Nerve cells—dyed red in the above image—are responsible for squids' shimmering displays of iridescence, new research shows.
A squid's shifting metallic sheen comes from clusters of tiny platelike structures inside their skin cells. (See squid pictures.)
Known as iridophores, the microscopic ensemble interferes with the way certain wavelengths of light are reflected.
"It's the same effect you get with shiny colors on a soap bubble or a thin layer of oil on the water surface in a harbor," said study co-author Paloma Gonzalez-Bellido, a neuroethologist at the Marine Biological Laboratory in Woods Hole, Massachusetts.
Exactly how squid turn these iridophores on and off has, until now, remained a mystery.
A new technique allowed the team to hook up electrodes to individual nerves in squid skin. When they sent electrical impulses into the nerves, the iridophores changed color and brightness.
Image courtesy Trevor Wardill and Paloma Gonzalez-Bellido
Longfin inshore squid (pictured) use nerves to control iridescence in their skin—and it's likely that other squid species do the same thing, said study co-author Trevor Wardill, also of the Marine Biological Laboratory.
However, it may take time to discover whether close relatives of squid—including cuttlefish and octopus—shimmer via the same process because of the complex neurons and muscles in their skin.
"We can stimulate the skin of cuttlefish, but they are very difficult to work with," said Wardill, whose study appeared recently in the journal Proceedings of the Royal Society B. "Squid are a simple version."