Sharks everywhere are in danger. The scientists at zoos and aquariums have a special responsibility to protect these animals, so they’re doing everything possible – from studying sharks’ natural habitats to playing matchmaker with the creatures that inhabit their tanks.
Matchmakers may sound like something out of an episode of “Love Connection,” but for conservationists it’s serious business: pairing up individuals in ways that increase genetic diversity.
Scientists are always looking for new ways to protect the environment and in this latest project, they used artificial insemination on sharks. Many of these scientists were surprised with their results which included 97 newborns! Some had moms who live miles apart from each other as well as fathers without dads 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,” says Jen Wyffels, the paper’s lead author who conducted the research for this paper with the South-East Zoo Alliance for Reproduction & Conservation and is currently a researcher at the University of Delaware.
“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,” says Kevin Feldheim, a researcher at Chicago’s Field Museum and a co-author of the study who led the DNA analysis of the newborn sharks to determine their parentage.
Sharks are complicated creatures. Figuring out who the father is can be tricky because female sharks sometimes store sperm for months after mating and they have been known to use that stored semen at any point in their life, not just during a specific pregnancy cycle. If this seems too confusing then consider one of many cases where females contain eggs with genetic material solely from her mother – parthenogenesis.
Figuring out shark parentage can be tricky because reproduction isn’t always straightforward among these animals — some species even allow females to reproduce without male contact through an incredible process called “parthenogenesis.” In rare instances, embryos created by such means will only possess DNA contributed by its mother and never know which individual was responsible for it’s conception.
To study shark reproduction, the researchers focused on whitespotted bamboo sharks. “When people think of sharks, they picture great whites, tiger sharks, and bull sharks—the big, scary, charismatic ones,” says Feldheim. “Whitespotted bamboo sharks are tiny, about three feet long. If you go to an aquarium, they’re generally just resting on the bottom.”
Before inseminating, scientists have to make sure that the potential mothers aren’t already carrying sperm from a previous rendezvous.
“Candidate females are isolated from males and the eggs they lay afterwards are monitored to make sure they are infertile,” says Wyffels.
Scientists have to examine the leathery, rectangular egg cases called “mermaid’s purses” in order for them to figure out if sharks are infertile. The shark is ready or not after six weeks of no fertilized eggs available.
Scientists collected and evaluated 82 semen samples from 19 sharks in order to tell the difference between good and bad. Some of the good samples went to nearby females for fertilization, while others were kept cold and shipped around or across country. Once it reached Ripley’s Aquarium of Smokies or Aquariums Pacific where a female was waiting, researchers sedated her then placed it inside her reproductive tract-the procedure took less than ten minutes. All in all 20 females were successfully inseminated as part of their study.
After 4 months of incubation, baby sharks hatched from fertilized eggs. Tissue samples were taken from the babies and their parents so that Feldheim could analyze their DNA at Field Museum’s Pritzker Laboratory for Molecular Systematics and Evolution to find out how they are connected.
“The hatchlings are about the size of your hand, and they have distinctive spot patterns that help to tell them apart,” says Wyffels.
Feldheim developed a suite of genetic markers to determine parentage. “We sequenced the DNA and found sections where the code repeats itself,” says 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 team found that freshly collected semen was effective in fertilizing eggs in 27.6% of cases; semen that had been cold-stored for 24 or 48 hours had 28.1% and 7.1% success rates, respectively.
In the genetic analysis of the offspring, it was discovered that two mothers reproduced on their own without using sperm from males.
“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,” says Wyffels.