly extracellular proteins when strain F6 was grown on keratinous substrates. The protease, in combination with other components, is effective in feather degradation. The strain F6 is more suitable for feather degradation than its purified keratinase. Significance and Impact of the Study:  The novel nonpathogenic T. atroviride F6 with high feather‐degrading activity showed potentials in biotechnological process of converting feathers into economically useful feather meal.     

The plumage and colouration of an enantiornithine bird from the early cretaceous of china

Brilliant colour displays and diverse feather morphologies that are often sexual ornaments are common throughout much of extant Avialae. Here we describe a new basal enantiornithine bird specimen recovered from the Early Cretaceous Jiufotang Formation of Liaoning Province in northeastern China. We present new information on the plumage of Bohaiornithidae as well as the first detailed colour reconstruction of an enantiornithine bird. The new specimen retains subadult skeletal characteristics, including periosteal pitting of the long bone epiphyses and unfused elements, while also preserving plumage evidence consistent with sexual maturity at the time of death. Exceptionally‐preserved feathers cover the body, including elongate crown feathers, body contour feathers, asymmetrically‐veined wing primaries, an alula and two elongate rachis‐dominated rectrices that may have been sexual ornaments. The crown, neck, and body contour feathers retain elongate melanosome morphologies associated with weakly iridescent colouration in extant feathers. We provide additional evidence of preserved melanin using Raman spectroscopy; a rapid, non‐destructive chemical technique. The new specimen provides data on skeletal ontogeny in the Bohaiornithidae as well as evidence for intraspecific communication functions of plumage.     

Taphonomic experiments resolve controls on the preservation of melanosomes and keratinous tissues in feathers

Fossils are a key source of data on the evolution of feather structure and function through deep time, but their ability to resolve macroevolutionary questions is compromised by an incomplete understanding of their taphonomy. Critically, the relative preservation potential of two key feather components, melanosomes and keratinous tissue, is not fully resolved. Recent studies suggesting that melanosomes are preferentially preserved conflict with observations that melanosomes preserve in fossil feathers as external moulds in an organic matrix. To date, there is no model to explain the latter mode of melanosome preservation. We addressed these issues by degrading feathers in systematic taphonomic experiments incorporating decay, maturation and oxidation in isolation and combination. Our results reveal that the production of mouldic melanosomes requires interactions with an oxidant and is most likely to occur prior to substantial maturation. This constrains the taphonomic conditions under which melanosomes are likely to be fossilized. Critically, our experiments also confirm that keratinous feather structures have a higher preservation potential than melanosomes under a range of diagenetic conditions, supporting hitherto controversial hypotheses that fossil feathers can retain degraded keratinous structures.     

Of 11 candidate steroids,corticosterone concentration standardized for mass is the most reliable steroid biomarker of nutritional stress across different feather types

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Tunneling nanotubes spread fibrillar α‐synuclein by intercellular trafficking of lysosomes

Synucleinopathies such as Parkinson's disease are characterized by the pathological deposition of misfolded α‐synuclein aggregates into inclusions throughout the central and peripheral nervous system. Mounting evidence suggests that intercellular propagation of α‐synuclein aggregates may contribute to the neuropathology; however, the mechanism by which spread occurs is not fully understood. By using quantitative fluorescence microscopy with co‐cultured neurons, here we show that α‐synuclein fibrils efficiently transfer from donor to acceptor cells through tunneling nanotubes (TNTs) inside lysosomal vesicles. Following transfer through TNTs, α‐synuclein fibrils are able to seed soluble α‐synuclein aggregation in the cytosol of acceptor cells. We propose that donor cells overloaded with α‐synuclein aggregates in lysosomes dispose of this material by hijacking TNT‐mediated intercellular trafficking. Our findings thus reveal a possible novel role of TNTs and lysosomes in the progression of synucleinopathies.     

A TLC bioautographic method for the detection of α‐ and β‐glucosidase inhibitors in plant extracts

