In the animal kingdom, it is typically the mother that gives birth to offspring. However, there are some unique exceptions where the male of the species takes on the birthing responsibilities. This rare phenomenon is known as male pregnancy or male gestation.
The most well-known example of an animal where the father gives birth is seahorses. When seahorses mate, the female deposits her eggs into a pouch on the male’s belly. The male then fertilizes the eggs and carries them to term, giving birth to fully developed seahorse babies.
Other animals where males get pregnant include pipefishes, sea dragons, sphinxes, certain species of frogs and fish, and even a few invertebrates. Scientists have identified over 120 different species that display male pregnancy.
How Does Male Pregnancy Occur?
For male pregnancy to occur, the species must have specialized anatomical adaptations that allow males to incubate fertilized eggs internally.
In seahorses, the egg transfer takes place through an elaborate courtship ritual. To mate, the female and male seahorse first drift around together, spiraling upward day after day, until the female inserts her ovipositor into the male’s brood pouch and deposits her eggs. Once the eggs are inside his pouch, the male fertilizes them by releasing sperm into the pouch. He now carries the fertilized eggs in his brood pouch where they will incubate until birth.
Other animals have different structures that allow for male pregnancy. Male pipefishes have a brood pouch like seahorses. Male sea dragons incubate the eggs on the underside of their tails. Male frogs and fish may carry eggs in their vocal sac or mouth.
Why Did Male Pregnancy Evolve?
Scientists are not entirely sure how the phenomenon of male pregnancy evolved in certain species. There are several theories as to why the male takes on the birthing duties in these animals:
- The eggs require protection – If eggs are very fragile, having the male carry them may protect them better than the female leaving them on their own.
- Limited female energy – Childbirth requires significant energy, so having males give birth may allow the female to conserve her strength for producing more eggs.
- Increased reproductive success – If the male cares for the young, they may have better survival rates which is evolutionarily advantageous.
- Role reversal – In some species where males provide most parental care, it makes sense for them to carry offspring as well.
- Low male competition – Male pregnancy occurs in species where few males mate with a female, so carrying offspring ensures they are his genetic progeny.
Researchers hypothesize that male pregnancy evolved independently in various species in response to these types of environmental and social pressures. Having the male give birth appears to improve reproductive success in the species where it occurs.
Stages of Male Pregnancy
Male pregnancy follows a similar gestational timeline as female pregnancy, just carried out in the male body. Here are the basic stages:
Fertilization
Fertilization occurs differently in various species – eggs may be deposited in the male’s pouch, mouth, or carried externally for a period before being internalized. Once inside the male, the eggs are fertilized with the male’s sperm.
Gestation
The fertilized eggs are incubated inside the male’s specialized brooding pouch or other gestational structure. As in female pregnancy, the embryos grow and develop inside the protective environment of the male’s body. Length of gestation varies by species from 2-6 weeks typically.
Birth
When the offspring are fully developed, the male goes into labor and gives birth through muscular contractions to expel the babies from his body. Most male animals give birth to live young, but some like sea horses and pipefishes may eject fully formed miniature versions of the adults.
Parental Care
After giving birth, the male parent often continues to care for the young through nursing, defending, and watching over them until they are mature enough to be independent. In seahorses, the male even practices “male lactation” by providing nutrients to newborns through a placenta-like structure in his pouch.
Notable Examples of Male Pregnancy
Here are some of the most fascinating examples of animals where the male becomes pregnant and handles childbirth duties:
Seahorses
Seahorses are the poster animals for male pregnancy. After mating, the female deposits eggs in the male’s brood pouch located on his abdomen. The pouch provides protection, oxygenation, osmoregulation, and nutrients to support the developing embryos. At the end of a 2-4 week gestation, the male seahorse arches his back, flexes his body, and pumps out the tiny baby seahorses.
Pipefishes
Male pipefishes in the Syngnathidae family have a brood pouch similar to seahorses. During mating the female transfers her eggs to the male’s pouch where they are fertilized. The male carries up to 300 eggs for 4-6 weeks until the young are ready to emerge fully developed.
Darwin’s Frogs
Darwin’s frogs from Chile and Argentina display a unique form of male pregnancy. After fertilizing the eggs externally, the male frog scoops them into his vocal sac for incubation. Tadpoles develop in the vocal sac for 6-8 weeks drinking their father’s blood and saliva secretions. He then “gives birth” by spitting out tiny froglets.
Anglerfish
In deep sea anglerfish, tiny males permanently fuse to much larger females. The male anglerfish attach to the female and slowly atrophy until just a pair of gonads remain. His sole purpose is to fertilize the female’s eggs internally. The female anglerfish then incubates the eggs and gives birth to fully formed young.
