Elemental characterisation of melanin in feathers via synchrotron X-ray imaging and absorption spectroscopy

Abstract

Melanin is a critical component of biological systems, but the exact chemistry of melanin is still imprecisely known. This is partly due to melanin’s complex heterogeneous nature and partly because many studies use synthetic analogues and/or pigments extracted from their natural biological setting, which may display important differences from endogenous pigments. Here we demonstrate how synchrotron X-ray analyses can non-destructively characterise the elements associated with melanin pigment in situ within extant feathers. Elemental imaging shows that the distributions of Ca, Cu and Zn are almost exclusively controlled by melanin pigment distribution. X-ray absorption spectroscopy demonstrates that the atomic coordination of zinc and sulfur is different within eumelanised regions compared to pheomelanised regions. This not only impacts our fundamental understanding of pigmentation in extant organisms but also provides a significant contribution to the evidence-based colour palette available for reconstructing the appearance of fossil organisms.

Root‐induced soil deformation influences Fe, S and P: rhizosphere chemistry investigated using synchrotron XRF and XANES

“…Arylsulfatase enzymes act on aromatic sulfate-esters, while alkyl-sulfatase acts on aliphatic sulfate-esters; both sulfate-releasing enzymes/ products are common in the rhizosphere. The use of X-ray absorption near-edge structure (XANES) in combination with synchrotron X-ray fluorescence (SR-XRF) mapping have been proven to be a powerful nondestructive technique for direct speciation of various elements in biological and geological samples (Egerton et al, 2015;Edwards et al, 2016). However, in order to mobilize sulfonate, an exclusive bacterial multicomponent enzyme known as monooxygenase complex is necessary (Kertesz & Mirleau, 2004).…”

Biological responses to environmental contamination. How can metal pollution impact signal honesty in avian species?

“…It induces aggregation of melanin particles, making feather more durable and resistant to mechanical stress (Niecke et al., 1999). Synchrotron X‐ray analyses showed that the distribution of calcium is controlled by melanin pigment and is nonuniformly distributed throughout feather parts (Edwards et al., 2016; Howell et al., 2017). In a study performed on male Barn Owls, Roulin, Dauwe, Blust, Eens, and Beaud (2006) demonstrated a positive relationship between enhanced calcium deposition in humerus bone and plumage spottiness.…”

“…It was also found in nonpigmented feather parts. Zinc appeared to have higher affinity for pheomelanin than eumelanin, and relative, not absolute concentrations correlating with pigment patterns (Edwards et al., 2016). …”

“…Similarly to zinc and calcium, copper is controlled by melanin pigment patterns in feathers (Edwards et al., 2016). Both analyses in this study employed a similar sample size in the calculation of average effect size.…”

Imaging techniques in the study of fossil spiders

“…Evidence for original colouration (rather than simply patterning), both structural and chemical, have been found in fossils (e.g. Colleary et al, 2012;Glass et al, 2012;Vitek et al, 2013;Vinther, 2015;Edwards et al, 2016). So, pigmentation and/or structural colours could be discovered in fossil spiders using these techniques.…”