Natures wonders: how male sea horses give birth (Introduction)

by David Turell , Saturday, September 03, 2022, 15:13 (600 days ago) @ David Turell

A description from a study:

https://www.sciencealert.com/study-reveals-the-wonderfully-unique-way-seahorse-dads-giv...

"In seahorses and pipefish, it is the male that gets pregnant and gives birth. Seahorse fathers incubate their developing embryos in a pouch located on their tail.

"The pouch is the equivalent of the uterus of female mammals. It contains a placenta, supporting the growth and development of baby seahorses.

"Seahorse dads provide nutrients and oxygen to their babies during pregnancy, using some of the same genetic instructions as mammalian pregnancy.

"However, when it comes to giving birth, our research shows male seahorses seem to rely on elaborate behaviors and their unique body structure to facilitate labor.

***

"When we examined the pouch under a microscope, we found it contains only scattered small bundles of smooth muscle, far less than the uterus of female mammals. This explained why the pouch did not contract in our experiments.

"In males, we found three bones positioned near the pouch opening, associated with large skeletal muscles.

"These types of bones and muscles control the anal fin in other fish species. In seahorses, the anal fin is minuscule and has little or no function in swimming.

"So, the large muscles associated with the tiny seahorse fin are surprising. The anal fin muscles and bones are much larger in male seahorses than in female seahorses, and their orientation suggests they could control the opening of the pouch.

"Seahorse courtship is an elaborate process. Males open and fill their pouch with water by bending forward and contracting their bodies to force water into the pouch, before "dancing" with the female.

"Similarly, during labor, male seahorses bend their body towards the tail, pressing and then relaxing.

"This "pressing" behavior is accompanied by brief gaping of the pouch opening, with a series of whole-body jerks.

"This movement combined with pouch opening allows seawater to flush through the pouch.

"Jerking and pressing continues, the pouch opening gets gradually bigger, and groups of seahorse babies are ejected with each movement. Many hundreds of babies are ejected in a short time.

"Our findings suggest the opening of the pouch for courtship and birth is facilitated by contractions of the large skeletal muscles located near the pouch opening.

"We propose that these muscles control the opening of the seahorse pouch, allowing seahorse fathers to consciously control the expulsion of their young at the end of pregnancy.

***

"Our unexpected results suggest male seahorses use different mechanisms to give birth compared to female pregnant animals.

"We speculate that oxytocin-family hormones, instead of primarily producing smooth muscle contractions, trigger the cascade of seahorse behaviors that lead to birth.

"Despite the similarities that male seahorses share with female mammals and reptiles during pregnancy, it seems seahorse fathers have a unique way of giving birth to their young."

Comment: this is convergent evolution with the use of oxytocin in perhaps new ways. The males produce 'many hundreds of babies' which makes it obvious only very few are expected to survive.