Danna Staaf

So, I was going to blog about the new baby giant octopus (complete with webcam!) at the Smithsonian. But, it's not really a squid.

Then I was going to talk about sperm whales collectively hunting squid, and point out that the BBC made a geographic error. (The study was conducted in the Gulf of California, on the Pacific side, not in the Gulf of Mexico, which is on the Atlantic side.) But that's really about mammals, which is just not what I do here.

So I dilly-dallied, and a good thing too, because what should show up in my inbox last night but an Australian fisherman's article about sexing squid! This is a great topic! And I was quite impressed by the author's squid savvy:

I know squid can change colour fast and can disappear in a cloud of ink, which they use as a smoke screen. Squid are cephalopods, have three hearts pumping blue blood, are jet-powered and can swim forwards and backwards . . .

Until he revealed that he hadn't known, until he started researching, that squid have "eight legs and two tentacles." In his own words,

The mind boggles.

Yeah, mine boggles too, but for a different reason. How can you know that squid have three hearts pumping blue blood (these are fairly obscure anatomical details, I claim!) but not know about squid appendages, which are a whole lot more obvious?

Yeesh.

Anyway, the question at hand is how to tell male and female squid apart, and like all good biological questions, the answer is, "it depends." It depends on species, for a start.

The California market squid, Doryteuthis (once was Loligo) opalescens, can ostensibly be sexed just by looking carefully. A postdoc in my lab showed me that the head and arms of males are much larger relative to their mantle than are those of females, and it made sense at the time, but I confess I'm still not terribly confident in my market squid sexing.

The Humboldt squid, that kerfuffle-causing cephalopod*, is even trickier. Some of my collaborators claim that mature females have an inverse hourglass shape, their mantles bulging out in the middle and narrowing towards the head and fins, while the males' mantle is more of a straight tube. But this is hardly definitive. The only way to collect scientific data on gender is to cut open the mantles and look at the gonads.

For yet another species, that Australian fishermen found out a surprising trick which relies not on the shape or size of body parts, but on the color pattern:

Colin emailed a Japanese contact, Masashi Arai, to ask him about squid genders. He sent back pictures of each type, showing the male squid with distinctive "dot" markings and the female squid with "line" markings. . . . Brendan fished with some Japanese squid-jig manufacturers last year. He knew from experience cleaning squid that the male tube was longer and the females had a shorter, broader tube. On the fishing trip with the jig manufacturers he discovered that male squid have lines that flare out from the tube to the edge of the wings, while female squid show a pattern of dots running run down to their wings and across their backs.

They didn't specify the species in the text of the article, but fortunately there's a picture! Based on the "wings" (fins) that run the entire length of the "tube" (mantle) I'm going to guess it's Sepioteuthis, that adorably cuttlefish-confused squid.



I've never heard of using dots vs. dashes to tell males from females, so this is pretty neat. Given how readily most cephalopods change their skin color and pattern, though, I suspect the "Morse code" technique won't be broadly applicable.

There is one sexing technique that can work across all cephalopods, and that is to look for the male's hectocotylus. This is a specialized arm that he uses to deliver packages of sperm to the female, and it's usually fairly recognizable, although again that depends on the species. Sometimes it's enlarged (the extreme example is the argonaut, in which the male's hectocotylus is longer than his body), sometimes it has a spoon-shaped tip, or a channel running the length of it, or distinctive suckers.

Bringing us full circle, this is probably the technique that the Smithsonian aquarists have used to sex their new baby octopus:

The Zoo’s octopus, which arrived at the end of January and will be named in early March, appears to be male, Peters said. But at a mere 2 ½ years of age, it may take more time before the Zoo can confirm the animal’s gender.

I'm guessing they saw what they thought was a hectocotylus, but they're waiting to see if it gets more obvious as he grows.


* The alliteration is better here if you adopt the Australian pronunciation, "kef-a-lo-pod."