A female zebra shark isolated for years from a partner has nonetheless birthed several pups ― all without any male input.
“Leonie” is the first shark ever recorded to have apparently adapted to asexual reproduction. She hatched three eggs in April 2016, three years after she last shared a tank (and bred with) a male shark.
Surprising though it may be, there’s nothing miraculous about it, says Dr. Christine Dudgeon, a postdoctoral researcher at the University of Queensland in Australia whose research on Leonie’s behavior was published Monday in the journal Scientific Reports.
Dudgeon said this form of asexual reproduction, known as “parthenogenesis,” is quite common in invertebrates. For vertebrates like sharks, however, it’s exceedingly rare (at least in captivity), and not fully understood.
“Exactly how this happens we don’t know,” she told The Huffington Post in an email. “There are a couple of different mechanisms that may lead to the genetic signatures we see.”
While some sharks in the past have saved sperm from a male partner for later use, that isn’t the case here.
“We thought she could be storing sperm but when we tested the pups and the possible parent sharks using DNA fingerprinting, we found they only had cells from Leonie,” she said.
Despite getting their genetic material from only one source, the pups aren’t exact clones of their mother, either, though they do have dramatically reduced genetic diversity compared to their sexually produced peers. As such, parthenogenesis is inadvisable as a long-term breeding strategy, but in a pinch it’s better than nothing.
“Many sharks and rays are naturally rare and possibly have periods of time where they cannot find mates and potentially use this strategy during those periods,” Dudgeon explained. “But because it results in such reduced genetic diversity it’s likely to only be a short term fix. Sexual reproduction is presumed to be important to mix up the gene pool and give larger animals the genetic resources to adapt to changing conditions such as much more rapidly mutating pathogens.”
The behavior is also encouraging for preservationists, as the zebra shark is an endangered species and would benefit from reproductive versatility.
“This has big implications for conservation and shows us how flexible the shark’s reproductive system really is,” Dudgeon said in a media release from the University of Queensland. “Leonie adapted to her circumstances and we believe she switched because she lost her mate. What we want to know now is could this occur in the wild and, if so, how often does it?”