Artificial insemination project confirms "virgin births" in sharks

In a new report from the Field Museum, scientists are describing the largest-ever trial of artificial insemination in sharks. The study has revealed that “virgin births” are more common than what was previously realized.

The project resulted in 97 baby sharks. According to the researchers, some of the babies have parents that live on opposite sides of the country, and a few have no fathers at all.

“Our goal was to develop artificial insemination as a tool that could be used to help support and maintain healthy reproducing populations of sharks in aquariums,” said study lead author Jen Wyffels, who conducted the research with the South-East Zoo Alliance for Reproduction & Conservation.

Through captive breeding programs, experts aim to pair up sharks in ways that will increase genetic diversity.

“Moving whole animals from one aquarium to another to mate is expensive and can be stressful for the animal, but now we can just just move genes around through sperm,” said study co-author Kevin Feldheim, who led the DNA analysis of the newborn sharks to determine their parentage.

Identifying the parents of a baby shark can be challenging. In some species, the females can store sperm for months after mating, so the father of a newborn shark is not necessarily the male that the mother most recently had contact with. 

Some female sharks are even capable of reproducing with no male at all. In a process called parthenogenesis, the female’s egg cells are able to combine with each other and create an embryo that only contains genetic material from the mother.

The current investigation was focused on whitespotted bamboo sharks, which are small and gentle.  

“When people think of sharks, they picture great whites, tiger sharks, and bull sharks – the big, scary, charismatic ones,” said Feldheim. “Whitespotted bamboo sharks are tiny, about three feet long. If you go to an aquarium, they’re generally just resting on the bottom.”

According to the researchers, whitespotted bamboo females do not require frequent and repeated mating during their laying season and use sperm that they have stored to fertilize eggs. These sharks are also known to reproduce parthenogenetically.

Overall, 20 female sharks located at Ripley’s Aquarium of the Smokies and the Aquarium of the Pacific were inseminated. Baby sharks hatched from fertilized eggs after 4 months of incubation. 

“The hatchlings are about the size of your hand, and they have distinctive spot patterns that help to tell them apart,” said Wyffels. 

Tissue samples were collected from all of the babies and the parents for DNA analysis at the Field Museum’s Pritzker Laboratory for Molecular Systematics and Evolution.

“We sequenced the DNA and found sections where the code repeats itself,” said Feldheim. “These repeating bits of code serve as signatures, and when we see them in the babies, we match them up to the potential dads.”

The experts determined that freshly collected semen was effective in fertilizing eggs in 27.6 percent of cases, while semen that had been cold-stored for 24 hours had a success rate of 28.1 percent.

The genetic analysis of the offspring revealed two instances of parthenogenesis – where the mother reproduced without using the sperm she had been inseminated with. 

“These cases of parthenogenesis were unexpected and help illustrate how little we know about the basic mechanisms of sexual reproduction and embryo development among sharks,” said Wyffels.

“One of the goals of this pilot project was to just see if it worked,” said Feldheim. “Now, we can extend it to other animals that actually need help breeding, from other species in aquariums to sharks under threat in the wild.”

The researchers noted that if their work contributes to the conservation of sharks in the wild, it will be largely thanks to aquariums. 

“Aquariums allow you to observe the same individual animals over time, and that’s very difficult to do in the wild,” said Wyffels. “Aquarists have eyes on their animals every day. They pick up on subtle changes in behavior related to reproduction, and they tell us what they see. Research like this depends on that collaboration.”

“We are already taking what we learned from this study and applying it to other species, especially the sand tiger shark, a protected species that does not reproduce often in aquariums.”

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer