Think you're having a hard time finding a date for Valentine's Day? Tell it to the male Australian cuttlefish, who sometimes has to dress up like a female if he wants to get the girl. This ScienCentral News video has more.
By Any Means Necessary
All is fair in love and war— especially when the two are intertwined. Just ask the male Australian cuttlefish.
"The male cuttlefish has quite a challenge on his hands when it comes to the end of their yearly life cycle," explains Roger Hanlon, senior scientist at the Marine Biological Laboratory. "There are four, five even ten males for every female on the spawning grounds, so the challenge they face is, 'How do I get my genes into the next generation?' There's enormous competition among the males for the relatively few females that are on the spawning ground."
Hanlon and his team spent five spawning seasons observing cuttlefish underwater in a remote coastal area of Australia. As one might expect, the largest males used their size advantage to find a female partner and guard her from other males. Hanlon observed that smaller males were able to get to the female while the guard male was fighting other males away, or by meeting the female in a "secret rendezvous" under a rock, for instance. But he found that the small males with the biggest success rate employ the same camouflage trick that allows them to escape predators: these so-called "sneaker" males change their skin pattern and body shape to disguise themselves as females, and swim right past a large guard male, who thinks he's getting another girlfriend.
"You certainly do not fight the big male because he's going to beat you up very quickly and very easily," explains Hanlon. "So [small males] don't even engage in a fight, but they do what we call sneaking tactics: He hides the fourth arms (females only have three sets of arms), bulges his arms up like he's holding an egg, and he puts on a coloration pattern that's typical of females. And then, he just waltzes right in. And every single time that this happens, the big male looks and thinks he's acquiring another female mate and he lets 'him/her' just swim right in next to the female. And as soon as he gets under the big male and he's next to the female, it's like, 'Okay, let's try a mating'."
The big cuttlefish on the right is fruitlessly guarding a female (unseen in this image). The cuttlefish on the left is a male disguised as a female, who will successfully get past the guard. image: Roger Hanlon
Hanlon reported in the journal Nature that although females reject 70 percent of mating attempts overall, they accepted the majority of advances from disguised males. He also found that eggs were in fact fertilized by these so-called "mimics." The female cuttlefish collects sperm from several males and then later uses some to fertilize the egg. So mating in and of itself does not necessarily lead to fertilization, or "genetic success." But using a genetic paternity test called DNA fingerprinting, Hanlon found that the female more often than not fertilized her next egg with sperm from the mimic male.
Is this a triumph of brains over brawn? "She's rejecting 70 percent of mating attempts, yet she's taking these small mimics at a much higher rate," he says. "Why is that? We don't know the answer, but there's something attractive, clever, some sign of fitness, of that male doing something clever, maybe an indirect sign of good genes in that animal. And so she will take the gamble, if you will, of mating with him and taking his DNA in the hope that he's a good match for her. So this is the explanation that we get from this kind of unusual study where we find a mating and a fertilization where we didn't expect it. One has to rethink the problem and say, 'Well, maybe there's an advantage to that female to get some of his genes. Maybe he's a pretty clever guy— he's very healthy, he's doing something bold, maybe that'll pay off to [her] progeny."
Hanlon says "sexual mimicry" like this is actually common in the animal kingdom. "The scientific literature is full of examples of sexual mimicry," he says.
"There are many cases— insects, birds, mammals— you name it. Sexual mimicry is very commonly known in almost every sexual mating system." But his study is the first evidence of sexual mimicry leading to genetic success in any animal. As such it's a new piece to the puzzle of Charles Darwin's 134-year-old theory of sexual selection. Now Hanlon hopes other biologists will use DNA fingerprinting technology to discover if cross-dressing for success is as effective in other animals as it is for cuttlefish.
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