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What Really Happens When Male Seahorses Are Pregnant

Illustration for article titled What Really Happens When Male Seahorses Are Pregnant

A male seahorse gets pregnant when his mate deposits her as-yet-unfertilized eggs into a pouch on his belly. He fertilizes them, then carries the developing embryos until they’re ready to feed themselves. At which point he forcefully shoots them into the world.


But his pouch isn’t just a bag for keeping baby seahorses safe. A new analysis of the active genes in the pouch lining during pregnancy published in Molecular Biology and Evolution suggests he’s doing a lot more for his embryos than just hauling them around. Lead author Camilla Whittington thinks seahorse dads are also supplementing their babies’ food supply, cleaning up their waste, and protecting them from bacteria inside the pouch.

As his pregnancy progresses, a male seahorse turns on genes that help him remodel his brood pouch to make it roomier as the embryos develop. He also turns on genes that make proteins responsible for moving nutrients, carbon dioxide, and urine across those tissues. Genes involved in regulating the immune system function also pop on.


Pregnancy isn’t unique to mammals like us–it evolved independently in many kinds of snakes and fish as well. Only one group of fish — the seahorses, pipefish, and sea dragons — make pregnancy a male affair.

Yet many of the genes the seahorses switch on during their pregnancies are also active in the mammalian uterus. And that’s really interesting, because it suggests that when each group evolved their own unique way of becoming pregnant, they took advantage of their shared toolkit of ancestral genes to solve physiological challenges like feeding their embryos, instead of evolving new proteins to solve the problem.

[Whittington et al. 2015]

Image by Rudie Kuiter, Aquatic Photographics

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Christian Corralejo

The biological world never ceases to amaze. Imagine encountering a humanoid alien race that reproduces like this or like those cave insects where the females have the “equipment”.