Chromatophores
by Hannah Rosen
When you wake up in the morning, you have to decide what you want to wear. You may use your clothing choice to try to say something about yourself. Well, squid do the same thing, but they never end up regretting their outfit, because they can change their body color in an instant.
But how is that possible? If you look at your squid, you'll see that its body is covered in what looks like thousands of tiny freckles. But unlike the freckles that we may have, squid can make these little dots bigger or smaller whenever they want. These freckles are called chromatophores. They are made of tiny sacs of color that can be stretched by muscles that are controlled by nerves coming from the brain. The color sacs are very elastic and stretchy, so when the muscles are relaxed the color sacs become very tiny. So tiny in fact that you can barely see them. When the squid wants to change its color, the muscles pull on the color sacs and they get big enough for the color to be seen. If you rub really hard on a white area of the squidâ's skin, you will be able to break open some of the color sacs and make the color more visible.
Many squid have different colors of chromatophores on their body, but Humboldt squid only have red chromatophores. They and other squid use their ability to stretch and relax their chromatophores to create different color patterns on their skin. They use these patterns for camouflage, and also to talk to each other. No matter what a squid wears, it is always making a statement! Humboldt squid are particularly chatty. When they get together you can often see them change their body color from red to white and back again really quickly, kind of like a swimming strobe light. We call this flashing, and we think it is a way the squid talk to each other. Unfortunately we don't speak squid (yet) so we don't know exactly what they are saying when they do this, or if they are even saying anything at all.
When the squid aren't flashing at each other they produce another display called flickering. When flickering, the squid expands and contracts its chromatophores independently of each other. The resulting pattern looks a little like static on a television screen. Why would squid want to do that? Well, we think this is a way for squid to hide in plain sight. That's because the patterns created while flickering look very similar to how the light looks underwater; think about the patterns light makes at the bottom of a swimming pool. Squid swimming in the open ocean don't have anything solid to blend in with since they aren't close to the seafloor, so they need to take advantage of anything they can to keep from getting eaten! By creating patterns on their skin that are similar to the light around them, it might help them blend seamlessly into the background and be less likely to become a tasty treat.
Links
National Geographic Article on the Critter Cam work
Hannah Rosen's research profile
References
Rosen, H., Gilly, W., Bell, L., Abernathy, K. & Marshall, G. Chromogenic behaviors of the Humboldt squid ( Dosidicus gigas ) studied in situ with an animal-borne video package. 265–275 (2015). doi:10.1242/jeb.114157
Hopkins Marine Station, Stanford University, 120 Ocean View Blvd., Pacific Grove, CA 93950 Lab Phone: 831-