The biggest effort ever to artificially inseminate sharks – and the occasional “virgin birth”
It’s a tough time to be a shark. Pollution, industrial fishing and climate change threaten marine life, and populations of many large ocean predators have declined in recent years.
In addition to studying sharks in the wild, scientists working to save sharks rely on those who live in zoos and aquariums so they can help create breeding programs and learn more about the conditions sharks need to thrive. An important way for scientists to do this is to play matchmaker with sharks, pairing individuals in ways that increase genetic diversity.
In a new study in Scientific reports, scientists have undertaken the largest effort ever to artificially inseminate sharks. Their work has resulted in 97 new baby sharks, including those whose parents live across the country and a few who have no father at all.
“Our goal was to develop artificial insemination as a tool that could be used to help support and maintain healthy shark populations in aquariums,” says Jen Wyffels, lead author of the article who conducted the research for this article with the Southeast Zoo. Alliance for Reproduction & Conservation and is currently a researcher at the University of Delaware.
“Moving entire animals from one aquarium to another to mate is expensive and can be stressful for the animal, but now we can just move genes through the sperm,” says Kevin Feldheim, Field Museum researcher. from Chicago and co-author of the study that analyzed the DNA of newborn sharks to determine parentage.
Determining the parentage of sharks can be tricky because shark reproduction is not always straightforward. In some species, female sharks can store sperm for months after mating and use it for ‘on-demand’ fertilization, so the father of a newborn shark is not necessarily the male. with whom the mother has most recently been in contact. Some female sharks are even able to reproduce without a male at all, a process called parthenogenesis. In parthenogenesis, the female’s eggs are able to combine, creating an embryo that contains only genetic material from the mother.
To study shark reproduction, researchers focused on bamboo white-spotted sharks. “When people think of sharks, they imagine great whites, tiger sharks and bulldog sharks – the big, scary and charismatic ones,” says Feldheim. “Bamboo white-spotted sharks are tiny, measuring about a meter in length. If you go to an aquarium, they are usually just resting on the bottom. But while the softness and small size of bamboo sharks make them unlikely candidates for Hollywood fame, these qualities make them ideal for researchers attempting to artificially inseminate.
Before attempting artificial insemination, researchers should make sure that potential mothers are not already carrying sperm from a previous appointment. “Candidate females are isolated from males and the eggs they subsequently lay are monitored to ensure they are infertile,” Wyffels explains. Laying sharks regularly lay eggs on a regular schedule, much like chickens, Wyffels says, to the point that they’re nicknamed “chickens of the sea.” To determine if the eggs are infertile, scientists project an underwater light through the leathery, rectangular egg cases (called “mermaid handbags”) to see if there is an embryo wriggling above them. yellow. If there are no fertilized eggs for six weeks or more, the shark is ready to be inseminated.
Scientists collected and evaluated 82 semen samples from 19 sharks in order to differentiate between good and bad samples. Some of the good samples went to neighboring females for insemination, while others were kept cold and shipped to and across the country. Once the sperm reached Ripley’s Smokie Aquarium or the Aquarium of the Pacific, where a female was waiting, the researchers sedated her and placed the sperm in her reproductive tract – the procedure took less than ten minutes. A total of 20 females were inseminated as part of the study.
Baby sharks hatch from fertilized eggs after 4 months of incubation. “Newborns are about the size of your hand and they have distinctive spot patterns that help distinguish them,” says Wyffels. Tissue samples were taken from all babies, as well as their parents, so that Feldheim could analyze their DNA at the Field Museum’s Pritzker Laboratory for Molecular Systematics and Evolution.
Feldheim has developed a suite of genetic markers to determine parentage. “We sequenced the DNA and found sections where the code repeats,” says Feldheim. “These repeated pieces of code serve as signatures, and when we see them in babies, we match them with potential dads.” The team found that the freshly collected sperm was effective in fertilizing the eggs in 27.6% of cases; sperm that had been kept cold for 24 or 48 hours had success rates of 28.1% and 7.1%, respectively. In the genetic analysis of the offspring, the team also found two cases of parthenogenesis, where the mother reproduced on her own without using the sperm with which she had been inseminated. “These cases of parthenogenesis were unexpected and help illustrate how little we know about the basic mechanisms of sexual reproduction and embryonic development in sharks,” says Wyffels.
From these preliminary results, scientists hope to help aquariums develop and manage their shark breeding programs. “There have been other reports of artificial insemination of sharks, but they include very few females. In this study, we are in the double digits and, therefore, we could study different methods of preparing and storing sperm for insemination, ”says Wyffels. “And a newborn baby of shark parents who live nearly 3,000 miles away from semen collected days in advance, this is certainly a first.”
“One of the goals of this pilot project was just to see if it worked,” says Feldheim. “Now we can extend it to other animals that really need help reproducing, from other species in aquariums to endangered sharks in the wild.”
The researchers also note that if studies like these contribute to shark conservation in the wild, it will be largely thanks to aquariums. “We wouldn’t know anything about parthenogenesis in sharks without aquariums,” says Feldheim.
“Aquariums allow you to observe the same animals over time, and that’s very difficult to do in nature,” says Wyffels. “Aquarists have eyes on their animals every day. They detect subtle changes in reproductive behavior and tell us what they see. Research like this depends on this collaboration. We’re already taking what we’ve learned from this study and applying it to other species, especially the sand tiger shark, a protected species that doesn’t often breed in aquariums.
Reference: “Artificial insemination and parthenogenesis in the bamboo white-spotted shark Chiloscyllium plagiosum»By Jennifer T. Wyffels, Lance M. Adams, Frank Bulman, Ari Fustukjian, Michael W. Hyatt, Kevin A. Feldheim & Linda M. Penfold May 13, 2021, Scientific reports.
DOI: 10.1038 / s41598-021-88568-y
This study was conducted by researchers at the South-East Zoo Alliance for Reproduction & Conservation in collaboration with the Aquarium of the Pacific, Ripley’s Aquarium of the Smokies, The Florida Aquarium, Adventure Aquarium and the Field Museum.