Researchers at the Texas A and M University are shedding light on the effects of male pregnancy on sex roles and sexual selection of mates, and how novel body structures are necessary for male pregnancy evolved with the help of male seahorses - nature's real-life Mr. Moms.
Adam Jones, evolutionary biology researcher from Texas A and M University along with his colleagues is overseeing the study.
"We are using seahorses and their relatives to address one of the most exciting areas of research in modern evolutionary biology: the origin of complex traits," said Jones.
"The brood pouch on male seahorses and pipefish where females deposit eggs during mating is a novel trait that has had a huge impact on the biology of the species because the ability for males to become pregnant has completely changed the mating dynamics," he added.
When seahorses mate, the female inserts her ovipositor into the male's brood pouch (an external structure that grows on the body of the male) and deposits her unfertilized eggs into the pouch. The male then releases sperm into the pouch to fertilize the eggs.
After the female deposits her unfertilized eggs into the male, the outer shell of the eggs breaks down, and tissue from the male grows up around the eggs in the pouch.
After fertilizing the eggs, the male closely controls the prenatal environment of the embryos in his pouch. The male keeps blood flowing around the embryos, controls the salt concentrations in the pouch, and provides oxygen and nutrition to the developing offspring through a placenta-like structure until he gives birth.
For studying the mating behaviour of gulf pipefish and seahorses, Jones' lab used molecular markers for forensic maternity analysis to figure out the mother of a male's offspring.
The lab found that where female gulf pipefish could mate with multiple males, on the other hand seahorses mate with one other seahorse. In this system, if there are equal sex ratios, there is not as much competition among females because there are enough mates for everyone, Jones explained.
Male pregnancy also results in a reversal in sex-related behaviours, Jones said.
"Females exhibit a competitive behaviour that's normally a male-type attribute, and males end up being choosy, which is normally a more female-type attribute," he said.
"From a research standpoint, it's interesting because there aren't very many species in which there is a sex role reversal. It provides a unique opportunity to study sexual selection in this reversed context."
The team is also studying how the brood pouch first evolved in seahorses and pipefish.
"A big question in evolutionary biology is how a novel structure gets all of the necessary genes and parts to function. So we are trying to understand how the brood pouch and the genes required for male pregnancy arose over evolutionary time," said Jones
"Ultimately, we hope to gain deeper insights into some of the evolutionary mechanisms responsible for the incredible changes in the structure of organisms that have occurred during the history of life on Earth," he added.