Introduction – Bioautographic assays using TLC play an important role in the search for active compounds from plants. A TLC assay has previously been established for the detection of β‐glucosidase inhibitors but not for α‐glucosidase. Nonetheless, α‐glucosidase inhibition is an important target for therapeutic agents against of type 2 diabetes and anti‐viral infections. Objective – To develop a TLC bioautographic method to detect α‐ and β‐glucosidase inhibitors in plant extracts. Methodology – The enzymes α‐ and β‐d ‐glucosidase were dissolved in sodium acetate buffer. After migration of the samples, the TLC plate was sprayed with enzyme solution and incubated at room temperature for 60 min in the case of α‐d ‐glucosidase, and 37°C for 20 min in the case of β‐d ‐glucosidase. For detection of the active enzyme, solutions of 2‐naphthyl‐α‐D‐glucopyranoside or 2‐naphthyl‐β‐D‐glucopyranoside and Fast Blue Salt were mixed at a ratio of 1 : 1 (for α‐d ‐glucosidase) or 1 : 4 (for β‐d ‐glucosidase) and sprayed onto the plate to give a purple background colouration after 2–5 min. Results – Enzyme inhibitors were visualised as white spots on the TLC plates. Conduritol B epoxide inhibited α‐d ‐glucosidase and β‐d ‐glucosidase down to 0.1 µg. Methanol extracts of Tussilago farfara and Urtica dioica after migration on TLC gave enzymatic inhibition when applied in amounts of 100 µg for α‐glucosidase and 50 µg for β‐glucosidase. Conclusion – The screening test was able to detect inhibition of α‐ and β‐glucosidases by pure reference substances and by compounds present in complex matrices, such as plant extracts. Copyright © 2009 John Wiley & Sons, Ltd.     

Evolution of the structure of tail feathers: implications for the theory of sexual selection

Bird tails are extraordinarily variable in length and functionality. In some species, males have evolved exaggeratedly long tails as a result of sexual selection. Changes in tail length should be associated with changes in feather structure. The study of the evolution of feather structure in bird tails could give insight to understand the causes and means of evolution in relation to processes of sexual selection. In theory, three possible means of tail length evolution in relation to structural components might be expected: (1) a positive relationship between the increase in length and size of structural components maintaining the mechanical properties of the feather; (2) no relationship; that is, enlarging feather length without changes in the structural components; and (3) a negative relationship; that is, enlarging feather length by reducing structural components. These hypotheses were tested using phylogenetic analyses to examine changes in both degree of exaggeration in tail length and structural characteristics of tail feathers (rachis width and density of barbs) in 36 species, including those dimorphic and nondimorphic in tail length. The degree of sexual dimorphism in tail length was negatively correlated with both rachis width and density of barbs in males but not in females. Reinforcing this result, we found that dimorphism in tail length was negatively associated with dimorphism in tail feather structure (rachis width and density of barbs). These results support the third hypothesis, in which the evolution of long feathers occurs at the expense of making them simpler and therefore less costly to produce. However, we do not know the effects of enfeeblement on the costs of bearing. If the total costs increased, the enfeeblement of feathers could be explained as a reinforcement of the honesty of the signal. Alternatively, if total costs were reduced, the strategy could be explained by cheating processes. The study of female preferences for fragile tail feathers is essential to test these two hypotheses. Preferences for fragile tails would support the evolution of reinforcement of honesty, whereas female indifference would indicate the existence of cheating in certain stages of the evolutionary process.     

The morphology of neoptile feathers: Ancestral state reconstruction and its phylogenetic implications

Avian neoptile feathers are defined as the first feather generation, which covers the chick after hatching, and usually described as simple structures consisting of numerous downy barbs which are radially symmetrically arranged and come together in a short calamus. In contrast, in some birds (e.g., Anas platyrhynchos, Dromaius novaehollandiae) the neoptile feathers have a prominent rhachis, and therefore display clear bilateral symmetry. Because the symmetrical variety found in neoptile feathers is poorly understood, their morphology was studied in a more comprehensive and phylogenetic approach. Neoptile body feathers from over 22 bird species were investigated using light microscopy, SEM, and MicroCT. Characters such as an anterior–posterior axis, a central rhachis, medullary cells, and structure of the calamus wall were defined and mapped onto recent phylogenetic hypotheses for extant birds. It can be shown that bilaterally symmetric neoptile feathers (with a solid calamus wall) were already present in the stem lineage of crown‐group birds (Neornithes). In contrast, simple radially symmetric neoptile feathers (with a fragile calamus wall) are an apomorphic character complex for the clade Neoaves. The simple morphology of this feather type may be the result of a reduced period of development during embryogenesis. To date, embryogenesis of neoptile feathers from only a few bird species was used as a model to reconstruct feather evolution. Because this study shows that the morphology of neoptile feathers is more diverse and even shows a clear phylogenetic signal, it is necessary to expand the spectrum of “model organisms” to species with bilaterally symmetric neoptile feathers and compare differences in the frequency of feather development from a phylogenetic point of view. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Feather‐degrading bacteria,uropygial gland size and feather quality in House Sparrows Passer domesticus

