A new piece of strange knowledge has been discovered: Why can’t female seahorses give birth to babies?

"Its head is like a horse, its body is like a shrimp, its back is hunched, with bamboo joints, it is two or three inches long, the female is yellow, the male is blue." This is the description of the characteristics of the seahorse by the ancients in "Ranxi Zhi".

Although it is called seahorse, it is not a little horse in the sea, but a member of the genus Hippocampus of the family Syngnathidae of the order Acanthophopoda. It is a real fish , but it does not look that much like a fish.

In addition to their unique appearance, seahorses, along with their relatives pipefish and pipefish, are one of the few known species of organisms to reproduce by males .

Leafy Sea Dragon

Of course, reproduction cannot be accomplished by males alone. In order to give birth to baby seahorses, males still have to mate with females.

But female seahorses are not just any "fish". Just like a boy may need to put in some effort to pursue a girl, before mating, the male also needs to court the female by dancing.

Every spring, during the seahorse breeding season, a large number of male and female seahorses will emerge from their hiding places and begin looking for their mates. When two seahorses fall in love, the male seahorse will take the female seahorse to dance together.

During this time, their body colors change, and they simultaneously grasp the same bunch of water grass with their tails or grasp each other with their tails, then spin and dance in side-by-side or symmetrical postures.

There is really no other meaning to dancing. It is really just to promote affection. Because seahorses swim vertically when mating, they need to gradually get familiar with each other's swimming speed and habits through dancing , so that during mating, they will not... Beep~

This dance lasts about 5 to 30 minutes. Once both parties confirm that they like each other, the female seahorse will swim to the surface of the water, and the male will follow closely behind.

Then begins an "indescribable" process: the female seahorse transfers the eggs in her body to the male's brood pouch (abdominal sac) through the ovipositor . Once all the eggs are safely in, the male will add sperm and close the opening of the brood pouch.

The whole process actually takes less than ten seconds, and when the brood pouch opens, seawater will quickly pour in. However, this is not a bad thing, because the sperm and egg meet in a hypertonic environment, which can promote the activation and movement of sperm and accelerate the completion of fertilization . Otherwise, it will take ten days or half a month to complete fertilization, and the mother seahorse can't wait. In addition, the baby seahorse is born in seawater, which is also conducive to better adaptation to the external seawater environment.

The fertilized eggs will be wrapped in the inner side of the brood pouch and covered with a lot of spongy tissue, which is somewhat similar to the function of the uterus of female mammals.

Pregnancy generally lasts two to four weeks, during which time the brood pouch provides oxygen and a controlled environment "incubator" for the fertilized eggs. The nutrients needed by the fertilized eggs come not only from the female's yolk, but also from the male seahorse, such as calcium and energy-rich lipids necessary for the development of the skeletal system. In addition, the brood pouch also provides immune protection and waste transportation .

When the baby seahorses are fully grown, the father seahorse will choose a dark and windy night (seahorses mostly give birth at night), then open the opening of his brood pouch, and then begin to spray groups of baby seahorses out from his abdomen, which looks very spectacular.

Unfortunately, when baby seahorses are born, they become "orphans" because the male seahorses consume too much energy during the birthing process and often take several hours to recover, leaving them with no time to take care of the baby seahorses. As a result, the baby seahorses can only float with the ocean currents on their own, which results in most of the baby seahorses being eaten by other marine creatures as zooplankton.

So even though a male seahorse can give birth to hundreds or even thousands of baby seahorses at a time, only one in ten of them will reach adulthood.

It turns out that the growth of every life is difficult.

So, if survival is so difficult, why don't female seahorses join the breeding army and have babies together? This way: "When both husband and wife are pregnant, the survival rate of the babies can be doubled" , which can also increase the population size.

However, in reality, females "lost" to males from the very beginning because they do not have an abdominal pouch (brood pouch), which is also a unique evolutionary mechanism of Syngnathidae, including sea dragons.

In most bony fish, the C6AST gene family of astaxanthin metalloproteases is involved in embryo hatching. Members of this family include hatching enzymes, high-chorionic lysozyme and low-chorionic lysozyme, which can cause egg membrane dissolution , leading to embryo hatching.

However, seahorses are slightly different. In 2016, the South China Sea Institute of Oceanology, Chinese Academy of Sciences, University of Konstanz, Germany, Agency for Science, Technology and Research, Singapore, and BGI published a research article on the seahorse genome in Nature magazine.

Through sequencing the seahorse genome, it was found that another subfamily of the C6AST gene family, the Patristacin (pastn) gene, is highly expressed in the brood pouch of pregnant male seahorses , while females without brood pouches have basically no expression of the Patristacin gene, and are naturally infertile.

Astaxanthin metalloproteinase C6AST gene family

However, one thing that can be seen is that female seahorses are actually quite concerned about reproduction. When the male seahorse gives birth to a baby seahorse at night and rests, the next morning, the female seahorse will pull the male seahorse to mate again, and then wait for the male seahorse to fertilize, become pregnant, and give birth, and then start the next round of mating until the breeding season ends...