'Discovering these pups were parthenotes was quite a surprise for the team at Shedd, given our previous success in encouraging breeding through sexual reproduction,' says Watson.' This news underscored exactly why regular, ongoing genetic testing of offspring is important.' So when the shark pups' DNA results came back homozygous, it meant that they had to be getting both of those DNA strands from their mother, rather than from two different parents. The genetic markers used in these sharks are more complicated than just B versus b-they have many more alleles, to the point that it's virtually impossible that they'd show up exactly the same way in two different individuals. You get one allele from each parent, and if they're the same (BB or bb), that's called homozygous. You probably made Punnett square grids with different gene types represented by upper and lowercase letters, like B as the dominant allele for brown eyes and b as the recessive allele for blue eyes. Think back to the genetics unit in your high school biology class. In addition to having genetic markers in common with their mother but none of the potential fathers, the pups had identical homozygous copies of some alleles. But they did match the female that laid the eggs,' says Feldheim. 'These pups didn't match any of the mature males that were in the enclosure. Credit: Shedd Aquarium / Brenna Hernandez The results seemed impossible.Īdult zebra shark at Shedd Aquarium. When the shark pups hatched, Jean Dubach of Loyola University analyzed the sharks' DNA to determine their parentage.

In 2008, Watson and her colleagues noticed a clutch of eggs they moved them to a nursery behind the scenes to safely hatch. Shedd's Wild Reef exhibition includes a massive floor-to-ceiling habitat containing a variety of sharks, including zebra sharks. 'By confirming the lineage of the offspring, we could more soundly make decisions on future breeding efforts to maintain maximum genetic diversity while supporting the Association of Zoos and Aquarium's Species Survival Plan for zebra sharks.' 'As we started to see successful breeding of zebra sharks at Shedd in 2004, we also began genetic testing to confirm which of the sharks were the parents of the offspring,' says Lise Watson, assistant director of animal operations and habitats at Shedd Aquarium and an author of the study. The study, published in the Journal of Fish Biology, focuses on endangered zebra sharks at Shedd Aquarium in Chicago. 'This latest paper is just another step in learning why these 'virgin births' happen.' 'We've known for several years that parthenogenesis occurs in animals like sharks, but some aspects of it remain unknown, like why it occurs and what triggers it,' says Kevin Feldheim, a researcher at Chicago's Field Museum and the study's corresponding author. This finding has implications for not only the continued care of zebra sharks in zoos and aquariums, but also for conservation efforts focused on their wild counterparts. However, a recent study has revealed an example of a female zebra shark in an aquarium reproducing via parthenogenesis, even though there were healthy, reproductive males in the same enclosure.

Zebra shark