, 2004). When they are present blue pigments are more likely to be found in the extracellular matrix for example in the copepod Pontella fera, the crayfish Procambarus clarkii and the abalone Haliotis discus hannai (Herring, 1965; Cheesman, Lee

& Zagalsky, 1967; Milicua et al., 1985). Also, many bird species blue pigments such as biliverdins occur in the extracellular matrix of their eggshells (Kilner, 2006; Stoddard & Prum, 2008). Goda & Fujii (1995) reported the first and only known cyanophores (true blue chromatophores) in the ectoderm of Synchiropus mandarin fishes. Within the cyanophores, the cyanosomes aggregate and disperse in response to various stimuli probably causing the colour change that occurs in these fish (Goda & Fujii, 1998). It seems unlikely that this is the only incidence BMN 673 nmr of a blue cyanophore in nature and research into potential blue pigments will likely turn up more examples. Structural colours are those whose wavelengths are reflected as a result of optical interference by nanoscale structures in or on an animal’s integument. Ultraviolets, violets, and blues are often structural colours (Bagnara et al., 2007). Examples of body parts on which colour-producing nanostructures occur include the scale

on a butterfly’s wing (Ghiradella, 1991), the barbule of a bird’s feather (Prum, 2003; D’Alba et al., 2011), or the arrangement of Doxorubicin in vitro fibres or granules embedded in a dermal layer (Filshie et al., 1975; Prum & Torres, 2003, 2004; Prum et al., 2004). In vertebrates, the iridophore is a chromatophore that contains crystalline structures (rather than pigments as in most chromatophores) that give rise to blue colouration (Rohrlich, 1974; Clothier & Lythgoe, 1987; Bagnara et al., 2007). Iridophores are often found in association with yellow pigments to produce green colours and when the yellow pigment is reduced (axanthism) the organism appears blue (Bagnara, Frost & Matsumoto, 1978). Blue colours medchemexpress are produced by a much greater diversity of structures than those found in iridophores. There

are several categories of structures that preferentially scatter blue light categorized by their degree of order (Fig. 2). Incoherent and quasi-coherent arrangements are subordered and produce low chroma non-iridescent colours. If ordered, however, structures can produce high chroma colours and iridescent effects (wavelength reflected changes based on the reviewer’s angle to the object). The effects mentioned earlier can be caused by a variety of mechanisms and there are number of dimensions at which structures are ordered. Structural colours are often purified by accompanying pigments (notably melanin) that lie underneath surface structures, and absorb non-targeted wavelengths (Shawkey & Hill, 2006). In amelanic phenotypes, therefore, some colours may be muddied, faded or completely lost (Siefferman & Hill, 2005a).