Sea Horses
One of the most unique examples of male pregnancy occurs in a relatives of seahorses called sea horses in the Hipocampus genus. When sea horses mate, the female deposits her eggs onto a spongy brood patch on the underside of the male’s tail. The eggs are fertilized and remain attached to the male, receiving oxygen and nutrients from blood vessels in the brood patch. After 3-6 weeks, the male sea horse goes into labor and forcefully ejects the baby sea horses from his tail.
Symbiotic Genderless Worms
The symbiotic marine worms of the genus Osedax consist only of females and genderless individuals. To reproduce, a female worm implants sperm and unfertilized eggs into a genderless individual who incubates the fertilized embryos in its body cavity before giving birth. This is one of the only examples of pregnancy in a genderless animal.
Advantages of Male Pregnancy
Biologists have identified several key advantages that may have led male pregnancy to develop as a reproductive strategy in certain species:
Enhanced Paternal Care
Since the offspring grow inside the male’s body, it promotes advanced paternal care and ensures the male parent is invested in providing for the young. Male pregnancy essentially forces the father to “care” in species where female parental involvement ends after egg laying.
Increased Number of Offspring
By shifting the burden of pregnancy to the male, the female can dedicate more of her energy to producing eggs and mating frequently. Removing gestation and lactation duties allows females to produce more batches of offspring per breeding season.
Protection from Predators
Carrying eggs internally protects the vulnerable embryos from predators and harsh environmental conditions during development. Males can hide the pregnancy or potentially better defend the young while they are incubating in his body.
Certainty of Paternity
When the male himself becomes pregnant, there is no doubt that the offspring are genetically his. Internal fertilization and gestation provide assurance that the male is investing resources into caring for his own progeny.
Disadvantages and Difficulties
Despite the advantages, male pregnancy also comes with costs and difficulties including:
- Increased energy expenditure – Gestating offspring requires extra energy investment from the male.
- Potential conflicts – Competing interests between mother, father, and offspring.
- Possible infertility – Resources devoted to pregnancy may reduce ability to produce sperm.
- Loss of mobility – Carrying a pregnancy can reduce mobility and increase vulnerability.
- Single parent burden – The male takes on the workload of both parents alone.
These challenges may help explain why male pregnancy is relatively rare across the animal kingdom. The disadvantages likely outweigh the benefits for most species.
Are There Other Examples?
In addition to seahorses, pipefishes, sea dragons, frogs, and fish, researchers have observed male pregnancy in other surprising creatures including:
- Some spiders – Male carries eggs in spider silk sac attached to its abdomen.
- Certain snakes and lizards – Male incubates eggs in its mouth brood pouch.
- Ghost pipefish – Male has a pouch for eggs on its tail like seahorses.
- Scissortail damselfish – Male mouthbrooder that holds eggs until hatching.
- Potbellied seahorse – Male has neck pouch for egg incubation.
- Gastric-brooding frogs – Male swallows fertilized eggs and broods tadpoles in its stomach.
Additionally, male pregnancy has been experimentally induced in mammals like mice through surgical implantation and transplantation of embryos into the male body but does not naturally occur in mammals.
Can Male Pregnancy Occur in Humans?
There have been a few extremely rare medical cases of human males showing “pregnancy” symptoms like abdominal distension, hormonal changes, lactation, and labor pains in various hoaxes and improbable medical oddities throughout history. However, it is biologically impossible for males of mammalian species like humans that gestate offspring internally to naturally become pregnant and give birth.
Human males lack the reproductive organs necessary to conceive, nurture, and deliver a baby. While an embryo or fetus implanted in a male could potentially grow for a time, the human male body cannot support a pregnancy all the way through to live birth.
Key Facts About Male Pregnancy
- Over 120 species exhibit male pregnancy including seahorses, pipefishes, sea dragons, and certain frogs, fish, spiders, and snakes.
- Male pregnancy likely evolved to enhance paternal investment in offspring when females have limited maternal duties.
- Male animals have specialized pouches, sacs, mouths, or areas on tails to incubate fertilized eggs.
- Seahorses are the most well-known example with the female depositing eggs into a pouch on the male’s abdomen.
- Male pregnancy follows similar gestational stages as female pregnancy just carried out internally in the male.
- Mammals like humans cannot naturally become pregnant or give birth due to lack of a womb and placenta.
Conclusion
While female pregnancy is the norm in mammals and most animal groups, some unique species have evolved reproductive adaptations to shift the burden of carrying offspring to males. This ensures paternal care and investment, while allowing females to conserve energy for maximizing egg production. The most famous example is seahorses where females lay eggs inside a pouch on the male’s belly for him to fertilize, nurture, and birth live young when they are mature. Male pregnancy provides an interesting look at how diverse reproductive strategies can develop in nature to promote species survival and continuation in unique ecological niches. Though rare in the animal kingdom, male animals giving birth exemplify the amazing ingenuity and variety of life on Earth.