Last Friday, Adam Jones, a professor at Texas A&M University, gave a presentation on an exceptional topic: male pregnancy in seahorses.
Seahorses and pipefish are the only species in which the male plays the dominant role in the development of offspring. Halfway through pregnancy, the female moves the eggs into a brood pouch on the male which can be located on the ventral surface of the abdomen or tail, depending on the species. In some species, the males can receive eggs from multiple females within a short period of time. The eggs are then allowed to grow within the male for up to six weeks until birth. Whereas smaller species usually have between five and 20 offspring, larger species can have 1,000 or more.
The primary role of the brood pouch is to provide protection and to transfer paternal nutrients to the offspring. Males can also control the osmotic pressures of the pouch. According to Jones, there “are no shenanigans” when it comes to male pregnancy, meaning that a male carrying the eggs is always the father of the offspring.
Jones performed mating selection studies on seahorses to determine the role of physical characteristics in mating and the effects this could have on offspring development. Pipefish infected with the Trematode parasite develop distinctive black spots on their bodies. Some researchers speculated that this phenomenon might contribute to sexual selection. In contrast to this hypothesis, Jones found that male pipefish did not differentiate between these females during mating, but they did choose to mate with the larger pipefish.
With this result, Jones then looked to see whether the size of the female was an indicator of offspring viability. Indeed, he found that larger females produced larger egg sacks, which increased the survival of the offspring. Jones also tested for cryptic choice in which the males restrict some of their nutrients during pregnancy in order to save those nutrients for larger mates, but found that this was not the case.
In the future, Jones hopes to uncover the genetic underpinnings for male pregnancy in seahorses.
Male giving birth to babies after taking care of the eggs for six weeks