Where Do Baby Seahorses Come From?

8:11 minutes

Seahorses are one of the few vertebrates where males become pregnant and give birth to offspring. A female will deposit her eggs in the male’s brood pouch, where he fertilizes and cares for the developing young. Evolutionary biologist Tony Wilson is researching the genetics behind this parental role reversal, and video producer Luke Groskin visited his lab at Brooklyn College to learn more about his work. Luke discusses what this research can tell us about the evolution of pregnancy in mammals.  

Segment Guests

Luke Groskin

Luke Groskin is Science Friday’s video producer. He’s on a mission to make you love spiders and other odd creatures.

Segment Transcript

IRA FLATOW: The ocean is filled with creatures that stretch of the imagination of us land-living bipeds. Maybe it’s the deep sea angler fish with its flickering fishing rod, or a favorite around the sci Fri office, the octopus. Yeah, basically a tentacled brain trawling the sea floor.

Well, I have another contender to add to the race of most bizarrely fascinating animal. You’re going to think this is kind of cool. It’s the seahorse. And I’m not nominating the fish– and yes, it is a fish– based on its giraffe-like snout or its monkey-like tail. Nope, today we’re talking about pregnancy. Male seahorses are the ones who give birth to little swimming sea ponies.

That’s the topic of our video pick this week. Our video producer Luke Groskin visited the lab at Brooklyn College, where they’re rearing and studying sea horses. Mus have been fun Luke.

LUKE GROSKIN: Oh, it definitely was.

IRA FLATOW: Tell us about that. Just let me tell our listeners that you can watch Luke’s video on our website at sciencefriday.com/seahorse.

I don’t think that most people have ever heard that it’s the male seahorse that’s becoming pregnant.

LUKE GROSKIN: Oh yeah, they’re the only vertebrates, seahorses and pipefish– which is a group of about 300 species– where the males become truly pregnant. There’s lots of males around there that will protect their young or care for their young or provide for their young. But these are the only ones that actually truly become pregnant. They’re the only ones that have an internal gestation, and they provide some sort of– have some sort of connection to their brood.

IRA FLATOW: And they have other unique adaptations, right?

LUKE GROSKIN: Oh, absolutely. Absolutely. So they have bony skin and scales, which is pretty not unique among fish, but it’s not exactly common. They have no dorsal fins. They have no teeth, and their jaws are fused. So they have this one, like you said, kind of like, almost giraffe-like mug that can– they can extend their mouth, but their jaws are one single jaw.

And as you mentioned, the seahorses have a prehensile tail, which they can use kind of like a monkey tail to grab on to things, and it’s pretty flexible. But of course, everybody knows them for their pouch, their brood pouch. So male seahorses have a belly on them, and it looks kind of like a belly. It looks exactly like a belly.

IRA FLATOW: I know you went out and filmed them, and I looked at the film, but it’s not like there is a kangaroo pouch.

LUKE GROSKIN: No No, it’s not like a kangaroo pouch. It really does– the best way to describe it? It just looks like a belly. It looks like they have this little belly. And that’s one of the distinguishing characteristics between the males and the females. Males of seahorses have a belly, this little, kind of fleshy belly that doesn’t look bony, and then the females don’t. Instead the females have an ovipositor.

So when a female and a male, they go through a mating ritual. They have an actual dance. It’s very romantic. The female quickly deposits– at the end of which, the female deposits her eggs inside the pouch of the male, and he fertilizes it. Or he can actually decide not to, but that’s another story.

And so when that happens, it happens very quickly, maybe five seconds. And once the embryos are in there, there’s a lot of stuff going on there. And I spoke to Tony Wilson, whose lab I visited, and he explained to me all the really cool things that are going on inside the brood pouch of a seahorse.

TONY WILSON: So the embryos will implant in the brood pouch wall so there’s a close connection between the male’s blood supply and the pouch. And then the male regulates the internal environment.

He provides oxygen to the embryos during their development. He regulates the salinity, such that when the offspring are released, the salinity within the pouch and outside the pouch which is identical. He has contractions, which are very similar to what we see in terms of labor in humans. And once the offspring are released, you have little baby seahorses, which are completely free living.

IRA FLATOW: Now I saw on the video of the baby seahorses being born. It’s something. You gotta see it to believe how it happens. Describe it.

LUKE GROSKIN: Well, it straddles the line between wondrous and completely disturbing because it’s all these adorable, beautiful, little seahorses coming out. But the male is going through these straight up contractions. It’s bending its body over. It’s seriously in labor, and it’s forcing out, in some species, thousands of little babies out of its pouch. It’s just spraying babies out into–

IRA FLATOW: Pop pop pop pop.

LUKE GROSKIN: Yes, it really does look like they’re just spraying out of him. And yeah, you don’t forget it once you see it.

IRA FLATOW: Talking with Luke Groskin on Science Friday from PRI Public Radio International. It’s our video pick of the week at sciencefriday.com/seahorse.

Besides the males getting pregnant, seahorse pregnancy really seems similar to other forms of pregnancy, right?

LUKE GROSKIN: Absolutely, yeah. So there’s been as Dr. Wilson mentioned, there’s a lot of care and actual biology that the male is actually applying to its babies. It’s actually giving it lots of nutrients and resources so there’s that similarity. There’s the fact that there’s contractions.

And then Dr. Wilson, he’s looking also at the hormones and and the genetics behind it. And his research has actually shown that about 5% to 10% of the genes that are involved in seahorse pregnancy are involved in other forms of pregnancy in other vertebrates, including mammals, including one suite of genes, which is known to regulate prolactin.

Now what is that– prolactin? That’s a hormone. That’s the hormone– if you listen to it, prolactin– that’s the hormone that allows, that promotes milk production in mammals. And what is a male seahorse doing with prolactin?

IRA FLATOW: Maybe it’s not a male. I mean, could it be that it’s really not a male?

LUKE GROSKIN: Oh, see now this is a horse of another color. Yeah so–

IRA FLATOW: That’s very fishy. Sounds like something fishy.

LUKE GROSKIN: Yeah, there is something very fishy going on with its genes. They haven’t actually found a sex chromosome, and they haven’t actually found any genetic evidence for sex determination. There are a lot of fish that where the males and females are decided by their environment, the temperature and things like that.

So they don’t know how a male or how a baby seahorse becomes male or becomes female. And when I spoke to Dr. Wilson, he said, you know, I can’t tell you for certain if basically a female seahorse when it’s born doesn’t develop sperm as it’s developing. And so this kind of– it’s not really clear exactly how this system actually works.

And if you look at the behavior of some of these species, the females are actually competing for the males, and everything is just completely topsy-turvy. It’s a complete mystery, this whole system.

IRA FLATOW: So it doesn’t have the genes that say you’re a male or you’re a female.

LUKE GROSKIN: They haven’t found them yet. They’re doing genetics work. The seahorse genome was recently published on one species, and Dr. Wilson and his team are working on another species. And what they’re hoping to do is do a little compare and contrast and hopefully, hone in on what are the different genes that regulate different things in the seahorse and cause it to be a seahorse.

IRA FLATOW: How much fun was it making this video? Was it a lot of work? Did you enjoy it?

LUKE GROSKIN: Oh yeah, absolutely. It was enlightening to see this species. It also was a really wonderful excuse to make some horrible dad jokes, which you can hear in the video.

IRA FLATOW: Ha, you say there are five puns.

LUKE GROSKIN: Yes there’s five dad jokes in there. If you can catch them, you’re shamed publicly.

IRA FLATOW: Not to mention all the fishy puns we said–

LUKE GROSKIN: Oh absolutely.

IRA FLATOW: –today. It’s Luke. Luke’s video is up on our website at sciencefriday.com/seahorse. Thanks Luke.


IRA FLATOW: And you can also watch that latest video of male seahorses giving birth, as I say on our website sciencefriday.com/seahorse. And you can read about the pygmy seahorse, the smallest one out there. It’s about the size of your pinky fingernail. It is one of the cutest little seahorses. It’s just cool. Check it out at our website at sciencefriday.com.

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Meet the Producer

About Alexa Lim

Alexa Lim was a senior producer for Science Friday. Her favorite stories involve space, sound, and strange animal discoveries.

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