Sleep and vigilance linked to melanism in wild barn owls

Understanding the function of variation in sleep requires studies in the natural ecological conditions in which sleep evolved. Sleep has an impact on individual performance and hence may integrate the costs and benefits of investing in processes that are sensitive to sleep, such as immunity or coping with stress. Because dark and pale melanic animals differentially regulate energy homeostasis, immunity and stress hormone levels, the amount and/or organization of sleep may covary with melanin‐based colour. We show here that wild, cross‐fostered nestling barn owls (Tyto alba) born from mothers displaying more black spots had shorter non‐REM (rapid eye movement) sleep bouts, a shorter latency until the occurrence of REM sleep after a bout of wakefulness and more wakefulness bouts. In male nestlings, the same sleep traits also correlated with their own level of spotting. Because heavily spotted male nestlings and the offspring of heavily spotted biological mothers switched sleep–wakefulness states more frequently, we propose the hypothesis that they could be also behaviourally more vigilant. Accordingly, nestlings from mothers displaying many black spots looked more often towards the nest entrance where their parents bring food and towards their sibling against whom they compete. Owlets from heavily spotted mothers might invest more in vigilance, thereby possibly increasing associated costs due to sleep fragmentation. We conclude that different strategies of the regulation of brain activity have evolved and are correlated with melanin‐based coloration.     

Human hair melanins: what we have learned and have not learned from mouse coat color pigmentation

Hair pigmentation is one of the most conspicuous phenotypes in humans. Melanocytes produce two distinct types of melanin pigment: brown to black, indolic eumelanin and yellow to reddish brown, sulfur‐containing pheomelanin. Biochemically, the precursor tyrosine and the key enzyme tyrosinase and the tyrosinase‐related proteins are involved in eumelanogenesis, while only the additional presence of cysteine is necessary for pheomelanogenesis. Other important proteins involved in melanogenesis include P protein, MATP protein, α‐MSH, agouti signaling protein (ASIP), MC1R (the receptor for MSH and ASIP), and SLC7A11, a cystine transporter. Many studies have examined the effects of loss‐of‐function mutations of those proteins on mouse coat color pigmentation. In contrast, much less is known regarding the effects of mutations of the corresponding proteins on human hair pigmentation except for MC1R polymorphisms that lead to pheomelanogenesis. This perspective will discuss what we have/have not learned from mouse coat color pigmentation, with special emphasis on the significant roles of pH and the level of cysteine in melanosomes in controlling melanogenesis. Based on these data, a hypothesis is proposed to explain the diversity of human hair pigmentation.     

Establishment of a mouse model for post‐inflammatory hyperpigmentation

Post‐inflammatory hyperpigmentation (PIH) is a common cutaneous condition that can cause a disfigured appearance. However, the pathophysiology of PIH remains poorly understood, at least in part, because an appropriate animal model for research has not been established. In order to analyze the pathomechanism of PIH, we successfully induced PIH in a hairless version of transgenic mice (hk14‐SCF Tg/HRM) that have a human‐type epidermis containing melanin by repeated hapten application of 2,4‐dinitrofluorobenzene. Histopathologic observation showed epidermal hyperplasia, predominant infiltrations of inflammatory cells, and melanin‐containing cells in the dermis just after elicitation of the atopic dermatitis‐like condition. At week 2, the findings were similar to the characteristics of PIH, that is, an increase of melanin without spongiosis or liquid degeneration in the epidermis and an increase in dermal melanophages. Dynamic analysis of melanin showed that the melanin in the dermis remained for a longer duration than in the epidermis. Furthermore, immunohistochemical staining revealed that the majority of cells containing melanin were positive for the anti‐CD68 antibody, but negative for the anti‐F4/80 antibody. These data suggest that novel treatments of PIH should be targeted against macrophages and should eventually lead to the development of new treatment modalities.     

Clinal variation in the morph ratio of Black Sparrowhawks Accipiter melanoleucus in South Africa and its correlation with environmental variables

The morph ratio distribution in polymorphic species often varies clinally, with a gradual change in morph ratios across the distributional range of the species. In polymorphic bird populations, clinal variation is rarely quantified. We describe a cline in the morph ratios of Black Sparrowhawks across South Africa, which is principally driven by a higher ratio of dark morph birds in the newly colonized southwest of the country. Across the 1400 km of our cline, the probability of a bird being a dark morph declined from over 80% close to the Cape Peninsula to under 20% in the northeast. Higher frequencies of dark morphs were associated with a higher proportion of rainfall falling during the winter breeding months. Further investigation revealed relationships between the proportion of dark morphs and altitude, amount of rainfall during the breeding months, and an interaction between this variable and temperature. These results provide some support for the suggestion that the higher frequency of dark morphs in the southwest is an adaptive response, rather than the result of a founder effect or genetic drift. These findings also suggest that, in theory, polymorphic species may be better adapted to cope with the challenges of climate change or may be able to expand their ranges more quickly into novel climatic areas, since selection pressure can act on a pre‐existing trait that may be beneficial in new conditions.     

