New research reveals that male seahorses give birth to babies

(Jessica Suzanne Dudley, Macquarie University and Camilla Whittington, University of Sydney)

Sydney, September 2 (The Conversation) Seahorses and pipefish are two species in which the male conceives and gives birth to a baby. The male horse incubates his growing embryos in a pouch attached to his tail.

This equine sac is similar to the uterus of female mammals. It contains a placenta, which is attached to the developing fetus.

Male horses provide nutrients and oxygen to their young according to the genetic characteristics of mammals.

However, when it comes to giving birth, our research shows that male seahorses use their unique body structure to manage the pain of childbirth.

what animals look like

Childbirth is a complex biological process that is controlled by hormones, including oxytocin, in pregnant females. In mammals and reptiles, oxytocin promotes the contraction of the smooth muscles of the uterus.

There are three main types of muscle: smooth muscle, skeletal muscle, and cardiac muscle.

Smooth muscle is found in the walls of most internal organs and blood vessels. This muscle does not require any type of control. For example, your intestines are lined with smooth muscle, which works to move food through your gut rhythmically, without your control or direction.

Skeletal muscle is found throughout the body and is attached to bones by tendons, which allow the body to move. This type of muscle is under conscious control. For example, you can consciously bend your arm when your bicep muscles contract.

Cardiac muscle is specialized for the heart and is also under involuntary control.

The wall of the uterus in female mammals has abundant smooth muscle. Oxytocin causes this smooth muscle to contract, leading to labor.

These uterine contractions are spontaneous and involuntary. We can measure these uterine contractions in response to oxytocin, and the results are consistent in both mammals and reptiles.

What do male seahorses look like?

Our team of researchers from the University of Sydney and the University of Newcastle set out to determine how labor occurs in male seahorses.

Our genetic data suggest that labor pain in seahorses may involve a similar process to labor in female mammals. A study in 1970 also showed that when non-pregnant seahorses were exposed to the fish version of oxytocin (also known as isotocin), they behaved during labor.

We therefore predicted that male seahorses would use oxytocin, the family’s hormone, to control the birthing process by contracting the smooth muscle within the brood pouch.

what we found

First, we exposed seahorse pouch fragments to isotocin. Istocin activated our control tissues (gut), surprisingly this hormone did not cause any contraction in the brood pouch.

This result led us to think about the structure of the bag. When we examined the sac under the microscope, we found that it contained only small scattered groups of smooth muscle, much smaller than the uterus of female mammals. This explained why the sac was not activated in our experiments.

We therefore predicted that male seahorses would use oxytocin, the family’s hormone, to control the birthing process by contracting the smooth muscle within the brood pouch.

Using 3D imaging techniques combined with microscopy, we then compared the anatomy of male and female bellied seahorses.

In males, we found three bones near the beginning of the sac, which were attached to large skeletal muscles. These types of bones and muscles control the anal fin of other fish species. In seahorses, the anal fin is small and has little or no function in swimming.

So the large muscles attached to the fins of a small seahorse are amazing. The muscles and bones of the anal fin are much larger in male seahorses than in female seahorses, and their orientation suggests that they may control the sac door.

During birth, male seahorses tilt their bodies toward their tails, press down, and then relax. During this process, the mouth of the sac opens with a jerk throughout the body and slowly hundreds of newborn seahorses are seen floating in the sea water.

Our findings suggest that opening of the sac for courtship and parturition is facilitated by the contraction of large skeletal muscles located near the mouth of the sac. We believe that these muscles control the opening of the seahorse pouch, allowing seahorse parents to consciously control the birth of their babies in late pregnancy.

Future biomechanical and electrophysiological studies are needed to investigate the force required to activate these muscles and to test whether they control the sac opening process.

Male seahorses during pregnancy take a unique approach to giving birth to their young, despite their resemblance to female mammals and reptiles.

The Ekta Conversation Unit


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