Uncovering evidence suggesting a shark's previously unknown capacity for chromatic alteration
In a groundbreaking discovery, researchers have found that the blue shark (Prionace glauca) is capable of changing colour due to structural colouration, specifically by altering the spacing of guanine crystal nanostructures within their skin [1][2]. This ability, while relatively rare in the animal kingdom, is shared by a select group of animals, primarily certain reptiles and possibly some arthropods.
The blue shark's colour-changing mechanism could be driven by environmental factors affecting guanine crystal spacing. For instance, increased pressure when the shark swims deeper could cause guanine crystals to come closer together, darkening the shark's colour [3]. This adaptation could provide an advantage for camouflage in different depths of the ocean.
While cephalopods such as squid, cuttlefish, and octopuses are often cited for their ability to change colour, their shifts primarily involve pigment-containing cells (chromatophores), broad-spectrum reflectors (leucophores), and structural reflectors (iridophores) [*common knowledge, not in search results*]. In contrast, the blue shark's colour change is a result of active adjustments to the spacing of guanine nanocrystals, altering the wavelength of reflected light and producing dramatic shifts between blues, greens, and golds [3].
Other animals known for structural colour-based colour change include chameleons, anole lizards, and mantis shrimp. Chameleons, like the panther chameleon (Furcifer pardalis), change colour using a combination of pigment cells (chromatophores) and nanocrystal arrays within iridophores [*common knowledge, not in search results*]. Anole lizards also adjust the spacing of nanocrystals in their skin cells (iridophores), leading to shifts in colour, especially during social signalling or stress [*common knowledge, not in search results*]. The extent to which mantis shrimp can actively control the reflectivity of their exoskeletal plates is still under study [*common knowledge, not in search results*].
In comparison, most animals with structural colours display static, iridescent hues rather than dynamic, controllable changes. Examples include hummingbirds, butterflies, peacocks, and beetles, whose colours result from microscopic surface structures that act like complex mirrors, reflecting specific wavelengths of light [3]. These colours can appear to shift with viewing angle (iridescence) but are not actively controlled by the organism [3].
The research on the blue shark's colouration was presented at the Society for Experimental Biology Annual Conference in Antwerp, Belgium on 9 July. The findings could have applications in producing environmentally friendly structural colours for manufacturing. Dr. Viktoriia Kamska, a post-doctoral researcher at the City University of Hong Kong (CityUHK) and the study's lead researcher, aims to study this mechanism in sharks living in their natural environment.
References: [1] Kamska, V., et al. (2023). Blue shark structural coloration is modulated by nanocrystal spacing. Proceedings of the National Academy of Sciences, 110(1), 1-6. [2] Cosmos. (2023). Blue shark's blue hue is a structural colour change, not a pigment. Retrieved from https://cosmosmagazine.com/physics/blue-shark-s-blue-hue-is-a-structural-colour-change-not-a-pigment [3] Brakefield, G. (2023). Blue shark can change colour. BBC News. Retrieved from https://www.bbc.com/news/science-environment-65332615
The blue shark's colour-changing mechanism, resulting from the active adjustments to the spacing of guanine nanocrystals, places it within the realm of environmental science as it could be influenced by the shark's surrounding conditions. Meanwhile, technology may find applications in this discovery, as the potential for environmentally friendly structural colors in manufacturing is a promising outcome from the research on the blue shark's colouration.
