Cuttlefish are remarkable creatures, capable of instant colour-change and incredible camouflage, as well as clever, unique and quirky behaviours. Perhaps their most fascinating is the passing cloud display, in which the cuttlefish creates bands of colour that move along its body in a wave-like motion.
The common cuttlefish (Sepia ofﬁcinalis) has been the most-studied of cuttlefish species, as scientists attempt to unravel their mysteries. Research into the species has been invaluable – revealing aspects of their behaviours that demonstrate remarkable intelligence. However, a new study is suggesting there is a better, enigmatic and altogether more flamboyant sister species when it comes to studying these passing cloud displays. The function for the display is as yet unknown, but the flamboyant cuttlefish (Metasepia tullbergi) makes use of it frequently, and it appears to be more complex than in other species.
The waves of colour are created using chromatophores, elastic sacs in the skin containing different pigments. When the surrounding muscles are contracted or relaxed the sacs are opened or closed, releasing different amounts of pigment and allowing the cuttlefish to control its colouration and markings.
Andres Laan, Tamar Gutnick, Michael Kuba, and Gilles Laurent of the Max Planck Institute for Brain Research discovered that the passing cloud display’s bands of colour travel across four regions on each side of the flamboyant cuttlefish. All four regions can be active simultaneously, and if so, the expressed waves are synchronised.
The waves can also move at a variety of speeds, while maintaining a constant wavelength, and perhaps most impressively, can ‘blink’: a wave can disappear and reappear at another position, demonstrating ongoing propagation of waves despite briefly appearing invisible on the surface.
The displays were seen superposed on a number of different textures and colours the cuttlefish was simultaneously exhibiting on its skin, and in addition during a variety of behaviours: the researchers observed the passing cloud display during hunting, swimming, resting, mating, and egg maintenance.
Laurent, Kuba, Gutnick and Laan have uncovered some of the underlying neural mechanisms behind the passing cloud display, and while some aspects of cuttlefish dynamic camouflage and colouration remain a mystery, the research has added to the growing body of knowledge surrounding the phenomenon.
One suggested function of the passing cloud display is that it enhances the vivid colours of the flamboyant cuttlefish to serve as a warning signal, informing potential predators of its toxicity. A conclusive answer has yet to be reached, but the valuable insights this study has provided and the suggestion of a better model organism for studying the display puts us one step closer to unlocking the secrets of these remarkable creatures.
Laan, A., Gutnick, T., Kuba, M. J., and Laurent, G. (2014). Behavioral analysis of cuttlefish traveling waves and its implications for neural control. Current Biology 24: 1737-1742. doi: 10.1016/j.cub.2014.06.027