Malleable skin coloration in cephalopods: selective reflectance, transmission and absorbance of light by chromatophores and iridophores

Abstract

Nature's best-known example of colorful, changeable, and diverse skin patterning is found in cephalopods. Color and pattern changes in squid skin are mediated by the action of thousands of pigmented chromatophore organs in combination with subjacent light-reflecting iridophore cells. Chromatophores (brown, red, yellow pigment) are innervated directly by the brain and can quickly expand and retract over underlying iridophore cells (red, orange, yellow, green, blue iridescence). Here, we present the first spectral account of the colors that are produced by the interaction between chromatophores and iridophores in squid (Loligo pealeii). Using a spectrometer, we have acquired highly focused reflectance measurements of chromatophores, iridophores, and the quality and quantity of light reflected when both interact. Results indicate that the light reflected from iridophores can be filtered by the chromatophores, enhancing their appearance. We have also measured polarization aspects of iridophores and chromatophores and show that, whereas structurally reflecting iridophores polarize light at certain angles, pigmentary chromatophores do not. We have further measured the reflectance change that iridophores undergo during physiological activity, from "off" to various degrees of "on", revealing specifically the way that colors shift from the longer end (infra-red and red) to the shorter (blue) end of the spectrum. By demonstrating that three color classes of pigments, combined with a single type of reflective cell, produce colors that envelop the whole of the visible spectrum, this study provides an insight into the optical mechanisms employed by the elaborate skin of cephalopods to give the extreme diversity that enables their dynamic camouflage and signaling.

Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model

“…Some cephalopod species (squid, cuttlefish and octopus) exhibit a remarkable colour change: the body pattern can be almost instantaneously changed for camouflage and signalling [31,32]. In particular, a unique structural variation has been observed inside a dermal iridophore of a squid, Lolliguncula brevis: a multilayer reflector is gradually formed using proteinaceous material during the appearance of iridescence [33,34].…”

Human Colors—The Rainbow Garden of Pathology: What Gives Normal and Pathologic Tissues Their Color?

“…Examples of structural coloration and iridescence can be appreciated in the shiny brilliant colors of peacock (Pavo cristatus) feathers, butterfly (Rhopalocera) wings, the exoskeleton of beetles (Coleoptera), the skin of fish and cephalopods, and the fruit of the African plant marble berry (Pollia condensata) (Figure 7, B and C). [39][40][41] Structural coloration is also crucial for the brilliant blue colors in several organisms 39 and may also be seen in sectioned skeletal muscle from mammals ( Figure 7, D through F). Type II collagen is white and is the main constituent of cartilage.…”

Quantifying the refractive index dispersion of a pigmented biological tissue using Jamin–Lebedeff interference microscopy

“…The dual effect of pigment absorption, namely, the absorption of short-wavelength light and the enhanced reflection of long-wavelength light, can also be recognized in reflecting pigment cells and tapeta in the eyes of crustaceans [18][19][20] and presumably also in the coloration caused by pigments in cephalopods. 21 We previously studied the pigmented wings of another damselfly, Calopteryx japonica. 22 The pigment in that case is melanin, causing brown-colored wings in the immature female, the mature female and the immature male.…”

“…We note that there are even several examples in which periodically arranged, structurally colored tissue contains additional pigment that selectively filters the reflected light, thus tuning and sharpening the reflectance spectrum. 21,30,31 Pigmentary and structural coloration thus are not strictly separable.…”