If there were to be a “best dad” award in the animal kingdom, seahorses would be a shoe-in. That’s because males, not females, of these peculiar fish carry their young to term. They fertilize and nourish eggs deposited on their bodies in specialized “brood pouches” that function much like a mother’s womb. By studying how these pouches form, researchers now have discovered many similarities between male and female pregnancies — with one big exception.
In women and other pregnant animals, female hormones stimulate reproductive tissue to form a womb and placenta. In these seahorses, a male hormone underlies “motherhood,” researchers report November 11 in Nature Ecology and Evolution.