Feathers are dead integumentary structures that are prone to damage and thus show gradual degradation over the course of a year. This loss of quality might have negative fitness consequences. Feather‐degrading bacteria are some of the most prevalent feather‐degrading organisms, yet the relationship between feather‐degrading bacteria load and flight feather quality has rarely been assessed. We studied this relationship in free‐living House Sparrows during breeding and non‐breeding annual lifecycle stages. We also considered the size of the uropygial gland, given the antimicrobial function of its secretions, and the effect of body condition. The number of feather holes was positively associated with feather‐degrading bacteria load and was negatively related to uropygial gland size and body condition during the breeding season in both sexes. In the non‐breeding season we found the same relationships, but only in females. The degree of feather wear was unrelated to any of the variables measured during the breeding season, whereas it was negatively associated with uropygial gland size and positively with feather‐degrading bacteria load in the non‐breeding season, but only in females. Our results suggest that feather‐degrading bacteria may induce the formation of feather holes, but play only a minor role in the abrasion of flight feathers.     

Comparative study of toxic effects of zearalenone and its two major metabolites α‐zearalenol and β‐zearalenol on cultured human Caco‐2 cells

Zearalenone (ZEN) is a fusarotoxin converted predominantly into α‐zearalenol (α‐Zol) and β‐zearalenol (β‐Zol) by hepatic hydroxysteroid dehydrogenases. The feeding of naturally contaminated grains with ZEN was associated with hyperestrogenic and adverse effects on humans and animals. There is a lack of information on the attribution of the toxic effects of these toxins. One wonders if these effects are due to the parent molecule (ZEN) or to its major metabolites (α‐Zol and β‐Zol). Using human Caco‐2 cells, we looked for the molecular mechanisms of toxicity of ZEN, α‐Zol, and β‐Zol. Toxicity effects were studied by MTT viability assay and oxidative stress induction by measuring malondialdehyde (MDA) generation. To check whether the oxidative stress induction was associated to DNA lesions, we looked for DNA fragmentation by means of the Comet and the diphenylamine assays. To specify cell death pathway, we investigated caspase‐3 activation, confirmed by poly(ADP‐ribose) polymerase cleavage and by Bcl‐2 depletion. Our results clearly demonstrated that ZEN as well as its two metabolites presented variable toxic effects. They induced cell death and an increase in MDA generation. These effects were associated to DNA fragmentation as well as caspase‐3 activation. The observed toxic effects seem to be relieved by the metabolism of ZEN into α‐Zol and β‐Zol. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:233–243, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20284     

Adventitious feather replacement favours a more rapid regeneration of primaries over rectrices in two passerine bird species

There is increasing evidence of adaptive preferential investment during moult in those feather tracts that are more advantageous for fitness. In this study, we assessed whether, after the manual removal of two functionally different flight feathers (one primary and one rectrix), birds from two common passerine species (Eurasian Blackcap Sylvia atricapilla and European Robin Erithacus rubecula) favoured the regeneration of primary (supposedly the most functionally important feathers) over rectrix feathers. Our results did not show differences between replaced primary and rectrix feathers in their final length, but demonstrated that the gap left by the loss of the primary feather was filled earlier, suggesting that a rapid repair of the most essential feather tracts is also evolutionarily advantageous during the adventitious replacement of plumage.     

Chronic coccidian infestation compromises flight feather quality in house sparrows Passer domesticus

Parasites usurp indispensable resources for birds during a moult, and this is particularly relevant for those parasites residing in host intestines. This might compromise the nutritionally demanding moult and, thus, feather functionality. Although lower feather quality has profound and multifaceted adverse effects on residual fitness, surprisingly, little is known about parasites' effect on feather traits, especially over the longer term. We conducted an aviary experiment by medicating half of a group of naturally infested house sparrows Passer domesticus against intestinal coccidians for 15 months, spanning two consecutive postnuptial moults, whereas the other half was kept infested (i.e. without medication). Coccidian infestation significantly and negatively affected the size of the uropygial gland during the second moulting period compared to the medicated group. Furthermore, wing length was significantly shorter after the second moulting in the non‐medicated compared to the medicated female birds, which indicates that the negative effects of coccidians emerge only after a prolonged exposure to parasite infestation. Non‐medicated birds grew poorer quality flight feathers detected in a large number of feather traits both after the first and second moults. In the case of non‐medicated birds, the primaries were lighter and shorter, and had a smaller vane area, thinner rachis and decreased stiffness, although a higher barb and barbule density, which may have various consequences for fitness through reducing flight performance. Our findings demonstrate that, besides the well‐known immediate consequences for host breeding success, parasites might also have serious, long‐lasting effects through influencing feather quality and, ultimately, fitness of the host. © 2013 The Linnean Society of London