Sarah McAnulty: the secret lives of squid

Sarah McAnulty, image courtesy of Sarah McAnulty

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Dr Sally Le Page sat down with squid biologist and science communicator, Dr Sarah McAnulty. First things first, what exactly is a squid?

Sarah: So a squid is a type of marine invertebrate, but effectively they're a type of cephalopod. The other cephalopods are octopuses, cuttlefish, squid, of course, and the nautilus. They have a mantle, they have eight arms and two tentacles.

Sarah: Arms are muscular and have suction cups all along the limb, and then tentacles are super rubbery and stretchy and are mostly used for grabbing. So that's generally speaking what a squid is.

Sally: Wait, so there's a difference between arms and tentacles? So do octopuses...octopuses have eight appendages. Do they have eight arms or eight tentacles?

Sarah: Good question. They have eight arms.

Sally: They don't have any tentacles!

Sarah: No tentacles. Honestly, if you call an octopus arm a tentacle, there's nothing wrong with that colloquially. That's totally normal to do so.

Sally: True, but if you're that person at parties that goes around saying, "How many tentacles does an octopus have?" Someone says, "Eight". You'll be like, "Well, actually an octopus doesn't have any!"

Sarah: You could be that person. Yeah. I would encourage you to not be that person

Sally: Because then you won't get invited to the parties.

Sarah: Exactly right. That's exactly right. We've got to lighten up a little, but you could if you wanted to be that person.

Sally: And you are a squid scientist. Squids are your life from what I can tell online.

Sally: What's so great about squids?

Sarah: Squid are the coolest. There are so many different ways to be a squid, I think that's really exciting. They live all over the world in shallow water, deep water, everywhere. But what I think is really interesting about squid, and cephalopods broadly, is that they diverged from us evolutionarily so, so long ago. We have had squids, or at least cephalopods, on Planet Earth before there were trees. They've had a lot of time to develop into these incredibly complex behaviourly - and other ways too - animals, right.

Sally: Wait, I'm just processing. We've had... squids are older than trees.

Sarah: Cephalopods broadly, yeah, we've had longer than trees, which is pretty... it's honestly hard to think about Earth without trees.

Sally: Yeah. So when you say they cephalopods not squids, what did they look like at that time? Because how do they fossilize? They're just balls of goo!

Sarah: You're right! They're just goo. So back then they had shells. So the first cephalopod about, about 500 million years ago, basically looked like a traffic cone with some arms sticking out the end.

Sarah: Pretty much at the beginning, there were just a bunch of molluscs walking around on the sea floor and then one invented the idea of floating above everybody. And so that was the first cephalopod. From there, a lot of them ended up with spiral shells. Some got huge as long as six metres. Some were three metres and round.

Sarah: I mean, they were really, really big.

Here be giants

A giant squid found in 1954, measuring 9.2m. Image by NTNU University Museum

Sally: How big is the giant squid? There's the giant squid and there's the colossal squid. I don't know which one's bigger.

Sarah: It depends on how you think about it. So the giant squid is a touch longer, but the colossal squid is bigger by mass, in general. They're there volumetrically bigger. They're huge. They're really, really chunky.

Sally: How long is it?

Sarah: I think we generally clock them between like 10 and 13 metres.

Sally: And how have squid been used in biology? Because I know famously they've got very big neurons and so they have visible-to-the-eye nerve cells that was key in dissecting and working out what nerve cells are. Was that a giant squid or do all squid have giant nerve cells?

Sarah: Great question. So this is a common misconception. It's not giant squid axons. It's a giant squid axon. A giant axon that happens to be present in squid. And the market squid, which is common all over the east coast of the US...

Sally: Called the market squid, I'm guessing it's the one that's sold at markets?

Sarah: It's the one that we're eating, yeah.

Sally: It's calamari.

Sarah: It's calamari, yeah. I often call it the calamari squid. But anyway, they have a big, big axon. Easy comparatively to manipulate and do this method called the "patch clamp method", which is basically a way that neuroscientists can measure action potentials or how neurons deliver messages to one another and really worked out how that all works. What chemicals were being exchanged between neurons. A lot of our really fundamental understanding of how neurons work came from squid axons.

Sally: One thing I found bizarre researching this episode was that the first squid was genetically manipulated only a couple of years ago.

Sarah: Yeah, yeah.

Sally: Catch up squid biologists! What's been going on? Why are squid so hard to genetically manipulate?

Incredibly cute

The Hawaiian bobtail squid, Euprymna scolopes. Image via NSF

Sarah: So they are hard to genetically manipulate cause they're hard to raise in the lab. They're a real pain in the butt to keep alive. So we just recently got their genome sequenced. We have the Hawaiian bobtail squid genome sequenced; that happened a couple of years ago.

Sally: Very cute looking squid.

Sarah: Incredibly cute, oh my gosh! They're relatively easy to raise, all things considered. The other squid, like the market squid, the squid that they did all of that fundamental neuroscience research on, they're very hard to raise. I don't know if anybody's successfully done it.

Sarah: There have been some other squid that are what we call 'pelagic', aka up and swimming in the sea water as opposed to sitting on the sand. If a squid or a cephalopod sits on the sand, they're easier to raise because you don't need as much space for them. They're not as energetically active. So they're easier to feed. They're easier to keep clean. They generally are just easier.

Sarah: If you have an animal that's up and swimming all the time, really metabolically active, it's just harder. It's harder to keep them fed. It's harder to prevent them from pooping so much that it makes their system dirty and then not healthy for them. They're not happy. And it's really important to keep your lab animals happy to do good science. So that's one of the reasons.

