Squid Sex and Babies
Biology's ultimate mandate is to reproduce itself. So how do Humboldt squid make more Humboldt squid? Like all squid species, they have separate male and female sexes. Also like all squid, Humboldt males package their sperm into spermatophores, which are passed to females during mating. Females keep these spermatophores until they are ready to spawn, at which time they'll use the stored sperm to fertilize their eggs before releasing them into the water in a huge gelatinous mass.
Most of what we know about Humboldt squid reproduction is educated guesswork. Some other species of squid aggregate in predictable places to mate and spawn, but no such behavior is known for Humboldt squid. Professor Gilly may have seen a couple mating once, in the Gulf of California, but the experience was short on intimate details.
A female Humboldt squid can mate and store sperm from a young age. The most common place to find stored spermatophores on a femaleâ€™s body is her buccal membrane the area of tissue surrounding her mouth. If you look on the reddish-purple membrane around the squid's beak and see soft white needles, a centimeter or less in length, these are spermatophores. You may also see spermatangia little whitish pimples full of sperm. Somehow, the sperm from inside the spermatophores migrates into these spermatangia, but the mechanism remains a mystery.
As well as on the buccal membrane, spermatophores are sometimes found attached to a female's arms or head. Rarely, they might even be found on a male squid. Scientists can't determine whether a Humboldt squid is male or female by looking at the outside, and it's possible that the squid aren't totally sure either.
When a female's eggs are ripe, her first task is to mix them with jelly inside her mantle. She has two different glands that produce two different kinds of jelly. The oviducal glands coat each egg with jelly that facilitates development. (We know this because successful laboratory fertilization of Humboldt squid eggs requires the addition of oviducal gland extract.) Jelly from the nidamental glands does not seem to be necessary for development, but provides the structure of the egg mass, and may repel predators and parasites.
Paralarva with proboscis extending down. Photo by Danna Staaf
Spawning itself has never been directly observed. On a research cruise in the Gulf of California in 2006, several females in aquaria on the deck of the ship spawned, but it happened in the middle of the night and no one saw them do it. Here's our working hypothesis for how an egg mass is created: the female mixes eggs and jelly inside her mantle, squirts this mixture out of her funnel, then holds it in her arms. In the center of her arms is her mouth, with its surrounding buccal membrane and the stored spermatophores and spermatangia, so this position allows the sperm to finally do their duty and fertilize the eggs.
As in almost all squid, there's no parental care. Mama Humboldt releases the egg mass into the open ocean and goes about her business. She'll probably continue to eat and grow as she spawns the rest of her eggs, over the course of a few weeks or months. Female Humboldt squid have about 10 million eggs each, and the only egg mass ever found and studied by scientists contained between half a million and a million eggs. The math suggests that a successful female may spawn 10-20 masses in her lifetime.
Finding that one egg mass was a fantastic accident. On the same 2006 cruise where the females spawned on deck, some scientists went diving in the middle of the Sea of Cortez to collect jellyfish. About 16 meters (52 feet) below the surface, they swam into a gelatinous blob the size of a small car. They collected parts of it in jars and brought them back to the boat. The jars were full of squid eggs, which began to hatch that very night, and later genetic analysis confirmed they were baby Humboldt squid.
Laboratory experiments indicate that it takes only a week for Humboldt squid to develop from fertilization to hatching, so egg masses are ephemeral things. That's one reason they're so hard to find. Another is that they're neither at the surface or the bottom, but floating in the middle of a vast three-dimensional environment.
The hatchlings are called paralarvae, a term that was invented to describe all baby octopus and squid. A true larva, like a caterpillar, goes through cataclysmic metamorphosis, which octopus and squid do not. And yet they are physically very different from adults, hence the term "œparalarva." In the case of Humboldt squid and a few other related squid species, the biggest difference between paralarvae and adults is a proboscis. This grows out of the animal's arms, looking somewhat like the trunk of an elephant, and eventually splits in half to form the two adult tentacles. No one knows why. It's yet another mystery in the strange and wondrous life of the Humboldt squid!
Gilly WF, Elliger CA, Salinas-Zavala CA, Camarillo-Coop S, Bazzino G, Beman M (2006) Spawning by jumbo squid Dosidicus gigas in the San Pedro MÃ¡rtir Basin, Gulf of California, Mexico. Mar Ecol Prog Ser 313:125â€“133
Staaf DJ, Camarillo-Coop S, Haddock SHD, Nyack AC, Payne J, Salinas-Zavala CA, Seibel BA, Trueblood L, Widmer C, Gilly WF (2008) Natural egg mass deposition by the Humboldt squid (Dosidicus gigas) in the Gulf of California and characteristics of hatchlings and paralarvae. J Mar Biol Assoc UK 88:759-770