Cross-dressing mourning cuttlefish make it hard for their fellow mollusks to tell male from female. (F1online digitale Bildagentur GmbH / Alamy/ALAMY)
A two-faced seducer of the deep

Talk about showing your feminine side. On one flank, a courting male cuttlefish looks like a normal male of his species, with tigerlike stripes extending horizontally down his body. But on the other, he resembles a female, displaying marbled browns and whites. He needs the male pattern to attract the female, while the female motif keeps competing males from fighting him. That is scientists’ best guess to explain the devious cuttlefish behavior that they’ve observed and reported for the first time.

“Cuttlefish are a very smart group,” says lead researcher and ecologist Culum Brown of Macquarie University in Sydney. “And it’s pretty obvious that they are specifically using this display in a tactical way.”

Researchers knew that cuttlefish (Sepia plangon) could camouflage their skin to match their surroundings and that they could show different patterns on each side. Their skin contains a highly concentrated layer of chromatophores — various-colored, pigment-containing cells — that can be moved closer or farther from the surface to change the pattern on the mollusk. But scientists had never seen a male mimicking a female on only one side as a trick of courtship.

Brown and his colleagues first observed the behavior in a large aquarium in their lab. They wondered whether males in the wild did the same thing, and if so, when and why. So they combed through photos of 108 distinct groups of cuttlefish taken on dives of Sydney Harbor. They found that when a male was in a group with one female and one other male, he displayed the dual patterns — a male side facing the female and a female side facing the male — 39 percent of the time. In other situations, such as an all-male group or a male matched with two females, the dual display was never seen.

Science Now, the daily online news service of the journal Science.