When a male seahorse isn’t pregnant, his brood pouch is open to the environment. But it seals up when the eggs arrive, creating a great place for bacteria or other pathogens to proliferate. Presumably to deal with this threat, changes occur in immune function during male pregnancy, with genes for bacterial resistance, pathogen recognition and antifungal activity turning up. And after the big day arrives and the kids are born, genes for tissue repair and remodeling (when tissues are reorganized or renovated) quickly turn on, letting dad get back his prepregnancy body fast enough to make any human mom jealous.