In a new study published Monday in the journal Current Biology, Stony Brook University researchers working with Florida scientists discovered seven endangered sawfish living in two rivers conceived through a process called parthenogenesis — the production of offspring without sex or male sperm, or in simpler terms, “virgin birth.”
So ladies, take a bow. Apparently we can do it all.
Scientists have long known that insects, crabs and other invertebrates can reproduce without partners. Female birds, reptiles and sharks in captivity have also occasionally surprised scientists with virgin births.
But until now, researchers never knew whether the behavior happened in the wild, said Andrew Fields, a Stony Brook doctoral student who discovered the “miracle” sawfish while doing DNA fingerprinting for fish captured in the Caloosahatchee and Peace rivers by the Florida Fish and Wildlife Conservation Commission.
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Fields also discovered that five of the fish appear to be siblings, another surprise since most parthenogenic offspring are produced one at a time.
“There was a general feeling that...parthenogenesis was a curiosity that didn’t usually lead to viable offspring,” said FWC fish biologist Gregg Poulakis. “This suggests parthenogenesis is not a reproductive dead end.”
Why it may be occurring in sawfish is more complicated. The snaggle-toothed ray that likes to cruise along muddy bottoms in search of prey once inhabited a range that stretched from North Carolina, around the tip of Florida to Texas and south to Brazil. Juveniles tend to stick close to shore, near tangled mangrove banks or the mouths of rivers. Adults can sometimes venture deep offshore. Researchers believe the prehistoric-looking fish, which can grow to 18 feet, live up to 20 or 30 years — the oldest dated was 14 — and are slow to mature.
But the fish have been decimated by commercial fishing — those thorny snouts can be a problem with nets — and loss of habitat. Their numbers are now just five percent of what they once were. In 2003, federal officials added the U.S. population of smalltooth sawfish to the Endangered Species List.
Poulakis captured the fish while researching juveniles near Charlotte Harbor in an effort to help the fish recover. All the fish appeared healthy. Two of the seven were at least a year old, suggesting they are hardy. Fields had intended to look at inbreeding in the fish when he stumbled on the the seven fish which had no DNA from a father fish.
Fields thinks the so-called virgin births may be their way of fighting back. But what researchers don’t know, he said, is whether sawfish possess some unique feature that makes them better equipped for immaculate conception or whether other species are equally prone to virgin births but have gone unnoticed. Fields believes researchers could easily find out with the trove of DNA being collected and examined around the world.
“We definitely have to find the trigger,” he said. “If we could monitor for that, it would be at least help us prioritize endangered species.”
After the fish were analyzed, researchers released them near where they were found and continued tracking them. The tags eventually fell off after six months, but Poulakis is hoping to catch at least some of the miracle seven as the years go by to see if they are growing, and more importantly, reproducing normally.
“Now we know that there’s some parthenogenic sawfish in the wild, do they live long enough to reproduce?” he asked. “That’s the next step.”