Scientists at the Steinhart Aquarium in California have documented a female bamboo shark in captivity that appears to have stored a male's sperm for close to four years before laying an egg that grew into a healthy juvenile.

The finding was made when an egg case dropped by a female shark isolated from males for 45 months. It displayed signs of healthy development.

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The birth could be explained by parthenogenesis, a method of reproduction in which females reproduce without male genetic contribution. But DNA analysis of the pup revealed genes absent from the mother's chromosomes, making a record-setting sperm storage the most likely explanation.

Luiz Rocha, Academy Curator of Ichthyology, said what happened is a remarkable adaptation that helps promote genetic diversity.

"In contrast, asexual reproduction produces offspring with very little genetic variation. Exploring the bamboo shark's ability to store sperm gives us hope that wild sharks can help protect their population's genetic diversity when mates are scarce and serious threats arise," Rocha said.

Researchers used advanced genetic tools to make the discovery. They collected DNA-rich slivers from the fins of shark pups and their mothers during their annual exam and did a number of genetic tests.

The shark pups also had genetic material that couldn't be explained through DNA analysis of the mother, suggesting it was inherited from the father.

Detailed findings were published in a recent edition of the Journal of Fish Biology.

Tagsfemale shark, female bamboo shark, parthenogenesis, shark reproduction, animal DNA, DNA