A Pregnant Mother’s Pipedream

I absolutely adore aquariums. Walking through a museum filled not with stuffed, but live animals makes me happy and the glowing water all around, with the fish lazily drifting in the artificial currents, distributes a sense of calm that despite its claims remains unattainable even in my yoga class. One sight that has always brought a smile to my face is the usually very small tank filled with seahorses and pipefish. Barely distinguishable from its habitat, these tiny ocean fairies float through the water or seem completely entangled in the seaweed and various other forms of aquarium decorations. They look so absolutely alien that I wasn´t surprised the day I learned about the reversed sex roles in seahorse pregnancy, though I did wonder if carrying the baby bump implies the male also carries the majority of the household chore burden.

Gender – equality silliness aside, male pregnancy is nowhere to be found in the mammalian kingdom. The benefits of female pregnancy seem to greatly outweigh its disadvantages. But since it did evolve in pipefish, seahorses and sea dragons (known as the group of Syngnathids), there must be an advantage, and this is exactly what a group of researchers from the Helmholtz Centre for Ocean Research in the small seaside town of Kiel, Germany set out to discover. Headed by Olivia Roth, they placed their bets on the benefit being immunity, which in sex – reversed pregnancy finally gives the males a chance to help out.

From what I´ve heard, most new fathers feel rather useless once the soon-to-be mother goes into labor. From an immunological viewpoint I´m sorry to say, it´s not just at that point when males are no good. The development of the immune defense starts in the womb with the egg. Males do not have large enough sperm to pass on genetic information on immunity they´ve acquired in their own life and also don’t share the same environment as the baby (now that would be creepy), leaving the newborn´s immunity entirely reliant on the mother and her hopefully well-established immune system.

In pipefish, the model organism used by the Roth group, this is an entirely different matter. Would being born to a dad affect the baby pipefish’s immune system? To answer this question, only the males or only the females or both sexes were immunochallenged before mating. “Immunochallenged” translates to the equivalent of being given a flu shot, meaning they were injected with heat-killed bacteria. This is the usual method to annoy the immune system in biology without causing any harm to the animal. Parts of the immune system were affected in three different ways:

• When both parents were exposed to a nasty infection before mating, the chances of the vital information being passed on against the pathogens were doubled. Twice the immunity, double the fun!
• Some parts of the immune defenses could only be established, if both parents were involved. For these pathways, it was not only beneficial, but necessary to have the dad’s immune system helping out.
• In some cases, the dad was able to pass on crucial information even if he’d only suffered a mild infection. The dad played not a beneficial, or necessary, but vital role. The mother would need to suffer a more severe infection if she wanted to influence her offspring’s immune system. Since an infection can never be guaranteed, it’s crucial for the dad to play the protective role and pass on as much information as he possibly can.

Now, all of this sounds like only the parent actually carrying the babies to term is important. Interestingly though, the offspring of immunochallenged mothers, grew to be much bigger than babies whose mothers hadn’t been given their injection. (Makes you think about vaccines a whole lot differently, doesn’t it, Jim Carrey? Get your annual flu shot and have taller children! I might have to give that one a try…) A possible explanation for this result is, that if the mother knows she’s ill, she’s more likely to invest more in her babies, because it’s unsure whether she’ll be able to have a new clutch next mating season. This logic is not unusual, and most animals (I was able to observe the same in house wrens) tend to take better care of their offspring, if their immune system has taken a beating.

Overall, sex-reversed roles in pregnancy play a huge role in terms of getting the baby’s immune system set up. Will we now change to paternal pregnancies as well, once we have the technology for it? I highly doubt it, but just to be on the safe side, I´ll ask my partner what he thinks of a baby bump of his own.

 

Reference

Male Pregnancy and Biparental Immune Priming, Roth et al