Three-dimensional soft tissue preservation revealed in the skin of a non-avian dinosaur

The most commonly preserved soft tissues associated with ornithischian dinosaurs are skin remains. The apparent resistance of hadrosaur skin to decay, and its abundance in the fossil record relative to that of other tetrapods, has been attributed to factors such as thickness and composition. Here we report additional intrinsic factors within hadrosaur skin: 3D-preserved eumelanin-bearing bodies, dermal cells and blood vessel fragments in an organic matrix composed of protein fossilization products. The skin is much thinner than that of living mammals of similar size. It is likely that the preservation of hadrosaur skin is related to the arrangement of the layers composing it.     

A Standardized Protocol for Assessing Regulators of Pigmentation

Varied effects of chemical or biological compounds on mammalian pigmentation have been reported by many groups, but to date, no standardized method has established necessary and/or optimal parameters for testing such agents. A standardized method has been developed to screen compounds with potential effects on pigmentation. The protocol comprises basic parameters to analyze melanogenic effects and allows for further characterization of candidate compounds, providing important insights into their mechanism of action. In this protocol (termed STOPR, for standardized testing of pigmentation regulators), compounds are initially screened using purified tyrosinase and are then tested on melanocytes in culture. After treatment of melanocytes with potentially bioactive compounds, cell proliferation and viability, total melanin accumulated, and melanogenic potential are measured. This protocol is an important first step in characterizing chemical regulation of effects on melanogenesis. When bioactive candidate compounds are identified, testing may proceed for pharmacological or otherwise commercial applications in coculture and/or organ culture models followed by in vivo testing. As an application of this method, results for compounds known to stimulate and/or inhibit melanogenesis (including arbutin, hydroquinone, kojic acid, melanocyte-stimulating hormone, and thymidine dimers) as well as some commercial skin whiteners are reported.     

Oxidative Stress in Relation to Lipid Peroxidation, Sclerotial Development and Melanin Production by Sclerotium rolfsii

Melanin pigments constituted 13.9% of the chemical composition of the sclerotial walls of Sclerotium rolfsii and was associated with proteins, reducing sugars and amino acids. The lipid and ash contents in the sclerotial walls were double those in the hyphal walls of the fungus. Increasing age of the culture and maturation of the sclerotia were always accompanied by elevation of lipid peroxides and melanin pigments. Such behaviour may indicate that lipid peroxidation and melanin formation are operating in parallel during sclerotial biogenesis and maturation. These two processes depend on the theory of oxidative stress, as affected by growth conditions. Both processes could be stopped or sharply retarded when subjected to some antioxidant growth factors such as vitamins (ascorbic acid), micro-elements (selenium) and sulfhydryl compounds (glutathione). A clear relation between oxidative stress, myceliogenic germination and lytic activity via melanin production was observed. This finding appears promising in applying a new control measure against diseases caused by sclerotia-producing fungi without using traditional toxic fungicides.     

Aluminum Enhances Melanin-Induced Lipid Peroxidation

The present study was conducted to characterize the possible interaction of Al³⁺ and Fe²⁺ with synthetic melanin in the potentiation of lipid peroxidation in liposomes and rat caudate-putamen homogenates. Al³⁺ stimulated melanin-initiated lipid peroxidation as measured by the production of 2-thiobarbituric acid-reactive substances (TBARS) and conjugated dienes. The effect of Al³⁺ was dependent on melanin (10–100 g/ml) and Al³⁺ (2.5–250 M) concentrations and no synergism between Fe²⁺ and Al³⁺ was observed. The prooxidant effect of Al³⁺ was partially inhibited by superoxide dismutase indicating the involvement of O ₂ ^- . Ga³⁺ and Be²⁺ which can increase NADH oxidation in the presence of O ₂ ^- , also were shown to stimulate melanin-initiated TBARS production. Based on the effect of Al³⁺ and other non redox metals, we suggest that Al³⁺ does not act through either the induction of melanin free radicals, or the induction of changes in membrane physical properties. Results show that Al³⁺ enhances melanin-initiated lipid peroxidation in part through an interaction with O ₂ ^- generated from the autoxidation of melanin. We speculate that Al³⁺ contributes to neuromelanin-mediated oxidative damage in dopaminergic neurons and subsequent neuronal degeneration and death in Parkinson's disease.     

An ultrastructural study of bruising in stored potato (Solarium tuberosum L.) tubers

Potato tubers of the cultivar Pentland Dell were investigated for ultrastructural changes following impact. Studies were carried out on tubers after 12 and 24 wk of storage using a falling bolt delivering 0.7 J of energy. Ultra-thin sections were examined by light and transmission electron microscopy. Tubers stored for 12 wk exhibited no visual bruise formation, whereas visible bruising resulted following impact of tubers stored for 24 wk. An ultrastructural sequence of events during bruising was established as (1) a collapse of intracellular compartmentation, (2) increased ribosomal and mitochondrial abundance within the cytoplasm, (3) increased density of cytoplasm adjacent to the cell wall and surrounding amyloplasts, and (4) the development of melanin in bruised cells. These observations are discussed in relation to tuber turgor and physiology during storage.