Seahorses have a unique mode of reproduction: male pregnancy, which closely resembles the pregnancy of female mammals, including humans. Brooklyn College Biology Professor Tony Wilson and an international team of researchers have taken a major step toward answering the question of whether the structures of complex reproductive systems—like the seahorse’s—reflect a common genetic architecture. The team, which included researchers from City University of New York (CUNY), University of Zurich in Switzerland and the University of Sydney in Australia, has recently published their findings in Molecular Biology and Evolution.

Male seahorses carry offspring in specialized brooding organs, providing protection, gas exchange, osmo-regulation and nutrients to offspring during their development. While the male brood pouch is functionally equivalent to the mammalian uterus, it is the result of a separate evolutionary experiment lasting more than 50 million years.

“Scientists have long been fascinated with the unique form of reproduction in the seahorse, and we were interested in understanding just how seahorse pregnancy takes place,” said Wilson, an evolutionary biologist whose research focuses on how and why animals reproduce the way they do. “Our findings provide a unique perspective on the origins of internal reproduction in animals.  We were surprised to learn that reproductive systems across species are not only superficially similar, but are also controlled in much the same way.”

Wilson and his colleagues tracked gene activity in the brood pouch of pot-bellied seahorses (Hippocampus abdominalis) over the duration of pregnancy. They identified genetic changes associated with critical morphological and physiological processes in the male brood pouch, including tissue remodeling and embryo implantation, nutrient and waste transport, gas exchange and immunological protection. The majority of these genes were previously unknown in the seahorse, opening the door for an entirely new range of functional genetic analyses in this system.

Systematic comparisons between the genes active in the male brood pouch during pregnancy and those responsible for other highly-developed forms of internal reproduction in mammals, reptiles and fishes revealed that many of the key genes are identical across species, a result that suggests the existence of a common evolutionary toolkit associated with internal reproduction.

“While the presence of these genes in all species reflects their common ancestry,” noted Wilson, “their repeated recruitment into reproduction suggests that diverse lineages of animals have overcome the challenges of pregnancy in similar ways. Genetic studies such as ours emphasize how the shared evolutionary ancestry of animals may help to facilitate the origin of new organ systems.”

Wilson and his team continue their work on the genetic basis of male pregnancy in the seahorse at Brooklyn College and are currently studying the genetic regulation of reproduction in species with more rudimentary forms of male pregnancy. “While all mammals exhibit quite complex forms of pregnancy, the seahorse and its relatives show a remarkable range of reproductive diversity. The seahorse system offers an amazing opportunity to study ‘evolution in action,’ and to identify specific genetic changes associated with the development of pregnancy in this group.”