RESUMO
Colour and pattern are key traits with important roles in camouflage, warning and attraction. Ideally, in order to begin to understand the evolution and ecology of colour in nature, it is important to identify and, where possible, fully characterise pigments using biochemical methods. The phylum Mollusca includes some of the most beautiful exemplars of biological pigmentation, with the vivid colours of sea shells particularly prized by collectors and scientists alike. Biochemical studies of molluscan shell colour were fairly common in the last century, but few of these studies have been confirmed using modern methods and very few shell pigments have been fully characterised. Here, we use modern chemical and multi-modal spectroscopic techniques to identify two porphyrin pigments and eumelanin in the shell of marine snails Clanculus pharaonius and C margaritarius. The same porphyrins were also identified in coloured foot tissue of both species. We use high performance liquid chromatography (HPLC) to show definitively that these porphyrins are uroporphyrin I and uroporphyrin III. Evidence from confocal microscopy analyses shows that the distribution of porphyrin pigments corresponds to the striking pink-red of C. pharaonius shells, as well as pink-red dots and lines on the early whorls of C. margaritarius and yellow-brown colour of later whorls. Additional HPLC results suggest that eumelanin is likely responsible for black spots. We refer to the two differently coloured porphyrin pigments as trochopuniceus (pink-red) and trochoxouthos (yellow-brown) in order to distinguish between them. Trochopuniceus and trochoxouthos were not found in the shell of a third species of the same superfamily, Calliostoma zizyphinum, despite its superficially similar colouration, suggesting that this species has different shell pigments. These findings have important implications for the study of colour and pattern in molluscs specifically, but in other taxa more generally, since this study shows that homology of visible colour cannot be assumed without identification of pigments.
Assuntos
Exoesqueleto/metabolismo , Pigmentação , Caramujos/anatomia & histologia , Caramujos/metabolismo , Animais , Pigmentos Biológicos/metabolismoRESUMO
The role of Antarctic epilithic lichens in the primary colonization of rocks and in the formation of soils is receiving attention because of the production of the stress-protective biochemicals needed to combat radiation, desiccation and extremes of temperature. Raman microscopy has been used here to study the encrustations produced at the interface between the rock substratum and Buellia spp. lichen thalli; in addition to whewellite, calcium oxalate monohydrate, the presence of weddellite, the metastable dihydrate form, was confirmed in the encrustations. An unusual pigmentation of the rock surface found on detachment of the lichen growths is identified as beta-carotene from its characteristic Raman bands at 1525, 1191, 1157 and 1003 cm(-1); normally, beta-carotene, which has been identified as a UV-radiation protectant, is found at the exposed upper surface of the biological organism. The interface between the detached lichen thalli and the rock also contains whewellite as the sole biomineralization product--which suggests a possible strategy for the formulation of weddelite in the growing Buellia spp. colony as an anti-desiccant.
Assuntos
Líquens/química , Regiões Antárticas , Meio Ambiente , Análise de Fourier , Líquens/efeitos da radiação , Microscopia/métodos , Protetores contra Radiação/análise , Análise Espectral Raman , Raios Ultravioleta/efeitos adversos , beta Caroteno/análiseRESUMO
Glass structure and fluorine motion dynamics are investigated in lead-cadmium fluorgermanate glasses by means of differential scanning calorimetry, Raman scattering, x-ray absorption (EXAFS), electrical conductivity (EC), and (19)F nuclear magnetic resonance (NMR) techniques. Glasses with composition 60PbGeO(3)-xPbF(2)-yCdF(2) (in mol %), with x+y=40 and x=10, 20, 30, 40, are studied. Addition of metal fluorides to the base PbGeO(3) glass leads to a decrease of the glass transition temperature (T(g)) and to an enhancement of the ionic conductivity properties. Raman and EXAFS data analysis suggest that metagermanate chains form the basic structural feature of these glasses. The NMR study leads to the conclusion that the F-F distances are similar to those found in pure crystalline phases. Experimental results suggest the existence of a heterogeneous glass structure at the molecular scale, which can be described by fluorine rich regions permeating the metagermanate chains. The temperature dependence of the NMR line shapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluorine mobility in these systems.