Oh Wondrous Holiday Wonder: Virgin Birth in the Zebra Shark Tank

A female zebra shark at Chicago's Shedd Aquarium brought some pups into the world by virgin birth, according to a new study appearing in the Journal of Fish Biology.

It took a few years for the aquarium researchers to realize the shark had produced offspring via parthenogenesis, in which an egg develops into a viable embryo without the hassle of sperm fertilization.

The miracle occurred within the Shedd’s “Wild Reef" exhibit, where the Philippine coral reef (“the world's richest aquatic ecosystem”) is recreated: a 27,500 square foot space with more than 750,000 gallons of saltwater that’s  home to 450 species of coral, 2,500 different fish species, and more than 30 sharks swimming among the live coral.

Researchers observed zebra sharks (Stegostoma tigrinum) reproducing the old fashioned way in the big tank in 2004, so they began genetic testing to confirm lineages. In 2008, a clutch of eggs hatched and the babies duly tested. The results seemed impossible. 

“These pups didn't match any of the mature males that were in the enclosure,” said Kevin Felheim, a co-author of the research. “But they did match the female that laid the eggs.” So, she did a parthenogenesis, only the second time such a thing has been observed in captivity. (It has also occurred at the Aquarium of the Pacific in Long Beach.)

As fascinating as the phenomenon is, parthenogenesis is bad news for the offspring, as they are prone to rare recessive genetic disorders. The shark pups in this study only survived a few months. The event shows that regular DNA testing of the inmates is warranted.

“This discovery throws a wrench in what we thought we knew about how and why parthenogenesis happens,” said Felheim. “And it illustrates a key aspect of science: we're continually learning.”

Photo credit: Shedd Aquarium