The genetics behind seahorse pregnancy

Biologist Tony Wilson and his lab at Brooklyn College in New York, have found that seahorse pregnancy may have a deeper genetic link to other forms of pregnancy than previously thought.


Although it's well known that seahorses and their cousins the pipefish are the only vertebrates where males become pregnant, researchers have only begun to understand how this unique adaptation works.

By studying their behavior and sampling molecules within the male's pouch, biologist Tony Wilson and his lab at Brooklyn College in New York have found that seahorse pregnancy may have a deeper genetic link to other forms of pregnancy than previously thought.

Our partner 'Science Friday' brings us the story.

Anybody who has ever seen a seahorse or a pipefish knows that they look very different from most other fishes.

They have bony plates across their body.

They've lost pelvic fins.

They've lost their teeth.

And most notably...

All the members of this group have one or another form of male pregnancy.

There are no other vertebrates that do male pregnancy.

None, not one, and this makes them a fertile research subject.

Any type of question that you want to ask in evolutionary biology, there is something which they do that is a little bit different from other fishes.

Dr. Tony Wilson is an associate professor at Brooklyn College, where he researches seahorses and pipefish, a group of 300 species who have evolved male pregnancy in some form or another.

So, we are involved in a whole variety of different projects.

I'm working on genome sequence.

We're doing studies on hormonal regulation of pregnancy, and studying the behavioral interactions of males and females.

All in the hopes of discovering how male pregnancy works.

That these males swim against the evolutionary tides to carry their own young requires a huge sacrifice of time and energy for their brood.

Which he could otherwise be using for other purposes, including mating with other individuals.

But there are clear ecological advantages, as well.

He has complete confidence in paternity.

All of the eggs which are within a male's pouch are the genetic offspring of that male.

He can even benefit from changing horses in midstream.

The males can absorb the energy that is contained within those eggs, and in theory, they could actually not fertilize the eggs with the female and wait for another, more attractive female.

So the males now have complete control.

The mating rituals of seahorses can be just as nuanced as their pregnancies.

When a male and a female encounter one another, there is a mating dance which will take between three and four days.

The two will lock tails and swim side by side, eyeing one another, until...

The male will point his head upwards, and that's an indication that he is going to start to swim upwards.

They'll do a tandem swim vertically in the water column.

And when they have reached perfect alignment...

The female will be above the male, and will transfer her eggs into the male's pouch.

As the eggs are being transferred to the males, the males fertilize them.

The eggs then are either stuck on the outside of the body of the male or the eggs are deposited into a completely enclosed pouch.

As in the case of the seahorse, and unlike fathers of other species who might carry or protect their young, a male seahorse provides some special care for it's brood.

So the embryos will implant in the brood pouch wall.

So there is 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.

There is suggesting that he provides energy, he regulates the salinity such that when the offspring are released, the salinity within the pouch and outside the pouch is identical.

And finally, he labors his offspring into the world.

He has contractions which are very similar in terms of 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.

Although male seahorse reproductive roles have been flipped, Dr. Wilson's lab has shown that the similarities between their pregnancy and mammalian pregnancy may run deep.

What we wanted to do is to sample males at various stages throughout pregnancy.

And then we look at the genes that were active at these various stages of the pregnancy.

By sequencing the RNA within the seahorse's pouch...

We discovered that a good proportion of the genes, about 5% to 10% of the genes, which are involved in male pregnancy in the seahorse are actually also involved in mammalian pregnancy, which frankly surprised all of us.

One important group of genes they identified are believed to regulate a hormone called Prolactin.

Which plays a very important role in mammalian pregnancy.

As its name implies, Prolactin helps mammal mothers to produce milk after birth.

What a male seahorse uses it for...?

Jury is still out.

Dr. Wilson and his lab are now working to solve that question, and he's got some theories.

Working hypothesis at the moment is that Prolactin was regulating the salinity within the male's pouch.

And for Dr. Wilson, the innovative usage of a pregnancy hormone by a male seahorse isn't hard to conceive.

When we look at animals, animals look so different from each other, and they do things in such different ways, but it actually makes a lot of sense when you think about it.

It doesn't make sense to invent something completely independently if you have mechanisms that could do it in a slightly different way.

So seahorse pregnancy may turn out to be pretty unoriginal, and exactly what you were expecting, in other words, just like a dad joke.

And that wraps it up for this time.