In the human world, a lot of fathers would claim that they would love to take on the aching back and painful contractions from their wives while being pregnant. But only the seahorse can do such a thing.
Seahorse bends the gender stereotype for being the animal that swaps the traditional roles of mothers and fathers. The male seahorse is the only male species that gets pregnant. Unlike most species, female seahorse transfers their egg cells to the male seahorse's abdominal pouch.
The Pregnancy of a Male Seahorse
The abdominal pouch, or also known as 'brood pouch,' can hold more than 1,000 embryos. Indeed, it is a very remarkable feat for a male species. They carry the embryos for about a month before delivering them in a series of spams, much like humans giving birth.
Scientists are curious as to how alike are male seahorse when they are pregnant with human pregnancy.
One species of seahorse that the researchers from the University of Sydney and La Trobe University investigated is the genus Hippocampus. They focused on answering how embryos from this genus receive nutrients while inside their father's care.
Seahorses, sea dragons and pipefishes belong to a unique group of sea creatures named Syngnathidae. For seahorses, pregnancy is solely the responsibility of the male sex. The female puts the fertilized eggs into the specialized incubation structure after a long courtship dance.
However, it is not yet clear how much male seahorse pregnancy is similar to human pregnancy. There are still many questions that are yet to be answered: are male seahorse just a glorified flesh for his young to suck on, or is there a more complicated thing happening inside its brood pouch?
These are more than just curious questions. Knowing and understanding how the males in a particular group of vertebrates facilitate their brood's embryonic development could open doors in discovering its evolution and other animals, including humans.
"My team is using a range of techniques to investigate the biology of seahorse pregnancy," says lead author Camilla Whittington, a geneticist from the University of Sydney.
"We want to understand more about the seahorse pouch and the ways it protects and supports the baby seahorses," Whittington said.
Male Seahorse Nourishes Embryo Inside Them
There are two ways that an embryo can get nutrients. One is through pre-packaged nutrients referred to as yolk in a process known as lecithrophy. The other one is matrotrophy, wherein nutrients are delivered to the embryo directly from the parents through a placenta.
A lot of animals rely on both processes throughout their entire embryonic development. They absorb nutrients from the yolk for a time before relying on the mother for nutrients.
For seahorses, their patrotophy index (matrotophy) reveals a total dry mass of the embryos had not changed so much while they are inside the 'brood pouch.' Their dry mass is expected to decrease as they started with a supply of yolk inside the pouch that they use for energy and construction.
The scientists found lipids that are most likely evidence that male seahorses also give their offspring nutrients aside from the yolk. An earlier study suggests that there could be some placenta-like structure involved in this process, and also enlarged blood vessels where the embryos are attached.