Secrets of the half-male, half-female cuttlefish revealed at last

Cuttlefish always seem to be among the most fascinating marine life forms — whether it's on account of their flashy battles for mating rights, or their ability to see the world through polarized light. And now, researchers have discovered yet another extraordinary thing they can do: Male cuttlefish can alter their physical appearance straight down the middle, depending on who's looking at them.

The cuttlefish do this to fool males into thinking that they're females, thus convincing them that they're not a threat. Meanwhile, they still appear as males to females, for obvious reasons.

The discovery was made by researcher and ecologist Culum Brown of Macquarie University in Sydney, Australia, whose findings were reported in Biology Letters.

Brown suspects that the behaviors might be learned — a strong indication of the species' complex social intelligence. In fact, cuttlefish have one of the largest brain-to-body size ratios of any invertebrate.

Writing in ScienceNow, Sarah Williams describes what's going on:

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 further from the surface to change the pattern on the fish. But scientists had never seen a male fish 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 previous dives of Sydney Harbour. 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% 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.

Brown has observed that the cuttlefish only perform this trick in one particular context. He says that the male's best strategy, should he find an attractive female, is to be sneaky about it, and hide the fact that he's found a hot date.

Be sure to read Williams' entire article at ScienceNow.

Image via ScienceNow/Culum Brown.