No Males Required: Shark Switches To Asexual Reproduction

S. fasciatum have stripes like a zebra as babies, leading to their name zebra sharks. However, as adults they have spots and are sometimes called leopard sharks. Rich Carey/Shutterstock 

Parthenogenesis is used by plants and many invertebrates. It is never seen in mammals, and while it does occur in reptiles and fish, it is thought to be rare among vertebrates because the loss of genetic diversity makes species that rely on it vulnerable to parasites and changing environments. However, Dudgeon and her co-authors note the capacity to switch might be useful for cases where females have expanded into new territory and can't find mates, allowing them to produce offspring for a generation or two while waiting for the males to catch up.

They note this may occur more often than we realize, since it would be difficult to detect in the wild, and some cases in captivity might have been wrongly assumed to involve sperm storage. Nevertheless, Dudgeon told IFLScience that the only case where the “signature of parthenogenesis” has been seen in the genetics of wild sharks or rays has been in the sawfish, where overfishing may have made it hard for females to find mates.

Dudgeon told IFLScience the team are very keen to see whether the daughters produce offspring and, if so, how. “There's never been a documented case of a vertebrate species where young produced through this sort of parthenogenesis went on to reproduce sexually,” she said.

Reef HQ has no plans to rename the shark Mary.

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