Embryo Killers

4 May

Shark Fetus, KillerSand tigers embryos offer another example of how nature ways are infinite and surprisingly effective. Sand tigers practice their role as apex predators before they even are born.

While most sharks have multiple babies or “pups” at once, sand tiger sharks only give birth to two at a time — one from each of their two uteri. That’s because the pup in each uterus has already eaten all the brothers and sisters that shared the womb with it — a phenomenon known as embryonic cannibalism.

“These guys have killed even before they’re born,” said Demian Chapman, who led a recent study on the sharks’ mating system.

Sand tiger sharks are closely related to great white sharks and grow up to three metres in length.

Typically, a female sand tiger shark mates with multiple males and becomes pregnant with around six or seven embryos in each uterus, Chapman told CBC’s Quirks & Quarks in an interview that airs Saturday.

But once the largest embryo reaches the size of 100 millimetres — about five months into the 12-month pregnancy — it breaks out of its egg capsule.

“And then it starts to go out and actively hunt and kill the other embryos,” Chapman said

As soon as it has consumed all the siblings accessible to it, the pup spends the rest of the pregnancy eating unfertilized eggs that have accumulated in the uterus. When the two remaining pups are born, they are each a whopping one metre in length.

So much for the sweet mercies of motherhood! It just shows that nature adapts to the organism, and is hardly a nurturing guide.


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