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Male pregnancy

Male pregnancy is the incubation of one or more embryos or fetuses by male members of some species. Most species that reproduce by sexual reproduction are heterogamous—females producing larger gametes (ova) and males producing smaller gametes (sperm). In nearly all animal species, offspring are carried by the female until birth, but in fish of the Syngnathidae family (pipefish, seahorses and the leafy seadragon), males perform this function. Male pregnancy is the incubation of one or more embryos or fetuses by male members of some species. Most species that reproduce by sexual reproduction are heterogamous—females producing larger gametes (ova) and males producing smaller gametes (sperm). In nearly all animal species, offspring are carried by the female until birth, but in fish of the Syngnathidae family (pipefish, seahorses and the leafy seadragon), males perform this function. Human males incubating fetuses are a subject of popular imagination and a recurring theme in speculative fiction. In some very rare genetic conditions, genotypical males develop as female and possess the anatomy required for gestation; these intersex women have carried fetuses to term and given birth. In the absence of uterus transplantation, cases of viable ectopic pregnancies in females provide a potential model for successful pregnancy in males, but any attempt at such would be extremely dangerous for both the father and the fetus. The Syngnathidae family of fish has the unique characteristic of a highly derived form of male brood care referred to as 'male pregnancy'. The family is highly diverse, containing around 300 different species of fish. Included in Syngnathidae are seahorses, the pipefish, and the weedy and leafy seadragons. The males of some of these species possess a brood pouch on the trunk or tail; in other species, the eggs are merely attached to the male's trunk or tail when the female lays them. Although biologists' definitions of pregnancy differ somewhat, all members of the family are considered by ichthyologists to display male pregnancy, even those without an external brood pouch. Fertilization may take place in the pouch or in the water before implantation, but in either case, syngnathids' male pregnancy ensures them complete confidence of paternity. After implantation in or on the brood pouch or brood patch, the male incubates the eggs. Many species osmoregulate the brood pouch fluid to maintain proper pH for the developing embryos. In at least some species, the male also provisions his offspring with nutrients such as glucose and amino acids through the highly vascularized attachment sites in or on his body. This period of incubation can take much longer than the production of another clutch of eggs by the female, especially in temperate regions where pregnancies last longer, leading to a reproductive environment in which sexual selection can be stronger on females than on males due to increased male parental investment. This reversal of traditional sex roles has only been found in pipefishes, whereas seahorses have largely been accepted as monogamous. Some pipefish species display classical polyandry because of this unique situation. Male syngnathids usually prefer females with large body size and prominent ornaments such as blue skin pigmentation or skin folds. Syngnathid males in some species are apparently capable of absorbing eggs or embryos while in the brood pouch. In these cases, embryos with the highest survival rate are those whose mothers display the preferred phenotype. Syngnathidae is the only family in the animal kingdom to which the term 'male pregnancy' has been applied. Human males do not naturally possess wombs to gestate offspring. The theoretical issue of male ectopic pregnancy (pregnancy outside the uterine cavity) by surgical implantation has been addressed by experts in the field of fertility medicine, who stress that the concept of ectopic implantation, while theoretically plausible, has never been attempted and would be difficult to justify – even for a woman lacking a uterus – owing to the extreme health risks to both the parent and child. Robert Winston, a pioneer of in-vitro fertilization, told London's Sunday Times that 'male pregnancy would certainly be possible' by having an embryo implanted in a man's abdomen – with the placenta attached to an internal organ such as the bowel – and later delivered surgically. Ectopic implantation of the embryo along the abdominal wall, and resulting placenta growth would, however, be very dangerous and potentially fatal for the host, and is therefore unlikely to be studied in humans. Gillian Lockwood, medical director of Midland Fertility Services, a British fertility clinic, noted that the abdomen has not evolved to separate from the placenta during delivery, hence the danger of an ectopic pregnancy. Bioethicist Glenn McGee said 'the question is not 'Can a man do it?'. It's 'If a man does have a successful pregnancy, can he survive it?'' Since 2000, several hoax web sites have appeared on the Internet purporting to describe the world's first pregnant man. While some rely on legitimate scientific claims, no such experiment has ever been reported. Fertility clinician Cecil Jacobson claimed to have transplanted a fertilized egg from a female baboon to the omentum in the abdominal cavity of a male baboon in the mid-1960s, which then carried the fetus for four months; however, Jacobson did not publish his claims in a scientific journal, and was subsequently convicted on several unrelated counts of fraud for ethical misconduct.

[ "Pregnancy", "Pipefish", "Syngnathidae", "Gulf pipefish" ]
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