The Illustrated Guide to Making Squid Babies:
By Danna Shulman Staaf Awards: Miller, Haderlie, Friends, Myers
The Gilly lab is studying the Humboldt squid, a.k.a. the jumbo flying squid, a.k.a. Dosidicus gigas. It is a principle prey item of virtually every large fish, bird, and mammal that can catch it—including humans. In fact, Dosidicus supports the largest invertebrate fishery in the world! These squid, in turn, are opportunistic predators of whatever they can find—usually crustaceans, fish, and fellow squid. Dosidicus must consume prey in enormous quantities to fuel a truly remarkable growth rate. During a life span that is probably two years or less, Dosidicus can grow from a hatchling of one to two millimeters to a fully grown adult of one to two meters.
My research focuses on these very small hatchlings, called paralarvae. However, wild paralarvae can't be found very reliably, so I've taken to making my own. All I need is one mature female, with some stored sperm from previous matings, and I can fill as many petri dishes as I could wish with artificially fertilized squid eggs.
Here's how it works:
Step 1: Catch squid. Not always as easy as it sounds! As seasoned fishermen like to remind me, it's called "fishing” not “catching". But then, on some evenings the squid are so thick in the water that you have to pull them up quickly, or they'll get ripped off the lure by their voracious fellows.
Step 2: Identify mature, mated female. This is fairly straightforward. Ripe eggs are a bright orange color and can be easily separated from the yellow-brown unripe eggs (lower left inset). If a female is mature enough to have ripe eggs, she always seems to have stored some sperm to fertilize them. She's gotten this sperm from male squid in packages called spermatophores, which we find stuck to the skin around her mouth. This "buccal membrane" can be removed and taken into the lab for easier spermatophore extraction (upper right inset).
Step 3: Extract gametes and perform artificial fertilization. This is "real science" involving gloves, petri dishes, pipettes, razor blades, etc. The spermatophores must be chopped up to release the sperm, which is then added to the eggs, along with filtered seawater and antibiotics to prevent bacterial growth. I also have to add a special powder made from one of the female's glands. If the female were spawning her own eggs, this gland would produce a jelly coating to help the eggs to develop normally. The powder is meant to accomplish the same task, but it doesn't work nearly as well. (I once vented my frustration in a poem.)
Step 4: Wait a few days, changing the embryos' water and monitoring their development. During the first day, you can observe the first cell divisions, which is very exciting. Then the individual cells become so small you can no longer see them dividing, and the embryos enter what I call the "boring stage." After another day or two, however, organogenesis begins, and things get exciting again. Eyes appear! Now chromatophores! The embryo starts spinning slowly, then pulsing! Soon: squid babies!
The goal of my research is to figure out the optimal temperature range for Dosidicus development. How warm is too warm? How cold is too cold? So I incubate petri dishes of eggs at different temperatures, ranging from 5-30°C. I find that the squid develop and hatch happily in the middle of this range, but the extremes on either end are not so good . . .
Why does it matter? Well, we know that Dosidicus can develop successfully in the warm waters of Mexico, because we've found naturally deposited eggs there. But the adults are moving north, invading California, Oregon, Washington--they're even found seasonally in Canada and Alaska! The big question is: are these invaders just adults on a feeding migration that have to swim back to the tropics to breed? Or could they be spawning at high latitudes, and establishing new populations in the north?