Baby sharks eat each other in the womb, with the largest embryo consuming all but one of its siblings. While the cannibalization has been known for a while, researchers weren’t quite sure why it was happening.
The researchers, who detailed their research on Tuesday in the journal Biology Letters, explained that the embryonic cannibalization is part of a struggle for paternity in utero where babies with different fathers fight with each other to be born.
Study co-author Demian Chapman, a marine biologist at Stony Brook University of New York, explained, “In some species, the struggle for paternity continues beyond the point where the female [mates with] the male.” For sand tiger sharks, that means eating your potential siblings.
Full-grown tiger sharks are about 8.2 feet long. Mothers usually give birth to two baby sharks, each of which is about 3.3 feet long. Researchers have known the embryos eat each other ever since the 1980s when detailed autopsies showed embryos in the stomachs of other embryos.
The cannibalization begins about five months into the sharks’ yearlong gestation. About 12 littermates usually start the journey to life together. But all but one ends up eaten by the biggest baby shark in the pack. The strategy allows the species to have stronger and larger babies at birth than other shark species.
But scientists weren’t sure why the baby sharks were eating each other. Now, however, they believe that females are mating with multiple partners and that the cannibalization of other embryos helped only one father’s genes remain dominant.
The team used 15 pregnant sharks that died in nets off the coast of South Africa to determine if their hypothesis was correct. Of the 15 sharks, 10 of them carried just two embryos. The remaining five were in earlier gestation and had between five and seven embryos in utero.
The team used DNA tests to determine paternity. The litters with five to seven embryos had at least two fathers, while the litters with just two sharks often had one father. The findings suggested that one baby shark tended to eat fellow sharks from other fathers before its full siblings.
Are you surprised to learn that baby sharks eat each other while still in the womb?
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