(ORDO NEWS) — In seahorses, unlike mammals, offspring are carried by males, whose pregnancy is similar to that of mammals.
However, when it comes to childbirth, expectant fathers have to rely on unusual body structure to make the process easier for themselves.
Childbirth is a complex biological process, which in pregnant females is controlled by hormones, including oxytocin.
In mammals and reptiles, oxytocin causes contractions in the smooth muscles of the uterus, a special type of muscle that is not under conscious control and is part of the walls of most internal organs and blood vessels.
In both mammals and reptiles, administration of oxytocin to a female induces uterine contractions, so the scientists hypothesized that administration of the hormone’s fish counterpart, isotocin , to gestating male seahorses would have a similar effect.
Seahorses are truly unique fish, in which the female only has the task of producing eggs: during mating, she throws them into a special bag on the male’s abdomen, after which it is the father who bears the offspring, providing it with oxygen and nutrients.
In 1970, scientists showed that the administration of isotocin to non-pregnant male seahorses induces behaviors similar to those of giving birth.
To clarify the effect of this hormone on the brood pouch, the scientists exposed the fragment to isotocin, expecting to see smooth muscle contraction.
The result surprised them: although isotocin had previously successfully caused contraction of the intestines of the ridge, whose walls are also covered with smooth muscles, it did not have much effect on the bag.
Having studied its structure under a microscope, the researchers found only scattered bundles of smooth muscle fibers in the walls of the bag – much less than in the uterus of terrestrial vertebrates.
It turned out that in seahorses, the bulk of the muscles of the brood pouch are skeletal muscles , which are under conscious control: in other words, male seahorses decide when they give birth.
Thanks to the “inflated press” (and the skeletal muscles on the abdomen in males are much larger than in females), future fathers literally “shoot” batches of tens or even hundreds of fry during childbirth, quickly emptying the brood pouch.
Scientists suggest that isotocin in seahorses only stimulates birth behavior, “starts” it, but they still have to do more research to clarify the exact mechanism of its action.
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