If there have been to be a “greatest dad” award within the animal kingdom, seahorses can be a shoe-in. That’s as a result of males, not females, of those peculiar fish carry their younger to time period. They fertilize and nourish eggs deposited on their our bodies in specialised “brood pouches” that operate very similar to a mom’s womb. By learning how these pouches kind, researchers now have found many similarities between female and male pregnancies — with one huge exception.
In ladies and different pregnant animals, feminine hormones stimulate reproductive tissue to kind a womb and placenta. In these seahorses, a male hormone underlies “motherhood,” researchers report November 11 in Nature Ecology and Evolution.
“The evolution of the brooding pouch was not lower from entire fabric de novo however was constructed like a quilt with completely different patches of genes and cells that operate the identical means in numerous animals,” says Invoice Cresko, an evolutionary geneticist on the College of Oregon in Eugene who was not concerned within the examine. “It’s means cool.”
The discovering helps clarify how being pregnant might have developed greater than 150 instances in animals, albeit virtually solely in females.
Most animals lay eggs, or else it’s the moms that incubate their younger. “Seahorses flip all of this on its head,” says Oliver Griffith, an evolutionary biologist at Macquarie College in Sydney. Thus, seahorses and their kin — pipefish and sea dragons — have lengthy fascinated biologists.
A household tree constructed greater than 20 years in the past revealed a progressive improve in male motherhood actions over evolutionary time on this group of fishes. Extra primitively, some species’ males simply present a sticky plate to maintain eggs hooked up to their physique because the eggs mature. Others present an open-faced shelter on their tails or bellies. And some, the seahorses, have developed this closed brood pouch and provide the younger inside with oxygen and vitamins.
“I don’t know of every other instance the place intercourse position reversal has gone up to now,” says Axel Meyer, an evolutionary biologist on the College of Konstanz in Germany.
The interpretation of the primary genetic instruction guide of a seahorse set the stage for Yali Liu, an evolutionary biologist on the Chinese language Academy of Sciences South China Sea Institute of Oceanology in Guangzhou, to find the genes that underlie male being pregnant. She eliminated stomach cells from 10 lined seahorses (Hippocampus erectus) throughout completely different levels of the male’s improvement and measured how energetic the cells’ genes had been at every stage.
“To our amazement,” she says, a definite set of pores and skin cells had been concerned. These cells activate among the similar genes that females of different animals depend on throughout their pregnancies, Liu, Meyer and their staff discovered. “This reveals a deep commonality within the biology of being pregnant, no matter intercourse,” she says.
However as a substitute of being activated by feminine hormones, the seahorse’s genes appeared to be turned on by a male hormone. It’s unclear whether or not that hormone was testosterone or one other androgen. However when Liu and her colleagues uncovered feminine seahorses to testosterone, which in people usually causes beards to develop and voices to get deeper in younger males, the feminine fish additionally developed brood pouches. This discovering confirmed the position of a male hormone in seahorse pregnancies — regardless that males even have feminine hormones.
Within the pregnant males, the hormone additionally stimulated the newly occupied pouch to thicken so it might provide the embryos with oxygen and vitamins, very similar to a placenta does. However on this case, this “placenta” was derived solely from the daddy’s pores and skin not reproductive tissue as in all different feminine animals, Meyer says.
The work “represents a fairly phenomenal instance of how genetic networks might be rewired to realize the identical finish,” says Thomas Boehm, an immunologist on the Max Planck Institute for Biology Tübingen.
Camilla Whittington, an evolutionary biologist on the College of Sydney, noticed comparable rewiring in 2022, when her staff in contrast gene exercise in pregnant feminine mammals, reptiles and sharks. Whereas among the similar genes get utilized in these species, different genes are distinctive, she says. “There are a number of evolutionary pathways that may produce the identical consequence: being pregnant.”
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