Sarah: Another reason is a lot of the micro-injections, so that's how they get the experimental juices in there in the first place. Figuring out how to effectively micro-inject a squid egg was one of the things that really drove scientists up the wall for a while there, because their eggs are really rubbery and the chorion, which is the last layer before you hit the embryo, is just tough to get through.

Eggs are like onions

Hawaiian bobtail squid eggs. Image by Macroscopic Solutions

Sarah: So we would be like... by 'we', I mean 'scientists'; I've tried this and totally failed. So I am not one of the people that succeeded at this, but you would put a little glass needle into the squid egg and it would just bend the needle. It would be like, "Nice, try. Not going to happen".

Sally: So wait, describe a squid egg to me. How big is it?

Sarah: It depends on the squid. Very variable. Some are as big as a small marble. Some of them are maybe like the head of a big pin, like one of those big pins.

Sally: Like a map pin?

Sarah: Yeah. Yeah. Like a map pin. Exactly. That's like a bobtail squid egg size.

Sally: Okay, so you can see it.

Sarah: Totally. It's not like a human egg.

Sally: What makes it so strong? Because I'm guessing it doesn't have a hard eggshell, like a calcium eggshell, like a chicken.

Sarah: Exactly. Correct. Yeah. So generally speaking, squid eggs have the chorion that holds the baby and then a bunch of layers of jelly on top of that. Many female squid, including bobtail squid, market squid, reef squid, they have this organ inside of them called an ANG. And the ANG houses a bunch of different kinds of bacteria that the female squid will put into the jelly coat of the eggs of the baby squid.

Sarah: And the reason that they do this is that this bacteria creates antibiotics and antifungals, which protect the baby squid when they lay the eggs. If you've ever seen an octopus laying eggs, they'll lay eggs, and then sit with those eggs until they hatch. And then the octopus dies.

Sally: Like in the Netflix film!

Sarah: Like in the Netflix film, right. So they have to like constantly be blowing air over the eggs. They need to be touching the eggs, cleaning the eggs, taking care of the eggs.

Sally: And they starve while they're doing it, right?

Sarah: And they starve while they're doing it, yeah. It's the end of their life. It's their last mission on Earth. But squid don't have to do that because they let the bacteria do all the work for them.

Sarah: And so there are, if you cut a squid egg in half - this is true of at least bobtail squid eggs and cuttlefish eggs - it kind of looks like onion layers of jelly. So all of the onion layers are like jelly and then a harder surface, jelly, harder surface, down to the chorion, which is that last layer before the baby and then the baby in the middle.

Sarah: And in all of those onion layers, you see little bacteria all throughout that jelly that are actively producing the antibiotics and antifungals. And there's a lot of work happening on that right now. And we're hoping over time to be able to say, "Okay, this bacterium produces this compound" and maybe we could take some of those compounds and use them for antifungals and the antibiotics for human use, because Lord knows we're running out of those.

Sally: Squid are really good at delegating work to bacteria.

Sarah: They are, yeah. For camouflage, for protecting their eggs, all kinds of things.

Sally: We're going to be talking later on the podcast about their relationship with light-producing bacteria and then sending them up into space.

Sally: But they also are like, "We don't need a hard egg shell. We'll just let bacteria do all the work for us. Exactly. We don't need to starve ourselves. We'll just let the bacteria do it."

Sarah: That's right. That's right. Very clever.

Sally: So it's physically getting the DNA into the egg that's the issue. They don't have weird DNA or they don't have strange genes that's the issue with genetically manipulating them. It's literally physically getting the liquid into the egg.

Sarah: I mean, I think the process that the scientists who were working on this, they were like every time they solved a problem, they'd run into a new headache. And two of the big problems were getting the liquid in there and keeping them alive after. So those were two of the issues and also not having enough genetic information, but we have that part covered now. We've got the genome we've gotten way better at keeping squid happy and healthy in captivity. And they figured out the right needles and everything to use for manipulating the eggs. So things have gotten a lot better. A lot of people put a lot of work in to make that happen.

Sally: And what do you think the next steps are going to be? Now we can finally genetically play around with these squid, what are the big questions in squid biology that people haven't been able to answer so far because they haven't had these genetic tools?

Sarah: That's a good question. I mean, it depends on what part of science you're in. One of them might be about how they do RNA editing. One of the things that cephalopods, that a lot of animals do, but cephalopods do a little bit more than average is... OK, so as I think people probably listening to a genetics podcast are aware, you've got your DNA, you've got your RNA, you take your RNA, you make a protein.

Sarah: And for most cases you make your RNA and you're good to go. You use that copy and you make your protein. With cephalopods, they can toss a step in there where they edit the RNA depending on what they're experiencing in life. So the famous example is this octopus that can change one of its proteins depending on whether it's in a cold environment or a warm environment. They change one of those proteins around to be better for that situation.

Sally: So rather than changing how the gene is expressed, it expresses the gene, it produces the same number of RNA copies, but then changes what protein is made as a result.

Sarah: Right.

Sally: That's bonkers.

Sarah: It's totally, totally bonkers. Yeah. It's basically the same protein, but it's like a different isoform of the protein, a different version of the protein.

Sally: I'm just thinking of what I would do if I was able to change my genes based on whether I'm hot or cold or not.

Sarah: That's right. Yeah. If you were in a famine or not, you know, maybe that is something that you would change. Maybe you'd change your metabolism. Maybe you'd change something about your skin. Any number of things. It's pretty cool.