Gender-bending cuttlefish trick rivals
SOME CUTTLEFISH CAN CLEVERLY put on a female disguise to avoid detection from rival males while still impressing the ladies, scientists have found.
Male mourning cuttlefish (Sepia plangon) – named from the blue tinge that often occurs around their eyes – show off an enticing display on one side of their bodies to attract potential mates and mimic female patterns on the other, so nearby rivals aren’t aware another male is around.
“It’s split down the middle of the mantle,” says Culum Brown, a behavioural ecologist at Macquarie University and co-author of the study. “On one side they’re doing their usual male display, a pulsating stripy pattern which is mesmerising to watch. On the other, they’re simultaneously mimicking the pattern of the female they’re courting.
“They’re sending out a true signal on one side, signalling to the girls, ‘yes I’m a male and jeez I’m sexy’, but simultaneously they’re sending out a message which is effectively a lie to the rest of the world, pretending to be a female on the other side so they don’t attract the attention of rival males.”
Cuttlefish, masters of disguise
Cuttlefish have a remarkable ability to change the colour and texture of their skin at will to communicate with others and camouflage themselves from predators, but split signalling has never been seen before.
Male mourning cuttlefish may use this dual-pattern tactic to avoid attracting attention, Culum says. “They’re trying to hide from their fellow males so they can get enough time to convince the females to mate with them.”
Mating can be a tricky business for male cuttlefish, as females are not easily seduced.
“There’s a lot of competition amongst the males. Generally, the population is male-biased, so there aren’t enough girls to go around,” Culum says. “These guys need to find a female for starters, but they also need to buy time to display for long enough to convince the female that they’re worth mating with.”
But if the feminine disguise is too convincing and the male rival comes sniffing around, the lover immediately switches to a fighter. “If the rival male comes within about four or five body lengths, the male who’s pretending to be a female on one side switches to a completely aggressive display. He knows the game’s up, and he has to go into fighting mode,” Culum says.
Then it’s down to a muscle match. “If the rival male is bigger, he nearly always wins. The little ones will just disappear, do a runner,” Culum says.
Cuttlefish use cross-gender patterns sparingly
Culum and his team trawled through several hours of footage of wild cuttlefish around Sydney, taken over six years, and also studied captive groups in an aquarium. They found that males only ever used the split tactic when there was one rival around, and even then only 40 per cent of the time.
“When you do the sums it’s something like less than 6 per cent of all males use this deceptive display,” says Culum. “Most of the time if you see a female display, it really is a female.”
Cuttlefish avoid mixed messages
The likely reason that cross-dressing patterns are used sparingly is there’s a risk of putting out so many false female patterns that the truth about being a male is not believed.
“Signals have to be honest most of the time. If I send out a signal saying that I’m a male, but 50 per cent of the time it turns out to be false, then that signal is no longer reliable,” says Culum. “Evolution rapidly removes any signal from the communication system which is unreliable. In this way the amount of cheating is kept under control.”
“Cephalopods have really complicated visual signals – they have incredible control over their chromatophores,” says John Endler, an evolutionary biologist at Deakin University who was not involved in the study. “This is the only case I know of where their bodies are being used for different purposes at will.”
The findings were published last week in the journal Biology Letters.
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